Journal of Colloid And Interface Science (v.374, #1)
Cover 1 (OFC).
Hydroxyapatite-armored poly(ε-caprolactone) microspheres and hydroxyapatite microcapsules fabricated via a Pickering emulsion route by Syuji Fujii; Masahiro Okada; Taiki Nishimura; Hayata Maeda; Tatsuya Sugimoto; Hiroyuki Hamasaki; Tsutomu Furuzono; Yoshinobu Nakamura (1-8).
Display Omitted► Apatite-poly(ε-caprolactone) particles are fabricated from Pickering emulsions. ► Apatite capsules are fabricated from apatite-poly(ε-caprolactone) particles. ► The diameters of apatite-poly(ε-caprolactone) particles can be successfully controlled.Hydroxyapatite (HAp) nanoparticle-armored poly(ε-caprolactone) (PCL) microspheres were fabricated via a “Pickering-type” emulsion solvent evaporation method in the absence of any molecular surfactants. It was clarified that the interaction between carbonyl/carboxylic acid groups of PCL and the HAp nanoparticles at an oil–water interface played a crucial role in the preparation of the stable Pickering-type emulsions and the HAp nanoparticle-armored microspheres. The HAp nanoparticle-armored PCL microspheres were characterized in terms of size, size distribution, morphology, and chemical compositions using scanning electron microscopy, laser diffraction, energy dispersive X-ray microanalysis, and thermogravimetric analysis. The presence of HAp nanoparticles at the surface of the microspheres was confirmed by scanning electron microscopy and energy dispersive X-ray microanalysis. Pyrolysis of the PCL cores led to the formation of the corresponding HAp hollow microcapsules.
Keywords: Hydroxyapatite; Pickering emulsion; Poly(ε-caprolactone); Microsphere; Hybrid;
Effect of poly (ethylene glycol) on coarsening dynamics of titanium dioxide nanocrystallites in hydrothermal reaction and the application in dye sensitized solar cells by Cong-Hua Zhou; Xing-Zhong Zhao; Bing-Chu Yang; Dou Zhang; Zhi-You Li; Ke-Chao Zhou (9-17).
Display Omitted► We examine the effect of PEG on particle growth dynamics of TiO2 sols. ► Growth of anatase particles is retarded, while that of rutile is favored. ► The synthesized TiO2 sols are utilized in dye sensitized solar cells. ► Low concentration of PEG benefits the performance parameters of the solar cells.Titanium dioxide sols were synthesized by hydrothermal reactions with addition of poly (ethylene glycol) (Mw = 20,000). Using techniques of X-ray diffraction, transmission electron microscopy, dynamic light scattering, and scanning electron microscopy, effect of PEG on the crystallographic properties, particle size, aggregating behavior, and the morphological properties of nanoparticles in the sols were studied. It was found that growth of anatase nanocrystallites was retarded by PEG. Average crystallite size of anatase nanocrystallites first decreased from 20.7 nm to 10.5 nm as the polymer concentration increased from 1 g/L to 3 g/L, and then changed little. Meanwhile, small amount of rutile phases like rutile nanowires, twin crystallites, and the “flowers” appeared continuously when the concentration increased from 3 g/L to 5 g/L. Mono-dispersion was obtained with relatively lower PEG concentration. The observed evolvement was discussed based on the interaction between the polymers and the nanocrystallites with assistance of FTIR. The coverage of polymer chains on surface of nanocrystallites leads to isolated reactors, which benefits the uniform coarsening rate of the nanocrystallites. The synthesized TiO2 sols were utilized in dye sensitized solar cells. Performance parameters of the solar cells were discussed with assistance of dye desorption experiments. The improved dispersion in sols was found to benefit the photovoltaic performance of the cells.
Keywords: Hydrothermal; Titanium dioxide; Dye sensitized solar cells; PEG; Ostwald ripening; Transmission electron microscopy;
Monodisperse conducting colloidal dipoles with symmetric dimer structure for enhancing electrorheology properties by Kyomin Shin; Daun Kim; Jun-Cheol Cho; Hyung-Seok Lim; Jin Woong Kim; Kyung-Do Suh (18-24).
Display Omitted► Symmetric colloidal dipole particles were fabricated for electrorheological applications. ► Shape anisotropy of conducting particles is critical for enhancing electrorheology effects. ► Shape anisotropy of suspending particles increases the dipole moment under the electric field. ► Colloidal dipoles form a well-structured colloidal gel network under electrical fields.This study introduces an electrorheological (ER) approach that allows us to obtain remarkably enhanced ER properties by using monodisperse colloidal dimer particles. Two sets of colloidal particles, which are spheres and symmetric dimers, were synthesized employing the seeded polymerization technique. The aspect ratio of dimer particles was ∼1.43. Then, the surface of the particles was coated with polyaniline by using the chemically oxidative polymerization method. After preparation of the particle suspensions having the same particle volume and concentration, their ER behavior was investigated with changing the electric field strength. At the same experimental condition, both shear stress and shear yield stress of the dimer particle suspension remarkably increased, compared with those of the spherical particle suspension. This attributes to the fact that the shape anisotropy of suspending particles effectively led to increase in the dipole moment under the electric field, thus resulting in formation of a well-structured colloidal chains between the electrodes.
Keywords: Colloidal dipoles; Dimer particles; Electrorheology; Shape anisotropy; Dipole moment;
A method for estimating effective coalescence rates during emulsification from oil transfer experiments by Andreas Håkansson; Christian Trägårdh; Björn Bergenståhl (25-33).
Display Omitted► A method for obtaining coalescence rates during emulsification is developed. ► The method is based on Taisnes oil transfer experiments and a simulation model. ► Taisnes experimental measure is largely independent of fragmentation rate. ► The method gives qualitative scaling of coalescence with operating parameters. ► The method is exemplified with homogenizer pressure and surface load of emulsifier.The Oil Transfer Technique (OTT) was developed by Taisne et al. to measure coalescence during emulsification and has been applied since in several studies. One of the main drawbacks of this technique is that it only gives a qualitative measure of coalescence. This paper proposes a new evaluation method of OTT experimental results for estimating qualitative coalescence rates, e.g. for investigating the scaling of coalescence with emulsification parameters (such as homogenizing pressure, and emulsifier concentration).The method is based on comparison with simulated OTT experiments using bivariate Population Balance Equation models. Simulations have been performed under a wide variety of conditions in order to investigate the influence of assumptions on coalescence and fragmentation kernels. These investigations show that the scaling of coalescence rates could be determined accurately when the scaling of efficient residence time of drops in the active region of homogenization is known. The proposed evaluation method is also exemplified by analyzing OTT data from two previously published studies.
Keywords: Coalescence; Emulsification; Population Balance Equations; High-pressure homogenization;
Template effect of hydrolysis of the catalyst precursor on growth of carbon nanotube arrays by S.H. Liu; X.W. Zhao; T.S. Pan; S. Wu; B. Zeng; H.Z. Zeng; M. Gao; Y. Zhang; W. Huang; Y. Lin (34-39).
Display Omitted► The hydrolytic extent of TEOS influences the size and density of catalysts. ► The catalyst size decreases with the increase of hydrolytic time. ► The hydrolytic product prevents catalysts from aggregating into big clusters. ► Ordered and high quality CNTs are prepared during the later hydrolytic process.Iron catalyst films for the growth of carbon nanotube (CNT) arrays are prepared using sol–gel technique during different hydrolytic periods. It is shown that the extent of hydrolysis of the catalyst precursor has strong impacts on the size and density of iron catalyst particles, which distributed on surface of the film. The iron catalysts formed big clusters in the early stage of the hydrolysis, whereas the particle size decreased dramatically to approximate 20 nm when the hydrolytic duration is as long as 150 h. The reaction between the hydrolytic product of ethyl orthosilicate and the iron oxide particles effectively influence the structure of catalysts during the process of annealing precursor films and reducing the iron oxide particles into iron catalysts. We believe that the hydrolytic product limits the mobility of the catalyst particles, preventing them from aggregating into big clusters by Ostwald ripening. This catalyst film may be utilized to create a template to control the length and quality of CNTs.
Keywords: Carbon nanotubes; Iron catalyst particles; Hydrolysis; SiO2; TEOS; Sol–gel; Ferric nitrate;
Morphologic evolution of Au nanocrystals grown in ionic liquid by plasma reduction by Yongbing Xie; Zhehao Wei; Chang-jun Liu; Lan Cui; Chao Wang (40-44).
Display Omitted► Au nanocrystals grown in an ionic liquid by glow discharge plasma reduction. ► Shape control in faceted NPs, peanut-like dimers, and nanorods by the growth time. ► A polymer-assisted oriented attachment mechanism for the morphologic evolution.Shape controlled Au nanocrystal growth in ionic liquid has been studied by glow discharge plasma reduction. In an 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) solution with poly(vinyl pyrrolidone) (PVP) as surfactant, Au nanocrystals grow from faceted NPs to peanut-like particle aggregates, and eventually worm-like nanorods and nanowires as the growth time increases. This process is further found to be dependent on the concentration of employed surfactant. Based on systematic microscopic analysis and control experiments, a polymer-assisted oriented attachment mechanism is proposed to explain the observed morphologic evolution. Our work may have great implications for the employment of ionic liquids for shape controlled synthesis of nanocrystals.
Keywords: Au nanocrystals; Shape control; Ionic liquids; Glow discharge; Plasma reduction;
Superparamagnetic and fluorescent thermo-responsive core–shell–corona hybrid nanogels with a protective silica shell by Thomas M. Ruhland; Paul M. Reichstein; Alexander P. Majewski; Andreas Walther; Axel H.E. Müller (45-53).
Display Omitted► Straightforward and detailed protocol for the synthesis of multifunctional inorganic/organic hybrid nanogels with core-shell-corona structure. ► Fluorescent and/or magnetic core (CdSe, Fe2O3), intermediate acid-protective silica shell and a smart and thermo-responsive polymer corona (PNIPAAm). ► Tunable thickness of the intermediate silica shell and control over encapsulation of single versus multiple nanoparticles. ► Hybrid nanogels retain all functionalities of the used building blocks and join the attractive functionalities of the inorganic and the soft matter domain.We present the preparation and the characterization of the solution behavior and functional properties of superparamagnetic and/or fluorescent, thermo-responsive inorganic/organic hybrid particles with an intermediate protective silica shell and a smart polymer corona. These well-defined multifunctional nanogels were prepared via two consecutive encapsulation processes of superparamagnetic Fe2O3 nanoparticles (NPs) and/or fluorescent CdSe(ZnS) semiconductor nanocrystals with a silica layer and a crosslinked poly(N-isopropylacrylamide) (PNIPAAm) polymer shell. First, the different NPs were entrapped into a silica shell using a microemulsion process. Therein, the precise adjustment of the conditions allows to entrap either several particles or single ones and to tailor the thickness of the silica shell in the range of 20–60 nm. In a second step, a polymer coating, i.e. thermosensitive PNIPAAm, was attached onto the surface of the multifunctional core–shell particles via free radical precipitation polymerization, furnishing multifunctional core–shell–corona hybrid nanogels. Analyses of the functional properties, i.e. optical brightness and magnetic moments, along with transmission electron microscopy reveal near monodisperse hybrid nanoparticles that retain the intrinsic properties of the original nanocrystals. Additionally, we demonstrate the drastically increased chemical stability due to the barrier properties of the intermediate silica layer that protects and shields the inner functional nanocrystals and the responsive character of the smart PNIPAAm shell.
Keywords: Core–shell–corona particles; Nanogels; Microgels; Fluorescent and magnetic nanoparticles; Hybrid particles; Inorganic nanocrystals; Stimuli-responsive particles;
Synthesis of block copolymer poly (n-butyl acrylate)-b-polystyrene by DPE seeded emulsion polymerization with monodisperse latex particles and morphology of self-assembly film surface by Wenwen Wang; Qiuyu Zhang (54-60).
Display Omitted► Block copolymer was firstly synthesized by DPE seeded emulsion polymerization. ► Monodisperse latex particles were obtained resulting from monomer swollen into seeded latex and DPE mechanism. ► High conversion and high solid content are beneficial for industrial application. ► Film with phase separation was got and potential for preparation of nanostructure materials.Synthesis of poly (n-butyl acrylate)-b-polystyrene (PnBA-b-PSt) with high molecular weight in an environmentally benign medium was carried out in seeded emulsion polymerization, using a novel chain transfer active DPE (1,1-diphenylethylene) agent. Seed latex containing precursor P(nBA-DPE) was prepared first, and the second monomer styrene was swelled into seed latex particles, yielding block copolymer at high conversion. Structures as well as molecular weight of precursor and block copolymer were characterized by FTIR, 1H NMR, and SEC, respectively. Furthermore, Transmission Electron Microscopy (TEM) observation and Laser Light Scattering (LLS) manifested that monodisperse latex particles were obtained. Self-assembly morphology of block copolymer membrane surface was examined by atom force microscopy (AFM). Phase separation was observed clearly, which was confirmed by the observation of two glass transitions in DSC curve.
Keywords: Seeded emulsion polymerization; DPE (1,1-diphenylethylene); Block copolymer; Phase separation;
Production of CaCO3/hyperbranched polyglycidol hybrid films using spray-coating technique by Kalina Malinova; Manfred Gunesch; Sabrina Montero Pancera; Robert Wengeler; Bernhard Rieger; Dirk Volkmer (61-69).
Display Omitted► Hyperbranched polyethers were prepared via efficient one-pot-synthetic route. ► Hyperbranched polymers are functionalized with sulfate, carboxylic or phosphate-esters groups. ► Hyperbranched polymers were employed to control CaCO3 particle morphology. ► Spray-coating technique led to dense vaterite, calcite–vaterite or calcite thin films. ► Mechanical properties of selected composites were compared to neat calcite.Biomineralizing organisms employ macromolecules and cellular processing strategies in order to produce highly complex composite materials such as nacre. Bionic approaches translating this knowledge into viable technical production schemes for a large-scale production of biomimetic hybrid materials have met with limited success so far. Investigations presented here thus focus on the production of CaCO3/polymer hybrid coatings that can be applied to huge surface areas via reactive spray-coating. Technical requirements for simplicity and cost efficiency include a straightforward one-pot synthesis of low molecular weight hyperbranched polyglycidols (polyethers of 2,3-epoxy-1-propanol) as a simple mimic of biological macromolecules. Polymers functionalized with phosphate monoester, sulfate or carboxylate groups provide a means of controlling CaCO3 particle density and morphology in the final coatings. We employ reactive spray-coating techniques to generate CaCO3/hybrid coatings among which vaterite composites can be prepared in the presence of sulfate-containing hyperbranched polyglycidol. These coatings show high stability and remained unchanged for periods longer than 9 months. By employing carboxylate-based hyperbranched polyglycidol, it is possible to deposit vaterite–calcite composites, whereas phosphate-ester-based hyperbranched polyglycidol leads to calcite composites. Nanoindentation was used to study mechanical properties, showing that coatings thus obtained are slightly harder than pure calcite.
Keywords: Spray coating; Calcium carbonate composites; Vaterite; Functionalization of polymers; Hyperbranched polyglycidol;
Correlation of macroscopic aggregation behavior and microscopic adhesion properties of bacteria strains using a dimensionless Tabor’s parameter by Xin Wang; Yueyun Li; Annalisa Onnis-Hayden; Ce Gao; April Z. Gu; Kai-tak Wan (70-76).
Display Omitted► Macroscopic aggregation of seven bacteria strains characterized by standard optical method. ► Microscopic mechanical characterization of single cells using AFM to yield elastic modulus, adhesion, shape and dimension. ► Strong correlation shown between microscopic and macroscopic properties via a modified Tabor’s parameter. ► Cost and time effective microscopic characterization method yields reliable prediction of macroscopic behavior. ► Results have significant impacts in adhesion–aggregation–transportation of bacteria in wastewater treatment and bioremediation.Macroscopic adhesion–aggregation, floc formation, and subsequent transportation of microorganisms in porous media are closely related to the microscopic behavior and properties of individual cells. The classical Tabor’s parameter in colloidal science is modified to correlate the macroscopic aggregation and microscopic adhesion properties of microorganisms. Seven bacterial strains relevant to wastewater treatment and bioremediation were characterized in terms of their macroscopic aggregation index (AI) using an optical method, and their microscopic coupled adhesion and deformation properties using atomic force microscopy (AFM). Single cells were indented to measure the range and magnitude of the repulsive–attractive intersurface forces, elastic modulus, thickness and density of the cellular surface substances (CSS). The strong correlation suggests that cost and time effective microscopic AFM characterization is capable of making reliable prediction of macroscopic behavior.
Keywords: Aggregation; Adhesion; Bacteria; AFM; Tabor’s parameter;
Detection of surface silanol groups on pristine and functionalized silica mixed oxides and zirconia by Florian M. Wisser; Matthias Abele; Matthias Gasthauer; Klaus Müller; Norbert Moszner; Guido Kickelbick (77-82).
Display Omitted► Hydroxyl content determination on metal oxide surface. ► Impact of surface modification on hydroxyl content. ► Validation of determination of surface OH groups by titration with lithium aluminum hydride.The surface hydroxyl content and surface structure of silica and other oxides with and without surface modification were systematically studied by solid state 29Si NMR, thermogravimetric analysis, and the lithium alanate method. Aerosil 90 as a well described reference system and functionalized zirconia–silica particles were used in the validation of the lithium alanate method. 3-Methacryloxypropyltrimethoxysilane and dodecylphosphonic acid were applied as surface modifiers. The determination of silanol content of Aerosil 90 by 29Si NMR and TGA confirms the results obtained by the lithium alanate method, which also allows for the determination of the remaining surface hydroxyl content after surface modification. For both silane coupling agents, the residual hydroxyl content of modified zirconia–silica is decreased by a factor of approximately 2 compared with that of the unmodified mixed oxide, whereas after modification with dodecylphosphonic acid, the hydroxyl content is slightly higher. These results are again in good agreement with those by 29Si NMR confirming that the lithium alanate method is a reliable and easily practicable method for surface hydroxyl determination.
Keywords: Surface-functionalization; Silanol content; Silica; Zirconia; Mixed oxides; Hydroxyl content;
Pt/titania/reduced graphite oxide nanocomposite: An efficient catalyst for nitrobenzene hydrogenation by Yanfei Zhao; Hongye Zhang; Changliang Huang; Sha Chen; Zhimin Liu (83-88).
Display Omitted► Pt/TiO2/RGO was obtained by immobilizing Pt particles onto TiO2/RGO. ► TiO2/RGO was prepared via redox reaction between TiCl3 and GO. ► Pt/TiO2/RGO showed high activity and selectivity for nitrobenzene hydrogenation. ► The catalyst can be reused for six times without any activity loss.In this work, a ternary composite, Pt/TiO2/RGO (reduced graphite oxide), was prepared via immobilizing Pt particles onto the TiO2/RGO composite that was obtained via redox reaction of TiCl3 and GO. The composite was characterized by different techniques including X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The TiO2 particles with size less than 10 nm were uniformly distributed throughout the RGO, and almost each Pt particle with size around 3 nm adhered to TiO2 particles, resulting in high dispersion of all Pt particles on the support. The Pt particles were in the electron-deficient state due to the strong interactions with the TiO2 particles and the RGO support. The catalytic performance of the composite for nitrobenzene hydrogenation was investigated under solvent-free condition. It was indicated that the Pt/TiO2/RGO catalyst exhibited high activity with a turnover frequency (e.g., 59,000 h−1) as well as superior selectivity to aniline (e.g., >99%). Moreover, the catalyst can be reused for six times without any activity loss, which resulted from the stable structure of the catalyst.
Keywords: TiO2; Reduced graphite oxide; Platinum; Nitrobenzene hydrogenation;
Fabrication of biomimetic high performance antireflective and antifogging film by spin-coating by Liang Zhang; Changli Lü; Yunfeng Li; Zhe Lin; Zhanhua Wang; Heping Dong; Tieqiang Wang; Xuemin Zhang; Xiao Li; Junhu Zhang; Bai Yang (89-95).
Display Omitted► We prepare antireflective, antifogging and mechanical stable films by spin-coating. ► Mesoporous SiO2 particles decrease the refractive index of the films. ► Mesoporous SiO2 particles increase the roughness of the films. ► SiO2 sol increase the mechanical stability of the films.In this paper, we report a facile way to fabricate biomimetic high performance optical hybrid films with excellent antireflective and antifogging properties by one-step spin-coating the mixture of mesoporous SiO2 particles and SiO2 sol. The production process of the films is easy, low-cost, and time-efficient. Mesoporous SiO2 particles containing surfactants disperse in SiO2 sol stably without any chemical modification, which decrease the effective refractive index and increase the transmittance of the films. In addition, such films possess superhydrophilic properties and exhibit high performance antifogging properties. Due to the good film forming performance of SiO2 sol, mesoporous SiO2 particles are embedded in the films and impart the films high mechanical stability and durability. The surface morphology of the films can maintain well after repeated friction, and the performances of antireflective and antifogging also do not change as well.
Keywords: Biomimetic; Mesoporous; Antireflective; Antifogging; Mechanical stability;
Synthesis and properties of Au–Fe3O4 heterostructured nanoparticles by Yang Sheng; Junmin Xue (96-101).
3.5–9 nm Au–Fe3O4 hetero-dimers synthesized with 0.6 M HDD and 2 mmol Fe(CO)5. The dark domain represented Au nanoparticle, while the low contrast part belonged to Fe3O4 nanoparticle.Display Omitted► Au–Fe3O4 hetero-dimers were synthesized via a hot injection method. ► The hetero-dimers showed plasmon absorption and magnetization dual functionalities. ► Star-like Au–Fe3O4 nanocomposites were developed from the hetero-dimers.Au–Fe3O4 composite nanoparticles have received much research interest due to their promising biomedical applications. In this work, Au–Fe3O4 composites with well-defined dimer-like nanostructure were synthesized via thermal decomposition route. The surfactant 1,2-hexandicandiol has proved to be critical for the formation of the Au–Fe3O4 hetero-dimers. The hetero-dimers production yield could be significantly improved to be 90% when the 1,2-hexandicandiol concentration was optimized at 0.6 M. The obtained Au–Fe3O4 hetero-dimers possess dual-functionalities of plasmon resonance and magnetization. Moreover, the Fe3O4 domain of the hetero-dimers can be tuned readily by adjusting the molar ratio between Fe and Au sources. Furthermore, it was demonstrated that these Au–Fe3O4 hetero-dimers could be further developed into star-like Au–Fe3O4 nanoparticles which showed plasmon absorption at NIR region.
Keywords: Nanocomposites; Hetero-dimer; Au; Fe3O4; Plasmon resonance;
Highly magnetizable superparamagnetic colloidal aggregates with narrowed size distribution from ferrofluid emulsion by Volodymyr Lobaz; Robin N. Klupp Taylor; Wolfgang Peukert (102-110).
Display Omitted► Emulsification of a ferrofluid for the production of spherical magnetite aggregates. ► Tailoring of bead size by optimized emulsification parameters. ► Tunable surface properties of spherical aggregates.The formation of spherical superparamagnetic colloidal aggregates of magnetite nanoparticles by emulsification of a ferrofluid and subsequent solvent evaporation has been systematically studied. The colloidal aggregates occur as a dense sphere with magnetite nanoparticles randomly packed and preserved particle–particle separation due to chemisorbed oleic acid. The voids between nanoparticles are filled with solvent and free oleic acid. The latter was found to influence the formation of colloidal aggregates and their surface properties. The choice of surfactant, whether low molecular weight or polymeric, was shown to lead to the colloidal aggregates having tailored interfacial behavior. Magnetization measurements at ambient temperature revealed that the magnetite colloidal aggregates preserve the superparamagnetic properties of the starting nanoparticle units and show high saturation magnetization values up to 57 emu/g. The size distribution of magnetite nanoparticle colloidal aggregates produced by such an approach was found to be a function of emulsion droplet breakup – coalescence and stabilization kinetics and therefore is influenced by the emulsification process conditions and concentrations of the emulsion compounds.
Keywords: Magnetite nanoparticle; Superparamagnetic particle; Colloidal aggregate; Emulsion;
Effect of natural organic matter on aggregation behavior of C60 fullerene in water by Hamid Mashayekhi; Saikat Ghosh; Peng Du; Baoshan Xing (111-117).
Display Omitted► Natural organic matter (NOM) affects fullerene aggregation through steric effect. ► High molecular weight NOM is more effective in stabilizing fullerene suspension. ► More polar NOM is less effective in stabilizing fullerene suspension. ► Sorption of NOM on fullerene is positively correlated with NOM molecular weight.The stability of C60 fullerene particles in water affects its mobility, bioavailability, and toxicity to organisms. Natural organic matters (NOMs) have pronounced effects on the aggregation behavior of C60 fullerene. This study was to examine the effects of NOM structural properties on the aggregation behavior of fullerene water suspension (FWS). Fulvic acid (FA), tannic acid (TA), and two structurally different humic acids (HA1 and HA7) were studied. HA1 and HA7 were sequentially extracted HAs, where HA7 was more hydrophobic than HA1 and had a higher molecular weight. Aggregation was induced by addition of varying amounts of Ca2+ to the FWS with 2 mg/L of each NOM. The absolute value of zeta potential |ζ| of pure FWS increased after addition of any type of NOM. Addition of Ca2+ to the FWS + NOM system decreased |ζ| of fullerene almost uniformly for all types of NOM. FWS critical coagulation concentration (CCC) was equal to 14.5, 6.5, 5.4, and 3.7 mM Ca2+ for HA7, HA1, FA, and TA, respectively. The order of increasing CCCs was positively correlated to the NOMs molecular weight and negatively to their polarity. A nearly constant ζ for FWS + NOM system at a wide range of Ca2+ concentrations suggested the steric stability rather than electrostatic one. This study highlighted the role of NOM in the fate of manufactured nanoparticles in the environment and linked the structural properties of NOM to their interaction with manufactured nanoparticles.
Keywords: Fullerene; Dispersion; Aggregation kinetics; Natural organic matter;
Characterization of synthetic hematite (α-Fe2O3) nanoparticles using a multi-technique approach by Claudio Colombo; Giuseppe Palumbo; Andrea Ceglie; Ruggero Angelico (118-126).
Display Omitted► Characterization of Fe-oxides morphologies. ► Nanoparticle sizes and shapes through AFM and TEM techniques. ► Polydispersity and hydrodynamic nanoparticle diameters. ► Particle surface charge and zeta potential.The aim of this work was to investigate the surface structure of aqueous hematite dispersions characterized by a large variability of morphology and particle size combining structural investigations obtained from Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) techniques with in vitro particle size distributions and zeta potential measurements from Dynamic Light Scattering (DLS) technique, and we achieved a self-consistent and detailed characterization of hematite particles whose sizes and morphologies could be correlated to the synthesis conditions (type of added anion, Al substitution and pH). Surface AFM characterization provided an accurate analysis of particle microstructure and also indicated that the growth of microcrystals followed different surface roughness. DLS, AFM, and TEM techniques furnished complementary information on the average particle dimensions, whose variation could be attributed to the morphological difference of hematites, ranging from platy to regular or irregular hexagonal or ellipsoidal shape. Finally, a correlation between the average particle dimensions and the measured zeta potential was also been found in aqueous dilute suspensions characterized by neither pH nor-ionic-strength-control, for which a drop of zeta potential from positive to negative values was detected for hematite particle dimensions larger than a threshold size of ∼150 nm.
Keywords: Hematite nanoparticles; Particle size; AFM; TEM; DLS; Zeta potential;
Aggregates and hydrogels prepared by self-assembly of amphiphilic copolymers with surfactants by Xiaohan Wu; Abdeslam El Ghzaoui; Suming Li (127-134).
A series of water-insoluble polylactide/poly(ethylene glycol) (PLA/PEG) block copolymers were synthesized by ring-opening polymerization of lactide in the presence of mono- or dihydroxyl PEG, using nontoxic zinc lactate as catalyst. Interactions between the resulting copolymers and sodium dodecyl sulfate (SDS) in water were studied by varying SDS fraction and copolymer concentration, using ultraviolet–visible spectrometer. Light transmission results show that all the insoluble copolymers strongly interact with SDS, and the solubility of the copolymers is improved with increasing SDS fraction. Copolymers with triblock structures or higher molar masses present larger variation of solubility as compared to those with diblock structures or lower molar masses. Transmission electron microscopy and dynamic light scattering were then employed to examine the microstructure of aggregates in the mixture solutions. Various aggregates such as vesicles, branch-like micelles, spherical micelles, or nanogels were observed, depending on the SDS fraction and copolymer concentration. It is assumed that at low SDS fractions, surfactant molecules attach to PLA segments and make the copolymers more soluble to form various aggregates. At high SDS fractions, junctions composed of SDS aggregates with PLA segments involved inside are formed in the case of triblock copolymers and diblock ones with high molar masses. These junctions lead to cross-linking of copolymer chains to yield a nanogel. Hydrogels can be obtained at high concentrations as confirmed by rheological measurements.
Keywords: Polylactide; Poly(ethylene glycol); Sodium dodecyl sulfate; Self-assembly; Aggregate; Hydrogel;
Exfoliation of montmorillonite in protein solutions by Krzysztof Kolman; Werner Steffen; Gabriela Bugla-Płoskońska; Aleksandra Skwara; Jacek Pigłowski; Hans-Jürgen Butt; Adam Kiersnowski (135-140).
Display Omitted► Sequential adsorption of proteins leads to exfoliation of montmorillonite stacks. ► At high protein-to-silicate ratio platelets form randomly structured secondary particles. ► Despite exfoliated, secondary gel-like aggregates retain submicron dimensions. ► Described method can be utilized to stabilize aqueous dispersions of clay particles.In the study we demonstrate a method to obtain stable, exfoliated montmorillonite–protein complexes by adsorption of the proteins extracted from hen-egg albumen. Analysis of the process by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS–PAGE) revealed that the complexes are formed by sequential adsorption of ovotransferrin, ovalbumins, ovomucoid and lysozyme on the surface of the silicate. Structural studies performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the adsorption of ovotransferrin and albumins is accompanied by disintegration of clay stacks into discrete platelets. Further analysis by dynamic light scattering (DLS) revealed that at protein to silicate weight ratios exceeding 20, the synergistic adsorption of albumen components leads to reaggregation of silicate platelets into disordered, microgel-like particles. By means of DLS it was found that exfoliation predominantly leads to formation of particles with average hydrodynamic radii (R h) of 0.19 μm while their aggregation causes formation of particles having R h in of approx. 0.5 μm and larger.
Keywords: Montmorillonite; Exfoliation; Nanoparticles; Proteins; Adsorption; TEM; DLS; Bionanocomposites;
Numerical study on dielectrophoretic chaining of two ellipsoidal particles by Dustin L. House; Haoxiang Luo; Siyuan Chang (141-149).
Display Omitted► We use a boundary-element method to model DEP interaction of two ellipsoid particles. ► Particles are 3D non-conducting, prolate spheroids. ► Results explain the chaining mechanism behind experimental phenomenon seen previously. ► Electro-orientation is completed much faster than global realignment.Electric field-induced assembly of biological and synthetic particles has proven useful in two- and three-dimensional fabrication of composite materials, microwires, photonic crystals, artificial tissues, and more. Biological particles are typically irregularly shaped, and using non-spherical synthetic particles has the ability to expand current applications. However, there is much to be understood about the dielectrophoretic (DEP) interaction that takes place between particles of general shape. In this work, we numerically study the DEP interaction between two prolate spheroid particles suspended in an unbounded fluid. The boundary-element method (BEM) is applied to solve the coupled electric field, Stokes flow, and particle motion, and the DEP forces are obtained by integrating the Maxwell stress tensor over the particle surfaces. Effects of the initial configuration and aspect ratio are investigated. Results show that the particles go through a self-rotation process, that is, electro-orientation, while translating slowly to form a chain pair. The final formation resembles the chaining pattern observed previously in experiments using densely distributed ellipsoidal particles. Thus, the transient behavior and particle–particle interaction exhibited in the current study could be used as the fundamental mechanism to explain the phenomenon in the experiment.
Keywords: Dielectrophoresis; Ellipsoid; Boundary-element method; Self-assembly;
Straightforward preparation of organic colloidal particles by harnessing spontaneous non-covalent interactions of active molecules from natural origin by Ashok R. Patel; Jack Seijen-ten-Hoorn; Patricia C.M. Heussen; Ellen Drost; Johan Hazekamp; Krassimir P. Velikov (150-156).
Display Omitted► Non-covalent spontaneous interactions between berberine and tannic acid. ► Stabilisation by Glycyrrhizin due to its interaction with both berberine and tannic acid. ► Straightforward preparation of spherical colloidal particles simply by mixing these components at certain molar ratio. ► Characterisation of particle size, surface potential and morphology.We demonstrate a straightforward method to prepare organic colloidal particles based on the spontaneous molecular interactions between small molecular weight actives of natural origin. Representative reactive natural actives from three of the most researched classes of phytochemicals including berberine (isoquinoline alkaloid), tannic acid (polyphenol) and glycyrrhizin (olenane type saponin) were chosen for the study. Binding parameters (association constant, binding enthalpy and entropy) obtained from isothermal titration calorimetry indicated that berberine strongly interacted with tannic acid to form insoluble colloidal complex which could be stabilised in the presence of glycyrrhizin (due to its interaction with both berberine and tannic acid and also due to its amphiphilic nature). Working on this principle, the mutual interactions of these three natural actives were exploited to obtain stable spherical particles with a mean diameter of less than 100 nm (77 nm) simply by mixing the aqueous solutions of berberine:tannic acid:glycyrrhizin at molar ratio of 2:1:1. The involvement of aromatic chromophore (π–π*) system and charged N atom of berberine in the spontaneous interaction between berberine and tannic acid was confirmed from spectral analysis. X-ray diffraction study suggested formation of amorphous organic colloidal particles, and the spherical shape of colloidal particles was confirmed by transmission electron microscopy.
Keywords: Berberine; Colloidal particles; Isothermal titration calorimetry; Non-covalent interactions; Natural bioactives;
Supra-long chain surfactants with double or triple quaternary ammonium headgroups by Tomokazu Yoshimura; Nagisa Chiba; Keisuke Matsuoka (157-163).
Display Omitted► Supra-long chain surfactants composed of C18–C22 and two or three headgroups. ► Their water solubility is improved by introducing additional hydrophilic groups. ► Their cmcs are smaller than the corresponding gemini and bolaform surfactants. ► Their adsorption is lower slightly at the air/water interface than comparable regular surfactants. ► Their behavior is because of the curved supra-long chain and the electrostatic repulsion between headgroups.Novel supra-long chain surfactants with double or triple quaternary ammonium salts (C n -2Am, C n -3Am, in which n represents a hydrocarbon chain length of 18, 20, and 22) were synthesized, and electrical conductivity and surface tension were used to characterize their properties depending on both the hydrocarbon chain length and number of hydrophilic groups. The Krafft temperatures decreased remarkably with an increase in the quaternary ammonium headgroups, resulting in a high solubility in water. The critical micelle concentration (cmc) increased with an increase in the number of quaternary ammonium moieties in the hydrophilic group, and the difference in the cmc was smaller for C n -2Am and C n -3Am than for C n -2Am and C n -Am of alkyltrimethylammonium bromide. The surface tension at the cmc was approximately 45 and 48 mN m−1 for C n -2Am and C n -3Am with n = 18–22, respectively. This indicated that the supra-long chain surfactants could not efficiently adsorb at the air/water interface and orient by themselves, as is known for conventional surfactants.
Keywords: Supra-long chain surfactant; Multi-hydrophilic groups; Critical micelle concentration; Surface tension; Free energy of micellization;
Scanning force microscopy as a tool to investigate the properties of polyglycerol ester foams by Corina Curschellas; Rabea Keller; Rüdiger Berger; Uwe Rietzler; Daniela Fell; Hans-Jürgen Butt; Hans Jörg Limbach (164-175).
Display Omitted► We investigated polyglycerol ester at interfaces by scanning force microscopy. ► Different film preparation and transfer techniques were applied. ► A new approach for the transfer of bubble skins was introduced. ► Interfaces are covered non-homogenously, by lamellar structures.Foamed products are a popular class of food products. The mechanism of stabilization of the air bubbles is often only partially understood. The current study aims at better understanding the stabilization of air–water interfaces through the low molecular weight surfactant polyglycerol ester (PGE). We chose PGE films as an exemplary case for a non-equilibrium situation at an air–water interface – a situation that requires the development of new experimental techniques. Several different film preparation and transfer methods onto solid substrates have been tested. The films were then investigated by scanning force microscopy, and structural artifacts associated to the sample preparation were identified and discussed. In addition to the study of Langmuir monolayers and Gibbs adsorption layers, we have proposed a new approach to investigate the skins of foam bubbles. We thereby were able to determine that PGE indeed covers bubbles by a multilayer structure and that the pH plays a role in the structuring of the films. We show that a combination of different film preparation methods allows us to get an insight into the aggregation behavior of PGE at the air–water interface and thereby better understand the stabilization mechanism of this particular surfactant.
Keywords: Polyglycerol ester; Foam films; Bubble; Scanning force microscopy; Lamella; Vesicle;
Aqueous mixtures of di-n-decyldimethylammonium chloride/polyoxyethylene alkyl ether: Dramatic influence of tail/tail and head/head interactions on co-micellization and biocidal activity by Gaétan Rauwel; Loïc Leclercq; Jacques Criquelion; Jean-Marie Aubry; Véronique Nardello-Rataj (176-186).
Display Omitted► Nonionic surfactants inhibit the biocidal activity of quaternary ammonium surfactants. ► Co-micellization decreases the concentration of unimers of the biocidal surfactant. ► Cationic unimers exhibit a biocidal activity unlike micellized cationic surfactants. ► The biocidal activity of cationic surfactants is maintained when mixed with C10Ej . ► The biocidal activity of cationic surfactants is strongly inhibited with C12Ej .Mixed aggregate formation and synergistic interactions of binary surfactant mixtures of di-n-decyldimethylammonium chloride, [DiC10][Cl], with polyoxyethylene alkyl ethers, C i E j (i = 10, 12, j = 4, 6, 8), have been investigated for various [DiC10][Cl]/C i E j ratios. The critical aggregation concentration of the binary mixtures has been determined by tensiometry, and the aggregate characteristics (i.e., size and composition, free ammonium concentration) have been estimated using the pulsed field gradient NMR spectroscopy and a [DiC10]-selective electrode. Diffusion coefficient measurements of micelles confirmed the synergistic interaction between the surfactants. It is thus shown that the formation of surface monolayers and mixed aggregates from [DiC10][Cl]/C10E j mixtures is driven by both tail/tail and head/head interactions, whereas [DiC10][Cl]/C12E j co-aggregation is mainly driven by tail/tail interactions. As a consequence, the co-aggregation phenomenon notably influences the biocidal activity of [DiC10][Cl] on the Candida albicans fungi. In the presence of C12E j , the biocidal activity of the ammonium salt is inhibited due to the trapping of the cationic surfactants in the mixed aggregates, whereas in the presence of C10E j , the biocidal activity of the surfactant mixture is maintained. The mode of action is also confirmed by a faster increase in the zeta potential of a C. albicans suspension in the presence of [DiC10][Cl]/C10E8 than in the presence of [DiC10][Cl]/C12E8 . Therefore, a judicious adjustment of the alkyl (i) and polyoxyethylene (j) chain lengths of C i E j avoids its antagonistic effect on the biocidal activity of [DiC10 ][Cl].
Keywords: Di-n-alkyldimethylammonium chloride; Polyoxyethylene alkyl ether; Binary surfactant systems; Mixed aggregates; Biocidal activity; Podand effect;
Synthesis and aggregation behavior of grafted maleic acid copolymers by Wei Zhang; Zhiping Du; Wanxu Wang; Tianzhuang Wang (187-196).
Display Omitted► Three comb-like maleic acid copolymers were prepared using a single batch method. ► The average monomeric molecular weight of each copolymer was obtained. ► The adsorption and aggregation parameters were evaluated. ► The rheological behavior of copolymer aqueous samples was evidently different. ► The aggregate structures of three products were deduced.Grafted SMA containing poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether) (SMA–PEG) and its hydrophobically modified products poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether & dodecyl) (SMA–PEG + C12) and poly(styrene-co-maleic anhydride)-g-(dodecyl) (SMA-C12) were prepared using a single batch method. Their adsorption and rheology behavior was investigated using equilibrium surface tension and rheological techniques. The adsorption parameters, saturation surface excess concentration (Γ max), and the minimum area (A min) of these copolymers were evaluated. The results show that Γ max increased and A min correspondingly decreased with increasing hydrophobicity. Aggregation standard free energy of SMA–PEG + C12 and SMA-C12 suggested that increased hydrophobicity enhanced the tendency for aggregation to occur. The distinctive differences in the macroscopic appearance were shown by aqueous samples of the copolymers. The samples of SMA-M behaved as Newtonian fluids at all concentrations (from 1.0 wt% to 20.0 wt%), indicating that there were no macromolecular chain entanglements or interactions between aggregates in solution. For SMA–PEG + C12, at concentrations above 10.0 wt%, the presence of cross-links between aggregates is presumed to be the reason for the viscoelastic behavior. Solid-like elastic behavior could occur at low concentration (5.0 wt%) of SMA-C12, suggesting the formation of networks by inter-chain aggregation of the hydrophobic dodecyl chains.
Keywords: Amphiphilic comb-like copolymer; Surface activity; Rheological property; Aggregation behavior;
Crystallization from the micellar phase of imidazolium-based cationic surfactants by Fu-Gen Wu; Nan-Nan Wang; Qing-Guo Zhang; Shu-Feng Sun; Zhi-Wu Yu (197-205).
Display Omitted► We study the phase behavior of the imidazolium-based surfactant C16mimCl. ► Two types of micelles form depending on the concentration of C16mimCl. ► The spherical micellar phase converts directly into a lamellar crystalline phase upon cooling. ► The cylindrical micellar phase converts to a lamellar crystalline phase via a lamellar gel phase. ► The submolecular mechanisms of the crystallization processes were studied.The self-assembly and phase behavior of the aqueous dispersions consisting of the cationic surfactant, 1-hexadecyl-3-methylimidazolium chloride (C16mimCl), were studied by differential scanning calorimetry, synchrotron small- and wide-angle X-ray scattering, freeze-fracture electron microscopy, polarizing optical microscopy, and Fourier transform infrared spectroscopy. We found that the crystallization of C16mimCl upon cooling is strongly concentration-dependent. At low concentrations (10–25 wt%), the samples change directly from a spherical micellar solution to a lamellar crystalline phase. While at high concentrations (50–67 wt%), the initial cylindrical micelles first convert to the lamellar gel phase and then to the lamellar crystalline phase. Particular efforts have been devoted to unveiling the submolecular mechanisms of the phase transition processes. The transformation from the initial micellar phase to the final crystalline phase upon cooling involves both an ordering rearrangement in the alkyl tails and a dehydrating process in the head region. At high concentrations, the transformation is divided into two steps, i.e., the gelation and subsequent crystallization processes, both involving evident rearrangements of the surfactant tails. Moreover, a significant dehydration of the surfactant head part takes place in the gelation step and a partial rehydration occurs in the crystallization step.
Keywords: Cationic surfactant; Micelle; Crystallization; Gelation; Submolecular mechanism;
Aggregation behavior of aqueous dioctadecyldimethylammonium bromide/monoolein mixtures: A multitechnique investigation on the influence of composition and temperature by Isabel M.S.C. Oliveira; João P.N. Silva; Eloi Feitosa; Eduardo F. Marques; Elisabete M.S. Castanheira; M. Elisabete C.D. Real Oliveira (206-217).
Display Omitted► Monoolein content strongly influences the structure of DODAB/MO mixtures. ► DODAB/MO mixtures present a two-region phase diagram, above and below χ DODAB = 0.5. ► Temperature increase mimics the effect of higher MO content on aggregate morphology. ► Both MO content and temperature can be tuned up to optimize nucleic acid delivery.A recently described non-viral gene delivery system [dioctadecyldimethylammonium bromide (DODAB)/monoolein (MO)] has been studied in detail to improve knowledge on the interactions between lamellar (DODAB) and non-lamellar-forming (MO) lipids, as a means to enhance their final cell transfection efficiency. Indeed, the morphology, fluidity, and size of these cationic surfactant/neutral lipid mixtures play an important role in the ability of these systems to complex nucleic acids. The different techniques used in this work, namely dynamic light scattering (DLS), fluorescence spectroscopy, differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), light microscopy (LM), and surface pressure–area isotherms, allowed fully characterization of the phase behavior and aggregate morphology of DODAB/MO mixtures at different molar ratios. Overall, the results indicate that the final morphology of DODAB/MO aggregates depends on the balance between the tendency of DODAB to form zero-curvature bilayer structures and the propensity of MO to form non-bilayer structures with negative curvature. These results also show that in the MO-rich region, an increase in temperature has a similar effect on aggregate morphology as an increase in MO concentration.
Keywords: DODAB; Monoolein; Pyrene; Differential scanning calorimetry; Langmuir monolayers; Fluorescence spectroscopy; Light microscopy; Cryo-TEM;
Probing the interactions between chlorpheniramine and 2:1 phyllosilicates by Guocheng Lv; Liu Liu; Zhaohui Li; Libing Liao; Meitang Liu (218-225).
Display Omitted► Charge density played an important role on chlorpheniramine (CP) adsorption and retention. ► Cation exchange was the dominant mechanism for CP adsorption on high charge density clays. ► At high adsorption, CP intercalated into the interlayer of montmorillonite. ► Molecular simulation resulted in interactions between N and the negatively charged mineral surfaces.Interactions between chlorpheniramine (CP), an antihistamine drug used to treat allergy, and 2:1 phyllosilicates were studied under batch kinetic and different solution conditions to investigate the effect of charge density of the substrates on CP removal from solution. The CP removal by Na-montmorillonite was instantaneous, with a very large rate constant and a fast rate, reaching a capacity of 0.64 mmol/g, compared to its cation exchange capacity of 0.85 mmol c /g. In contrast, CP removal by talc was 10 times lower at 0.06 mmol/g. Stoichiometric desorption of exchangeable cations accompanying CP removal by Na-montmorillonite confirmed cation exchange as the dominant interaction mechanism. Solution pH had a minimal effect on CP removal by Na-montmorillonite until pH 11. On the contrary, a slight increase in CP removal by talc was observed as the solution pH increased, due to increased negative charges on the pH-dependent surfaces of talc. Interactions between CP and Na-montmorillonite occurred on both external and interlayer sites, resulting in a d-spacing expansion from 12.5 Å to 15.2 Å. In contrast, interactions between CP and talc were only limited to the external surfaces. It was the charge density that ultimately controlled the amount of CP removal by 2:1 phyllosilicates. Thus, montmorillonite offers a superior option for the removal of cationic drugs from aqueous solution.
Keywords: Adsorption; Chlorpheniramine; Clays; Conformation; Intercalation; Layer charge;
Influence of pH and surface oxygen-containing groups on multiwalled carbon nanotubes on the transformation and adsorption of 1-naphthol by Wenhao Wu; Wei Jiang; Wenxiang Xia; Kun Yang; Baoshan Xing (226-231).
Display Omitted► Oxidization transformation and adsorption of 1-naphthol onto CNTs are pH-dependent. ► Neglecting oxidization loss causes overestimation of 1-naphthol adsorption on CNTs. ► Oxygen-containing groups of CNTs can promote adsorption of 1-naphthol. ► CNTs can interact with 1-naphthol by polymerization of oxygen-containing groups.The pH-dependent behavior, including the transformation of 1-naphthol by oxidative polymerization to form precipitates in solution and the adsorption of 1-naphthol onto carbon nanotubes (CNTs), was examined. Neglecting the precipitate loss of 1-naphthol and possibly of similar chemicals may result in the overestimation of their adsorption and inadequate interpretation of the underlying adsorption mechanisms. Surface oxygen-containing groups on CNTs and the dissociated species of these groups can interact with the dissociated and neutral species of 1-naphthol in a way similar to polymerization, thus promoting the adsorption of 1-naphthol onto CNTs. Adsorption onto CNTs may reduce the polymeric precipitates of 1-naphthol in solution by possibly decreasing aqueous 1-naphthol concentrations. These observations and the underlying mechanisms are important for predicting the fate and risks of naphthalene and carbaryl in the environment because 1-naphthol is a primary metabolite of naphthalene and carbaryl. In addition, it is possible to enhance the removal of 1-naphthol and similar chemicals by controlling the pH and designing specific surface functional groups for CNTs.
Keywords: 1-Naphthol; Carbon nanotubes; pH; Adsorption; Polymerization;
Fluorine sorption by soils developed from various parent materials in Galicia (NW Spain) by C. Gago; A. Romar; M.L. Fernández-Marcos; E. Álvarez (232-236).
Display Omitted► Most Galician natural soils are acid and show a high F sorption. ► F sorption by natural Galician soils fitted both Langmuir and Freundlich isotherms. ► A horizons sorbed generally more fluoride than B horizons. ► Non-crystalline materials were the main responsible for F sorption in Galician soils. ► The risk of fluoride phytotoxicity increased above pH 6.Fluorine is a phytotoxic element that can reach the soil from various industrial activities. Fluorine sorption by soil is crucial to protect water and food chain from fluorine pollution. In Galicia (NW Spain), various activities emit fluorine into the atmosphere, mainly ceramic industries and an aluminium smelter. This study, aiming to investigate fluorine sorption by Galician soils, was conducted on natural soil horizons representative of the area. Most soils were acid and rich in organic matter and showed strong fluorine sorption. The lowest sorptions were exhibited by a near-neutral serpentinite-derived soil (1001 mg kg−1) and the B horizons of soils developed from quartz schist (989 mg kg−1), and the highest by the A horizons of amphibolite-derived soils (1783 mg kg−1). In soils developed from quartz schist, biotitic schist and amphibolite, A horizons sorbed more fluoride than the corresponding B horizons (average 1621 and 1324 mg kg−1, respectively), while the opposite is true in granite-derived soils (average 1644 and 1324 mg kg−1, respectively). In the A horizons, the F sorption significantly correlated to soil pH (r = −0.79), pH in NaF (r = 0.83) and oxalate Al (r = 0.81). In the B horizons, sorption correlated to soil pH (r = −0.78), oxalate Fe (r = 0.71) and organic C (r = 0.66). F sorption can be described by both the Langmuir and Freundlich equations. The concentration of free fluoride in the equilibrium solutions increased above pH 6.
Keywords: Fluoride sorption; Free fluoride; Total fluoride; Sorption isotherms;
Polystyrene-coated micro-sized particles by “in situ” surface initiated polymerization in accord with Langmuir model adsorption by Leïla Ghannam; Laurent Billon (237-240).
Display Omitted► Adsorption of polystyrene chains “in situ” growth from micro-sized flat silicate particles was studied. ► A radical initiator was pre-adsorbed onto the inorganic surface. ► The adsorption isotherms were obtained from TGA and SEC data obtained during the direct polymerization. ► PS monolayer coverage increases with polymerization time and dependents on the monomer diffusion.This study describes the mechanism of adsorption of polystyrene chains PS “in situ” growth from micro-sized commercial silicate particles, i.e. Feldspar. The main aim is to derive adsorption isotherms from thermal gravimetric analysis (TGA) and size exclusion chromatography (SEC) data obtained during the direct polymerization of PS initiated by a pre-adsorbed radical initiator onto the inorganic surface. The adsorption isotherm plot indicates that the PS adsorption is in accord with the Langmuir Model. The amount of PS monolayer coverage increases with polymerization time, and it is highly dependent on the monomer diffusion to the surface during the hybrid inorganic/organic synthesis. Such behavior depends on the concentration gradient between monomer concentration in solution and that adsorbed by polymerization onto the micro-sized particles surface of Feldspar.
Keywords: Adsorption; Isotherm; In situ polymerization; Nitroxide-mediated polymerization;
Electrochemical characterization of Self-assembled Monolayers (SAMs) of silanes on indium tin oxide (ITO) electrodes – Tuning electron transfer behaviour across electrode–electrolyte interface by A. Muthurasu; V. Ganesh (241-249).
Display Omitted► Tuning of electron transfer by choosing a proper spacer and terminal group for SAMs. ► Systematic investigation of silane monolayer formation on semiconductor electrodes. ► Silanes with diverse spacer (aliphatic vs. aromatic) and terminal (–SH and –CH3) groups. ► Heterogeneous electron transfer rate constant is reduced by 3–4 orders of magnitude. ► Pinhole analysis and capacitance measurement using impedance spectroscopy.In this work, we have systematically investigated the formation and characterization of Self-assembled Monolayer (SAM) films of several silanes on indium tin oxide (ITO) surfaces. Silane molecules having different domains namely substrate binding domain (siloxanes), electron transport region (aliphatic and aromatic spacer) and terminal functional groups (–SH, –CH3 groups) are employed for the study in order to tune the electron transfer (ET) behaviour across SAM modified electrode–electrolyte interface. Structural characterization of these monolayer films is carried out using X-ray photoelectron spectroscopy (XPS) studies. Wettability (hydrophilic and hydrophobic nature) of such modified electrodes is evaluated using contact angle measurements. ET behaviour of these modified electrodes is investigated by electrochemical techniques namely cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using K4FeII(CN)6|K3FeIII(CN)6 redox couple as a probe. Disappearance of redox peaks in the CV measurements and formation of semicircle having a higher charge transfer resistance (R ct) values during EIS studies suggest that the resultant monolayer films are compact, highly ordered with very low defects and posses good blocking property with less pinholes. The heterogeneous ET rate constant (k) values are determined from EIS by fitting them to an appropriate equivalent circuit model. Based on our results, we comment on tuning the ET behaviour across the interface by a proper choice of spacer region.
Keywords: Blocking behaviour; Contact angle; Cyclic voltammetry; Electrochemical impedance spectroscopy; Electron transfer; Redox probe; Self-assembled Monolayer (SAM);
Interactions between GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + and cellulosic materials by Ola Sundman; Per Persson; Dipanjan Banerjee; Lars-Olof Öhman (250-257).
Display Omitted► GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 24 7 + seem to initially adsorb as intact ε-Keggin structures to cellulose fibres – EXAFS evidence. ► GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 24 7 + seem to slowly degrade into smaller Ga and Al species. ► The adsorption of GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 24 7 + is very strong on all cellulose materials investigated. ► The Donnan model cannot be used to simply interpret the adsorption of GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 24 7 + on fibres.The adsorption qualities of GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + , a polycation with ε-Keggin structure, and its stability in contact with anionic cellulosic materials, was investigated under different concentration and ionic strength conditions. The cellulosic materials employed were two different fully bleached fibre materials, carboxyl methyl cellulose (CMC), and a spin-coated cellulose model surface. As analytical techniques, pH-measurements, potentiometric titrations, ICP-OES, QCM-D, equilibrium calculations and Extended X-ray Absorption Fine Structure (EXAFS) were used. The adsorption is substantial and the addition of GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + to a fibre suspension results in a rapid decrease in pH, followed by a small and slow increase in pH. This behaviour can be explained as due to a rapid and strong (log β > 2) equilibrium adsorption of intact GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + ions, followed by a slow, and minor, 3–8%, decomposition into different monomers. Alternative layer by layer adsorption of this ion, and CMC, on a spin-coated cellulose model surface constitutes further evidence for the strong interactions between the anionic cellulose materials and GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + . It is shown that the adsorption observed could not be described as due to an unspecific Donnan adsorption behaviour, neither of GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + nor Ga and Al monomers, and specific surface complex formation is therefore discussed and applied. The (≡COO)7GaO4Al12(OH)24(H2O)12 species found to explain the pH- and metal adsorption data should be considered strictly as a stoichiometric entity.
Keywords: EXAFS; GaO 4 Al 12 ( OH ) 24 ( H 2 O ) 12 7 + ; Ionic exchange; Donnan equilibrium;
Surface speciation of Eu3+ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC) by Keisuke Ishida; Takumi Saito; Noboru Aoyagi; Takaumi Kimura; Ryuji Nagaishi; Shinya Nagasaki; Satoru Tanaka (258-266).
Display Omitted► Three Eu3+ surface complexes with kaolinite were obtained from TRLFS with PARAFAC. ► The intensity profiles of the species explained the measured adsorption of Eu3+. ► Detailed information of the species was deduced from their fluorescent properties.Time-resolved laser fluorescence spectroscopy (TRLFS) is an effective speciation technique for fluorescent metal ions and can be further extended by the parallel factor analysis (PARAFAC). The adsorption of Eu3+ on kaolinite as well as gibbsite as a reference mineral was investigated by TRLFS together with batch adsorption measurements. The PAFAFAC modeling provided the fluorescence spectra, decay lifetimes, and relative intensity profiles of three Eu3+ surface complexes with kaolinite; an outer-sphere (factor A) complex and two inner-sphere (factors B and C) complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu3+. Based on the TRLFS results in varied H2O/D2O media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu3+ aquo ion, because of the energy transfer to the surface. Factor B was an inner-sphere complex, which became dominant at relatively high pH, high salt concentration and low Eu3+ concentration. Its spectrum and lifetime were similar to those of Eu3+ adsorbed on gibbsite, suggesting its occurrence on the edge face of the gibbsite layer of kaolinite. From the comparison with the spectra and lifetimes of crystalline or aqueous Eu(OH)3, factor C was considered as a poly-nuclear surface complex of Eu3+ formed at relatively high Eu3+ concentration.
Keywords: Europium; Kaolinite; Adsorption; Time-resolved laser fluorescence spectroscopy; Parallel factor analysis; Surface complexation;
Catalytic reduction of NO with decomposed methanol on alumina-supported Mn–Ce catalysts by I. Spassova; T. Tsontcheva; N. Velichkova; M. Khristova; D. Nihtianova (267-277).
Display Omitted► Mn–Ce/Al2O3 performes good activity in integrated devices of SCR of NO x with CO from decomposed methanol at 723 K. ► The activity was related to the formation of mixed Mn3+/Ce4+ and Ce3+/Mn4+ sites. ► The interaction between the active species depends on the composition of bicomponent materials.A series of manganese–ceria supported on alumina catalysts with various Mn/Ce ratios are investigated in both methanol decomposition to CO and hydrogen and SCR of NO x with CO. The study is aimed at the potential application of both reactions in integrated devices, where NO x is reduced with the products of the decomposed methanol. The samples are characterized by nitrogen physisorption, XRD, TEM, XPS, UV–Vis, and TPR. It was established that manganese–ceria supported on alumina catalysts are perspective in both methanol decomposition and NO reduction at temperatures above 723 K, which are typical for exhausted gases from the vehicles and some stationary stations. The best catalytic activity and selectivity to the desired products under these conditions was found for the samples with Mn/Mn + Ce ratio of 0.5 and 0.7. This superior catalytic performance is related to the formation of mixed valence Mn3+/Ce4+ and Mn4+/Ce3+ active sites.
Keywords: Manganese–ceria supported on alumina catalysts; SCR of NO x with CO; Methanol decomposition;
Catalysts for heterogeneous oxidation reaction based on metalloporphyrins immobilized on kaolinite modified with triethanolamine by Guilherme Sippel Machado; Pedro Braga Groszewicz; Kelly Aparecida Dias de Freitas Castro; Fernando Wypych; Shirley Nakagaki (278-286).
.Display Omitted► Modified clay mineral kaolinite as a support for catalyst immobilization. ► Metalloporphyrin heterogenized on kaolinite as an easy process to obtain a catalyst. ► Solids for heterogeneous catalysis with reuse capacity. ► Catalyst with efficiency and selectivity in oxidation reaction.Raw kaolinite was modified with triethanolamine (TEA), in an attempt to create a new support for the immobilization of metalloporphyrins. Anionic metalloporphyrins containing Fe3+ or Mn3+ as metallic centers were immobilized on the prepared support, and the obtained solids were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD), thermal analysis (thermogravimetric and differential thermal analyses – TGA/DTA), and scanning electron microscopy (SEM). The solids were used in heterogeneous oxidation catalysis of cyclooctene and cyclohexane. The yields from the oxidation of cyclooctene depended on the amount of TEA and/or water present in the solids. Good reaction yields were obtained for the oxidation of cyclohexane, with selectivity for the alcohol. In one specific case, a possible co-catalytic activity was verified for TEA during the oxidation of cyclohexane.
Keywords: Porphyrin; Oxidation; Heterogeneous catalysis; Kaolinite; Triethanolamine; Surface modification;
Adsorption of nanoparticles at the solid–liquid interface by Thorsten Brenner; Michael Paulus; Martin A. Schroer; Sebastian Tiemeyer; Christian Sternemann; Johannes Möller; Metin Tolan; Patrick Degen; Heinz Rehage (287-290).
Display Omitted► We present an X-ray reflectivity study of a liquid–solid interface. ► Positively charged maghemite nanoparticles form a monolayer on a silica surface. ► Negatively charged gold nanoparticles are repelled from the interface. ► Logarithmic particle distribution functions are able to describe the layers profile. ► The stability of such adsorbed films against rinsing is demonstrated.The adsorption of differently charged nanoparticles at liquid–solid interfaces was investigated by in situ X-ray reflectivity measurements. The layer formation of positively charged maghemite (γ-Fe2O3) nanoparticles at the aqueous solution–SiO2 interface was observed while negatively charged gold nanoparticles show no adsorption at this interface. Thus, the electrostatic interaction between the particles and the charged surface was determined as the driving force for the adsorption process. The data analysis shows that a logarithmic particle size distribution describes the density profile of the thin adsorbed maghemite layer. The size distribution in the nanoparticle solution determined by small angle X-ray scattering shows an average particle size which is similar to that found for the adsorbed film. The formed magehemite film exhibits a rather high stability.
Keywords: Nanoparticle; Adsorption; X-ray reflectivity; Small angle X-ray scattering;
Flower-like surface modification of titania materials by lithium hydroxide solution by George Hasegawa; Kazuyoshi Kanamori; Yoshihiro Sugawara; Yuichi Ikuhara; Kazuki Nakanishi (291-296).
Display Omitted► Titania surfaces are modified to generate flower-like structures with platy crystallites. ► The surface modification is successful only when treated with diluted LiOH aq. ► The platy crystallites are composed of layered hydrous lithium titanate.Surface modification of titania materials to give flower-like structures has been achieved simply by the treatment in lithium hydroxide aqueous solution under mild conditions. The flower-like structured materials were characterized by X-ray diffraction, thermogravimetric analysis, and Raman scattering. The analyses indicate that the flower-like materials are composed of layered hydrous lithium titanate. It is suggested that the unique intercalation behavior of lithium ions into titania allows dissolution and re-precipitation of titania to form the flower-like structure. The obtained flower-like structure can be retained up to 700 °C, while the crystal phase transforms into Li4Ti5O12.
Keywords: Surface modification; Flower-like structure; Titania; Crystalline layered titanate; Lithium intercalation;
Experimental investigation and population balance equation modeling of solid lipid nanoparticle aggregation dynamics by Yihui Yang; Alessandro Corona; Michael A. Henson (297-307).
Display Omitted► Experimentally determined polymorphic transformation is the rate limiting step. ► Incorporated polymorphic transformation into population balance model. ► Considered effect of surface coverage and shape change of particles. ► Model captured bimodal size distribution and approximate size of aggregates.Solid lipid nanoparticles (SLNs) have applications in drug delivery and the encapsulation of bioactive, lipophilic compounds. However, SLNs tend to aggregate when stored due to the lipid crystals undergoing a polymorphic transformation from the unstable α form to the stable β form. We developed a population balance equation (PBE) model for prediction of average polymorph content and aggregate size distribution to better understand this undesirable behavior. Experiments with SLNs stored at room temperature showed that polymorphic transformation was the rate determining step for our system, SLNs with smaller initial size distributions aggregated more rapidly, and aggregates contained particles with both α and β crystals. Using parameter values estimated from our data, the PBE model was able to capture the bimodal nature of aggregate size distributions, the α-to-β polymorph ratio, and the faster aggregation dynamics of SLNs with smaller initial size distributions. However, the model was unable to adequately capture the fast disappearance rate of primary particles, the broad size distributions of formed aggregates, and the significant α content of aggregating particles. These discrepancies suggest that a PBE model which accounts for polymorph content as an internal variable along with aggregate size may be required to better reproduce experimental observations.
Keywords: Solid lipid nanoparticles; Population balance; Polymorphic transformation; Aggregation; Surface coverage; Tristearin; Triacylglycerides;
A simple approach to covalent functionalization of boron nitride nanotubes by Gianni Ciofani; Giada Graziana Genchi; Ioannis Liakos; Athanassia Athanassiou; Dinuccio Dinucci; Federica Chiellini; Virgilio Mattoli (308-314).
Display Omitted► A novel and simple method for the chemical functionalization of boron nitride nanotubes (BNNTs) is presented. ► Surface is modified through 3-aminopropyl-triethoxysilane (APTES), thus exposing amino groups on the BNNT walls. ► The efficacy of the procedure is assessed with EDS and XPS analyses. ► In vitro toxicity and cell up-take have been evaluated.A novel and simple method for the preparation of chemically functionalized boron nitride nanotubes (BNNTs) is presented. Thanks to a strong oxidation followed by the silanization of the surface through 3-aminopropyl-triethoxysilane (APTES), BNNTs exposing amino groups on their surface were successfully obtained. The efficacy of the procedure was assessed with EDS and XPS analyses, which demonstrated a successful functionalization of ∼15% boron sites. This approach opens interesting perspectives for further modification of BNNTs with several kinds of molecules. Since, in particular, biomedical applications are envisaged, we also demonstrated in vitro biocompatibility and cellular up-take of the functionalized BNNTs.
Keywords: Boron nitride nanotubes; APTES; Covalent modification; Nanomedicine;
Structural characterization of nanoparticles from thermoresponsive poly(N-isopropylacrylamide)-DNA conjugate by Wei-Yang Ooi; Masahiro Fujita; Pengju Pan; Hui-Ying Tang; Kumar Sudesh; Kazuki Ito; Naoki Kanayama; Tohru Takarada; Mizuo Maeda (315-320).
Display Omitted► Micellization of PNIPAAm-g-DNA and its particle aggregation were examined. ► The nanoparticle consists of PNIPAAm core surrounded by hydrophilic DNA strands. ► The core size decreased with DNA fraction, while the shell thickness little changed. ► The nanoparticles with dsDNA overlap each other while the shells interpenetrating.Poly(N-isopropylacrylamide) (PNIPAAm) grafted with single-stranded (ss) DNA conjugate (PNIPAAm-g-DNA) self-assembles above its lower critical solution temperature to form colloidal particles. When the ssDNA within the particle hybridizes with its complementary DNA, the particles aggregate above a certain threshold of salt concentration with drastically increased turbidity in solution. Detailed structural information of the particle was obtained mainly by small-angle X-ray scattering. The influence of copolymer composition on the morphology of particle and non-crosslinking aggregation was examined. The particle consists of hydrophobic PNIPAAm core surrounded by hydrophilic DNA strands. The increase in DNA fraction brought about a significant decrease in core size, whereas the shell thickness little changed and corresponded to the length of DNA. A structural model with a sticky potential was applied to the analysis of particle aggregate. This analysis provided that the particles aggregate while the coronal layers interpenetrate each other. The interaction between the particles was quantified in terms of the sticky potential and showed a trend to be influenced by the particle size rather than the graft density of DNA strands on the particle.
Keywords: PNIPAAm; DNA; Soft interface; SAXS;
Synthesis of microporous eskolaite from Cr(VI) using activated carbon as a reductant and template by A. Cruz-Espinoza; V. Ibarra-Galván; A. López-Valdivieso; J. González-González (321-324).
Display Omitted► A technique was devised to prepare eskolaite from dichromate ions, Cr(VI). ► Activated carbon was used to reduce the Cr(VI) to amorphous Cr2O3. ► Amorphous Cr2O3 deposited in the pores of the activated carbon. ► Ultrafine eskolaite was obtained by calcining the chromium-loaded activated carbon.A novel technique has been devised for the synthesis of microporous α-Cr2O3 (eskolaite). The technique was based on the formation of amorphous-Cr2O3 onto microporous activated carbon through adsorption–reduction of dichromate ions ( Cr 2 O 7 2 - ) at the activated carbon/aqueous solution interface. Then, the Cr2O3-loaded carbon was thermally processed under oxidizing conditions to remove the carbon and recover the chromium oxide as α-Cr2O3. Both the Cr2O3-loaded carbon and the synthetic product were characterized by XRD, SEM, surface area and pore volume measurements. The synthetic eskolaite assayed 97.3% Cr2O3 and its specific surface area was 15.48 m2/g and pore size of 16.1 Å.
Keywords: Chromium oxide; Eskolaite; Activated carbon; Synthesis; Adsorption; Dichromate;
Removal of low concentration Cr(VI) from aqueous solution by magnetic-fluids fixed bed using the high gradient magnetic separation by Qiang Wang; Yueping Guan; Xiufeng Ren; Mingzhu Yang; Xiang Liu (325-330).
Display Omitted► The original magnetic-fluids fixed bed using HGMS has been explained. ► The feasibility was studied by extraction experiments of Cr(VI). ► The optimum extraction conditions were investigated. ► The method obtained a high extraction capacity with a continuous process.The focus of this paper was a novel model of Cr(VI) extraction process. The original so-called “magnetic-fluids fixed bed” (MFFB), which bridged the solvent extraction and the fixed-bed extraction by the theory of the high gradient magnetic separation (HGMS), has been explained. The MFFB integrated the advantages of the two above mentioned classical extraction methods and overcame their drawbacks. The feasibility of this method was studied by extraction experiments of Cr(VI) from aqueous solution. The influences of the design of ferromagnetic steel wires in magnetic separation column, the pH value of feed solution, TBP concentration in magnetic fluids, and flow rate of aqueous solution in column were investigated. Under the optimum conditions, the proposed method obtained high extraction efficiency with continuous process.
Keywords: Magnetic fluids; Fixed bed; Extraction; Heavy metal ions; High gradient magnetic separation;
Controllable synthesis of aniline oligomers into uniform, dispersed cross and needle morphologies by Wenguang Leng; Shuxue Zhou; Bo You; Limin Wu (331-338).
Display Omitted► Two novel kinds of aniline oligomer assembly morphologies can be easily obtained. ► Uniformity, dispersity, and morphology can be controlled. ► A possible formation mechanism is proposed to account for the assembly process.Two kinds of homogeneously dispersed aniline oligomer assemblies, namely “cross” and “needle” morphologies, can be conveniently synthesized on a large scale in a near-neutral aqueous medium using sodium dodecylsulfate (SDS) as a surfactant. The effects of oxidant type, premixing time, amount of SDS, monomer concentration, and temperature on the final morphology were investigated in detail. A possible mechanism for the formation of both “cross” and “needle” structures is given.
Keywords: Homogeneous; Aniline; Assembly; SDS; Morphology; Mechanism;
Fabrication of one-dimensional Fe3O4/P(GMA–DVB) nanochains by magnetic-field-induced precipitation polymerization by Mingliang Ma; Qiuyu Zhang; Jinbo Dou; Hepeng Zhang; Dezhong Yin; Wangchang Geng; Yanyang Zhou (339-344).
One-dimensional (1D) magnetic Fe3O4/P(GMA–DVB) peapod-like nanochains have been successfully synthesized by magnetic-field-induced precipitation polymerization.Display Omitted► 1D Fe3O4/P(GMA–DVB) nanochains were synthesized by MFI precipitation polymerization. ► The length of peapod-like nanochains can be controlled by magnetic field intensity. ► The thickness of polymer shell can be tuned by the amount of monomers. ► These nanochains can be oriented and aligned along the direction of magnetic field.One-dimensional (1D) magnetic Fe3O4/P(GMA–DVB) peapod-like nanochains have been successfully synthesized by magnetic-field-induced precipitation polymerization using Fe3O4 as building blocks and P(GMA–DVB) as linker. The Fe3O4 microspheres without surface modification can be arranged with the direction of the external magnetic field in a line via the dipolar interaction between Fe3O4 microspheres and linked permanently via P(GMA–DVB) coating during precipitation polymerization. The length of peapod-like nanochains can be controlled by magnetic field intensity, and the thickness of polymer shell can be tuned by the amount of monomers. Magnetic measurement revealed that these 1D peapod-like nanochains showed highly magnetic sensitivity. In the presence of magnetic field, 1D magnetic Fe3O4/P(GMA–DVB) peapod-like nanochains can be oriented and aligned along the direction of external magnetic field.
Keywords: One-dimensional nanochains; Self-assembly; Precipitation polymerization; Fe3O4/P(GMA–DVB);
Oscillations in the capacitance of a nanopore containing an electrolyte due to pore width and nonzero size ions by Douglas Henderson (345-347).
Display Omitted► Oscillations in the capacitance due to nonzero particle size. ► Conventional theory lacks oscillations. ► Modern theory predicts oscillations. ► The mean spherical approximation suggests a simple expression. ► Oscillations may explain the capacitance anomaly.Jiang, Jin, and Wu (Nano Lett., 11 (2011), pp. 5373–5377) have reported the results of a density functional theory (DFT) study of the capacitance of a nanopore containing an electrolyte consisting of charged hard spheres of equal diameter and charge. They find that the capacitance of the nanopore and electrolyte oscillates. The ‘period’ of the oscillations is of the order of the ionic diameter. Intuitively, the capacitance should tend to zero when the pore diameter is too small to accommodate the electrolyte ions and, thus, would contains no charge. A superficial glance at their table of contents figure might lead one to think that this does not occur in their calculation. However, they do not report results for exceedingly small pore diameters. In order to gain insight into their results, the Poisson-Boltzmann (PB) theory, which does not account for the diameter, is examined briefly. Unsurprisingly, the PB capacitance decreases monotonically to zero as the pore diameter decreases. The effect of a nonzero ion diameter is included in a semi-empirical manner by appealing to the results of the mean spherical approximation (MSA). The resulting capacitance oscillates and is qualitatively similar to the DFT results; it is zero at small pore diameter.
Keywords: Nanopore; Planar double layer; Mean spherical approximation;