Journal of Colloid And Interface Science (v.337, #1)
Cover 1/Editorial Board (OFC).
Recent advances in the mixed systems of bolaamphiphiles and oppositely charged conventional surfactants by Yun Yan; Ting Lu; Jianbin Huang (1-10).
Possible Self-assembly in mixed system of bola/oppositely charged surfactant.Researches on the bolaamphiphiles have attracted considerable attentions in the last three decades. Among which, the mixed systems with conventional surfactants are of special interest. This review focuses on the recent advances in the research of the bolaamphiphile/oppositely charged conventional surfactant mixed systems. The following contents are covered: (1) surface properties, which include (i) the general properties of the mixed systems, (ii) the effect of rigid group on the surface properties, and (iii) the slow adsorption process of bolaamphiphiles on solid surface; (2) aggregation behaviors in the bulk solution, including (i) the superior vesicle formation ability, (ii) superior vesicle stability, (iii) dynamic morphology of the aggregates, and (iv) tunable morphologies; (3) perspective for the future.
Keywords: Bolaamphiphiles; Catanionic mixed systems; Surface property; Aggregation; Self-assembly; Vesicles;
Sorption models in cyclodextrin polymers: Langmuir, Freundlich, and a dual-mode approach by Iñigo X. García-Zubiri; Gustavo González-Gaitano; José Ramón Isasi (11-18).
Langmuir and Freundlich models correspond to sorption within cyclodextrin cavities and interactions with the polymeric network, respectively.The classic Langmuir and Freundlich sorption models and a dual-mode approach have been tested to study the sorption of aromatic molecules onto β-cyclodextrin polymers as well as onto analogous sucrose polymers, obtained using the same crosslinking agents (epichlorohydrin, succinyl chloride, toluene diisocyanate, and hexamethylene diisocyanate). The host–guest interaction of the sorbate within the cyclodextrin cavities corresponds to the hole-filling mechanism considered in the dual-mode approach, while the polymer crosslinking networks are capable of entrapping more sorbate molecules via partition. In some cases, when the sorption is governed by the inclusion within the cyclodextrin moieties, a simple Langmuir isotherm fits the data properly. The classic Freundlich equation is also appropriate when phenol is the sorbate because its interaction with β-cyclodextrin is less specific than that of 1-naphthol.
Keywords: Sorption; Cyclodextrin polymers; Sucrose polymers; Host–guest systems; Dual-mode;
Synthesis, characterization, and adsorption properties of phenolic hydroxyl group modified hyper-cross-linked polymeric adsorbent by Jianhan Huang; Xiaomei Wang; Xing Deng (19-23).
A phenolic hydroxyl group modified hyper-cross-linked polymeric adsorbent with dominant micropores and mesopores HJ-02 is prepared successfully from macroporous chloromethylated PS and it exhibits excellent adsorption behavior for p-aminobenzoic acid.A kind of phenolic hydroxyl group modified hyper-cross-linked polymeric adsorbent HJ-02 was prepared from macroporous crosslinked chloromethylated styrene-divinylbenzene copolymers by Friedel–Crafts post-cross-linked reaction and esterified reaction. Its chemical structure and pore structure were characterized by chemical analysis, infrared spectroscopy, and N2 adsorption–desorption experiments. It was thereafter applied to adsorb p-aminobenzoic acid in aqueous solution for its potential application in separation and purification. The p-aminobenzoic acid aqueous solution, pH unadjusted, was the optimum for the adsorption and the salinity posed a positive effect. The adsorption dynamic curves obeyed the pseudo-second-order rate equation and the adsorption was controlled by an intraparticle diffusion model. The adsorption enthalpy was calculated to be negative and decreased with the increase of the p-aminobenzoic acid uptake. The surface character of HJ-02 resin was described with function of the adsorption enthalpy by Do’s model and the result indicated that it exhibited surface energy heterogeneity.
Keywords: Polymeric adsorbent; Adsorption; Adsorption enthalpy; Surface heterogeneity;
Interparticle forces in spherical monodispersed silica dispersions: Effects of branched polyethylenimine and molecular weight by B.C. Ong; Y.K. Leong; S.B. Chen (24-31).
Adsorption of branched polyethylenimine on spherical silica dispersions resulted in the large increase in the yield stress of the dispersion.The effect of branched polyethylenimine (PEI) of molecular weight (Mw) 600, 1800 and 70,000 on the surface forces interacting between ‘uniform size’ spherical silica particles in water was investigated via the yield stress and zeta potential techniques. This silica has a point of zero charge at pH ∼ 2.0. All PEIs caused the zeta potential–pH curve and the high pH zero zeta potential to shift to a higher pH and the extent of the shift increases with increasing PEI concentration and is not affected by PEI Mw. PEI adsorption on silica is low or negligible at pH less than 3.5 and this is due to a very low negative charge density. Adsorption of PEI beyond 3.5 caused a maximum zeta potential to occur at pH between 4 and 6. The maximum yield stress located at the point zero zeta potential is many times larger than that with no added PEI. It ranged from 20 to 42 times for low Mw PEI and as high as 68 times for Mw 70,000. At low surface coverages, the force responsible for the high yield stress is charged patch–bridging attraction. At complete surface coverage, particle bridging via hydrogen bond and unlike charged attraction between monomeric, dimeric and tetrameric silicate ions with the adsorbed PEI layers of the interacting particles was responsible.
Keywords: Monodispersed silica; Dispersions; Charged patch attraction; Bridging forces; Polyethylenimine; Soluble silica ionic species;
Reactive Black dye adsorption/desorption onto different adsorbents: Effect of salt, surface chemistry, pore size and surface area by A.W.M. Ip; J.P. Barford; G. McKay (32-38).
The enhanced adsorption capacity by increasing the ionic strength of the solution is compared with the original adsorption capacity.The adsorption of a large reactive dye, Reactive Black 5 dye, onto two bamboo based active carbons using phosphoric acid in a two stage activation process and three conventional adsorbents, carbon F400, bone char and peat, has been studied. The monolayer saturation adsorption capacities for Reactive Black 5 were determined by the Langmuir isotherm analysis and are: 176, 157, 7, 447 and 545 mg dye/g adsorbent for active carbon F400, bone char, peat, bamboo carbon (2123 m2/g) and bamboo carbon (1400 m2/g), respectively. The equilibrium experiments were analysed using three isotherms, Langmuir, Freundlich and Redlich–Peterson and the based on the lowest SSE values, the Redlich–Peterson was the best fit correlation. The effect of adding salt, in the form of sodium phosphate, on the adsorption capacities has been studied and was found to increase the adsorption capacities of both bamboo carbons to over 900 mg/g.
Keywords: Adsorption; Desorption; Reactive dye; Bamboo activated carbon; Bone char; Peat; Ionic strength;
Thermodynamics of adsorption at the aqueous–air interface by Risto Pajarre; Pertti Koukkari (39-45).
Adsorption at the air–water interface was studied based on a monolayer surface model. The deduced relationship between the bulk and surface layer activity coefficients is shown.A thermodynamic model is presented for the aqueous–air interface. For common organic solutes a relationship between the activity coefficients in the bulk solution and on the surface layer is deduced by using the concept of a surface monolayer. This relation has enabled development of an equation expressing the air–water surface adsorption coefficient as a function of bulk activity coefficients, surface tensions, molar volumes and vapour pressures of the adsorbing species. The data for 51 compounds, including alkanes, cycloalkanes, aromatics, halogenated hydrocarbons, alcohols, ethers and esters, and ketones were used in the study.
Keywords: Adsorption; Air–water interface; Monolayer model; Thermodynamic modeling; Surface tension;
Temperature-induced formation of strong gels of acrylamide-based polyelectrolytes by Ranjith Krishna Pai; Jovice B.S. Ng; Saju Pillai; Lennart Bergström; Niklas Hedin (46-53).
Very strong physical gels have been formed by moderate temperature increases of concentrated aqueous dispersions of acrylamide-based copolymers.Very strong physical gels have been formed by moderate temperature increases of concentrated aqueous dispersions of acrylamide-based copolymers. The results of rheometry, confocal laser scanning microscopy, and differential scanning calorimetric studies of acrylamide-based copolymers with acrylic acid (poly[AM-AA]) and the sodium salt of 2-acrylamido-2-methylpropane acid (poly[AM-NaAMPS]) suggest that the temperature-induced swelling of the polymer beads and dissolved chains creates strongly entangled polymer networks above the upper critical solution temperature. Analysis of the viscoelastic response showed that the time scale for the gelation process is about minutes to hours. The addition of high concentrations of Ca2+ resulted in a significant reduction in the modulus.
Keywords: Polyelectrolyte; UCST; Rheology; Storage modulus; Salt stability; Gelation;
Ultrasound-induced modulations of tetrapeptide hierarchical 1-D self-assembly and underlying molecular structures via sonocrystallization by Damei Ke; Chuanlang Zhan; Xiao Li; Xi Wang; Yi Zeng; Jiannian Yao (54-60).
Ultrasound was observed to modulate either underlying molecular structures or morphologies of tetrapeptide self-assembly from microtapes into nanotapes, nanofibers, and then nanorods with a different period of sonication.Herein, we report the ultrasound-induced modulations of the morphologies and underlying molecular structures of tetrapeptide 1-D self-assembly. The self-assembly of the tetrapeptide (TTR108–111) precipitating out of the 1:1 mixed methanol/water is modulated from microtapes into nanotapes, nanofibers, and then bundles of nanorods when subjected to sonication for a period. The sonication-treated and untreated self-assemblies all give a set of equatorial pattern and a series of meridional pattern, indications of a typical “cross-β-structure” as the core structural motif. FTIR data indicate that all the assemblies contain a mixed pattern of β-sheets (dominant) and unstructured conformations (minor), and the relative proportion of unbound structures to β-sheets is as a function of sonication time, suggesting an ultrasound-induced modulation of β-sheet interactions. Accordingly, a possible model regarding a dynamic equilibrium between re-dissolution and re-assembling processes, e.g., a typical sonocrystallization process was proposed for such ultrasound-induced modulations of morphologies and underlying molecular structures.
Keywords: Tetrapeptide; Self-assembly; Ultrasound; Hierarchical structures;
Tuning the stability of TiO2 nanoparticles in various solvents by mixed silane alkoxides by Motoyuki Iijima; Murino Kobayakawa; Hidehiro Kamiya (61-65).
The surface of TiO2 nanoparticles were modified by mixed silane alkoxides in order to achieve their complete redispersion into solvents with different polarities.The surface of TiO2 nanoparticles which were well dispersed into acidic aqueous solution was successfully modified by silane alkoxides without strong aggregate formations. By adding decyltrimethoxysilane (DTMS) as silane alkoxides into the TiO2 aqueous solution which were carefully diluted with methanol, DTMS slowly attached onto the TiO2 surface without rapid hydrolysis and condensation reaction among DTMS. Because of the hydrophobicity of DTMS, the dispersed TiO2 nanoparticles slowly formed flocks as DTMS reacted on TiO2. These flocks were able to be completely redispersed into nonpolar solvents even after they were collected by centrifugation and drying under vacuum as dry powder. Furthermore the surface of TiO2 nanoparticles have been successfully tuned by combining silane alkoxides which contains hydrophobic and hydrophilic groups such as DTMS and 3-aminopropyltrimethoxysilane (APTMS), respectively, toward their complete redispersion into various solvents. While TiO2 nanoparticles modified by DTMS were redispersible into toluene, those modified by mixed alkoxides of 50 mol % DTMS and 50 mol % APTMS were redispersible into a mixed solution of toluene and methanol. Further when they were modified by mixed alkoxides of 25 mol % DTMS and 75 mol % APTMS, they were redispersible into polar solvents such as methanol with a little addition of acids.
Keywords: TiO2; Nanoparticle; Surface modification; Dispersion stability; Silane;
High solids loading ceramic colloidal dispersions in UV curable media via comb-polyelectrolyte surfactants by Yoram De Hazan; Judit Heinecke; Alfred Weber; Thomas Graule (66-74).
A general scheme for high loaded colloidal ceramic dispersions in UV curable resins using comb-polyelectrolyte surfactants is presented. The method is demonstrated for Al2O3, ZnO and mixed Al2O3/ZnO colloidal dispersions.Ceramic articles and ceramic/polymer composites with complex 3d shapes can be produced by rapid prototyping techniques such as stereolithography of ceramic dispersions in UV curable resins. Nanometer and submicrometer ceramic particles are advantageous for high resolution microstructures, surface quality and reduced sintering temperatures. Frequently, special surfactants are needed to maximize solids loading while maintaining suitable rheological properties for stereolithography applications (viscosity <5 Pa s, 30 1/s). We present here a general scheme for relatively high loading/low viscosity dispersions of nanometer and submicrometer particles in UV curable resins using comb-polyelectrolyte surfactants. In the present approach, adsorption is favorably carried out in aqueous media and the dry particles with adsorbed surfactant are transferred to the organic media through centrifugation, washing, drying and dry milling. The method is demonstrated for Al2O3, ZnO and mixed Al2O3/ZnO colloidal dispersions. Dispersions containing >48 vol% particles suitable for stereolithography have been achieved. Dispersions containing 36 vol% particles are predicted to have viscosities in the range suitable for direct inkjet printing applications at 75 °C. The particle stabilization and transfer schemes, rheological behavior and UV curing characteristics are presented.
Keywords: Al2O3; ZnO; Nanoparticle; Comb-polyelectrolyte; Nanocomposite; Acrylate; Rheology; UV; Cure; Thick film;
Surface modification of hydrophobic nanocrystals using short-chain carboxylic acids by Duc Quy Vo; Eui-Jung Kim; Sunwook Kim (75-80).
The picture shows TEM image of TiO2 nanorods after ligand exchange with acrylic acid. The acrylic acid-exchanged TiO2 nanorods showed excellent stability and did not agglomerate in polar media.Acrylic, acetic and methacrylic acids which are short-chain carboxylic acids have been applied to modify the surface of oleic acid-coated TiO2 nanorods (NRs) and oleic acid/oleylamine-coated Fe3O4 nanoparticles (NPs). The short-chain carboxylic acids not only acted as modifying ligands but also as anti-solvents during the ligand exchange processes. The prepared products have been characterized using TEM, HRTEM and FTIR spectroscopy. The results show that the acrylic acid-exchanged TiO2 and Fe3O4 solution remain stable even after six months, showing no agglomeration. Such acrylic acid-exchanged nanocrystals (NCs) prepared in this work could also be well-dispersed in other polar solvents such as ethanol and ethanol/water mixtures. On the contrary acetic acid and methacrylic acid-exchanged TiO2 solutions were not stable due to the presence of remaining oleic acid on the TiO2 surface. This approach has been shown to be effective in making hydrophilic TiO2 NRs and Fe3O4 NPs and can also be applied to other NCs covered by different hydrophobic ligands.
Keywords: Surface modification; Ligand exchange; Anti-solvent; Carboxylic acid; Fe3O4; TiO2;
Effect of PEG on rheology and stability of nanocrystalline titania hydrosols by Pierre Alphonse; Rudina Bleta; Regis Soules (81-87).
Rheological behaviour and stability of TiO2 colloidal dispersions in water are explained through the aggregation of primary nanoparticles and change in the fractal dimension of aggregates.Very stable titania hydrosols were prepared by fast hydrolysis of titanium isopropoxide in a large excess of water. XRD patterns show that these sols contain nanocrystals (5–6 nm) of anatase (70%) and brookite (30%). TEM images indicate that these primary particles form aggregates whose mean hydrodynamic diameter, determined by photon correlation spectroscopy, is in the range of 80–90 nm. The flow curves of these colloids, recorded for several volume fractions of nanoparticles, can be perfectly fitted, in the range 0–100 s−1, with a power-law model. In this range the behavior is Newtonian but for larger shear rates a shear thinning is observed. The viscosity dependence on particle concentration can be predicted by a Batchelor-type model were the volume fraction of particles is replaced by an effective volume fraction of aggregates, taking into account their fractal dimension. Addition of polyethylene glycol (PEG 2000) induced a marked decrease (more than 50%) of the sol viscosity down to a minimum. This is explained by assuming that PEG adsorbs on the surface of TiO2 particles producing stabilization by steric effects and leading to formation of more compact aggregates. Without PEG the sol viscosity strongly decreases on aging. This effect is not caused by the growth of primary particles. It is rather interpreted as a progressive reorganization of the aggregates toward a more compact packing.
Keywords: Sol–gel; Titanium dioxide; Colloid; Nanofluid; Rheology; PEG;
Lanthanide complexes on Ag nanoparticles: Designing contrast agents for magnetic resonance imaging by Talha S. Siddiqui; Ashish Jani; Florence Williams; Robert N. Muller; Luce Vander Elst; Sophie Laurent; Fang Yao; Youssef Zaim Wadghiri; Marc A. Walters (88-96).
Uptake of gadolinium by nitrilotriacetate tethered to the surface of a silver nanoparticle. The gadolinium containing colloid induces the relaxation of proton spins in aqueous solution.This paper describes colloidal particles that are designed to induce hyper-intensity contrast (T 1 relaxation) in MRI. The contrast agents consist of discrete gadolinium complexes tethered to 10 nm diameter silver nanoparticles. The gadolinium complexes (1) [Gd(DTPA-bisamido cysteine)]2− and (2) [Gd(cystine–NTA)2]3−, undergo chemisorption to particle surfaces through thiol or disulfide groups, respectively, to form two new contrast agents. The resulting nanoparticulate constructs are characterized on the basis of their syntheses, composition, spectra and contrast enhancing power. The average r 1 relaxivities of the of the surface bound complexes (obtained at 9.4 T and 25 °C) are 10.7 and 9.7 s−1 mM−1, respectively, as compared to 4.7 s−1 mM−1 for the clinical agent MagnevistTM. Correspondingly, the respective whole particle relaxivities are 27927 and 13153 s−1 mM−1.
Keywords: MRI; Contrast; Silver; Nanoparticles; Monolayer protected; Relaxivity; Longitudinal relaxation;
Nature of organic fluid–montmorillonite interactions: An FTIR spectroscopic study by Priyanthi M. Amarasinghe; Kalpana S. Katti; Dinesh R. Katti (97-105).
Shifts observed in the H–O–H bending vibration band of interlayer water in montmorillonite with various environmental fluids of varying dielectric constants.The changes in the H–O–H stretching vibration in the interlayer water and Si–O stretching vibration of a Na-montmorillonite (MMT) structure in the FTIR (Fourier transform infrared) spectra provide insight into the effect of fluids of different dielectric constants on the clay structure. Mechanisms by which the different fluids of varying polarities enter into the clay interlayer and the rates at which these molecules interact with the clay structure and the interlayer water are studied at the molecular level using six different fluids with dielectric constants ranging from 110 to 2.4. The shift in H–O–H bending vibrations of interlayer water and changes in the Si–O vibration bands of MMT occur almost immediately after mixing with the solvent regardless of the polarity of the solvent. However, the extent and the rate of changes in H–O–H bending and Si–O stretching are dependent on the polarity of the solvent. Results show a very good correlation between the polarity of the solvent and the shift in H–O–H bending of interlayer water, and also between the polarity of the fluids and the d (001) spacing of the MMT–solvent samples. Low polar fluids such as methanol tend to make weak electrostatic interactions with clay surface oxygen and interlayer-water molecules, which result in an increase in interlayer spacing. Although, the alteration of the Si–O structure due to high polar molecules such as formamide is a continuous process, the influence of nonpolar fluids such as TCE (trichloroethylene) on the Si–O structure is almost instantaneous, which may result in high hydraulic conductivity in the clay.
Keywords: FTIR; Na-montmorillonite; XRD; d Spacing; Dielectric constant; Polarity; Organic fluid;
Experimental device for chemical osmosis measurement on natural clay-rock samples maintained at in situ conditions: Implications for formation pressure interpretations by Pauline Rousseau-Gueutin; Vincent de Greef; Julio Gonçalvès; Sophie Violette; Serge Chanchole (106-116).
In order to characterize the so-called coupled processes occurring in compacted clay rocks, the coupling coefficients must be identified. For this purpose, an original device which allows such measurement for undisturbed (natural) samples in their in situ conditions was developed. The present experimental device minimizes the fluid leaks improving the accuracy of the coupling parameter determination. Three chemical osmotic tests were performed on a cylindrical sample of Callovo-Oxfordian argilite. Room temperature variations during the chemical osmosis experiments required the implementation of temperature effects in the numerical model used for the interpretations. These variations offered the opportunity of an alternative method to estimate the compressibility of the fluid in the circuit connected to a measurement chamber located in the center of the sample. An osmotic efficiency of almost 0.2 for a concentration of 0.094 mol L−1 is obtained for the Callovo-Oxfordian argilite. This value would explain only some part (approximately 0.10–0.15 MPa) of the overpressures (0.5–0.6 MPa) relative to the surrounding reservoirs measured in this formation. Others processes, such as thermo-osmosis, hydrodynamic boundary condition changes due to climate variations or creep behavior of the shale, could explain the remainder of the overpressures.
Keywords: Coupled processes; Chemical osmosis; Experiments; Clay rock; Modeling;
Photostability enhancement of anionic natural dye by intercalation into hydrotalcite by Yoshiumi Kohno; Koichi Totsuka; Shuji Ikoma; Keiko Yoda; Masashi Shibata; Ryoka Matsushima; Yasumasa Tomita; Yasuhisa Maeda; Kenkichiro Kobayashi (117-121).
Anionic natural dyes intercalated between the layers of hydrotalcite are stabilized against irradiation.The aim of this study is the improvement of the photostability of several natural anionic dyes, carmine (CM), carthamus yellow (CY), and annatto dye (ANA), by complexation with hydrotalcite. The composite of the dyes and hydrotalcite is prepared by the coprecipitation method. CM is successfully intercalated in the hydrotalcite layer when the amount of introduced CM is large. The photostability of CM in CM/HT composites is superior to the CM adsorbed on silica surface. The effect of the stability enhancement is larger when the amount of introduced CM exceeds 0.23 g/g-host, or when the layer charge density of the hydrotalcite is larger. CY is also stabilized by complexation with hydrotalcite, whereas ANA is not stabilized by complexation with hydrotalcite. The photostability of an anionic natural dye can be improved by intercalation into the hydrotalcite layer, if the dye has a hydrophilic nature and a rather planar structure. The intercalated dye is stabilized by the protection from the attack of the atmospheric oxygen. In addition, contribution of the electrostatic interaction between the positively charged hydrotalcite layer and the intercalated anionic dye is also proposed.
Keywords: Anionic natural dye; Hydrotalcite; Layered double hydroxide; Photostability; Stabilization; Intercalation;
RETRACTED: Designed pendant chain covalently bonded to analogue of heulandite for removal of divalent toxic metals from aqueous solution: Thermodynamic and equilibrium study by Denis L. Guerra; Rúbia R. Viana; Claudio Airoldi (122-130).
This article has been retracted at the request of the Editors of the Journal of Colloid and Interface Science.Fraudulent results have been found in this article and other publications in Elsevier journals by the same authors, namely: J. Colloid Interf. Sci., 337 (2009) 122-130; Inorg. Chem. Commun., 12 (2009) 1145-1149; J. Environ. Radioactiv., 101 (2010) 122-133; Process Saf. Environ., 88 (2010) 53-61; J. Phys. Chem. Solids, 70 (2009) 1413-1421; Appl. Surf. Sci., 256 (2009) 702-709; Inorg. Chem. Commun., 11 (2008) 20-23; Inorg. Chem. Commun., 12 (2009) 1107-1111; J. Hazard Mater., 172 (2009) 507-514; J. Hazard Mater., 171 (2009) 514-523; J. Colloid Interf. Sci.,338 (2009) 30-39. Publication of an article in a peer-reviewed journal is an important building-block in the development of science. Elsevier has defined policies and ethical guidelines that have to be obeyed by authors and editors and Elsevier takes its duties of guardianship over the scholarly record extremely seriously. The Editors of the Elsevier journals involved found that the allegations of fraud are conclusive and they have decided that these papers should be retracted from the journals.
Effects of dynamic contact angle on liquid infiltration into horizontal capillary tubes: (Semi)-analytical solutions by Markus Hilpert (131-137).
(Semi)-analytical solutions are derived for the displacement of a gas by a liquid in a horizontal capillary tube where contact angle depends on interface velocity.We generalize Washburn’s analytical solution for capillary flow in a horizontally oriented tube by accounting for a dynamic contact angle. We consider two general models for dynamic contact angle: the uncompensated Young force on the contact line depends on the capillary number in the form of either (1) a power law with exponent β or (2) a power series. By considering the ordinary differential equation (ODE) for the velocity of the gas–liquid interface instead of the ODE for the interface position, we are able to derive new analytical solutions. For both dynamic contact angle models, we derive analytical solutions for the travel time of the gas–liquid interface as a function of interface velocity. The interface position as a function of time can be obtained through numerical integration. For the power law and β = 1 (an approximation of Cox’s model for dynamic contact angle), we obtain an analytical solution for both interface position and velocity as a function of time. For the power law and β = 3 , we can express the interface velocity as a function of time.
Keywords: Dynamic contact angle; Capillary flow; Analytical solution; Washburn equation; Wetting;
Effects of dynamic contact angle on liquid infiltration into inclined capillary tubes: (Semi)-analytical solutions by Markus Hilpert (138-144).
(Semi)-analytical solutions are derived for the displacement of a gas by a liquid in an inclined capillary tube where contact angle depends on interface velocity.In a recent paper, we generalized Washburn’s analytical solution for capillary flow in a horizontally oriented tube by accounting for a dynamic contact angle. In this paper, we derive solutions for flow in inclined tubes that account for gravity. We again consider two general models for dynamic contact angle: the uncompensated Young force on the contact line depends on the capillary number in the form of (1) a power law with exponent β , or (2) a polynomial. A dimensional analysis shows that, aside from the parameters for the model for the uncompensated Young force, the problem is defined through four nondimensional parameters: (1) the advancing equilibrium contact angle, (2) the initial contact angle, (3) a Bond number, and (4) nondimensional liquid pressure at the tube inlet relative to the constant gas pressure. For both contact angle models, we derive analytical solutions for the travel time of the gas–liquid interface as a function of interface velocity. The interface position as a function of travel time can be obtained through numerical integration. For the power law and β = 1 (an approximation of Cox’s model for dynamic contact angle), we obtain an analytical solution for travel time as a function of interface position, as Washburn did for constant contact angle. Four different flow scenarios may occur: the interface moves (1) upward and approaches the height of capillary rise, (2) downward with the steady-state velocity, (3) downward while approaching the steady-state velocity from an initially higher velocity, or (4) downward while approaching the steady-state velocity from an initially smaller velocity.
Keywords: Dynamic contact angle; Capillary flow; Analytical solution; Washburn equation; Wetting;
Droplet formation under the effect of a flexible nozzle plate by S. Sangplung; J.A. Liburdy (145-154).
The droplet generator shown was numerically simulated for droplet formation using a flexible nozzle plate. Results were obtained for a range of fluid properties and vibration al properties of the nozzle.Droplet formation from a flexible nozzle plate driven by a prescribed-waveform excitation of a piezoelectric is numerically investigated using a computational fluid dynamics (CFD) model with the volume of fluid (VOF) method. The droplet generator with a flexible nozzle plate, which is free to vibrate due to the pressure acting on the plate, is modeled in a CFD computational domain. The CFD analysis includes the fluid–structure interaction between fluid and a flexible plate using large deflection theory. The problem is characterized by the nondimensional variables based on the capillary parameters of time, velocity, and pressure. The CFD model is validated with the experiment results. This study examines the characteristics of the applied waveforms and nozzle plate material properties to change the vibrational characteristics of the nozzle plate. The effect of fluid properties on the droplet formation process is also investigated focusing on surface tension and viscous forces. Increasing the impulse of the piezoelectric can be used to cause a higher droplet velocity and it is shown that the vibration of the nozzle plate has a strong effect on the droplet velocity, shape, and volume. Surface tension has a strong influence on the droplet formation characteristics in contrast to viscous forces. For the combination of a fluid with high surface tension and the most flexible nozzle plate, this system cannot cause the droplet ejected out of the nozzle.
Keywords: Droplet formation; Dynamic surface tension;
Layer-by-layer self-assembly of conducting multilayer film from poly(sodium styrenesulfonate) and polyaniline by Qunwei Tang; Jihuai Wu; Xiaoming Sun; Qinghua Li; Jianming Lin (155-161).
A poly(sodium styrenesulfonate)/polyaniline multilayer film (PSS/PANI) n was layer-by-layer self-assembled by repeatedly dipping highly oriented polyaniline and poly(sodium styrenesulfonate).Highly oriented polyaniline (PANI) fiber was prepared by a polymerization at higher temperature and growth in lower temperature. Poly(sodium styrenesulfonate)/polyaniline multilayer film (PSS/PANI) n was layer-by-layer molecular-level self-assembled by a simple technique. The morphology and structure of the oriented PANI fiber were characterized, showing an emeraldine state and ordered molecular structure. The growth process and surface topography of the (PSS/PANI) n multilayer film were characterized by UV–vis spectroscopy and atomic force microscopy. Absorbance plotted against the bilayers exhibited a linear dependence, indicating a progressive and uniform deposition process of the multilayer film. The (PSS/PANI) n multilayer film exhibited an electrical conductivity in the order of 1 S cm−1, and when bilayer number exceeded a threshold value of 4, the conductivity of the multilayer film increased dramatically. The electrochemical properties were studied through cyclic voltammograms, and it was found that the electrochemical activity of the (PSS/PANI) n film increased with the increase of the bilayer number.
Keywords: Self-assembly; Layer-by-layer; Multilayer film; Poly(sodium styrenesulfonate); Oriented polyaniline fiber;
The uniform capillary model for packed beds and particle wettability by Nate Stevens; John Ralston; Rossen Sedev (162-169).
The uniform capillary model provides a framework for the determination of advancing and receding contact angles.The distribution and movement of fluids in porous media are important in a variety of situations arising naturally and industrially (e.g., water migration in soils, oil recovery, chromatography, filtration and separation processes). Our specific interest is in deriving advancing and receding contact angles from capillary pressure measurements in packed beds of particles partially saturated with liquids. The simplest model of a porous medium treats the porous body as an equivalent uniform capillary giving rise to the same capillary pressure. Pressure measurements were performed successfully with advancing as well as receding liquids. For an advancing liquid front a measurement with a second liquid is needed to calibrate the equivalent capillary radius and obtain the advancing contact angle. For a receding liquid front – an additional determination of the amount of liquid trapped behind in smaller pores is required. The equivalent capillary radius is mainly determined by the porosity of the packed bed and is easily corrected to account for capillary retention. Only then can the receding contact angle be obtained reliably. This new methodology for contact angle measurement was validated with model systems and applied successfully to various real particulate systems.
Keywords: Wettability; Porous medium; Capillary pressure; Contact angle; Particle; Capillary retention;
Superhydrophobicity of cotton fabrics treated with silica nanoparticles and water-repellent agent by Geun Yeol Bae; Byung Gil Min; Young Gyu Jeong; Sang Cheol Lee; Jin Ho Jang; Gwang Hoe Koo (170-175).
The superhydrophobic water-repellent cotton fabrics have been obtained by treating hydrophilic fabrics with silica nanoparticles and/or a cost-effective water-repellent agent.To obtain the superhydrophobic water-repellent cotton fabrics, cotton fabrics were treated with silica nanoparticles and/or a cost-effective water-repellent agent (WR agent). Two different silica nanoparticles were synthesized via a sol–gel process and their shapes, sizes, and compositions were characterized. It was found that silica particles are spherical and have diameters of 143 and 378 nm. For the cotton fabrics treated with the WR agent alone, the water contact angles on the fabric surface remained lower than 20° at the WR agent concentration of 0.3 wt% or less. Silica nanoparticle treatment itself did not change the hydrophilic surface of cotton fabric, indicating that water drops were adsorbed into fabrics due to the hydroxyl groups on both cotton and silica nanoparticle surfaces. However, for the cotton fabrics treated with both silica nanoparticles and the WR agent, a contact angle above 130° can be obtained even at the very low WR agent concentration of 0.1 wt%. Therefore, superhydrophobic cotton fabrics could be obtained via the combined treatment of silica nanoparticle and WR agent, which is cost effective compared with fluorinate silane treatment.
Keywords: Superhydrophobicity; Cotton fabric; Silica nanoparticle; Water-repellent agent; Sol–gel process;
Evaporating drops on patterned surfaces: Transition from pinned to moving triple line by Neeharika Anantharaju; Mahesh Panchagnula; Sudhakar Neti (176-182).
Evaporation of a sessile drop in pinned triple line (TL) and moving TL phases on a micropatterned hydrophobic surface of uniformly arranged square holes.Evaporation of sessile drops on micro-patterned surfaces is investigated over a range of heterogeneity length scales and solid area fractions. The surface topology is generated by a uniform arrangement of square pillars or square holes. The evaporation process is captured using high resolution imaging techniques and later post-processed for such information as contact angle, contact circle diameter and drop volume. It is observed that two distinct phases of evaporation existed for all substrate characteristics: pinned triple line (TL) phase and moving TL phase. In both phases, the process follows a linear decrease of surface area. The dimensionless evaporation rate constant is found to be higher during the moving TL phase in comparison with the pinned TL phase. In addition, it is found that the triple line topology has no effect on the evaporation rate constant.
Keywords: Evaporation; Superhydrophobicity; Triple line; Pinned and moving triple line;
Long-chain alkyl thiols in Langmuir monolayers by Marcin Broniatowski (183-190).
The paper concerns Langmuir monolayers of long alkyl thiols. The picture contains the surface pressure–area isotherm and BAM images of eicosane-1-thiol monolayers.A series of homologous alkyl thiols C n H2n+1SH (n = 14–18, 20, 22) have been synthesized and Langmuir monolayers have been thoroughly characterized using surface pressure, electric surface potential measurements and Brewster angle microscopy. Although the –SH group cannot form strong hydrogen bonding with the water subphase, thereby causing weak anchoring, it has been found that alkyl thiols having more than 15 carbon atoms are capable of Langmuir monolayer formation at room temperature. The stability of the investigated films is not very high, however, but quite sufficient for LB transfer at low surface pressures. The increase in aliphatic chain length does not lead to any considerable improvement of the monolayer stability. The influence of subphase temperature and the presence of various cations in the aqueous subphase have also been studied. Contrary to literature, it has been found that the presence of alkaline earth metals cations does not improve the monolayer stability, and although the collapse pressure is higher, the equilibrium surface pressure remains the same as on pure water.
Keywords: Long-chain alkyl thiols; Langmuir monolayers; Relaxation in Langmuir monolayers; Equilibrium surface pressures; Surface potential;
Miscibility behavior of two-component monolayers at the air–water interface: Perfluorocarboxylic acids and DMPE by Hiroki Yokoyama; Hiromichi Nakahara; Takahiro Nakagawa; Satoshi Shimono; Kunihiko Sueishi; Osamu Shibata (191-200).
Perfluorocarboxylic acids have a different influence on DMPE phase morphology in the monolayer state: The AFM images show a miscible pattern for DMPE/FC12 and immiscible pattern for DMPE/FC18.Surface pressure (π)–molecular area (A) and surface potential (ΔV)–A isotherms have been measured for two-component monolayers of four different perfluorocarboxylic acids [FCn; perfluorododecanoic acid (FC12), perfluorotetradecanoic acid (FC14), perfluorohexadecanoic acid (FC16), and perfluorooctadecanoic acid (FC18)] and dimyristoylphosphatidylethanolamine (DMPE) on 0.15 M NaCl (pH 2) at 298.2 K. The present study is focused on the miscibility and the interfacial behavior for the binary DMPE/FCn monolayers upon compression. From the isotherms, the miscibility has been elucidated in terms of the additivity rule, the interaction parameter, and the interaction energy. The interaction parameter (or energy) is compared with that for the previous dipalmitoylphosphatidylcholine (DPPC)/FCn systems [Colloids Surf. B 41 (2005) 285–298] to understand the effect of phospholipids’ polar headgroup on the binary miscibility. Furthermore, the phase behavior of the DMPE/FCn systems has been morphologically examined using fluorescence microscopy (FM) and atomic force microscopy (AFM). These images reveal the different interaction modes among the four systems; DMPE can be miscible with FC12 and FC14 and immiscible with FC16 and FC18 in the monolayer state. These systematic examinations indicate that the miscibility of perfluorocarboxylic acids and phospholipids depends on combination of hydrocarbon and fluorocarbon chain lengths and on phospholipids’ polar headgroups within a monolayer.
Keywords: Langmuir monolayer; Perfluorocarboxylic acid; DMPE; Surface potential; Fluorescence microscopy; Atomic force microscopy;
Langmuir monolayer miscibility of single-chain partially fluorinated amphiphiles with tetradecanoic acid by Hiromichi Nakahara; Minami Tsuji; Yukiko Sato; Marie Pierre Krafft; Osamu Shibata (201-210).
The two-component system (MA/F8C5PC) generates (a) homogeneous image within a monolayer and (b) fern-like networks as 3-D structures in the monolayer collapse state.The surface pressure (π)–molecular area (A) and surface potential (ΔV)–A isotherms have been measured for monolayers of tetradecanoic acid (myristic acid: MA), partially fluorinated amphiphiles [single-chain (perfluorooctyl)pentanol (F8C5OH) and single-chain (perfluorooctyl)pentylphosphocholine (F8C5PC)], and their two-component combinations in order to investigate their miscibility at the air/water interface. The data for these systems were analyzed in terms of an additivity rule and excess Gibbs free energy. An interaction parameter and an interaction energy between the two components were calculated from the Joos equation, which allows description of collapse pressures of miscible monolayers. Two-dimensional phase diagrams for the binary systems were constructed and found to be a positive azeotropic type. These results indicate that the two-component MA/F8C5OH and MA/F8C5PC monolayers are miscible in the monolayer state. To confirm their miscibility and phase behavior upon compression, morphological observations with fluorescence microscopy (FM), Brewster angle microscopy (BAM), and atomic force microscopy (AFM) have been performed. These observations show that the addition of F8C5OH or F8C5PC to MA makes MA ordered domains in the monolayer region fluidize very effectively and that a fern-like network is formed as a 3-D structure by over-compression beyond the monolayer collapse. The present paper systematically clarifies the miscibility between MA and F8C5OH or F8C5PC within the monolayer and indicates that these fluorinated chemicals may have a possibility of biomedical uses and applications.
Keywords: Langmuir monolayer; Partially fluorinated amphiphile; Tetradecanoic acid; Surface pressure; Surface potential; Brewster angle microscopy (BAM); Fluorescence microscopy (FM); Atomic force microscopy (AFM);
The spreading behaviour and spreading mechanism of new glucosamide-based trisiloxane on polystyrene surfaces by Yue Zhang; Fu Han (211-217).
The spreading behaviour and spreading mechanisms of five new glucosamide-based trisiloxane surfactants on polystryene surface were investigated.In order to evaluate the spreading behaviour of new glucosamide-based trisiloxane surfactants on hydrophobic surfaces, the time- and concentration-dependent spreading performance was investigated. Dynamic light scattering (DLS) was applied to investigate the role of surfactant aggregates on the spreading process. The results suggest that glucosamide-based trisiloxane surfactants show superspreading behaviour on hydrophobic surfaces; however, the spreading mechanism differs from that of ethylene oxide trisiloxane. The existence of large aggregates at low concentrations and relatively large spreading areas during the initial stages of wetting is helpful for generating the Marangoni effect, but the gemini-structure does not show good spreading characteristics. Synergistic effects between these five surfactants were also investigated, and considerable synergism was observed. Furthermore, both the spreading behaviour of mixed and single component systems suggests that the hydrophilic–lipophilic balance of surfactants play an important role in superspreading and an optimal HLB value is important for achieving good spreading behaviour.
Keywords: Superspreading; Glucosamide; Trisiloxane; Marangoni flow; HLB value;
Small-angle neutron scattering study of shearing effects on drag-reducing surfactant solutions by Yunying Qi; Kenneth Littrell; Pappannan Thiyagarajan; Yeshayahu Talmon; Judith Schmidt; Zhiqing Lin; Jacques L. Zakin (218-226).
SANS 2D plots of Arquad 16-50/NaSal (5 mM/5 mM) drag-reducing surfactant solution at shear rates of 0 s−1 and 1000 s−1 at room temperature.Drag-reducing surfactant solutions are very sensitive to shear. Shear can induce nanostructural transitions which affect drag reduction effectiveness and rheological properties. Literature reports on the effects of shear on different micellar solutions are inconsistent. In this paper, the effects of shear on three cationic drag-reducing surfactant solutions each with very different nanostructures and rheological behaviors, Arquad 16-50/sodium salicylate (NaSal) (5 mM/5 mM) (has thread-like micelles, shear-induced structure and large first normal stress (N 1)), Arquad S-50/NaSal (5 mM/12.5 mM) (has branched micelles, no shear-induced structure and first normal stress is about zero) and Arquad 16-50/sodium 3,4-dimethyl-benzoate (5 mM/5 mM) (has vesicles and thread-like micelles, shear-induced structure and high first normal stress (N 1)) are studied by small-angle neutron scattering (SANS), together with their rheological properties, drag reduction behavior and nanostructures by cryogenic-temperature transmission electron microscopy(cryo-TEM). The differences in the rheological behavior and the SANS data of the solutions are explained by the different responses of the nanostructures to shear based on a two-step response to shear.
Keywords: Surfactant; Drag reduction; Rheology; SANS (small-angel neutron scattering);
Aggregation, adsorption, and clouding behaviors of Triton X-100 in formamide by J. Das; K. Ismail (227-233).
The ratio of the solvent surface tension to the limiting surface tension, γ 0/γ cmc, is proposed as a novel scale for expressing solvophobicity, which works similar to the Gordon parameter.The critical micelle concentration (cmc) of TX-100 in formamide (FA) was determined from surface tension measurements as functions of temperature and NaCl concentration. At 25 °C, cmc was also determined by the fluorescence method. For the sake of comparison, micellization parameters of TX-100 were also determined in water. cmc, aggregation number, and standard free energy of micellization in FA are about 400 times higher, 10 times lower, and 2 times higher than in water, respectively. On increasing the temperature, cmc in FA shows a slight increase, whereas in water it decreases. The logarithm of relative cmc decreases linearly with added NaCl concentration in both FA and water, and the rate of this decrease is surprisingly equal in the two solvents. Micellization of TX-100 is exothermic in FA, but endothermic in water. The cloud point (CP) of TX-100 was determined in FA + water medium and that in pure FA was estimated to be ∼233 °C when [TX-100] = 0.15 mol kg−1. Surface excess values of TX-100 were calculated from Gibbs and Langmuir adsorption isotherms. Values of standard free energy of adsorption calculated from the Rosen–Aronson equation and from the Langmuir adsorption isotherm are comparable. The ratio of the surface tension of the solvent to that at the cmc has been demonstrated as a novel scale for measuring solvophobicity.
Keywords: TX-100; Formamide; Sodium chloride; Critical micelle concentration; Aggregation number; Cloud point; Free energy; Surface excess;
Mixing behaviour of charged and non-charged surfactants described by BET isotherms by Pierre Letellier; Alain Mayaffre; Mireille Turmine (234-239).
Mixed micelles made of non-ionic (BRIJ35) and cationic (DTABr) surfactants can be well described by means of the fBET model (open points).We analysed various sets of published results concerning the mixing behaviour of charged and non-charged surfactants, beyond their aggregation threshold, by means of the BET model modified by Stokes and Robinson. This approach, which is mainly used to account for properties of concentrated aqueous salt solutions, provides a good description of the properties of mixed micelles across the complete scale of compositions between the two pure surfactants. We use analyses of the behaviour of several systems reported in the literature for illustration. We consider the significance of the parameters C and r introduced in the BET model. For mixed micelle solutions in the presence of a support electrolyte, the value of the solvation enthalpy of the charged amphiphile by the non-ionic surfactant is small (C close to one). This model is compared to the regular solution theory (RST).
Keywords: Surfactant; Mixed micelle; Thermodynamics; BET model;
Micelle formation of polyoxyethylene-type nonionic surfactants in bmimBF4 studied by 1H NMR and dynamic light-scattering by Tohru Inoue (240-246).
Thermodynamic evidence is presented to demonstrate that micellization is caused by desolvation around hydrocarbon tails of surfactant molecules.Critical micelle concentrations (cmc) of polyoxyethylene (POE)-type nonionic surfactants in a room temperature ionic liquid, bmimBF4, were determined from the 1H NMR chemical shift of the surfactant as a function of concentration at various temperatures. Thermodynamic parameters derived from the temperature dependence of the cmc revealed that the micelle formation process of the surfactants in bmimBF4 is entropy-driven at low temperature, while it changes to enthalpy-driven at high temperature. Similarity of this behavior to the case of aqueous system suggests that the micellization of surfactant molecules in bmimBF4 is caused by a solvophobic interaction between hydrocarbon tails of the surfactants, which is analogous to a hydrophobic interaction in aqueous system. Compared with aqueous system, the solvophobic effect in bmimBF4 is much weaker. It was demonstrated that the enthalpy–entropy compensation relation holds for the micelle formation in bmimBF4 as well as in aqueous system.
Keywords: Room temperature ionic liquid; Nonionic surfactant; Micelle formation; Solvophobic effect; Enthalpy–entropy compensation;
Cloud point phenomena for POE-type nonionic surfactants in imidazolium-based ionic liquids: Effect of anion species of ionic liquids on the cloud point by Tohru Inoue; Takeshi Misono (247-253).
Cloud points of C n E m in bmimPF6 are higher than those in bmimBF4, because the interaction of bmim cation with PF6 anion is weaker than that with BF4 anion.Cloud point temperatures, T c, of polyoxyethylene (POE)-type nonionic surfactants in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), were measured and compared with those previously obtained for the surfactant solution in bmimBF4. The T cs for bmimPF6 solution are higher than those for bmimBF4 solution by approx. 40 °C. This means that the surfactant molecules are more solvophilic in bmimPF6 compared to bmimBF4. The analysis of 1H NMR chemical shift measurements proved that the higher solvophilicity of the surfactants in bmimPF6 is attributed to weaker hydrogen-bond interaction between bmim cation and PF 6 - anion than that between bmim cation and BF 4 - anion. This interpretation is consistent with the interaction energy parameters derived from the thermodynamic analysis of cloud point curve applying the Flory–Huggins model for phase separation in polymer solution. The present work demonstrates that the property of imidazolium-based ionic liquids as a solvent is determined by a balance of interactions among imidazolium cation, counter anion, and solute molecule.
Keywords: Polyethyleneglycol alkyl ether; Nonionic surfactant; Cloud point; Room temperature ionic liquid; Surfactant in ionic liquid; Solute–solvent interaction in ionic liquid; 1H NMR;
Effect of polar interactions on the magnetorheology of silica-coated magnetite suspensions in oil media by Julien Pacull; Stephanie Gonçalves; Ángel V. Delgado; Juan D.G. Durán; Marı´a L. Jiménez (254-259).
Nonmagnetic forces are also important for the magnetorheological effect: silica-coated magnetite particles exhibit different magnetorheological behaviors, depending on their hydrophilic or hydrophobic character.This work deals with the role of nonmagnetic interactions on the magnetorheological (MR) response of suspensions of magnetic particles in nonaqueous carriers (MR fluids). Although electrostatic interactions between particles are negligible, van der Waals and, eventually, polar forces might be present. Nevertheless, they are typically neglected when compared to magnetic or hydrodynamic ones. In order to perform a comparative evaluation of the contributions of these interactions, we carried out an MR investigation on two samples of silica-coated magnetite: one (MagSilica 50-H8) is hydrophobic and the other (MagSilica 50-85) is hydrophilic. We describe a careful surface thermodynamic characterization of the two kinds of silicas, confirming their very different hydrophobicities. MR measurements show that only the suspensions of 50-85 particles change from Newtonian to pseudoplastic when a magnetic field is applied, with a yield stress increasing with field strength H, and saturating when H ≅ 100 kA/m. The experimental values of yield stress are compared to theoretical predictions based on the chain model, and it is found that the theory overestimates the experimental values. It is suggested that the nonnegligible interfacial interactions are responsible for both the absence of MR effect in 50-H8 samples and the low yield stress in 50-85 suspensions.
Keywords: Magnetorheological fluids; Hydrophobicity; Polar interactions;
Single colloid electrophoresis by I. Semenov; O. Otto; G. Stober; P. Papadopoulos; U.F. Keyser; F. Kremer (260-264).
Electrokinetic measurements on single colloid using Optical Tweezers are carried out. Electrophoretic mobility of the colloid under study and the electroosmotic effect on the surrounding medium is determined using the identical colloid.Optical tweezers enable one to trap a single particle without any mechanical contact and to measure its position and the forces acting on it with high resolution (±4 nm, ±160 fN). Taking advantage of a specially designed microfluidic cell the electrophoretic response of the colloid under study and the electroosmotic effect on the surrounding medium are determined using the identical colloid. The former is found to be by more than one order of magnitude larger than the electroosmotic effect. It is shifted in phase with respect to the external field, hence giving rise to a complex electrophoretic mobility which can be theoretically described by a strongly damped driven harmonic oscillator model. By exchanging the medium surrounding the colloid it is possible to deduce the (KCl) concentration dependence of the single colloid electrophoretic response. The results are compared with conventional Zetasizer measurements.
Keywords: Electrophoresis; Electroosmosis; Electrophoretic mobility; Single colloids; Optical tweezers;
Control of uniform nanostructured α-Ni(OH)2 with self-assembly sodium dodecyl sulfate templates by Ming-Yao Cheng; Bing-Joe Hwang (265-271).
The synthesized α-Ni(OH)2 shows uniform 2-D hexagonal shape, indicating effective template by sodium dodecyl sulfate bilayers. The shape of the synthesized α-Ni(OH)2 may change according to the synthetic conditions.Morphological control of the nanostructured α-Ni(OH)2 is achievable via self-assembly of sodium dodecyl sulfate (SDS) as templates accompanied with microwave-assisted homogeneous alkalization process. The synthesized α-Ni(OH)2 can be 2-D hexagonal nano-sheets, macroporous micro-spheres or irregular-shaped platelets, depending on the SDS concentration. Further, the interlayer spacing of the synthesized α-Ni(OH)2 crystalline was determined to be 2.47 nm, indicating the intercalation of DS− anions between brucite layers. The results explain the morphological change of the synthesized α-Ni(OH)2 with SDS concentration, which provides a way to morphological control of metal hydroxides. The corresponding electrochemical properties for the α-Ni(OH)2 synthesized with and without SDS are characterized as well, showing the advantages of the 2-D hexagonal nano-sheets.
Keywords: α-Ni(OH)2; Template; Nano-sized; Homogeneous alkalization; Sodium dodecyl sulfate;
Decoration of multiwalled carbon nanotubes with CoO and NiO nanoparticles and studies of their magnetism properties by Xiuying Wang; Feng Zhang; Xingfu Zhu; Baiying Xia; Jiesheng Chen; Shilun Qiu; Jixue Li (272-277).
Multiwalled carbon nanotubes (MWNTs) have been successfully decorated with magnetic CoO and NiO nanoparticles. Magnetic measurements indicate that both the CoO/MWNT and NiO/MWNT composites present superparamagnetic behavior.Multiwalled carbon nanotubes (MWNTs) have been successfully decorated with magnetic CoO and NiO nanoparticles via the interaction of M ( NH 3 ) x 2 + (M = Co, Ni) ions and the carboxyl groups on the surface of acid-treated MWNTs. The obtained composites were characterized by X-ray diffraction, scanning electron and transmission electron microscopies. The soaking time plays an important role in the preparation of the composites. Magnetic measurements indicate that both the CoO/MWNT and NiO/MWNT composites present superparamagnetic behavior which can be attributed to the small size of CoO and NiO nanoparticles.
Keywords: Carbon nanotubes; Decoration; Nanoparticles; Superparamagnetic;
Synthesis and self-assembly of amphiphilic hyperbranched polyglycerols modified with palmitoyl chloride by Haixing Cheng; Siguang Wang; Jintian Yang; Yongfeng Zhou; Deyue Yan (278-284).
An amphiphilic multiarm copolymer with a hydrophilic hyperbranched polyglycerol core and many hydrophobic alkyl chains can self-assemble into either vesicles or large multimolecular micelles depending on selective solvents or graft ratios.A series of palmitoyl chloride-grafted hyperbranched polyglycerols were synthesized through cationic ring-opening polymerization and end-group modification. The obtained grafted copolymer of HPG-C16 possesses a hydrophilic hyperbranched polyether core and many hydrophobic alkyl arms, which shows interesting self-assembly behavior in THF and water. The results indicate that the copolymers with a relatively high alkyl grafting ratio can form unimolecular micelles in THF and will further assemble into giant vesicles around 1–10 μm in THF/water mixed solvents. However, the HPG-C16 with a low alkyl grafting ratio of 15.6% can directly assemble into vesicles in THF and form micelles in water.
Keywords: Hyperbranched; Self-assembly; Polyglycerols; Vesicles; Micelles;
Complex permittivity of FeCl3/AOT/CCl4 microemulsions probed by AC impedance spectroscopy by Pietro Calandra; Angela Ruggirello; Vincenzo Turco Liveri (285-288).
Under the effect of an electric field, the ionic species in FeCl3 clusters easily rearrange within the confined space of the micellar cores giving rise to the unusual dielectric properties of FeCl3 clusters.The complex permittivity of FeCl3/AOT/CCl4 microemulsions in the 1–105 Hz frequency range has been measured by the conventional AC complex impedance technique. Measurements as a function of the volume fraction of the dispersed phase (FeCl3 + AOT) and temperature at fixed salt-to-AOT molar ratio (R, R = 0.5) show that the entrapment of FeCl3 clusters significantly enhances the local permittivity of the AOT reverse micelles and the number density of charge carriers resulting from the peculiar state of the confined inorganic salt. An estimate of the apparent static permittivity of the FeCl3 ionic clusters entrapped in the core of AOT reverse micelles gives the very high and quite surprisingly value of about 237.Moreover, a thorough analysis of conductivity data and of their temperature dependence strongly supports the hypothesis that the charge transport in these systems is mainly sustained by a mechanism of hopping consisting in the continuous jumping of charged species within supra-micellar aggregates of AOT reverse micelles whose aggregation is driven by fluctuating opposite charges on contacting micelles.
Keywords: Solubilization; Confinement effects; Ferric chloride; AOT reverse micelles; Ionic clusters;
Direct deposition of size-tunable Au nanoparticles on silicon oxide nanowires by Jung Hoon Kim; Hyeun Hwan An; Hee Soo Kim; Young-Ho Kim; Chong Seung Yoon (289-293).
Silicon oxide nanowires (SiO X NWs) was decorated with 3- to 6-nm-sized Au nanoparticles by direct deposition of Au on the nanowire surface without any surface pretreatment.Silicon oxide nanowires (SiO X NWs) was decorated with 3- to 6-nm-sized Au nanoparticles by direct deposition of Au on the nanowire surface without any surface pretreatment. The nanowire surface was uniformly coated with Au nanoparticles with a density of 2 × 1012 particles cm−2. It was found that the Au nanoparticles grown on the SiO X NWs was much finer in size compared to the Au nanoparticles deposited on a flat SiO2 substrate because of the high curvature of the nanowires and abundant surface defects resulting from the oxygen non-stoichiometry. Moreover, the particle size as well as the particle density can be tuned at will by simply altering the growth condition of the SiO X NWs. The tuning of the Au particle provides an opportunity to tailor the Au nanoparticles for desired applications.
Keywords: Silicon oxide nanowire; Au nanoparticle; Catalyst; Size-tuning;
Fragmentation of molecule-induced γ-cyclodextrin nanotubular suprastructures due to drug dosage by S. Syed Jaffer; Subit K. Saha; Pradipta Purkayastha (294-299).
Compound induced γ-cyclodextrin nanotubular suprastructure formation is found to be highly sensitive to the concentration of the guest molecule, increasing concentration of which affects the length of the clusters.The guest–host concentration has already been proved to be a very important factor in the drug delivery process. In the present work we demonstrate the formation of compound induced γ-cyclodextrin nanotubular suprastructure. The nanotubes formed are found to be highly sensitive to the concentration of the guest molecule. The increasing concentration of the compound in solution initiates a competition toward their existence inside the core of the nanotubes affecting the extent of nanotubular cluster formation. The hydrogen bonding responsible for the building of the cyclodextrin nanotubes is found to be partially disrupted because of this increasing competition. The continuous replacement of the guest molecules inside the nanochannels is supposed to be responsible for the instability in some of the hydrogen bondings that develop during the primary and the secondary interactions between the formed nanotubes resulting into fragmentation of the suprastructures. The steady state and time-resolved fluorescence experiments coupled with fluorescence anisotropy and atomic force microscopy illustrate the guest concentration dependence of the formation of the γ-cyclodextrin nanotubes.
Keywords: γ-Cyclodextrin; Nanotubes; Host–guest interaction; Drug dosage; Fragmentation;
Electrocatalytic properties of graphite nanofibers-supported platinum catalysts for direct methanol fuel cells by Soo-Jin Park; Jeong-Min Park; Min-Kang Seo (300-303).
TEM images of the PtRu/GNF catalysts revealed that PtRu particles were successfully deposited and uniformly dispersed on GNF surfaces with 2.5–5.0 nm.Graphite nanofibers (GNFs) treated at various temperatures were used as carbon supports to improve the efficiency of PtRu catalysts. The electrochemical properties of the PtRu/GNFs catalysts were then investigated to evaluate their potential for application in DMFCs. The results indicated that the particle size and dispersibility of PtRu in the catalysts were changed by heat treatment, and the electrochemical activity of the catalysts was improved. Consequently, it was found that heat treatments could have an influence on the surface and structural properties of GNFs, resulting in enhancing an electrocatalytic activity of the catalysts for DMFCs.
Keywords: GNFs; PtRu catalysts; DMFCs; Heat treatment temperature;
Linkage by elimination/addition: A simple synthesis for a family of oligomeric alkylpyridinium surfactants by Kathryn A. White; Gregory G. Warr (304-306).
New method for producing and studying oligomeric alkylpyridinium surfactants.Homologous oligomeric alkylpyridinium surfactants have been prepared by an elimination–addition reaction that is simpler to perform and easier to control than conventional synthesis or polymerization. It can be carried out in a variety of protic solvents, or performed in situ on aqueous solutions of self-assembled monomeric surfactant.
Keywords: Oligomeric surfactant; Gemini surfactant; Reverse anionic polymerization; Elimination/addition; Synthesis; Chromophoric; Alkylpyridinium;
Experimental approach of the relation between surface tension and interfacial thickness of simple liquids by Jean Marc Douillard (307-310).
Various values of the thickness of the liquid–vapor interface deduced from ellipsometry compared with the surface tension for a set of pure liquids.It is possible to calculate the thickness of liquid–vapor interfaces starting from ellipsometry data. Some data are available since a long time but not sufficiently known. Using these data, a basic trend showing that the interface thickness increases when the surface tension decreases is shown. This trend is in agreement with which is generally expected from approach of the critical point considerations. Such a trend extended to the solid–liquid interface could be used to interpret some phenomena at the solid–liquid interface, where the thickness of the interface does not seem to vary, when considering only the liquid part of the interface. It implies that the number of molecular layers of the solid participating to adsorption should be different for various systems.
Keywords: Surface tension; Interface thickness; Ellipsometry; Interface sharpness;
by Arthur Hubbard (311).