Journal of Colloid And Interface Science (v.332, #1)

Electrokinetic modeling of metal oxides by Stuart Allison (1-10).
The focus of this study is the electrokinetic transport of metal oxide colloidal particles. These transport properties include electrophoretic mobility and the primary electroviscous effect of dilute suspensions of spherical particles that may contain a “gel layer” of uniform density on their outer surface. Charge on the surface or in the gel layer is assumed to arise from specific protonation, deprotonation, or complex formation reactions of oxide sites. Charge regulation, or the modulation of the equilibrium constants due to high absolute charge densities, is examined. Both the electrostatics and electrokinetic transport properties are solved numerically within the framework of the continuum-primitive model. With regards to the electrokinetics, detailed account is taken of the finite size of the particle as well as the “electrophoretic effect” and the “relaxation effect.” The methodology is then applied to two metal oxide systems: Ludox (a silica sol) and goethite. The charge density, electrophoretic mobility, and primary electroviscous effect of Ludox at pH 8.7 in KCl salt solutions, can be well explained by a gel layer model that expands as the salt concentration is lowered. A spherical model containing no gel layer is unable to account for the electrophoretic mobility of goethite in 0.01 M KNO3. However, a “sparse” gel layer model that contains 7.5% of the charge sites and consists of 96% solvent can account for both the experimental charge density and mobility over the pH range 4.0 to 11.0.Mobility versus pH profile for the metal oxide, goethite. Experiment (filled circles), model sphere without a gel layer (solid line), model sphere with a gel layer (dashed line).
Keywords: Electrokinetic modeling; Electrophoresis; Viscosity; Transport of metal oxides; Silica sols; Goethite;

The adsorption of polymers on clay is important in many applications. However the mechanisms of poly(ethylene oxide) (PEO) adsorption on smectite is not well elucidated at present. The aim of this study was to investigate the effect of layer charge density on the adsorption of PEO by smectite. The results indicated that both the hydrophobic interaction (between CH2 ―CH2 ― groups and siloxane surface) and the hydrogen bonding (between ether oxygen of PEO and structure OH of smectite) lead to PEO preferential adsorption on the surface of low-charge smectite. In addition, the delamination of low-charge smectite in water is enhanced upon PEO adsorption presumably due to the hydrophilic ether oxygen of adsorbed PEO.The hydrophobic interaction (between CH2 ―CH2 ― groups and siloxane surface) and the hydrogen bonding (between structure OH and PEO's ether oxygen) are responsible for PEO adsorption on smectite.
Keywords: Poly(ethylene oxide); Smectite; Adsorption; Layer charge; IR spectra;

Modification of montmorillonite surfaces using a novel class of cationic gemini surfactants by Limei Zhou; Hua Chen; Xiaohui Jiang; Fang Lu; Yafen Zhou; Wenmin Yin; Xiaoyang Ji (16-21).
A novel class of cationic gemini surfactants were prepared and used as modifiers for sodium montmorillonite (MMT-Na). The modified montmorillonites were characterized by X-ray diffraction (XRD), thermal analysis (TG), Fourier transform infrared spectroscopy (FTIR), dispersibility measurement, and scanning electron microscopy (SEM). The results show that the surfactants have been intercalated into the montmorillonite layers successfully. XRD measurements indicate that the gemini surfactant is more effective at expanding the interlayer space of the MMT than the corresponding single chain surfactant. Moreover, the high efficiency can be obtained by lengthening the hydrophobic chains of gemini surfactants. Thermal analysis shows that there are four different molecular environments for gemini surfactants in the modified montmorillonite. The dispersibility measurement and SEM results indicate that the modified montmorillonite are more hydrophobic and prone to agglomerate in water than MMT-Na. These modified materials have the potential for removal of environment pollutants such as pesticides, phenol, etc. or being used as antimicrobial materials.Novel cationic gemini surfactants were synthesized and used as modifiers for sodium montmorillonite. XRD patterns indicate that the gemini surfactant is more effective at expanding the interlayer space of the MMT than the corresponding monomeric surfactant. Moreover, the high efficiency can be obtained by lengthening the hydrophobic chains of gemini surfactants.
Keywords: Gemini surfactants; Montmorillonite; Surface modification;

A combined QCM and XPS investigation of asphaltene adsorption on metal surfaces by Amit Rudrake; Kunal Karan; J. Hugh Horton (22-31).
To investigate asphaltene–metal interactions, a combined quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS) study of asphaltene adsorption on a gold surface was conducted. Adsorption experiments were conducted at 25 °C with solutions of asphaltenes in toluene at concentrations ranging from 50 to 1500 ppm. QCM measurements yielded information on the kinetics of adsorption and further assessment of the data allowed the estimation of equilibrium adsorption levels. XPS analysis of adsorbed and bulk asphaltene demonstrated the presence of carboxylic, thiophenic, sulfide, pyridinic and pyrrolic type functional groups. The intensity of the main carbon (C–H) peak was related to surface coverage of adsorbed asphaltene as a function of asphaltene concentration by a simple mathematical model. The mass adsorption data from the QCM experiments also allowed estimation of the surface coverage, which was compared to those from XPS analyses. Surface coverage estimates as a function of asphaltene concentration could be described by a Langmuir (type-I) isotherm. The free energy of asphaltene adsorption was estimated to be − 26.8 ± 0.1 and − 27.3 ± 0.1 kJ / mol from QCM and XPS data, respectively assuming asphaltene molar mass of 750 g/gmol. QCM and XPS data was also analyzed to estimate adsorbed layer thickness after accounting for surface coverage. The thickness of the adsorbed asphaltene estimated from both XPS and QCM data analyses ranged from 6–8 nm over the entire range of adsorption concentrations investigated.Asphaltene adsorption on gold surface. (a) Adsorption kinetics measured by QCM. (b) C 1s intensity of adsorbed layer examined by XPS. (c) Adsorption isotherm generated from QCM and XPS data.
Keywords: Asphaltene adsorption; Asphaltenes; Functional group; QCM and XPS;

Positive and negative micropatterned copper sulfide thin films were successfully fabricated through chemical bath deposition methods. The thin films were deposited on patterned Si substrates with two different self-assembled monolayers (SAMs), i.e., NH2/CH3 and NH2/OH terminated silane, respectively. Under an optimal depositing condition, the copper sulfide thin films were selectively deposited on ―NH2 regions. The resultant Cu2S crystal films, in positive and negative circle patterns, respectively, were verified by SEM, XPS, XRD spectra. UV–vis spectrum analysis demonstrated that the prepared Cu2S films exhibited high optical transmission in the visible light regions (vis) and near-infrared region (NIR), and a low band gap of 2.48 eV.Micropatterns of copper sulfide were fabricated on patterned self-assembled monolayers. The SEM images showed that the regular and compact patterning films were deposited over a large area and had relatively high selectivity.
Keywords: Copper sulfide; Self-assembly monolayer; Micropattern; Optical property;

Lignin-based activated carbons for adsorption of sodium dodecylbenzene sulfonate: Equilibrium and kinetic studies by Luis M. Cotoruelo; María D. Marqués; José Rodríguez-Mirasol; Juan J. Rodríguez; Tomás Cordero (39-45).
The adsorption of sodium dodecylbenzene sulfonate (SDBS) from its aqueous solution at different temperatures has been studied using three activated carbons prepared in our laboratory. Lignin was used as raw material for the preparation of activated carbons (ACs). The results of the adsorption equilibrium were analyzed and fitted to the Langmuir model. Thermodynamic magnitudes were estimated as well, and their values indicated that the adsorption processes were spontaneous and exothermic. The kinetic study showed that the processes are of second apparent order related to the concentration of the vacant active centers on the surface of the activated carbons. The values of the effective internal diffusion coefficients have been calculated applying the equations developed by Crank and Vermeulen.Activated carbons from kraft lignin revealed high capacities to remove SDBS in the aqueous phase. If the hyperbolic model is suitable for the adsorbate concentration in the liquid phase, its parameters make the adsorption kinetic constant of second order related to the solid phase.
Keywords: Adsorption; Lignin; Activated carbon; Equilibrium; Kinetics; Sodium dodecylbenzene sulfonate;

Removal of methylene blue from colored effluents by adsorption on montmorillonite clay by C.A.P. Almeida; N.A. Debacher; A.J. Downs; L. Cottet; C.A.D. Mello (46-53).
In this study, montmorillonite clay (MC) has been utilized as the adsorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solution by the batch adsorption technique under different conditions of initial dye concentration, adsorbent concentration, contact time, solution pH, and temperature. Attempts were made to fit the isothermal data using Langmuir and Freundlich equations. The experimental results have demonstrated that the equilibrium data are fitted well by a Langmuir isotherm equation. Thermodynamic parameters such as the changes in enthalpy, entropy, and Gibbs' free energy were determined, showing adsorption to be an endothermic yet spontaneous process. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were considered to evaluate the rate parameters. The experimental data fitted the pseudo-second-order kinetic model, with an activation energy of +28.5 kJ mol−1. The results indicate that MC adsorbs MB efficiently and could be employed as a low-cost alternative in wastewater treatment for the removal of cationic dyes.Effect of initial methylene blue concentration on the adsorption onto montmorillonite clay. More MB was retained and the adsorption mechanism became more efficient, as the initial dye concentration increased.
Keywords: Adsorption; Montmorillonite clay; Isotherms; Methylene blue; Kinetics;

Diffuse sorption modeling by Sergey Pivovarov (54-59).
This work presents a simple solution for the diffuse double layer model, applicable to calculation of surface speciation as well as to simulation of ionic adsorption within the diffuse layer of solution in arbitrary salt media. Based on Poisson–Boltzmann equation, the Gaines–Thomas selectivity coefficient for uni–bivalent exchange on clay, K GT (Me2+/M+) = ( Q Me 0.5 / Q M ){M+}/{Me2+}0.5, (Q is the equivalent fraction of cation in the exchange capacity, and {M+} and {Me2+} are the ionic activities in solution) may be calculated as [surface charge, μeq/m2]/0.61. The obtained solution of the Poisson–Boltzmann equation was applied to calculation of ionic exchange on clays and to simulation of the surface charge of ferrihydrite in 0.01–6 M NaCl solutions. In addition, a new model of acid–base properties was developed. This model is based on assumption that the net proton charge is not located on the mathematical surface plane but diffusely distributed within the subsurface layer of the lattice. It is shown that the obtained solution of the Poisson–Boltzmann equation makes such calculations possible, and that this approach is more efficient than the original diffuse double layer model.Poisson–Boltzmann equation allows calculate ionic adsorption within diffuse layer in arbitrary salt media. Titration curves of oxide surfaces may be modeled assuming diffuse distribution of net proton charge.
Keywords: Gouy–Chapman model; Diffuse double layer; Poisson–Boltzmann equation; Ferrihydrite; Surface charge; Adsorption; Ionic exchange; Gaines–Thomas selectivity coefficient;

Chloromethylated styrene-divinylbenzene copolymers were post-crosslinked through Fredel–Crafts alkylation reaction and a water-compatible hypercrosslinked resin HJ-1 was developed successfully. It can be wetted directly by water and can be used without any wetting process. It was applied to remove p-nitrophenol in aqueous solution in comparison with the commercial Amberlite XAD-4 resin. Their adsorption behaviors for p-nitrophenol were conducted and it was found the adsorption dynamics obeyed the pseudo-second-order rate equation and the intra-particle diffusion was the rate-limiting step. The adsorption isotherms can be correlated to Freundlich isotherm and the adsorption capacity onto HJ-1 resin was much larger than XAD-4. The maximum adsorption capacity of p-nitrophenol for HJ-1 resin was measured to be 179.4 mg/g with the equilibrium concentration at 178.9 mg/l and the maximum removal percentage was predicted to be 98.3%. The adsorption thermodynamic parameters were calculated and the adsorption was mainly driven by enthalpy change. The micropore structure, the size matching between the pore diameter of HJ-1 resin and the molecular size of p-nitrophenol, and polarity matching between the formaldehyde carbonyl groups of HJ-1 resin and p-nitrophenol bring the larger adsorption capacity and higher adsorption affinity.The batch adsorption experiment shows that HJ-1 resin exhibits much larger adsorption capacity and higher adsorption affinity to p-nitrophenol than the commercial Amberlite XAD-4 in aqueous solution.
Keywords: Hypercrosslinked; Adsorption; p-Nitrophenol; HJ-1 resin; Amberlite XAD-4 resin;

Control of interfaces on electrical properties of SiO2–Parylene-C laminar composite dielectrics by Pratyush Tewari; Ramakrishnan Rajagopalan; Eugene Furman; Michael T. Lanagan (65-73).
The interfacial interactions and their effects on electrical properties are reported for thermally grown SiO2–Parylene-C laminar composites. The segmental chain mobility of the interfacial Parylene-C was found to be enhanced in the composites. TSDC (thermally stimulated depolarization current) measurements showed the presence of dipolar interfacial energy states in these laminar composites. Functionalization of the oxide surface with 3-aminopropyltriethoxysilane (APTES) created dipolar energy states with larger activation energy at the interface between Parylene-C and SiO2. In addition to the modification of interfacial states, incorporation of APTES interfacial layer also increased polarizability (real part of permittivity) and reduced the quasi-DC conductivity of laminar composites. The systematic changes in interfacial characteristics with thickness of APTES layer were explained based on structural orientation and cross linking of silane molecules.Enhancement in polarizability of laminar composite with incorporation of APTES interfacial layer.
Keywords: Chain mobility; Interfacial modification; Polarizability; Conductivity;

A facile route to ultra-long polyaniline nanowires and the fabrication of photoswitch by Xiuhua Wang; Mingwang Shao; Guang Shao; Zhengcui Wu; Shaowu Wang (74-77).
Ultra-long polyaniline nanowires with an average diameter of 60 nm and length up to tens of micrometers were successfully synthesized via chemical oxidation polymerization in an aqueous solution. These nanowires exhibited reversible electrochemical behavior judged from cyclic voltammetry curves. The excellent photosensitivity and photoresponse of a bundle of nanowires were also investigated, which showed that the photocurrent enhanced by ca. 4 times under irradiation of an incandescence lamp (12 V, 10 W). This work might be useful in the fabrication of photosensor and photoswitch nanodevices in the future.Ultra-long PANI nanowires were synthesized via a facile synthesis, which showed high photosensitivity and photoresponse according to switching the light source on/off.
Keywords: Polyaniline; Nanowires; Photocurrent; Cyclic voltammetry;

H-binding groups in lignite vs. soil humic acids: NICA-Donnan and spectroscopic parameters by Marios Drosos; Maria Jerzykiewicz; Yiannis Deligiannakis (78-84).
A comparative study has been carried out for two sets of humic acids isolated from lignites and soils. H-binding data were analyzed using the NICA-Donnan model, for three Greek lignite humic acids (HA) plus IHSS Leonardite reference HA, and five Greek soil HAs plus a commercial peat HA. 13C-CP-MAS NMR and H-binding data provide quantitative estimates for functional groups, showing that lignite HAs of diverse origin have strikingly homogeneous properties, while the H-binding structural units of soil HAs are characterized by a large degree of variability. Consistent differences between soil HA vs. lignite HA are revealed at the level of functional groups' concentrations. In the pH range 4 to 10, soil HA showed a charge variation <3 [equiv kg−1] while lignite HAs showed a higher charge variation >3.5 [equiv kg−1].
Keywords: Humic acid; Lignite; Soil; Greek; NICA; H-binding; 13C NMR; Spectroscopy;

In the preparation of a thermo-responsive, poly(N-isopropylacrylamide) (PNIPAAm)-grafted polydimethylsiloxane (PDMS) surface by means of benzophenone-initiated photopolymerization, we observed that thick ( > 1 mm ) PDMS substrates were much more difficult to be grafted with PNIPAAm than thin ones. Investigations revealed that the shortage of diffused benzophenone molecules in the surface region of the thick substrate might be the reason. By prolonging the time spent for treating the substrate with a benzophenone solution, PNIPAAm could be successfully grafted onto thick PDMS substrates. The PNIPAAm-grafted PDMS surface was highly thermo-responsive. The contact angle on a grafted surface increased from 38 to 91° in response to the temperature increase from 20 to 38 °C. An electroosmotic flow (EOF) mobility of 5 × 10 −4 cm 2 / V s was supported by a PNIPAAm-grafted PDMS channel at 50 °C, whereas negligible EOF was observed at 20 °C. Doxorubicin (DX), an anticancer drug, was adsorbed by the grafted surface at 40 °C, and the majority of the adsorbed DX was quickly released from the surface to a stripping solution at 5 °C. Osteoblast cells adhered onto the PNIPAAm-grafted PDMS surface and proliferated therein at 37 °C, while the cell sheet detached from the surface by lowering the temperature to 25 °C without using any enzymatic agent.The thickness of PDMS substrate was a critical factor for a successful grafting reaction of PNIPAAm.
Keywords: Polydimethylsiloxane; Poly(N-isopropylacrylamide); Thermal-responsive surface; Drug release; Cell culture; Microfluidic chip;

Surface micellization of poly(2-oxazoline)s based copolymers containing a crystallizable block by Charles-André Fustin; Nathalie Lefèvre; Richard Hoogenboom; Ulrich S. Schubert; Jean-François Gohy (91-95).
The micellization on surfaces of copoly(2-oxazoline) diblock copolymers consisting of a crystallizable poly(2-nonyl-2-oxazoline) (pNonOx) block linked to a poly(2-ethyl-2-oxazoline) (pEtOx) block is investigated. Those micelles are not pre-existing in the initial ethanol solution but are formed during the spin-coating process by the evaporation of the solvent inducing the precipitation of the less soluble pNonOx block. The morphology and size of the surface micelles vary according to the pNonOx molar fraction in the copolymers. Reorganization of the micelles and evolution of the surface energies after a thermal annealing are also studied.Surface micelles whose morphology and size depend on the copolymer composition are prepared from copoly(2-oxazoline) diblock copolymers consisting of a crystallizable poly(2-nonyl-2-oxazoline) block linked to a poly(2-ethyl-2-oxazoline) block.
Keywords: Micelles; Morphology; Spin-coating; Surfaces; Block copolymers;

Lysozyme mediated calcium carbonate mineralization by Xiaoqiang Wang; Hailing Sun; Yongqing Xia; Cuixia Chen; Hai Xu; Honghong Shan; Jian R. Lu (96-103).
Lysozyme, a major component of egg white proteins, has been speculated to participate in the calcification of avian eggshells. However, its detailed role during the eggshell formation is not well understood. In this work, the influence of lysozyme on the precipitation of CaCO3 has been investigated using a combined study of FTIR, XRD, and SEM. The precipitation was produced from (NH4)2CO3 vapor diffusion into CaCl2 aqueous solution using a specially built chamber. In the absence of lysozyme, hexagonal platelets of vaterite and their spherical aggregates dominated the precipitates during the first 3–12 h crystallization period studied, with the (001) crystal face well expressed in the hexagonal direction. In contrast, calcite was favored to precipitate in the presence of lysozyme during the same period and the effect was found to be proportional to lysozyme concentration. Furthermore, the (110) face of calcite was expressed in addition to the common (104) face, and the morphological modification was also lysozyme concentration dependent. We attributed these phenomena to the selective adsorption of ammonium ions and lysozyme onto different crystal faces. Our findings have clearly revealed the concentration and face dependent role of lysozyme in CaCO3 precipitation. This, together with the abundance of lysozyme in the uterine fluid, implies its direct contribution to the hierarchical structures of calcite during the initial stage of eggshell formation.The presence of lysozyme favored the precipitation of calcite crystals and the influence is protein concentration dependent.
Keywords: Biomineralization; Mineralization; Lysozyme; Calcite; Vaterite; Protein adsorption;

Shear modulus of colloidal suspensions: Comparing experiments with theory by Rasmus Eriksson; Heikki Pajari; Jarl B. Rosenholm (104-112).
In this work, the experimentally determined shear modulus of a colloidal suspension has been compared to a calculated shear modulus based on an ordered lattice model. The experiments were performed on a well characterized calcite suspension. The calcite suspension was confirmed to be in a flocculated state, thus exhibiting strong elastic character. The experimental shear modulus was estimated from the elastic modulus in the linear viscoelastic region. This is contrary to established convention, where the high frequency limiting modulus is used. However, the network structure breaks down at high frequencies, resulting in a different system. Therefore the shear modulus was estimated from the response of the intact particle network structure, which resides within the linear viscoelastic region. Calculation of the shear modulus is based on an ordered lattice model, where the particles are arranged in regular 3D-arrays. Interaction forces between the particles are also considered, based on the well known DLVO-theory. Calculations of the shear modulus for flocculated colloidal suspensions are not trivial however, because of the random distribution of particles. Due to this fact the average interparticle distance is impossible to determine exactly and therefore the comparison between experimental and calculated shear modulus was made by calculating the shear modulus as a function of interparticle separation. Some different models for interaction forces between particles were tried, and the results were compared to rheological data. These preliminary results show that useful suspension properties can be evaluated by combining rheological measurements with theories for interactions between particles arranged in ordered lattices.The calculated shear modulus varies depending on which model is chosen for the particle interactions.
Keywords: Colloidal suspensions; Calcite; Shear modulus; Ordered lattice; Particle interactions; DLVO;

Liposome rupture and contents release over coplanar microelectrode arrays by Jit Kang Lim; Hao Zhou; Robert D. Tilton (113-121).
The vulnerability of vesicles to electroporation and rupture by externally applied electric fields, combined with the ability of dielectrophoresis and/or AC electroosmosis to manipulate suspended vesicles over micropatterned electrodes suggests new techniques to electrically trigger localized chemical reactions at predetermined positions in microfluidic devices. The electric field conditions needed to rupture giant unilamellar phospholipid vesicles were determined as a function of vesicle size in a simple coplanar microelectrode array geometry. Rupture results were interpreted in terms of the spatially varying electric field strength, calculated via the Poisson equation and accounting for frequency effects on electrode impedance, and the experimentally measured vesicle elevation. The vesicle transmembrane voltage scales linearly with the applied electric field strength according to the Schwan theory of electroporation, so that larger vesicles are usually more prone to electric field induced rupture than smaller ones in the uniform electric fields that are typically employed to cause electroporation and rupture. Yet, in the coplanar microelectrode arrangement, larger vesicles preferentially reside at larger elevations where the local field strengths are weaker. As a result, there is a sensitive range of vesicle radii that are most prone to electric field induced rupture over a micropatterned electrode array that leaves the largest vesicles resistant to rupture.Non-uniform electric fields manipulate and then induce rupturing of phospholipid vesicles over a microelectrode strip. Here a ruptured vesicle releases fluorescent tagged proteins that subsequently adsorb to nearby polystyrene latex particles.
Keywords: Electroporation; Dielectrophoresis; Contents release; Vesicle; Microfluidics;

The sol–gel transformation of aqueous solutions of aluminium ions into aluminium (oxy)hydroxides induced by the addition of a ‘soft base’—‘Tris-buffer’ ( p K a = 8.2 ) has been investigated using monotonous single-batch titrations and a combination of four complimentary techniques for monitoring pH, conductivity, viscosity and ultrasound parameters (velocity and attenuation). The multi-probe monitoring of the formation of aluminium (oxy)hydroxides enabled important stages of the sol–gel transformation process including: the structural conversion of aluminium Keggin-like polynuclear clusters into nanoparticles of aluminium (oxy)hydroxide; the aggregation of primary nuclei of aluminium (oxy)hydroxide into larger particles, and the ‘arrested growth’ of the aggregates with the formation of the three-dimensional gel network to be followed. The effect of aluminium ion molecular speciation on the sol–gel transformation stages is discussed. The data presented show that ultrasonic spectrometry, although a novel tool for sol–gel studies, is beneficial for the non-invasive monitoring of the latter stages of aluminium (oxy)hydroxide formation and its eventual breakdown in the presence of excess base.The hydrolytic gelation of Al(O)OH has been followed using pH, conductivity, viscometry and ultrasonic spectrometry measurements. Ultrasonic spectrometry is especially useful for monitoring the later stages of Al(O)OH formation.
Keywords: Sol–gel transformation; Ultrasonic; Aluminium hydroxides; Speciation; Ultrasound parameters; Hydrolysis ratio; Aluminium colloidal suspension;

Surface-enhanced Raman scattering of hydroxybenzoic acids adsorbed on silver nanoparticles by J.L. Castro; J.F. Arenas; M.R. López-Ramírez; D. Peláez; J.C. Otero (130-135).
Surface-enhanced Raman scattering (SERS) of hydroxybenzoic acids has been studied on silver sols in H2O and D2O solutions. The adsorption behavior of 4-hydroxybenzoic acid (4HBA) is different from that of salicylic (2HBA) and 3-hydroxybenzoic (3HBA) acids. It was concluded that 4HBA is adsorbed on silver nanoparticles (Agn) as either oxidobenzoate (A2−) or hydroxybenzoate (A), depending on the pH of the solution, given rise to a flat orientation. Both 2HBA and 3HBA acids are always adsorbed as hydroxybenzoates anions (A) at pH ⩾5 and link to the metal through the carboxylate group (Agn ―A), standing more or less perpendicular to the metal surface. In the case of these monoanions, the selective enhancement of the bands is due mainly to a resonant electron or charge transfer process (ET or CT) from the metallic nanoparticles to the adsorbates, yielding the transient formation of the respective radical dianions (Ag+ n ―A 2−). It is found that the enhanced bands, and especially the mode 8a; ν ring , are related to the difference between the equilibrium structures of the adsorbate in its ground (A) and CT-excited (A 2−) states. In the SERS spectrum of 4HBA dianion, the contribution of CT mechanism is not observed.Different enhancement mechanisms are observed in the SERS of hydroxybenzoic acids. It is shown that the charge-transfer mechanism depends on the ionization degree which is in turn related to the position of the substituent.
Keywords: SERS; Surface-enhanced Raman; Raman; Hydroxybenzoic acids; Salicylic acid; Charge transfer; Radical anion;

Catalytic activity of rare earth phosphates for SF6 decomposition and promotion effects of rare earths added into AlPO4 by Daishin Kashiwagi; Asami Takai; Takeshi Takubo; Hisatoshi Yamada; Takanori Inoue; Katsutoshi Nagaoka; Yusaku Takita (136-144).
SF6 was selectively hydrolyzed to SO3 over rare earth (RE) phosphates above 800 K. CePO4 was the most active catalyst, followed by GdPO4, YbPO4, DyPO4, ErPO4, SmPO4, PrPO4, TbPO4, NdPO4, and LaPO4. The middle RE phosphates were found to be more active than the light RE phosphates, but the reason for the high activity of CePO4, which belongs to the light RE group, is not clear. The catalytic activity was independent of the specific surface area (SSA), acid amount, and acid concentration of the catalysts. RE phosphates were single-phase, and a broad inversely proportional relation was observed between the crystallite size and SSA, except in the case of CePO4. The combination of highly active AlPO4 and CePO4 creates synergetic effects in the catalytic activity and SO3 selectivity over all ranges of composition. Binary catalysts were a mixture of small crystalline AlPO4 and CePO4. The addition of Ce promoted the crystallization of AlPO4, which was controlled to about 10 nm at 10–50% Ce content. The turnover frequency for SF6 decomposition was proportional to the surface concentration of hydroxyls of binary catalysts. Therefore, synergy effects may come from the number of hydroxyl (OH) pair sites on which a bidentate intermediate of hydrolysis of SF6 may be formed by the moderate crystallization of AlPO4. The addition of Ce, Pr, or Y to AlPO4 brings about a small promotion effect for SF6 decomposition, but the addition of La, Nd > Gd > Yb diminishes the activity. The addition of Gd, Pr, or Nd greatly improved the SO3 selectivity. A linear relationship between catalytic activity and the concentration of surface hydroxyls of the catalysts supports a reaction mechanism in which two F atoms of an SF6 molecule interact with two surface hydroxyls to form a bidentate intermediate.Rare earth phosphates are effective for SF6 decomposition and highly selective for SO3 formation. Reaction proceeds via a bidentate intermediate in which two F atoms interact with two surface hydroxyls.
Keywords: SF6; Decomposition; Hydrolysis; Rare earth phosphates; Synergy effects; Crystallite size;

Polymer composite electrolytes (PCE) based on poly(ethylene oxide) (PEO) and alkylammonium-functionalized clay materials were fabricated. Structural modification and the electrochemical properties were investigated in order to understand the effects of organically modified montmorillonite (OMMT) in the polymer matrix on the ion conductivity. Nanosize layer-structured clay fillers were used having an organic modifier with different alkyl lengths and positions. The X-ray diffraction (XRD) results revealed that the interlayer spacing (2.55 nm) for MMT-20A was increased compared with that (1.16 nm) for Na-MMT. Both the XRD and the thermal analysis results indicated that the PCE showed reduced crystallinity after the introduction of the OMMT fillers. From the ion-conductivity results, the PCE containing MMT-20A showed higher conductivity ( 6.1 × 10 −4   S / cm ) than that containing Na-MMT ( 2.2 × 10 −4   S / cm ) . This indicated that the improved ion conductivity was dependent on the reduced crystallinity that was correlated with the d-spacing of the MMT. Furthermore, the PCE/OMMT showed improved tensile strength. Finally, it was shown that the conducting and mechanical properties were dependent on the interlayer spacing of the modified clays.Composites containing modified MMT (b) showed an increased interlayer spacing in comparison to composite containing pristine MMT (a), resulting in the improved ion conducting behavior.
Keywords: Composite electrolytes; Poly(ethylene oxide); Montmorillonite; Conducting behavior; Interlayer spacing;

Role of the Mg/Al atomic ratio in hydrotalcite-supported Pd/Sn catalysts for nitrate adsorption and hydrogenation reduction by Dongjin Wan; Huijuan Liu; Xu Zhao; Jiuhui Qu; Shuhu Xiao; Yining Hou (151-157).
Hydrotalcite-supported Pd/Sn catalysts with different Mg/Al atomic ratios (2, 3, 4, and 5) for nitrate adsorption and hydrogenation reduction were successfully synthesized by a coprecipitation method. The results showed that different atomic ratios of Mg/Al resulted in different interlayer spacings and zeta-potentials of the catalysts, which thus influenced its adsorption capacity. With the increase of Mg/Al atomic ratio, the interlayer spacing rose and zeta-potential decreased. The adsorption properties of the catalysts were mainly affected by interlayer spacing when Mg/Al atomic ratios increased from 2 to 4. However, when Mg/Al atomic ratios further increased from 4 to 5, there was a negative impact on the adsorption properties of zeta-potential. Also, the adsorption capacity of the catalysts for nitrate followed the order: Mg/Al = 2 < Mg/Al = 3 < Mg/Al = 5 < Mg/Al = 4. In the catalytic reduction process, the adsorbed nitrates were further reduced to nitrites that remained in the same position in catalysts, but some of superabundant nitrites were released into water as primary and unstable products. The concentration of released nitrites was in the reverse order of the adsorption capacity. The catalytic selectivity and activity of the catalysts for nitrate reduction had the same sequence as its adsorption capacity.
Keywords: Mg/Al atomic ratio; Hydrotalcite; Nitrate; Hydrogenation; Adsorption; Reduction; Nitrite;

Sorption of Cm(III) and Gd(III) onto gibbsite, α-Al(OH)3: A batch and TRLFS study by N. Huittinen; Th. Rabung; J. Lützenkirchen; S.C. Mitchell; B.R. Bickmore; J. Lehto; H. Geckeis (158-164).
Gd(III) and Cm(III) sorption onto a pure aluminum hydroxide, gibbsite (α-Al(OH)3), is studied by batch experiments and time-resolved laser fluorescence spectroscopy (TRLFS). The experiments are conducted under argon atmosphere to exclude the influence of atmospheric CO2 on solution and surface speciation. Batch experiments are done in two different electrolytes 0.1 M NaClO4 and 0.1/0.01 M NaCl at a constant gibbsite concentration of 2.2 g/L. Gadolinium concentrations are varied from 6.4 × 10 −9 to 6.4 × 10 −5 M . pH-dependent sorption is found to be congruent at Gd(III) concentrations up to 6.4 × 10 −7 M and a shift of the pH edge to higher pH values is observed for higher metal ion concentrations. Type of background electrolyte anion and ionic strength do not affect the metal ion sorption. The spectroscopic investigations are performed with Cm(III) and gibbsite concentrations of 2 × 10 −7 M and 0.5 g/L, respectively. From the strongly red-shifted emission spectra two different inner-sphere surface complexes can be identified. A third species appearing at pH 6–11 is assigned to a coprecipitated or incorporated Cm(III) species. This incorporated species is most likely formed as a consequence of the applied experimental procedure. By continuously increasing the pH from 4 we move from high to low gibbsite solubility domains. As a result, aluminum hydroxide precipitates from oversaturated solutions, either covering already adsorbed curium or forming a Al/Cm(OH)3 coprecipitate. Fluorescence lifetimes for the surface-bound Cm(III) complexes and the incorporated species are at 140–150 and 180–200 μs, respectively. Emission bands of the Cm(III) gibbsite surface complexes appear at comparable wavelengths as reported for Cm(III) species bound to aluminum oxides, e.g., γ-Al2O3; however, lifetimes are longer. This could presumably arise from either shorter binding distances of the Cm to Al―O sites or a coordination to more surface sites.pH-dependent sorption of Gd(III) onto gibbsite, α-Al(OH)3 (left), and Cm(III) emission spectra of curium complexes on gibbsite (right) are presented.
Keywords: Cm(III); Gd(III); Gibbsite (α-Al(OH)3); Sorption; TRLFS; Surface complexation; Incorporation;

The preparation of honeycomb scaffold with hierarchical controllable porous structures is reported. The ABA three block amphiphilic copolymer PS-b-P(St-Alt-AMn)-b-PS was synthesized through reversible addition fragmentation chain transfer polymerization (RAFT) and subsequently self-assembled to core–corona nanoparticles with the middle block P(St-Alt-AMn) as the core and two side block PS as the corona. The formed core–corona nanoparticles were further crosslinked through the reaction of amino diphenyl methane with anhydride in chains. The core-crosslinked core–corona nanoparticles were used as the building block to fabricate the controllable porous scaffold with hierarchical structure. The micrometer level honeycomb mesostructures can be obtained by an inverse emulsion template method which is consisted in the formation of the high internal phase ratio emulsions (HIPRE) while the nanometer level pores are formed by the close-packed core–corona block copolymer nanoparticles. As carboxylic group is formed in the crosslink step of the core, the growth factor can be easily incorporated into the matrix in order for the growth of the cell in the tissue engineering application. This kind of hierarchical honeycomb structure is an ideal candidate for the tissue engineering and drug delivery applications.The porous scaffold with hierarchical controllable pore structures has been fabricated from the core-crosslinked core–corona nanoparticles.
Keywords: Emulsion template; Honeycomb scaffold; Core–corona nanoparticles; Amphiphilic block copolymer;

ZnO2/poly(acrylic acid) sandwich structures were prepared by layer-by-layer (LbL) self-assembly. The structure and optical behavior of the hybrid films were controlled by changing the surface charge and conformation of the poly(acrylic acid). The buildup of the films was followed by UV–vis absorption and reflection spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), and quartz crystal microbalance (QCM) measurements. It was found that the ionic strength of the polymer solution had a great influence on the film thickness which, in turn, affected the optical properties. The water vapor adsorption isotherms of the films determined by QCM showed an adsorption hysteresis characteristic of porous thin layer structures. The adsorption of water molecules inside the films changed the effective refractive index resulting in a change of the reflection properties. This phenomenon is shown to be exploited for the application of the films as optical sensors. The polarizability of water molecules in the adsorption layer was also determined. It was found that polarization of water molecules in the adsorption layer is much lower than in the liquid water when the surface coverage (Θ) is low.Controlling the ionic strength of the PAA solution. ZnO2/PAA hybrid films were prepared with different layer thicknesses. The structural, optical, and water vapor adsorption properties are discussed in the paper.
Keywords: ZnO2; Polyelectrolyte; Layer-by-layer; QCM; Vapor adsorption; Optical sensor; Thin layer;

A simple thermodynamic theory is presented for water swollen complex salts formed by ionic surfactant and oppositely charged polyions. The description takes into account, on approximate level, free energy contributions from attractive and repulsive polyion-mediated interactions between the micelles, the mixing of micelles, polyion chains and water, and the hydrophobic effect. Explicit expressions for the chemical potentials of water, polyion, and surfactant ion are derived and used to calculate phase diagrams at various degrees of polymerization and linear charge density of the polyion and for surfactants with 12 and 16 carbons in the tail group. In all calculations the aggregation number is optimized and the phase structure (disordered or fcc) is determined. The effect of varying the charge densities of spheres interacting with a cross-linked polyion network is also investigated. Results from theory are compared with experimental and Monte Carlo simulation data reported in the literature.Schematic drawing of an aqueous polyion–surfactant ion complex salt showing cationic surfactant micelles surrounded by anionic polyion chains.
Keywords: Polyelectrolyte; Surfactant; Micelle; Complex salt; Opposite charge; Phase diagram; Cubic phase;

Surface tension reduction (STR) in aqueous solutions of anionic surfactants with cobalt(III) complexes by Sieng Sovanna; Takayoshi Suzuki; Masaaki Kojima; Satoshi Tachiyashiki; Masakazu Kita (194-200).
It has been observed that, at 25.0 ± 0.1 ° C , [Co(NH3)6](ClO4)3, [Co(en)3](ClO4)3, [Co(bpy)3](ClO4)3, and [Co(phen)3](ClO4)3 in the regions of 1.25–5.00 mM aqueous solutions cause a significant surface tension reduction (STR) of water by the surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SBS), suggesting the formation of the 1:1 and 1:2 association complexes, {[complex]3+(S)}2+ and {[complex]3+(S)2}+ where [complex]3+  = [Co(NH3)6]3+, [Co(en)3]3+, [Co(bpy)3]3+, or [Co(phen)3]3+, S  = DS or BS. The effect of [Co(en)3]3+ on STR in SDS–water system is the largest due to a strong hydrophilic interaction between amino protons of [Co(en)3]3+ and sulfate oxygen atoms of DS. The effects of [Co(en)3]3+, [Co(bpy)3]3+, and [Co(phen)3]3+ on STR in SBS–water system are significant and almost same, meaning that the hydrophilic interaction between [Co(en)3]3+ and the sulfonate group is comparable to the hydrophobic interaction between [Co(bpy)3]3+ or [Co(phen)3]3+ and the phenyl group of BS. The Co(III) complexes of 1.25–5.00 mM are precipitated as {[complex]3+(S)3} at 0.0295–0.173 mM of S. The precipitates, {[Co(bpy)3]3+(S)3} and {[Co(phen)3]3+(S)3} can be dissolved at higher molar ratio of [S]/[complex3+] than 3.5 for SDS and 4.0 for SBS. This observation suggests that the aggregated premicelle [Co(bpy or phen)3]2(DS) 7 or aggregated premicelle [Co(bpy or phen)3](BS) 4 is formed.The effect of [Co(en)3]3+ on STR in aqueous solutions of SDS is largest due to a strong hydrophilic interaction between amino protons of [Co(en)3]3+ and oxygen atoms of the surfactant.
Keywords: Surface tension; Hydrophilic interaction; Hydrophobic interaction; Co(III) complexes; Sodium dodecylsulfate; Sodium dodecylbenzenesulfonate;

Polymerizable semi-fluorinated gemini surfactants designed for antimicrobial materials by Laurent Caillier; Elisabeth Taffin de Givenchy; Richard Levy; Yves Vandenberghe; Serge Geribaldi; Frederic Guittard (201-207).
Introduction of biocide monomers during the process of polymerization is one of promising approaches in the development of new permanent non leaching biocide materials. In this perspective, new polymerizable semi-fluorinated gemini surfactants, with quaternary ammonium groups as polar heads and an acrylic function as the polymerizable moiety, were synthesized and tested to evaluate their surface active properties alongside with their antibacterial and antifungal properties. Four microbial strains, known for their implication in nosocomial infections, were used to perform the study: Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus niger. The biocide efficacy measured by bacterial and fungal growth inhibition expressed as MIC (minimal inhibitory concentration) and MLC (minimal lethal concentration) values was discussed as a function of molecular parameters. As compared to homologue compounds without acrylic part, this study shows that even the introduction of a polymerizable moiety allows to keep remarkable both surfactant and bacteriostatic activities, and allows us to envisage the use of these surfactant monomers to build up advanced biocide materials. Moreover, semi-fluorinated gemini surfactant monomers with an amide connector came out as broad spectrum biocides (against Gram positive and negative bacteria and fungi).The synthesis and evaluation of properties of new polymerizable semi-fluorinated gemini surfactants show that the introduction of a polymerizable moiety allows to keep remarkable both surfactant and bacteriostatic activities.
Keywords: Antimicrobial agents; Gemini; Surfactants; Bacteriostatic; Semi-fluorinated surfactants; Surfactant monomers;

Effects of surfactant and electrolyte concentrations on bubble formation and stabilization by Qingyi Xu; Mitsutoshi Nakajima; Sosaku Ichikawa; Nobutaka Nakamura; Poritosh Roy; Hiroshi Okadome; Takeo Shiina (208-214).
As interest in the application of microbubbles grows, it is becoming increasingly important to understand the factors affecting their formation and properties in order to effectively generate microbubbles. This paper investigates the effect of surfactant concentration and electrolyte addition on the size distribution and stability of microbubbles. The anionic surfactant sodium dodecyl sulfate (SDS) was used as the surfactant. Minimum bubble diameter and maximum stability were achieved at surfactant concentrations above the CMC. The effect of the electrolyte addition was studied by adding sodium chloride (NaCl) at an SDS concentration below the critical micelle concentration (CMC). Addition of NaCl decreased bubble size and improved bubble preparation to a certain extent. The addition of salt at low concentrations did not affect the surface tension; however, the surface tension was reduced as salt concentration was increased and reached a constant value for NaCl concentrations above 0.25%. The presence of NaCl resulted in a significant decrease in zeta-potential, implying a reduction in the surface charge of SDS micelles. This result suggests that the presence of NaCl may improve the generation and stability of bubbles by enhancing the structures of the adsorption monolayer and interfacial film.
Keywords: Microbubbles; Size and size distribution; Stability; Surface tension; Zeta-potential;

Electrophoretic characterization of gold nanoparticles functionalized with human serum albumin (HSA) and creatine by Julián López-Viota; Subhra Mandal; Angel V. Delgado; José Luis Toca-Herrera; Marco Möller; Francesco Zanuttin; Maurizio Balestrino; Silke Krol (215-223).
The synthesis of composite nanoparticles consisting of a gold core coated with a human serum albumin (HSA)/creatine layer is described, and their possible application as novel drug carriers for brain delivery is discussed. In this paper, the effect of the concentration of creatine and HSA in the different formulations is studied by electrophoretic mobility measurements as a function of pH and ionic strength. Due to the permeable character of the coatings surrounding the gold cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed on the basis of three theoretical models of the electrokinetics of soft particles. As a result, information is obtained on both the surface potential and the charge density of the surrounding layer. The three models used reproduce properly the experimental behavior, although Duval and Ohshima's calculations appear to yield a more accurate fit of the data. It is shown that the albumin/nanogold particles absorb large amounts of creatine. In addition, the low surface charge and the albumin layer are expected to make it possible to deliver the particles through the blood–brain barrier.TEM micrographs of gold nanoparticles: (a) citrate-stabilized, (b) creatine-coated with a negative stain, (c) overview of albumin/creatine–nanogold particles, (d) negatively stained albumin/creatine–nanogold particle.
Keywords: Creatine; Electrophoretic mobility; Human serum albumin; Soft particles; Surface potential;

Phase-transfer and film formation of silver nanoparticles by Anjana Sarkar; Ridhima Chadha; Nandita Biswas; Tulsi Mukherjee; Sudhir Kapoor (224-230).
In this article, a simple method for either transfer of silver nanoparticles from formamide to chloroform or to form a film at their interface is demonstrated. The transfer of the particles is a two-step size-dependent process. The size distribution of the colloidal hydrophobic silver particles in chloroform was almost the same as that before its transfer. Particles can be isolated by evaporation of chloroform. During evaporation, the hydrophobic particles become hydrophilic (charged) due to the formation of bilayer of CTAB over their surface. The isolated particles can be re-dispersed easily in polar solvents such as water and methanol. Nanocrystalline film of Ag is also prepared at the formamide–chloroform interface using suitable stabilizers in two immiscible layers. The nanocrystals have been characterized by various microscopic and spectroscopic techniques. The free standing film could be easily transferred on solid support.Schematic representation for the formation of Ag film at the interface.
Keywords: Metals; Chemical synthesis; Electron microscopy; X-ray diffraction;

In this paper, we report the successful synthesis of Ni12P5 hollow spheres via a facile hydrothermal route, employing white phosphorus (WP) and nickel nitrate as the reactants in the presence of hexamethylenetetramine (HMT) and polyethylene glycol 10000 (PEG-10000). The phase and morphology of the product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). HMT and surfactant (PEG-10000) played important roles in the formation of Ni12P5 hollow microspheres. Furthermore, research also showed that the as-prepared Ni12P5 hollow spheres could photocatalytically degrade some organic dyes such as Safranine T and Pyronine B under irradiation of 365 nm UV light.Ni12P5 hollow microspheres were successfully prepared via a simple hydrothermal route in the presence of hexamethylenetetramine and polyethylene glycol 10000.
Keywords: Transition metal phosphides; Hollow microspheres; Polyethylene glycol 10000; Transmission electron microscopy;

Using sound to study bubble coalescence by W. Kracht; J.A. Finch (237-245).
Frothers are surfactants used in flotation to aid generation of small bubbles, an effect attributed to coalescence prevention. Studying coalescence at the moment of bubble creation is a challenge because events occur over a time frame of milliseconds. This communication introduces a novel acoustic technique to study coalescence as bubbles are generated at a capillary. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has the resolution to detect events that occur within 1–2 ms. The results show that for common flotation frothers and n-alcohols (C4–C8) coalescence prevention is not simply related to surface activity. A total stress model is used to give a qualitative explanation to the action observed. Results for salt (sodium chloride) are included for comparison.A novel acoustic technique to study coalescence as bubbles are generated at a capillary is presented. Results of coalescence prevention in presence of surfactants and salt are also included.
Keywords: Bubble coalescence; Bubble sound; Frothers;

Influence of atmospheric fluorine plasma treatment on thermal and dielectric properties of polyimide film by Soo-Jin Park; Hee-Jin Sohn; Sung-Kwon Hong; Gwi-Su Shin (246-250).
Plasma treatment of polyimide surfaces not only causes structural modification during the plasma exposure, but also leaves active sites on the surfaces that are subject to post-reaction. In this work, the effects of atmospheric fluorine plasma treatment on the surface properties and dielectric properties of polyimide thin film were investigated by using X-ray photoelectron spectroscopy (XPS), Fourier transform-IR (FT-IR) spectroscopy, and contact angle measurement. The results indicated that plasma treatment successfully introduced fluorine functional groups on the polyimide surfaces. The polyimides also exhibited good thermal stability and a lower dielectric constant. It appears that the replacement of fluorine led to the decrease of the local electronic polarizability of polyimide. Consequently, it was found that the atmospheric fluorine plasma-treated polyimides possessed lower dielectric characteristics than the untreated polyimides.The dielectric constants ranged between 2.43–2.95 at 1 MHz and 25 °C, which was lower than those of the untreated polyimide film. It can be seen that the dielectric constant decreased with increasing fluorine content of the polyimide film when the temperature was kept constant.
Keywords: Polyimide; Atmospheric fluorine plasma treatment; Contact angle measurement; Dielectric characteristics;

An expression for the van der Waals interaction energy between two parallel torus-shaped colloidal particles is derived. It is shown that for small particle separations the torus–torus interaction energy is well approximated by the interaction energy between two parallel cylinders, each being produced by cutting a torus and unrolling it. In particular, in the limit of very small particle separations, the interaction energy between two parallel tori and that between the corresponding two parallel cylinders tend to the same limiting value. This limiting value also agrees with the result of applying Derjaguin's approximation to the interaction between two parallel cylinders.Interaction between two parallel torus-shaped particles.
Keywords: van der Waals interaction; Torus-shaped particles; Cylindrical particles;

A liquid/liquid interface excited by stimulation with water by Satoshi Nakata; Kumika Ishibashi; Kouhei Kawata; Yutaka Sumino; Shuji Nakanishi; Kentaro Sonoda (254-257).
An immiscible interface, which was composed of CaCl2 aqueous and ester phases, was excited by the addition of a small amount of water. The excitation, i.e., burst and flow at the interface, was observed above a critical concentration of CaCl2 in the aqueous phase. The critical concentration and degree of excitation depended on the kind of ester. The mechanism of excitation is discussed in relation to the interfacial tension and the Marangoni effect.An excitable phenomenon is driven by the difference in concentration of an inorganic ion at the ester/aqueous interface.
Keywords: Excitation; Interface; Nonequilibrium; Liquid/liquid interface; Marangoni effect;

Capacitive deionization (CDI) is an ion removal technology based on temporarily storing ions in the polarization layers of two oppositely positioned electrodes. Here we present a thermodynamic model for the minimum work required for ion separation in the fully reversible case by describing the ionic solution as an ideal gas of pointlike particles. The work input is fully utilized to decrease the entropy of the outflowing streams compared to that of the inflow. Based on the Gouy–Chapman–Stern (GCS) model for planar diffuse polarization layers—with and without including additional ion volume constraints in the diffuse part of the double layer—we analyze the electric work input during charging and the work output during discharging, for a reversible charging–discharging cycle. We present a graphical thermodynamic cycle analysis for the reversible net work input during one full cycle of batchwise operation of CDI based on the charge–voltage relations for different ionic strengths. For the GCS model, an analytical solution is derived for the charge efficiency Λ, which is the number of salt molecules removed per electron transferred from one electrode to the other. Only in the high voltage limit and for an infinite Stern layer capacity does Λ approach unity.
Keywords: Capacitive deionization; Desalination; Diffuse double layer theory; Thermodynamic cycle analysis;

For the first time, the interaction of casein micelle (CM) with gold nanoparticles (GNPs) was studied using TEM, UV–visible, FTIR and fluorescence spectroscopy methods. The results show that GNPs bind to CM surface, leading to the formation of GNP–CM conjugates. GNPs exhibit similar particle diameters, and the CM structure is retained in GNP–CM conjugates. Furthermore, GNP–CM conjugates display good stability against salt concentration and pH. The combination of these measurements suggests that GNPs presumably bind to CM surfaces via complexation with the carboxylate or amine groups on CM surfaces, but not by electrostatic action.Diagram illustrating gold nanoparticles binding on casein micelles.
Keywords: Protein aggregates; Gold nanoparticles; Interaction; Bioconjugates;