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Journal of Colloid And Interface Science (v.344, #1)

Cover 1 (pp. ofc).

Templated one step electrodeposition of high aspect ratio n-type ZnO nanowire arrays by Satinder K. Sharma; Amritha Rammohan; Ashutosh Sharma (pp. 1-9).
Growth characteristics of high aspect ratio, aligned ZnO nanowire arrays by one step electrodeposition from Zn(NO3)2·6H2O electrolyte in polycarbonate membranes.High aspect ratio Zinc Oxide (ZnO) nanowires (NWs) were synthesized by template based one-step electrochemical deposition (OSECD) technique. The electro-reduction of hydroxide ions in the presence of Zn2+ ions within Zn(NO3)2 is involved in the growth of ultra thin NWs arrays. Field Emission Scanning Electron Microscopy (FESEM) images revealed that the growth rates of different crystal faces, (0001) and(0001¯), were different at different deposition potential for the high aspect ratios ZnO NWs arrays. The n-type semiconductor conductivity of ZnO NWs was ascertained by a Hot-Probe approach. X-ray diffraction results demonstrated that the grown ZnO NWs had wurtzite crystal structure with unit cell parameters a=2.93Å, c=5.45Å and a deterioration of preferred (101) orientation is observed at more negative deposition potentials. Small angle X-ray scattering (SAXS) results evidenced that the NW arrays grown at −1.2V have higher fraction of larger crystallites. Micro-Raman spectroscopy analysis showed that the variation in E2 (high) vibration mode at 435cm−1 is coupled with an increase in electro acceptor oxygen atoms incorporated within ZnO NWs at −1.2V.

Keywords: ZnO nanowire; Aligned nanowire; Electrochemical synthesis; Templated synthesis; Nanowire growth kinetics; n; -Type nanowire; Hot-Probe; Nanowire characterization; μ-Raman

Birefringent physical gels of N-(4- n-alkyloxybenzoyl)-l-alanine amphiphiles in organic solvents: The role of hydrogen-bonding by Trilochan Patra; Amrita Pal; Joykrishna Dey (pp. 10-20).
This article explores the mechanisms of physical gelation and liquid crystal properties of N-(4- n-alkyloxybenzoyl)-l-alanine amphiphiles in organic solvents.A new class of amphiphiles, N-(4- n-alkyloxybenzoyl)-l-alanine was designed and synthesized. These amphiphiles have been shown to form thermoreversible gels in organic solvents such as aromatic hydrocarbons, cyclohexane, and chlorinated hydrocarbons at room temperature. The effects of amide functionality, chain length of the hydrocarbon tail, and the chirality of the head group of the amphiphiles on the ability to promote gelation in organic solvents have been studied. The n-tetradecyl derivative showed the best gelation ability, whereas the amphiphile withdl-alanine as the head group formed weak organogels. The 4-dodecyloxybenzoic-1-carboxyethyl ester derivative in which the amide group is replaced by an ester group also formed weak organogels at a slightly lower temperature (293K). The gelation number and the gel melting temperature of the gelators in different solvents were determined. The rheological measurements suggested that the organogels of n-tetradecyl derivatives are stronger than those of amphiphiles containing n-dodecyl chains. Also the organogels of the amphiphiles, except the one with an ester group, were found to have gel-to-sol transition temperatures, Tgs, higher than room temperature (∼303K), which increased with the increase of chain length and total concentration of the gelator. SEM pictures of the gels show fibrous structures. Small-angle XRD and optical microscopy were also employed to characterize the gels. The organogels of alanine derivatives, except that of 4-dodecyloxybenzoic-1-carboxyethyl ester, showed optical birefringence. The mechanism of gelation was studied using1H NMR and FTIR spectroscopy. Hydrogen-bonding between –CO2H groups as well as π–π interactions were found to be important for the gelation process.

Keywords: Organogels; Amino acid-based amphiphiles; Hydrogen bonding; Microscopy; XRD; Rheology

Comparison of protein–polysaccharide nanoparticle fabrication methods: Impact of biopolymer complexation before or after particle formation by Owen G. Jones; Eric A. Decker; David Julian McClements (pp. 21-29).
Biopolymer nanoparticles can be formed using two methods: Type 1 particles are formed by creating β-lactoglobulin nanoparticles by heating, and then coating them with pectin; Type 2 particles are formed by heating β-lactoglobulin and pectin complexes together.The nature of protein–polysaccharide nanoparticles prepared using two fabrication methods was compared: Type 1 particles were formed by creating β-lactoglobulin nanoparticles, and then coating them with pectin; Type 2 particles were formed by heating β-lactoglobulin and pectin complexes together. Protein nanoparticles ( d=180nm) were created by heating β-lactoglobulin above its thermal denaturation temperature ( Tm) at pH 5.8. Type 1 particles were then formed by mixing these particles with high methoxy (HM) pectin under conditions where pectin adsorbed to the protein (pH<6). Type 2 particles were created by heating β-lactoglobulin-HM pectin electrostatic complexes above Tm at pH 4.75. At pH 4.5, Types 1 and 2 particulates had similar charge (−33mV), protein content, and shapes (spheroid), however, Type 1 particulates were larger ( d=430nm) than Type 2 particulates ( d=300nm).The influence of pH, ionic strength and protein:pectin mass ratio ( r) on the physical stability of the two types of particles was tested. A weight ratio of 2:1 (protein:pectin) gave good pH stability of the particles against aggregation by imparting more surface charge. Type 2 particles had a higher electrical charge, better stability to aggregation at lower pH values (pH<4), and better stability to aggregation at high salt concentrations (200mM NaCl) than Type 1 particles. These differences suggested that Type 2 particulates had a higher surface coverage with pectin, thereby reducing their tendency to aggregate. These results have important consequences for the design of biopolymer nanoparticles based on thermal treatment of proteins and polysaccharides.

Keywords: β-lactoglobulin; Pectin; Nanoparticles; Stability; Comparison

Bimetallic Aucore–Agshell nanoparticles from interfacial redox process using poly( o-methoxyaniline) by Pratap Mukherjee; Arun K. Nandi (pp. 30-36).
The intensity of the plasmon band of Ag nanoparticles in chloroform gradually decreases on aging with Au3+, indicating oxidation of silver nanoparticles to Ag+ and entry of Au nanoparticles into the core.Stable Aucore–Agshell bimetallic nanoparticles are produced in organic medium through an interfacial redox method using the redox property of an organically soluble conducting polymer poly( o-methoxyaniline) (POMA). The transition of the emeraldine base (EB) form of POMA to its pernigraniline base (PB) form occurs during nanoparticle formation and also the nitrogen atoms of POMA (PB) stabilize the nanoparticles via coordination. TEM images indicate that the interfacial redox replacement reaction between Au (III) in aqueous medium and Ag (0) in organic medium produces bimetallic nanoparticles with Aucore–Agshell morphology. The formation of such type of core–shell morphology is due to the different standard reduction potentials of the metal ions. The core–shell thickness of the bimetallic nanoparticle can be regulated by changing the POMA (EB) concentration in the organic layer.

Keywords: Core–shell; Interface; Redox process; Poly(; o; -methoxyaniline); XPS

Application of the Cluster–Cluster Aggregation model to an open system by Hailing Xiong; Hang Li; Weiping Chen; Jian Xu; Laosheng Wu (pp. 37-43).
Morphology of the final aggregates for different evaporation rates in the regime of rapid aggregation (DLCA).Colloid aggregation is often induced by the change of internal or external conditions. In order to account for the dynamic features of the evolutional open system, a conceptual model for colloid aggregation in open systems was developed based on the classic Cluster–Cluster Aggregation (CCA) model. The extended model allows the important parameters of the classic CCA model, diffusion coefficient D1 and sticking probability P1 of primary particles, time-dependent. Consequently, the new model can be used to simulate colloid aggregation in open systems. To demonstrate the applicability of the extended model, the diffusion coefficient D1 and sticking probability P1 were defined as a function of solvent evaporation rate and aggregation time in this study. For the simplicity purpose, this study only evaluate D1( t) while kept P1( t) as a constant for the simulations. Simulation results indicate that the solvent evaporation altered the aggregation mechanism in various degrees depending on the solvent evaporation rate. This research shows that the extended model based on the classic CCA model is valuable and applicable to open systems.

Keywords: Cluster–Cluster Aggregation; Open system; Solvent evaporation; Sweepage aggregation

Adsorption of serum albumin on silica – The influence of surface cleaning procedures by Olof Svensson; Thomas Arnebrant (pp. 44-47).
Adsorption of bovine serum albumin on (A) untreated silica (B) silica treated with plasma and (C) silica treated with alkaline and acidic hydrogen peroxide solutions.The objective of the investigation was to study how different surface cleaning procedures affect the subsequent adsorption of bovine serum albumin (BSA) on silica. Ellipsometry was used to monitor the adsorbed amount and thickness of the protein films in situ at physiological buffer conditions. Plasma treatment was found to effectively reduce the amount of BSA on silica and on surfaces cleaned with hydrogen peroxide solutions (RCA method) adsorption was essentially absent. On clean silica surfaces the ellipsometric data furthermore suggest that a depletion zone is present at the surface where the BSA concentration is lower than in the bulk solution. Additional experiments showed that calcium did not promote the adsorption of BSA and that the adsorption of human serum albumin (HSA) is essentially absent on clean silica surfaces in agreement with the results obtained for BSA. The presented work contributes to the general understanding of protein adsorption as well as provides information on how to control serum albumin adsorption on silica based biomedical devices.

Keywords: Albumin; Silica; Adsorption; Surface treatment; Ellipsometry

One-step UV lithography for activation of inert hydrocarbon monolayers and preparation of protein micropatterns by Chang-Ying Xue; Kun-Lin Yang (pp. 48-53).
One-step UV lithography under ambient conditions was developed to pattern inert monolayers with reactive groups, which subsequently leads to the spontaneous formation of water and covalently immobilized protein micropatterns on surfaces.Materials with chemical micropatterned surface have broad applications in many fields. In this article, we report a simple one-step UV lithography method to activate inert hydrocarbon monolayers for spontaneous formation of water and covalently immobilized protein micropatterns on the surface. Two types of hydrocarbon monolayers including octadecyltrichlorosilane (OTS) on silicon oxide and 1-hexadecene on hydrogen-terminated silicon were studied. It was found that after UV modifications, water can form micropatterns spontaneously on both surfaces. Furthermore, when protein solutions were used, covalently immobilized protein micropatterns can be formed. Our XPS results and controlled reducing experiments showed that UV exposure transformed inert monolayers into active surfaces with aldehyde groups, which are responsible for the covalent immobilization of proteins. The method reported herein can be applied under ambient conditions without having a high vacuum system. It can also be extended to pattern other biomolecules bearing amine groups.

Keywords: UV lithography; Inert monolayers; Protein micropatterns

Protein adsorption on dopamine–melanin films: Role of electrostatic interactions inferred from ζ-potential measurements versus chemisorption by Falk Bernsmann; Benoît Frisch; Christian Ringwald; Vincent Ball (pp. 54-60).
Protein adsorption on dopamine–melanin has an electrostatic component as well as irreversible aspect due to covalent binding.We recently showed the possibility to build dopamine–melanin films of controlled thickness by successive immersions of a substrate in alkaline solutions of dopamine [F. Bernsmann, A. Ponche, C. Ringwald, J. Hemmerlé, J. Raya, B. Bechinger, J.-C. Voegel, P. Schaaf, V. Ball, J. Phys. Chem. C 113 (2009) 8234–8242]. In this work the structure and properties of such films are further explored. The ζ-potential of dopamine–melanin films is measured as a function of the total immersion time to build the film. It appears that the film bears a constant ζ-potential of (−39±3) mV after 12 immersion steps. These data are used to calculate the surface density of charged groups of the dopamine–melanin films at pH 8.5 that are mostly catechol or quinone imine chemical groups. Furthermore the ζ-potential is used to explain the adsorption of three model proteins (lysozyme, myoglobin, α-lactalbumin), which is monitored by quartz crystal microbalance. We come to the conclusion that protein adsorption on dopamine–melanin is not only determined by possible covalent binding between amino groups of the proteins and catechol groups of dopamine–melanin but that electrostatic interactions contribute to protein binding. Part of the adsorbed proteins can be desorbed by sodium dodecylsulfate solutions at the critical micellar concentration. The fraction of weakly bound proteins decreases with their isoelectric point. Additionally the number of available sites for covalent binding of amino groups on melanin grains is quantified.

Keywords: Dopamine; Dopamine–melanin; ζ; -Potential; Protein adsorption; Quartz crystal microbalance

Thermally-triggered gelation of PLGA dispersions: Towards an injectable colloidal cell delivery system by Michael R. Fraylich; Ruixue Liu; Stephen M. Richardson; Pauline Baird; Judith Hoyland; Anthony J. Freemont; Cameron Alexander; Kevin Shakesheff; Francesco Cellesi; Brian R. Saunders (pp. 61-69).
We investigate thermally-triggered gelation of PLGA dispersions and show that this new family of responsive fluid has long term application as a colloidal cell delivery system.In this study the properties of poly(d,l-lactide- co-glycolide) (PLGA) dispersions containing a thermoresponsive cationic copolymer were investigated. The PLGA dispersions were prepared by interfacial deposition in aqueous solution and were rendered thermoresponsive by addition of a cationic poly( N-isopropyl acrylamide) (PNIPAm) graft copolymer. The copolymers used had the general compositionPDMAx+- g-(PNIPAm n) y. DMA+ is quarternarized N, N-dimethylaminoethyl methacrylate. ThePDMAx+- g-(PNIPAm n) y copolymers have x and y values that originate from the macroinitiator used for their preparation; values for n correspond to the PNIPAm arm length. The thermoresponsive dispersions were characterised using photon correlation spectroscopy, turbidity measurements and electrophoretic mobility measurements. A strong electrostatic attraction between the anionic PLGA particles and cationic copolymer was present and the dispersions showed thermally-triggered gelation at total polymer volume fractions as low as 0.015. These new PLGA gels, which formed at about 32°C, had elastic modulus values that could be controlled using dispersion composition. Scanning electron micrographs of the gels showed high porosity and interconnectivity of elongated pores. Remarkably, the gels were flexible and had critical yield strains as high as 160%. The ability of the gels to support growth of bovine nucleus pulposus cells was investigated using two-dimensional cell culture. The cells proliferated and remained viable on the gels after 3days. The results suggest that this general family of biodegradable thermogelling PLGA dispersions, introduced here for the first time, may have longer-term application as an injectable colloidal cell delivery system.

Keywords: Isopropylacrylamide; Thermoresponsive; Thermogelling; PLGA dispersions

Kinetic asymmetry in the gel–liquid crystalline state transitions of DDAB vesicles studied by differential scanning calorimetry by Eloi Feitosa (pp. 70-74).
For DDAB vesicles the gel to liquid crystalline state transition is much faster than the reverse liquid crystalline to gel state transition.Didodecyldimethylammonium bromide (DDAB) (1.0mM) vesicles in water were investigated by differential scanning calorimetry (DSC) to highlight the existing kinetic asymmetry in the gel–liquid crystalline (LC) state transitions. The experiments were performed in the range of temperature, scan rate and pre-scanning time 5–45°C, 15–90°C/h and 0–16h, respectively, in the up- and down-scanning modes. Depending on the input parameters and number of heating–cooling cycles, the DSC thermograms exhibit a sharp peak, a broad band or a flat shape. A melting temperature Tm=15.6–16.0°C, given by the peak position, was obtained independently of the scan rate used in the up-scanning mode. The data reveal that DDAB vesicles exhibit much slower kinetics for the LC to gel state than for the opposite transition. Such an asymmetry is supported by: (a) the absence of peak for shorter pre-scanning times but longer scan rates, (b) the increasing intensity of the DSC peak with increasing pre-scanning time and decreasing scan rate, and (c) the complete absence of peak in the down-scan mode. Longer pre-scanning time, however, yields crystal precipitates due to a Krafft phenomenon, which also reduces the peak intensity. The overall results depend on whether the sample is fresh or not, that is, after some heating–cooling cycles, the melting peak requires a longer pre-scanning time to be detected. The kinetic asymmetry explains, for example, the lack of any DSC melting peak reported for “non-fresh” DDAB vesicles, which was as yet unexplained.

Keywords: DDAB; DSC; Cationic vesicles; Melting temperature; Thermal hysteresis; Krafft point

Effect of spacer length on the micellization and interfacial behavior of mixed alkanediyl-α,ω-bis(dimethylcetylammonium bromide) Gemini homologues by Kabir-ud-Din; Mohmad Shafi Sheikh; Mohammad Amin Mir; Aijaz Ahmad Dar (pp. 75-80).
Plots of interaction parameters ( βσ) with stoichiometric mole fractions.The interfacial and micellization properties of binary and ternary mixtures of Gemini homologues, viz., tetramethylene-1,4-bis( N-hexadecyl- N, N-dimethylammonium bromide), pentamethylene-1,5-bis( N-hexadecyl- N, N-dimethylammonium bromide), and hexamethylene-1,6-bis( N-hexadecyl- N, N-dimethylammonium bromide), with various compositions were investigated at 25°C using conductometric and tensiometric measurements. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameter, minimum area per molecule, free energy of micellization and adsorption have been evaluated and compared. The ideality/nonideality of the mixed micelles were tested in light of Clint, Rubingh, and Rubingh–Holland approaches. The mixed systems were found to undergo synergistic interaction, more so in mixed monolayer than in mixed micelle formation, and the micellar and interfacial properties were found to depend on the selection of surfactant pairing.

Keywords: Mixed micelles; Gemini surfactants; Binary systems; Ternary systems; Interfacial properties

Nanostructure of PEO–polyurethane–PEO triblock copolymer micelles in water by Beth L. Caba; Qian Zhang; Matthew R.J. Carroll; Robert C. Woodward; Timothy G. St. Pierre; Elliot P. Gilbert; Judy S. Riffle; Richey M. Davis (pp. 81-89).
Variation in the micellar nanostructure for triblock copolymers as a function of aggregation number.Novel hydrophilic triblock copolymers which form micelles in aqueous solution were studied by static and dynamic light scattering (SLS and DLS), small angle neutron scattering (SANS) and densitometry. The polymers were symmetric A–B–A block copolymers having two poly(ethylene oxide) (PEO) tail blocks and a polyurethane (PU) center segment that contained pendant carboxylic acids. The aggregation number of the micelles decreased with increasing PEO mass content. When attempting to fit the SANS data it was found that no single model was suitable over the entire range of block lengths and PEO mass concentrations investigated here. For the polymer with the highest aggregation number, the data were fitted with a triblock model consisting of a homogeneous core with a corona of non-interacting Gaussian chains for which only two free parameters were required: the radius of the core and the radius of gyration of the corona. In this case, the core was found to be effectively dry. At lower aggregation numbers, a star polymer model generated significantly better fits, suggesting the absence of any identifiable central core structure. Good agreement was found between the sizes measured by DLS, SANS and theoretical predictions of micelle size from a density distribution theory. These results show that when significant changes in aggregation number occur, the nanostructure of the micelle can change substantially even for polymers that are remarkably similar.

Keywords: Triblock copolymer; PEO; Charged micelle; SANS; DLS; SLS

Anion effects on anti-microbial activity of poly[1-vinyl-3-(2-sulfoethyl imidazolium betaine)] by Godawari Garg; Ghanshyam S. Chauhan; Reena Gupta; J.-H. Ahn (pp. 90-96).
A series of polysulfobetaines was prepared by anion exchange reactions. Polysulfobetaines exhibited strong anion-dependent antifungal as well as anti-bacterial properties, and are good candidates for biomedical applications.Recent investigations in the anti-microbial properties of the functional polymers are predominantly focused on the structure of the cationic moieties. In the present study, we investigated that the nature of the anion present in polysulfobetaines affects activity against certain microorganisms and their anti-microbial properties have been rationalized in terms of the structure–activity relationship. Vinyl imidazolium-based polysulfobetaines were prepared by the quaternization of poly( N-vinyl imidazole) with sodium salt of 2-bromo ethanesulfonic acid. The bromide counter anion of the resulting polymer was exchanged with different anions to generate a series of polymers. These were characterized by FTIR, DSC, XRD, SEM, elemental analysis (C, H, N and S) and viscosity measurements. The anti-microbial activity studies were carried against three fungi ( Aspergillus niger, Byssochlamys fulva and Mucor circenelliods) and two bacteria ( Bacillus coagulans BTS-3 and Pseudomonas aeruginosa BTS-2). The nature of the anion affects the structure of polysulfobetaine by realignment of polymer chains. The anion-dependent anti-microbial properties of polysulfobetaines result from the interaction of the microbes at the polymer interface.

Keywords: Anti-microbial activity; Anion exchange; Polysulfobetaines; Quaternization; Structure–activity relationships

Fluorescent probe studies of micropolarity, premicellar and micellar aggregation of non-ionic Brij surfactants by M. Sowmiya; Amit K. Tiwari; Subit K. Saha (pp. 97-104).
The dipolar nature of trans-2-[4-(dimethylamino)styryl]benzothiazole in its twisted intramolecular charge transfer excited state makes it useful as a surface probe for phenomena such as premicellar and micellar aggregation of non-ionic Brij surfactants.The dipolar nature of trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) in its twisted intramolecular charge transfer (TICT) excited state makes it useful as a surface probe for phenomena such as premicellar and micellar aggregation of non-ionic Brij surfactants. The process of micellization of Brij 35, Brij 58, Brij 78, and Brij 98 through the formation of smaller premicellar aggregates results in a progressive change in the nature of the DMASBT molecule and its location in the aggregates, reflecting the changes in its photophysical properties, which have been studied using steady-state fluorescence, fluorescence anisotropy, and time-correlated single-photon counting measurements. The microenvironment polarity around the DMASBT probe in the micellar phase is greater than that in corresponding premicellar phases. The orders of premicellar as well as micellar concentrations are Brij 35>Brij 58>Brij 98>Brij 78. The lower fluorescence anisotropies observed in the case of Brij 78 aggregates compared to those in other Brijs studied could be due to the accessibility of a nonrigid environment as a result of a folded conformation of a part of the nonpolar long chain of surfactant molecules near the core of aggregates. Three different locations of DMASBT were noted for Brijs 35, Brij 78, and Brij 98, whereas for Brij 58 only two locations are observed. The micropolarity of the environment around DMASBT in aggregation states has been determined.

Keywords: DMASBT; Brij; TICT fluorescence; Anisotropy; Premicellar aggregates; Micropolarity

Behavior of papain in mixed micelles of anionic–cationic surfactants having similar tails and dissimilar head groups by S.K. Mehta; Bhawna; Ganga Ram (pp. 105-111).
The interactions between papain and SDS–DDAB have been explored by using spectroscopy and physico-chemical methods. The polar head group of surfactant has been found to have a profound effect on papain.The mixed micellar behavior of anionic surfactant, sodium dodecylsulfate (SDS) and cationic surfactant, dodecylethyldimethylammonium bromide (DDAB) at varying mole fractions of DDAB, i.e. αDDAB in aqueous solution of papain has been investigated with the aid of spectroscopy and physiochemical measurements. Thermodynamic parameters have been computed over the entire mole fraction range of DDAB. The Clint equation and the regular approximation method have been used to investigate the interactions between mixed surfactants in the presence of protein. The two surfactants have similar tails, however, the charges on respective polar head groups are expected to have significant effect on their colloidal behavior. The cmc values of mixed surfactants have been estimated from fluorescence, conductivity, surface tension, ultrasonic speed and density measurements. The results show that lower and higher mole fractions of DDAB give negative departure from ideality whereas intermediate mole fractions have positive deviation. The aggregation number, Nagg of mixed micelles has also been calculated. The turbidity or cloudiness at intermediate mole fractions demonstrates a reduction in the background free monomer concentration due to neutralization of the monomers of opposite charge. The effect of concentration of papain on mixed micellar behavior indicates that with increase in the concentration of protein, the cac and cmc values increase. The unfolding of polypeptide chain in the presence of mixed surfactant has been observed.

Keywords: DDAB; SDS; Papain; Fluorescence; cmc; Clint equation; Mixed micelle

The interaction between multi-charged organic salts and poly(vinylpyridine) microgel particles by Kaizhong Fan; Melanie Bradley; Brian Vincent (pp. 112-116).
The effect of organic salt valency on the deswelling properties of pH-responsive microgel particles.The interaction between negatively charged organic salts, with one two and three sulfonate groups respectively, and positively charged poly(2-vinylpyridine) microgel particles has been investigated. Absorption isotherms are used to describe the uptake of organic salt into the microgel network and the particle size and electrophoretic mobility of the dispersions have been discussed in terms of the electrostatic attraction between the organic salts and microgel network. The results suggest that all organic salts interact weakly with the microgel particles, and there is a tendency towards more noticeable changes in the microgel dispersion properties at lower concentration as the number of sulfonate groups within the organic salts increases.

Keywords: Microgel; pH; Multivalent salt; Adsorption

Systematic study of synergistic and antagonistic effects on adsorption of tetracycline and copper onto a chitosan by Jin Kang; Huijuan Liu; Yu-Ming Zheng; Jiuhui Qu; J. Paul Chen (pp. 117-125).
Tetracycline sorption can take place on the sites where copper ions are specifically adsorbed; thus, tetracycline sorption on chitosan is enhanced in the presence of copper ions.Sorption of tetracycline and copper onto chitosan is systematically investigated in this study. The sorption of tetracycline and copper occurs rapidly in the first few hours and 90% of completed uptake occurs in the first 11–12 and 6h, respectively. The sorption equilibrium of both contaminants is established in 24h. The solution pH largely affects the sorption of both contaminants. The tetracycline uptake increases as pH is increased from 2.8 to 5.6, and 2.5 to 7 in the absence and the presence of copper, respectively. The presence of copper significantly improves the tetracycline adsorption likely due to the formation of cationic bridging of copper between tetracycline and chitosan. The maximum adsorption capacity and the adsorption affinity constant for tetracycline dramatically increase from 53.82 to 93.04mmolkg−1 and from 1.22 to 10.20Lmmol−1 as the copper concentration is increased from 0 to 0.5mmol L−1. The uptake of copper increases with an increase in pH from around 3.5–6.0 in the absence and the presence of tetracycline. The presence of tetracycline decreases the copper adsorption, which may be ascribed to the competition of tetracycline with copper ions for the adsorption sites at the chitosan surface. The adsorption isothermal data of both tetracycline and copper are fit well by the Langmuir equation. The maximum adsorption capacity and adsorption affinity constant of copper ions decrease from 1856.06 to 1486.20mmolkg−1 and from 1.80 to 1.68Lmmol−1 in the absence and the presence of tetracycline. FTIR and XPS studies reveal that amino, hydroxyl, and ether groups in the chitosan are involved in the adsorption of tetracycline and copper.

Keywords: Adsorption; Copper; Tetracycline; Chitosan; XPS; FTIR

Adsorption and adsolubilization of polymerizable surfactants on aluminum oxide by Chodchanok Attaphong; Emma Asnachinda; Ampira Charoensaeng; David A. Sabatini; Sutha Khaodhiar (pp. 126-131).
Adsorption isotherms of polymerizable surfactants with different EO group numbers. These data provide useful information for designing surfactant-based surface modification processes for use in groundwater treatment barriers and industrial applications.Surfactant-based adsorption processes have been widely investigated for environmental applications. A major problem facing surfactant-modified adsorbents is surfactant loss from the adsorbent due to loss of monomers from solution and subsequent surfactant desorption. For this study, a bilayer of anionic polymerizable surfactant (Hitenol BC 05, Hitenol BC 10 and Hitenol BC 20) and non-polymerizable surfactant (Hitenol N 08) was adsorbed onto alumina. The results of adsorption studies showed that as the number of ethylene oxide (EO) groups of the surfactants increased, the area per molecule increased and the maximum adsorption decreased. The lowest maximum adsorption onto alumina was for Hitenol BC 20 (20 EO groups) corresponding to 0.08mmol/g or 0.34molecule/nm2 while the highest level of adsorption was 0.30mmol/g or 1.28molecule/nm2 for Hitenol BC 05 (5 EO groups). This variation in adsorption was attributed to the increased bulkiness of the head group with increasing number of EO groups. Relative to the adsolubilization capacity of organic solutes, ethylcyclohexane adsolubilizes more than styrene. Styrene and ethylcyclohexane adsolubilization were both independent of the number of EO groups of the surfactant. For surfactant desorption studies, the polymerization of polymerizable surfactants increased the stability of surfactants adsorbed onto the alumina surface and reduced surfactant desorption from the alumina surface. These results provide useful information on surfactant-based surface modification to enhance contaminant remediation and industrial applications.

Keywords: Admicellar polymerization; Adsolubilization; Irradiation; Polymerizable surfactants; Polymerization

Influence of the composition of core–shell Au–Pt nanoparticle electrocatalysts for the oxygen reduction reaction by Xiaowei Li; Juanying Liu; Wei He; Qinhong Huang; Hui Yang (pp. 132-136).
Au–Pt core–shell nanoparticles proved an enhanced Pt utilization. The catalyst with an Au–Pt atomic ratio of 2:1 had the maximized specific mass activity for ORR.Carbon-supported bimetallic Au–Pt nanoparticle catalysts with a core–shell structure were prepared by the successive reduction method. UV–vis spectra, TEM, XPS, and XRD techniques were used to characterize the prepared core–shell and the monometallic catalysts. Results of all the physical characterizations showed the continuous growth of the Pt shell on the Au core. The electrocatalytic activities for oxygen reduction were characterized using the rotating disk electrode technique in an acid electrolyte, and were compared with those obtained on a Pt/C catalyst under the same measurement conditions. It was found that these core–shell nanoparticles exhibited the structural characteristics of mainly fcc Au nanocrystals but the electrochemical properties of a Pt surface. The electrocatalytic activities of these core–shell nanoparticles showed a transition from the low activity of Au to the high activity of Pt, and the catalyst with a Au–Pt atomic ratio of 2:1 had a maximized specific mass activity, proving the enhanced Pt utilization with the core–shell structure.

Keywords: Nanoparticle; Electrocatalyst; Core–shell; Au–Pt; Oxygen reduction reaction

Bioconjugation of 32-macrocyclic polyammonium cations-functionalized gold nanoparticles with BSA by Tarun Kumar Misra; Kuan-Pin Huang; Chuen-Ying Liu (pp. 137-143).
32-macrocyclic polyammonium chloride, [32]ane-(NH2+)8·8Cl- (32-MCPAC) stabilized water dispersed Au-NPs conjugate with biomolecule, BSA. BSA strongly binds Au-NPs at the isoelectric point (p I=4.6).Water-dispersed, spherical, underivatized Au-NPs with particle size less than 5nm were synthesized from an aqueous solution of 32-macrocyclic polyammonium chloride, [32]ane-(NH2+)8·8Cl- (32-MCPAC) using sodium borohydride (NaBH4) as the reducing agent. The bioconjugation of the synthesized Au-NPs at different pHs (3.6–5.6) with bovine serum albumin (BSA) protein was studied using UV–Vis, fluorescence, and Raman spectroscopy. These studies support that the Au-NPs were incorporated into the protein moiety and bound to it chemically. The binding constants (K b) and stoichiometries ( n) (i.e., the number of Au-NPs bound by the proteins) of BSA protein to the Au-NPs at different pHs were determined by measuring the quenching of the fluorescence intensity of the tryptophan residues of the protein molecules after conjugation. The values forK b ( n) were found to be 1.05×1010M−1 (1.66), 2.09×1010M−1 (2.30), and 1.86×1010M−1 (1.75) at pH 3.60, 4.60, and 5.60 for BSA–Au-NPs conjugations, respectively. The results show that BSA binds to the Au-NPs strongly at pH 4.60, which is equivalent to its isoelectric point (p I 4.6).

Keywords: Gold nanoparticles; Macrocyclic polyammonium chlorides; Water dispersion; Bioconjugation; Protein

Electrokinetic characterization of magnetite nanoparticles functionalized with amino acids by J.L. Viota; F.J. Arroyo; A.V. Delgado; J. Horno (pp. 144-149).
Composition of the colored-ninhydrin supernatants corresponding to the magnetite–amino acid mixtures for different pHs and concentrations of amino acid. Examples of the original amino acid solutions are displayed in the row labeled REF.The synthesis of nanoparticles consisting of a magnetite core coated with one or more layers of amino acid (l-arginine,l-lysine, glycine, andl-glutamine) is described in this paper. For all the amino acids it is found that adsorption increases with concentration in solution in the range 0.5–10mg/mL. The adsorption, however, differs substantially from one amino acid to another, depending on the length of the hydrocarbon chain and the polarity and charge of the side group. Thus, for given concentration and pH, adsorption is found to increase in the orderl-arginine

Keywords: Amino acid adsorption; l; -Arginine; Electrophoretic mobility; l; -Glutamine; Glycine; l; -Lysine; Magnetite

Fabrication of oriented poly-l-lysine/bacteriorhodopsin-embedded purple membrane multilayer structure for enhanced photoelectric response by Rui Li; Xiaoqiang Cui; Weihua Hu; Zhisong Lu; Chang Ming Li (pp. 150-157).
As it is schematic shown on the left, an oriented poly-l-lysine/bacteriorhodopsin-embedded purple membrane multilayer structure is constructed and an enhanced photoelectric performance is obtained as shown on the right.A poly-l-lysine (PLL)/bacteriorhodopsin-embedded purple membrane (bR-PM) multilayer film has been successfully constructed by a layer-by-layer (LbL) assembly process to enhance the photoelectric response of bR. The assembly conditions were investigated and optimized. The PLL/bR-PM adsorption process was in situ studied by surface plasmon resonance and the growth of multilayer was further characterized by UV–vis absorption spectroscopy. The results indicate that the amount of adsorbed bR-PM vs. the assembled layer number exhibits linear relationship. The atomic force microscopy images of sequentially assembled PLL/bR-PM bilayers show that the patch structure of bR-PM in the structure is well preserved and the roughness increases with increase of the bilayer number. The peak photocurrent generated from PLL/bR-PM film increases with increase of the PLL/bR-PM bilayers until achieving a maximum value. The photocurrent of bR-PM from the film through PLL assembler is higher than those assembled by other polycations, thus rendering a new platform to effectively enhance the bR photoelectric responses.

Keywords: Bacteriorhodopsin; Purple membrane; Poly-; l; -lysine; Layer-by-Layer; Photocurrent

Novel layer-by-layer assembly molecularly imprinted sol–gel sensor for selective recognition of clindamycin based on Au electrode decorated by multi-wall carbon nanotube by Zhaohui Zhang; Yufang Hu; Huabin Zhang; Shouzhuo Yao (pp. 158-164).
A sensitive and selective electrochemical sensor was fabricated for detection of clindamycin via stepwise modification of the MWNT and a thin imprinted sol–gel on Au electrode by electrodeposition.A novel sensitive molecularly imprinted electrochemical sensor was constructed for selective detection of clindamycin by combination of a multi-wall carbon nanotube (MWNT) layer with a thin molecularly imprinted sol–gel film. The sensor was fabricated onto Au electrode via stepwise modification of MWNT and a thin sol–gel film of molecularly imprinted polymers (MIP) by using electrodeposition method. The molecularly imprinted film displayed excellent selectivity towards clindamycin. Due to such combination, the sensor responded quickly to clindamycin. The response peak current was linear to the concentration of clindamycin in the range from 5.0×10−7molL−1 to 8.0×10−5molL−1, and the detection limit was 2.44×10−8molL−1. This imprinted sensor was applied to the determination of clindamycin in human urine samples successfully. These results revealed that the imprinted sensor fulfilled the selectivity, sensitivity, speed and simplicity requirements for clindamycin detection, and provided possibilities of clinical application in physiological fluids.

Keywords: Imprinted sol–gel sensor; Layer-by-layer assembly; Multi-wall carbon nanotube; Clindamycin

Binding stoichiometry in sorption of divalent metal ions: A theoretical analysis based on the ion-exchange model by Wojciech Plazinski; Władysław Rudzinski (pp. 165-170).
A theoretical comparative analysis of the two (MX2 and M1/2X) stoichiometric assumptions.Two stoichiometric assumptions have been compared for describing divalent metal ion binding by protonated sorbent/biosorbent. The first one corresponds to the classical model in which each metal ion (M) binds to two binding sites (X) forming a single MX2 complex while the second one, proposed by Schiewer and Volesky and used for description of biosorption equilibria, assumes the existence of M1/2X complexes. Mathematical expressions corresponding to both these models have been developed by applying the ion-exchange model and methods of statistical thermodynamics. The M1/2X model appears to be nonphysical because it does not take into account the basic fact that two sites binding one metal ion must be neighboring. On the other hand, this latter assumption is the part of the MX2 model which has been shown using Nitta’s approach. Nevertheless, equations associated with the M1/2X model can be successfully used for description of the experimental data as they can simulate quite well the behavior predicted by the MX2 model. This is especially true when considering the range of relatively high metal concentrations in the bulk solution and significant degree of surface heterogeneity characteristic of the sorbent surface.

Keywords: Sorption; Biosorption; Surface complexes; Statistical thermodynamics; Binding stoichiometry; Heavy metals

Capillary rise between parallel plates under dynamic conditions by Fabiano G. Wolf; Luís O.E. dos Santos; Paulo C. Philippi (pp. 171-179).
Comparison between LBM simulations and theoretical results provided by the Bosanquet model for the capillary rise between parallel plates.A Lattice-Boltzmann method based on field mediators is proposed to simulate the capillary rise between parallel plates by considering the effect of long-range interactions between the fluids and the solid walls. As a starting point, a liquid–vapor system was employed, which was modeled using a known model described in the literature. The simulations were compared with theoretical solutions of the Bosanquet equation. The results obtained are in good agreement with theoretical predictions, particularly when the dependence between the dynamic contact angle and the capillary number is taken into account. This dependence shows that on smooth and homogeneous solid surfaces, where pinning effects in the contact line are weak, the dynamic contact angle is linearly dependent on the capillary number, in good agreement with theoretical and experimental results available in the literature. Some discrepancies were observed in the first stages of the capillary rise when the distance between the parallel plates is large, considering the high complexity involved in predicting the initial meniscus formation. The results presented in this work appear to indicate that the inclusion of long-range forces does not change significantly the fluid flow dynamics at the mesoscopic level, at least, when ideally flat and homogeneous solid surfaces are used in the simulations.

Keywords: Capillary rise; Lattice-Boltzmann model; Long-range interactions; Dynamic contact angle and capillary number

Experimental contribution to the understanding of the dynamics of spreading of Newtonian fluids: Effect of volume, viscosity and surfactant by Thibault Roques-Carmes; Vincent Mathieu; Alexandra Gigante (pp. 180-197).
The number and the nature of the spreading regimes during the spreading of glycerol–water mixtures on hydrophilic glass surfaces have been investigated by varying the viscosity, drop volume and non-ionic surfactant concentration.The dynamics of drop spreading of glycerol–water mixtures with and without surfactant on hydrophilic glass surfaces has been investigated. The influence of different factors, such as viscosity, drop volume and non-ionic alkyl (8–16) glucoside (Plantacare) surfactant concentration on the number and the nature of the spreading regimes is systematically investigated. More than 25 spreading experiments have been performed in order to obtain clear trends. The results confirm the existence of several spreading regimes for the duration of an experiment (200s). For each regime, the radius can be expressed by a power law of the form R=Kt n. Both n and K are necessary to identify the regime. The experimental data are compared with the analytical predictions of the combined theory of spreading. One of the main results of this study is that the nature of the regimes is strongly affected by the drop volume, the viscosity and the surfactant concentration. This behavior is not predicted by the theory. For drop volume less than or equal to 15μL, a succession of two different regimes which depend on the viscosity and surfactant concentration are observed in the following order: a molecular-kinetic regime followed by a hydrodynamic regime (for high viscosity in the presence of surfactant) or a hydrodynamic regime and lastly a final asymptotic regime corresponding to a long relaxation time to equilibrium (for high viscosity in absence of surfactant and for low viscosity regardless of the presence of surfactant). The spreading follows quantitatively the predictions of the theory. Our results demonstrate that the theory is still valid for low viscosity liquids and in the presence of surfactant. The contact angle for which the crossover between molecular-kinetic regime and hydrodynamic regime occurs is thoroughly estimated since the theories do not allow the exact calculation of this value. Here for the first time, an empirical power law exponent ( n=0.08±0.05) is proposed for the last asymptotic regime since its quantitative estimation was not provided by the theory. For drop volume larger than 15μL, the combined theory is still valid and the spreading process goes through a combination of two different regimes. In absence of surfactant, the succession of a molecular-kinetic regime and lastly a hydrodynamic regime, is demonstrated.

Keywords: Spreading; Dynamics; Surfactant; Drop; Model; Experimental

Explicit analytical solutions for liquid infiltration into capillary tubes: Dynamic and constant contact angle by Markus Hilpert (pp. 198-208).
We derive explicit analytical solutions for liquid infiltration into capillary tubes and develop diagrams to predict the different types of infiltration. Contact angle depends on interface velocity or is constant.We derive new analytical solutions for liquid infiltration into a gas-filled capillary tube, whose inlet is connected to a liquid reservoir held at a constant pressure. We generalize the Lucas–Washburn theory to account for a model for dynamic contact angle that assumes the nonequilibrium Young force to depend linearly on the velocity of the gas–liquid interface. Like Lucas and Washburn, we neglect inertial forces. Using the Lambert function, we derive explicit analytical solutions for the interface position, velocity, and acceleration as a function of time. Consistent with previous work, which used more general models for dynamic contact angle, we can distinguish between five infiltration scenarios: horizontal infiltration, upward infiltration (capillary rise), as well as steady-state, accelerating, and decelerating downward infiltration. We determine the mutually exclusive conditions for the different infiltration scenarios to occur in terms of the nondimensional parameters that define the problem. Moreover, we develop 2D and 3D diagrams that show which parameter combination results in which infiltration scenario. Our analytical solutions are also valid in the limit where the dynamic contact angle becomes constant. For a constant contact angle, accelerating downward infiltration occurs only if the initial interface is not located at the tube inlet but further down the tube. For the special case in which the contact angle is constant, the liquid pressure at the tube inlet is equal to the gas pressure, and the interface is initially located at the tube inlet, our solution for upward infiltration is identical to a solution previously reported in the literature.

Keywords: Dynamic contact angle; Capillary rise; Infiltration; Analytical solution; Lambert function; Wetting; Lucas–Washburn equation

Thermodynamic quantities of surface formation of aqueous electrolyte solutions by Norihiro Matubayasi; Ken Takayama; Takeshi Ohata (pp. 209-213).
The surface tensions of aqueous ammonium salt solutions are measured as a function of temperature and concentration.The properties of aqueous ammonium salt solutions at the air/water surface are presented. By comparison of the properties of ammonium halides solutions with those of sodium halide, we note a close similarity, which indicates that the increments in surface tension may be explained in relation to the hydration enthalpy of anions. We find that the behaviors of the salts with nitrate anions which are polyatomic are also explained by hydration enthalpy in the same way. On the other hand, salts with ammonium cations which are polyatomic show deviation from a monotonous relationship between the surface tension increments and the hydration enthalpies observed for alkali metal halides. These results can be explained by ion pair formation in the surface region.

Keywords: Surface tension; Electrolytes; Surface ions

Advective flow of permeable sphere in an electrical field by Zhen Yang; Duu-Jong Lee; Tao Liu (pp. 214-220).
Flow streamlines and pressure patterns at Re=10 and Ψ=−1 for spheres of different β values subjected to both pressure gradient and an electrical field.Advective flow of a permeable sphere in an electrical field is comprehensively studied. The sphere has a uniform permeability and is subject to an incoming Newtonian flow. The electrical field generates an electro-osmotic flow inside the sphere, which markedly affects sphere flow dynamics. A numerical model elucidates the effects of flow dynamic parameters on the drag coefficient and ratio of drag forces to a permeable and solid sphere. The model solves the Navier–Stokes equations both inside and outside the porous sphere. The unique flow field and pressure patterns of the permeable sphere flow are characterized in detail, and utilized to interpret the distinguishing flow behaviors of spheres induced by electro-osmotic flow. Drag force decreases and or reverses in direction when the intensity of the electro-osmotic flow in the sphere increases. When the electro-osmotic flow is counter to the incoming flow, drag force increases significantly, and vortices form near the sphere. As the sphere becomes highly permeable, the influence of the electro-osmotic flow and incoming flow velocity are reduced markedly.

Keywords: Drag force; Permeable sphere; Electro-osmotic flow; Advective flow

Charge properties of membranes modified by multilayer polyelectrolyte adsorption by Abdoul-Nasser Dirieh Egueh; Boris Lakard; Patrick Fievet; Sophie Lakard; Cédric Buron (pp. 221-227).
Evolution of the zeta potential as a function of the number of PAS/PSS bilayers.Alternate adsorption of polyanions and polycations on a polyethersulfone (PES) membrane was studied by the tangential streaming potential method using a parallel-plate channel to investigate the properties of the outer surface of the membrane. These streaming potential data were complemented by diffusion experiments and by membrane potential measurements in order to characterize the inner surface of the membrane. Tangential streaming potential measurements demonstrated that after completing a bilayer of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS), periodic variations in the zeta potential between positive and negative values appeared for multilayer films obtained from membrane dipped in polyelectrolyte (PE) solutions at 10g/L. On the contrary, the zeta potential was always positive when multilayer films were obtained from 1 and 5g/L polyelectrolyte concentration solutions. Diffusion experiments carried out with unmodified and modified membranes showed a decrease in the solute flux after functionalization of the membrane by several polyelectrolyte bilayers, indicating that the diffusional resistance of the PE layers contributes significantly to the overall resistance to diffusion of the modified membrane. By means of membrane potential measurements the pore walls of the membrane were functionalized since the charge of its pore walls was modified even if it is difficult to discriminate between the contribution of the membrane and that of the multilayer buildup.

Keywords: Polyelectrolyte multilayer; Layer-by-layer adsorption; Organic membrane; Streaming potential; Membrane potential

Investigation of the nonlinear effects during the sedimentation process of a charged colloidal particle by direct numerical simulation by Florian Keller; Markus Feist; Hermann Nirschl; Willy Dörfler (pp. 228-236).
Direct numerical simulation of the sedimentation process of a charged colloidal particle in a Newtonian electrolyte. Effect of increasing the fluid Reynolds number on the sedimentation velocity.In this article we study the settling process of a colloidal particle under the influence of a gravitational or centrifugal field in an unbounded electrolyte solution. Since particles in aqueous solutions normally carry a non-zero surface charge, a microscopic electric field develops which alters the sedimentation process compared to an uncharged particle. This process can be mathematically modelled via the Stokes–Poisson–Nernst–Planck system, a system of coupled partial differential equations that have to be solved in an exterior domain. After a dimensional analysis we investigate the influence of the various characteristic dimensionless numbers on the sedimentation velocity. Thereby the linear-response (weak-field) approximation that underpins almost all existing theoretical work on classical electrokinetic phenomena is relaxed, such that no additional assumption on the thickness of the double layer as well as on its displacement is needed. We show that there exists a strong influence of the fluid Reynolds number and the ionic strength on the sedimentation velocity. Further we have developed an asymptotic expansion to describe the limit of small values of the surface potential of a single particle. This expansion incorporates all nonlinear effects and extends the well-known results of Booth (1954) [1] and Ohshima et al. (1984) [2] to higher fluid Reynolds numbers.

Keywords: Colloidal particle; Sedimentation; Electrochemical double layer; Zeta potential expansion; Direct numerical simulation

Chemical shift imaging NMR to track gel formation by Åsa Östlund; Diana Bernin; Lars Nordstierna; Magnus Nydén (pp. 238-240).
1H NMR image (1 hour diffusion time) along the position of the sample tube with the chemical shift resolution giving a concentration profile of the molecules in the sample, wherefrom the growth of the gel, D, could be extracted.In this work we have combined1H and19F NMR chemical shift images to investigate the dynamic processes of gel formation of a cellulose solution. Chemical shift imaging (CSI) NMR is shown to be a valuable technique for studying phase changes in soft materials. The technique provides spatial position of each chemical component, and by repeatedly recording sample images the dynamic rearrangements in the material can be followed in detail. CSI NMR follows the same principles as magnetic resonance imaging, but can be performed on most of the nowadays commercial NMR probes. Position resolution of the chemical shift gives the opportunity to derive diffusion rate data of individual components during the gel formation process. The results suggest that the method can be used for detailed studies of dynamic processes in multi-component systems and to extract diffusion coefficients for the components investigated.

Keywords: Chemical shift imaging; Diffusion; 1; H CSI NMR; Gel formation; 19; F CSI NMR; Magnetic resonance imaging (MRI)

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