Journal of Colloid And Interface Science (v.322, #2)
Adsorption of copolymers aggregates: From kinetics to adsorbed layer structure
by Bogdan Zdyrko; Pazit Bar-Yosef Ofir; Alina M. Alb; Wayne F. Reed; Maria M. Santore (pp. 365-374).
We examined the adsorption, on hydrophobic and hydrophilic surfaces, of 4 rake-type poly(dimethyl siloxane) (PDMS) copolymers varying the amount of poly(ethylene glycol) (PEG) graft arms from 41 to 72%. The copolymers formed large aggregates in solution, complicating their adsorption kinetics and layer structures. We found the adsorption process always to be dominated by the adsorption of large aggregates, with strongly bound layers resistant to rinsing in adsorbing buffer. Adsorbed amounts were nearly independent of the substrate. However, subtleties in the adsorption kinetics suggested different layer structures for the different systems. On hydrophilic silica, aggregates adsorbed at the transport limited rate until surface saturation, and associated interfacial structures were likely retained. On the hydrophobic surface, a subset of the copolymers exhibited retarded late stage adsorption kinetics suggestive of brush formation. This work demonstrates how subtle differences in adsorption kinetics provide insight into potential interfacial layer structures.
Keywords: Polymer brush adsorption; Aggregate adsorption; Micelle adsorption; Associated adsorbed layer; Mushroom layer; Adsorbed copolymers; Copolymer layers; Adsorption kinetics
Enhanced fluoride sorption using La(III) incorporated carboxylated chitosan beads
by Natrayasamy Viswanathan; S. Meenakshi (pp. 375-383).
The carboxylated chitosan beads (CCB), which have a defluoridation capacity (DC) of 1385 mg F−/kg, have been further chemically modified by incorporating La3+ ion (La-CCB) and its DC was found to be 4711 mg F−/kg whereas the raw chitosan beads (CB) possess only 52 mg F−/kg. The fluoride removal by La-CCB is governed by both adsorption and complexation mechanism. The functional groups present in beads were identified by FTIR analysis. The surface condition and existence of fluoride on the beads was confirmed by SEM with EDAX analysis. The experimental data have been analyzed using Freundlich and Langmuir isotherm models. Thermodynamic parameters such asΔGo,ΔHo andΔSo were calculated to predict the nature of sorption. The kinetic studies were investigated with reaction-based and diffusion-based models. A field trial was carried out with fluoride water collected from a nearby fluoride-endemic village.
Keywords: Chitosan bead; Carboxylated chitosan bead; La-CCB; Defluoridation; Adsorption; Complexation; Freundlich; Langmuir; Reaction-based model; Diffusion-based model
Kinetics and energetics of phosphate sorption in a multi-component Al(III)–Fe(III) hydr(oxide) sorbent system
by O.R. Harvey; R.D. Rhue (pp. 384-393).
Multi-component Al–Fe hydr(oxides) are ubiquituous in soil and aquatic environments, where they exhibit biogeochemical controls on nutrients and contaminants. Although, sorption on single-component Al and Fe hydr(oxides) have been extensively studied, limited studies have been done on their multi-component counterparts. In this study, effects of Al/Fe content on the kinetics and energetics of phosphate sorption in a poorly-crystalline co-precipitated mixed Al–Fe hydr(oxide) system were investigated using a combination of traditional batch techniques and flow adsorption calorimetry. Differences in Al/Fe content was found to influence the structural development and anion exchange capacity of the hydr(oxides) and subsequently their phosphate sorption characteristics. Higher structural development decreased phosphate sorption, while higher AEC was associated with increased phosphate sorption, initial sorption rate, and smaller losses in sorption with increasing pH. Results from flow adsorption calorimetry indicated that at pH 4.8 phosphate sorption: (i) occurred irreversibly on anion exchange sites, with a loss of 1.9 moles of AEC per mole of phosphate sorbed, and (ii) was exothermic, with molar heats of adsorption between −25 and−39kJmol−1. Molar heats of adsorption were ten times that for anion exchange and independent of hydr(oxide) composition with the amount of energy evolved being directly proportional to the quantity of phosphate sorbed.Differences in the kinetics and energetics of phosphate sorption on multi-component Al–Fe hydr(oxides) of varying compositions were elucidated using traditional batch experiments and flow adsorption calorimetry.
Keywords: Multi-component sorbents; Al/Fe hydr(oxides); Flow adsorption calorimetry; Kinetics; Energetics; Anion exchange; Phosphate sorption
Inhibition of nitrobenzene adsorption by water cluster formation at acidic oxygen functional groups on activated carbon
by Yuichi Kato; Motoi Machida; Hideki Tatsumoto (pp. 394-398).
The inhibition effect of nitrobenzene adsorption by water clusters formed at the acidic groups on activated carbon was examined in aqueous and n-hexane solution. The activated carbon was oxidized with nitric acid to introduce CO complexes and then outgassed in helium flow at 1273 K to remove them completely without changing the structural properties of the carbon as a reference adsorbent. The amounts of acidic functional groups were determined by applying Boehm titration. A relative humidity of 95% was used to adsorb water onto the carbon surface. Strong adsorption of water onto the oxidized carbon can be observed by thermogravimetric analysis. The adsorption kinetic rate was estimated to be controlled by diffusion from the kinetic analysis. Significant decline in both capacity and kinetic rate for nitrobenzene adsorption onto the oxidized carbon was also observed in n-hexane solution by preadsorption of water to the carbon surface, whereas it was not detected for the outgassed carbons. These results might reveal that water molecules forming clusters at the CO complexes inhibited the entrance of nitrobenzene into the interparticles of the carbon.A decline in nitrobenzene adsorption capacity was observed in n-hexane solution by in water for pre-adsorbed (WPA) oxidized activated carbon (Ox-AC), suggesting water cluster formation, comparing in contrast to nonoxidized AC (NO-AC).
Keywords: Activated carbon; Acidic functional groups; Water adsorption; Hexane solution; Nitrobenzene
Copper and arsenate co-sorption at the mineral–water interfaces of goethite and jarosite
by Markus Gräfe; David A. Beattie; Euan Smith; William M. Skinner; Balwant Singh (pp. 399-413).
The co-sorption reaction products of arsenate (As(V)) and copper (Cu(II)) on goethite ( α-FeOOH) and natro-jarosite (Na3Fe3(SO4)2(OH)6) were investigated with extended X-ray absorption fine structure (EXAFS) spectroscopy to determine if Cu(II) and As(V) would form precipitates or compete with each other for surface sites. The reaction products were prepared by mixing 250 μM Cu(SO4) with 10, 25, or 50 μM Na2HAsO4 at pH 5.65 and allowing the mixture to react in 10 m2 L−1 goethite or jarosite suspensions for 12 days. In addition, EXAFS data of Cu(SO4) and As(V) sorbed on goethite and jarosite were collected as control species. All reaction conditions were under-saturated with respect to common copper bearing minerals: tenorite (CuO), brochantite (Cu4(OH)6SO4), and hydrated clinoclase (Cu3(AsO4)2⋅2H2O). The extents of the As(V) and Cu(II) surface adsorption reactions showed a strong competitive effect from Cu(II) on As(V) adsorption for a nominal Cu:As mole-ratio of 25:1. With increasing nominal As(V) concentration, As(V) sorption on goethite and jarosite increased without diminishing the amount of Cu(II) sorption. In the absence of either co-sorbate, As(V) and Cu(II) formed the expected surface adsorption species, i.e., bidentate binuclear and edge-sharing surface complexes, consistent with previously published results. In each other's presence, the local bonding environments of As(V) and Cu(II) showed that the co-sorbates form a precipitate on the goethite and jarosite surface at nominal concentrations of 10:1 and 5:1. At nominal Cu:As mole-ratios of 25:1, Cu(II) did not form significantly different surface complexes on goethite or jarosite from those in the absence of As(V), however, As K-edge EXAFS results distinctly showed Cu(II) atoms in As(V)'s local bonding environment on the goethite surface. The structures of the two precipitates were different and depended on the anion-layer structure and possibly the presence of structural oxyanions in the case of jarosite. On goethite, the copper–arsenate precipitate was similar to hydrated clinoclase, while on jarosite, a euchroite-like precipitate (Cu2[AsO4](OH)⋅3H2O, P 2(1)2(1)2(1)) had formed. Despite under-saturated solution conditions, the formation of these precipitates may have occurred due to a seed-formation effect from densely surface adsorbed Cu(II) and As(V) for which the “new” saturation index was significantly lower than homogeneous values would otherwise suggest. Synergistic reactions between two co-sorbates of fundamentally different surface adsorption behaviour can thus be achieved if the number of available sites for surface adsorption is limited.Jarosite supplied in small amounts triggers the formation of small euchroite-like clusters on its surface. One of the reaction steps appears to be the exchange of structural SO4 by AsO4.
Keywords: EXAFS spectroscopy; Clinoclase; Euchroite; Coprecipitation; Saturation index
Formation and catalytic activity of spherical composites with surfaces coated with gold nanoparticles
by Xi Chen; Dongyun Zhao; Yingli An; Yan Zhang; Jing Cheng; Beilei Wang; Linqi Shi (pp. 414-420).
Micelle-supported gold composites with a polystyrene core and a poly(4-vinyl pyridine)/Au shell are synthesized using NaBH4 to reduce a mixture of micelle and HAuCl4 in acidic aqueous solution (pH ∼2). The template micelle with a polystyrene core and a poly(4-vinyl pyridine) shell is formed by self-assembly of block copolymer polystyrene- block-poly(4-vinyl pyridine). The gold nanoparticles coated onto the surfaces of the composites possess an average diameter of about 15 nm. The composites are applied to catalyze the reduction of p-nitrophenol in the presence of NaBH4, and the results indicate that the kinetic constant of the reaction increases when the composite concentration and the reaction temperature increase. In addition, research results also indicate that composites with high content of gold show higher catalytic activity and higher catalytic efficiency.The metal ions (AuCl−4) are confined within the shell of the core–shell micelles. Reduction of the metal ions leads to the nanosized gold particles on the core surface.
Keywords: Gold; Nanoparticle; Composite; Core–shell; Micelle; Self-assembly; Block copolymer
Preparation and characterization of a strong basic anion exchanger by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) fiber
by Qikun Zhang; Sujuan Zhang; Shuixia Chen; Peiyuan Li; Tingyan Qin; Siguo Yuan (pp. 421-428).
A novel anion-exchange fiber with strong basic groups has been prepared by grafting styrene onto poly(tetrafluoroethylene) fibers via irradiation. Experiments were carried out to analyze the effects of synthesis conditions on the grafting degree and to characterize the physicochemical properties of the anion-exchange fibers. The experimental results showed that preirradiation grafting styrene onto poly(tetrafluoroethylene) fiber could significantly reduce the waste of raw material and the formation of homopolymer, although the grafting degree was relatively low. The grafting reaction could be effectively enhanced through the addition of magnesium powder into the reaction system. The optimal temperature and time for preirradiation grafting were 80 °C and 6 h, respectively. The experimental results also showed that the anion-exchange fibers had excellent mechanical properties and thermal stability at a temperature up to 420 °C. The fibers were stable in acidic, alkali, and oxidative solutions. The static ion-exchange capacity of the fibers was as high as 6.08 mmol/g. The static adsorption capacities for Cr2O2−7 and MnO−4 ions were 214.08 and 290.98 mg/g, respectively.A strong basic anion-exchange fiber has been effectively prepared, which not only has the desirable advantages of anion-exchange fiber but also has the merits of PTFE.
Keywords: Poly(tetrafluoroethylene) fiber; Anion-exchange fiber; Irradiation grafting; Adsorption
Surface modification of polyaniline using tetraethyl orthosilicate
by Xingwei Li; Na Dai; Shirong Pan; Gengchao Wang (pp. 429-433).
A well-dispersible conducting polyaniline/silica hybrid is prepared by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) on the surface of polyaniline in water/ethanol solution. It provides a simple and environmentally sound route for preparing the processable conducting polyaniline/silica hybrid at the nanometre level. The conductivity of polyaniline/silica hybrid is 2.43 S cm−1 at 25 °C, and its powder is easily dispersed in the anhydrous ethanol or aqueous solution without any stabilizer. In addition, the structure, morphology and cyclic voltammorgram of this hybrid are also reported.Well-dispersible conducting polyaniline/silica hybrid was synthesized. Its conductivity was 2.43 S cm−1 at 25 °C, and showed good electrochemistry active.
Keywords: Polyaniline; Hybrid; Dispersibility; Cyclic voltammorgram
Photochemical fixation of structures in binary polymer brushes—influence of layer thickness and grafting method
by Frank Hoffmann; Thomas Wolff (pp. 434-447).
Polymer brushes consisting of hydrophilic and hydrophobic polymer components (poly-4-vinylpyridine, polymethacrylic acid and polystyrene, respectively) change their surface properties (as revealed by contact angles) when they are exposed to various solvents. In brushes prepared via grafting-from methods (using a specific surface initiator) layer thicknesses up to 300 nm were obtained. Copolymerization of the brush component monomers with 2-(4′-styryl)-indene yielded photo-cross-linkable brushes, which were used to fix the brushes in either the hydrophilic or hydrophobic state. Structural patterns differing in surface properties were produced and fixed by photo-cross-linking the hydrophobic component in that samples were irradiated through a mask. The patterns turned out most stable in moderately thick layers. AFM pictures confirm the contact angle results but reveal micro-domains of the two immiscible polymers in the grafted layers.Si-wafer covered with a binary (hydrophilic/hydrophobic) polymer brush: right half photochemically fixed in the hydrophilic state, left half in the hydrophobic state.
Keywords: Polymer brushes; Grafting-from; Photocrosslinking; Photodimerization; Surface microstructures; Switchable surface properties
The effect of PEO block lengths on the size and stability of complex coacervate core micelles
by Dave J. Adams; Sue H. Rogers; Peter Schuetz (pp. 448-456).
We report on a series of polyion complexes from mixtures of poly(ethylene oxide)- block-poly(N,N-diethylaminoethylmethacrylate) (PEO–PDEAMA) and poly(ethylene oxide)- block-poly(aspartic acid) (PEO–PAsp). As expected, the micelle size, polydispersity and stability are dependant on the relative and absolute lengths of the polyelectrolyte chains. However, we also demonstrate that whilst the length of the charged polyelectrolyte blocks is important, the length of the PEO chains is an equally relevant variable in determining both the size and stability of the final micelles as well as the degree of charge neutralisation at which micellisation occurs. We also show that the kinetics of formation can result in very different stability of the final micelles.Normalised scattering intensities for PEO113PDEAMA43 with (●) PEO45PAsp26, (○) PEO113PAsp26 and (□) PEO226PAsp26.
Keywords: Polyelectrolyte; Kinetics; Micelle; Block copolymer
EPR characterization of gadolinium(III)-containing-PAMAM-dendrimers in the absence and in the presence of paramagnetic probes
by Xue-gong Lei; Steffen Jockusch; Nicholas J. Turro; Donald A. Tomalia; M. Francesca Ottaviani (pp. 457-464).
Gd(III)-containing dendrimers are promising contrast agents for magnetic resonance imaging (MRI). An important issue in the effectiveness and toxicity of a Gd(III) based MRI contrast agent is knowledge of the relative locations and concentrations of Gd(III) in dendrimer drug delivery hosts. In order to provide experimental information on this issue, we have investigated the electron paramagnetic resonance (EPR) of a stable Gd(III) complex with diethylenetriaminepentaacetic acid (DTPA) in various polyammidoamine (PAMAM) dendrimers as a function of dendrimer generation (G2, G4, and G6), dendrimer core (ethylenediamine = EDA, and cystamine = cys), and dendrimer surface functionality (NH2, 5-oxo-3-pyrrolidinecarboxylic acid methyl ester = pyr, and tris(hydroxymethyl) methylamine = tris). The dendrimer systems were investigated in the presence and absence of paramagnetic probes, that is, Cu(II) and nitroxide radicals (4-(trimethylammonium and dodecyl-dimethylammonium) 2,2,6,6-tetramethylpiperidine 1-oxyl bromide = CAT1 and CAT12, respectively). The analysis of the EPR spectra revealed anisotropic locations of Gd-DTPA inside the dendrimer. Computer analysis of the EPR spectra of the probes identified the interactions of the Gd-dendrimers with ions and organic molecules. The interaction between the probes and the dendrimer internal and external surface depends on the type of core, the composition of the external surface and the generation of the dendrimer. The negatively charged Gd-DTPA complex attracts the positively charged species and this provokes spin–spin interactions between Gd and the probes, which increases with a decrease in generation, mainly from G6 to G4, and with an increase in both the Gd-dendrimer concentration and the probe concentration. The cys core increases the internal volume and decreases the packing of the branches.Gd-DTPA containing PAMAM dendrimers with different size, surface function, and core, promising MRI contrast agents, were characterized by analyzing the EPR spectra of Gd(III) and added paramagnetic external probes.
Keywords: Dendrimers; EPR; MRI; Copper; Nitroxide radicals; Gd-DTPA
Fabrication of highly insulating tethered bilayer lipid membrane using yeast cell membrane fractions for measuring ion channel activity
by Sachin R. Jadhav; Dexin Sui; R. Michael Garavito; R. Mark Worden (pp. 465-472).
A tethered bilayer lipid membrane (tBLM) was fabricated on a gold electrode using 1,2-dipalmitoyl- sn-glycero-phosphothioethanol as a tethering lipid and the membrane fractions of Saccharomyces pombe yeast cells to deposit the upper leaflet. The membrane fractions were characterized using transmission electron microscopy and dynamic light scattering and found to be similar in size to small unilamellar vesicles of synthetic lipids. The dynamics of membrane-fraction deposition and rupture on the tethering-lipid layer were measured using quartz crystal microgravimetry. The electrochemical properties of the resulting tBLM were characterized using electrical impedance spectroscopy and cyclic voltammetry. The tBLM's electrical resistance was greater than1MΩcm2, suggesting a defect-free membrane. The suitability of tBLM produced using membrane fractions for measuring ion-channel activities was shown by a decrease in membrane resistance from 1.6 to0.43MΩcm2 following addition of gramicidin. The use of membrane fractions to form high-quality tBLM on gold electrodes suggests a new approach to characterize membrane proteins, in which the upper leaflet of the tBLM is deposited, and overexpressed membrane proteins are incorporated, in a single step. This approach would be especially useful for proteins whose activity is lost or altered during extraction, purification, and reconstitution, or whose activities are strongly influenced by the lipid composition of the bilayer.A high-quality tethered bilayer lipid membrane (tBLM) fabricated on a gold electrode using the membrane fractions of Saccharomyces pombe yeast cells was found suitable for carrying out ion channel assays.
Keywords: Biomimetic interface; Tethered bilayer lipid membrane; Yeast cell membrane fractions; Electrochemical impedance spectroscopy; Gramicidin; Ion channel
ZnSe colloidal nanoparticles synthesized by solvothermal method in the presence of ZrCl4
by Sunirmal Jana; In Chan Baek; Mi Ae Lim; Sang Il Seok (pp. 473-477).
The nanocrystalline ZnSe was synthesized from precursors of zinc acetate and Se powder in a high boiling trioctylphosphine (TOP), oleic acid, and ZrCl4 by solvothermal method. The produced ZnSe nanoparticles showed gradual absorption edge shifting towards blue wavelength region as well as transformation of crystal phase from cubic to hexagonal with increasing ZrCl4 concentrations in precursor solutions. The particle size calculated from XRD measurements for ZnSe nanoparticles was decreased with increasing ZrCl4 concentrations for a reaction time of 240 min, from 6.5 nm to 5.1 nm whereas from TEM measurements it was 7.0 to 6.1 nm at 0.0 and 22.5 mol% of ZrCl4, respectively. No trace of zirconium was found in solid ZnSe nanoparticles by SEM-EDS analysis but the atomic percentage of Se with respective to Zn was decreased with increasing ZrCl4. The absorption edge blue shifting was explained on the basis of decreased particle size. The crystal phase transformation may be due to the combined effect of small internal energy difference between the two phases and the decrease of crystallite size.XRD patterns of ZnSe QDs: 1, undoped; 2, 5 mol% ZrCl4 doped, 3, 17.53 mol% ZrCl4 doped during the hot solution synthesis. The reflections from various planes show that with increasing ZrCl4 concentration hexagonal ZnSe QDs increases (1, h-ZnSe, ∼0%; 2, h-ZnSe, 47.8%; 3, h-ZnSe, 48.5%).
Keywords: Semiconductor nanocrystals; ZnSe nanoparticles; Absorption edge; Crystal phase transformation
Stable aqueous film coating dispersion of zein
by H.X. Guo; J. Heinämäki; J. Yliruusi (pp. 478-484).
The effects of plasticizers, pH, and electrolytes on film formation and physical stability of aqueous film coating dispersions (pseudolatexes) of zein were evaluated. The influence of plasticizer on film formation mechanism and minimum film-formation temperature (MFT) were monitored by means of hot stage microscopy (HSM). Furthermore, the effects of pH and electrolytes on the short-term physical stability of pseudolatexes were investigated by measuring relative absorbance, zeta potential, and particle size of the dispersions. With aqueous coating dispersions of zein, stages of film formation were identified. The dispersions plasticized with 20% (w/w) PEG 400 or glycerol formed mechanically strong and flexible films with the lowest glass transition temperature (Tg). Physical stability of the aqueous zein dispersions was dependent on both pH and electrolyte content. At a pH ranging from 3 to 4, the aqueous dispersions of zein were stable for at least 2 months exhibiting the highest values for zeta potential, the smallest particle size, and a low volume of aggregates. The stable dispersion could be obtained containing a lower concentration of electrolytes (e.g., 10−5 M). The physical stability of aqueous zein dispersions can be determined by the combined measurements of relative absorbance, zeta potential, and particle size.Stable aqueous film coating dispersion of zein could be achieved at certain pH and electrolyte content. The dispersion plasticized with PEG 400 can form flexible and continuous film.
Keywords: Zein; Aqueous dispersion; Film formation; Plasticizers; pH and electrolytes; Physical stability
Facile fabrication of multi-colors high fluorescent/superparamagnetic nanoparticles
by Bingbo Zhang; Jing Cheng; Xiaoqun Gong; Xiaoqing Dong; Xuhui Liu; Guiping Ma; Jin Chang (pp. 485-490).
We developed a novel method to prepare multi-colors high fluorescent/superparamagnetic nanoparticles (FMNPs) employing hydrophobic multi-color quantum dots (QDs) and hydrophobic Fe3O4 (MNPs) via ultrasonic emulsification method. This structural procedure was simple, one-off, and timesaving. Different-sizes FMNPs with encoding single/multi-color QDs and MNPs were achieved. Analysis with transmission electron microscopy (TEM) and particle size analyzer demonstrated that the as-prepared samples were spherical, uniform in size distribution; Ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurement showed the FMNPs had good optical properties, lacking of fluorescence resonance energy transfer (FRET) inside FMNPs; vibrating sample magnetometer (VSM) indicated that FMNPs were superparamagnetic. These results indicate that the as-prepared FMNPs have potential of serving as a hybrid of QDs and MNPs in bioanalysis communities.A novel method to prepare multi-color high fluorescent/superparamagnetic nanoparticles (FMNPs) employing hydrophobic multi-color quantum dots (QDs) and hydrophobic Fe3O4 (MNPs) via ultrasonic emulsification method.
Keywords: Quantum dots; Superparamagnetic; Nanoparticles; Multi-color; Fluorescent
Fabrication and characteristics of organic semiconductor nanoparticles of copper phthalocyanine oligomers
by Zhi-Min Dang; Yan Gao; Hai-Ping Xu; Jinbo Bai (pp. 491-496).
Nanoparticles of copper phthalocyanine oligomers (O-CuPc) with peripheral carboxylic acid groups have successfully been prepared by a simple method of liquid phase direct precipitation in the presence of different surfactants. X-ray diffraction patterns, transmission electron microscopy, and UV–visible spectra are employed to characterize the novel organic nanoparticles. The sizes and size distribution of the resulting O-CuPc nanoparticles show a noticeable dependence on surfactants. Nonionic surfactant is helpful in forming uniform nanoparticles. Also we observe a remarkable nanosize effect of the O-CuPc particles.(Left) TEM micrograph of O-CuPc nanoparticles obtained in the presence of MPEG. (Right) Schematic representation of the structures of MPEG-capped O-CuPc nanoparticles.
Keywords: Copper phthalocyanine oligomer; Nanoparticles; Surfactants; Precipitation
Comparative examination of titania nanocrystals synthesized by peroxo titanic acid approach from different precursors
by Yong-Jun Liu; Mami Aizawa; Zheng-Ming Wang; Hiroaki Hatori; Naofumi Uekawa; Hirofumi Kanoh (pp. 497-504).
Titanium dioxide nanocrystalline particles were synthesized by peroxo titanium acid (PTA) approach from titanium alkoxide and inorganic salt precursors, and their structural and surface properties, porosities, and photocatalytic activities were comparatively examined by XRD, TG/DTA, DRIFT, UV–vis, low temperature N2 adsorption, and methyl orange (MO) degradation. It was found that nanoparticles with single anatase phase can be obtained from alkoxide precursor even near room temperature if synthesis conditions are appropriately controlled. PTA-derived anatase nanoparticles from titanium alkoxide precursor have smaller crystalline sizes and better porosities, and contain less amount of peroxo group and no organic impurities as compared to those from TiCl4 precursor. The advantages in structural property, porosity, and surface properties (few deficiencies) lead to a much better photocatalytic activity for TiO2 nanoparticles from titanium alkoxide precursor in comparison with those from TiCl4 precursor.
Keywords: Titania; Nanocrystal; Chemical synthesis; Characterization; Photocatalytic activity
Strategies to control the particle size distribution of poly- ε-caprolactone nanoparticles for pharmaceutical applications
by Federica Lince; Daniele L. Marchisio; Antonello A. Barresi (pp. 505-515).
In this work turbulent precipitation through solvent displacement for the production of poly- ε-caprolactone (PCL) nanoparticles is investigated; two different PCL molecular weights have been employed, using acetone and water as solvent and anti-solvent, respectively. The main important thermodynamic and kinetic parameters, such as solubility and interfacial tension of PCL in water–acetone mixtures, are determined and the effect of the process operating conditions on the final particle size distribution is also investigated. Particles produced under different conditions into a Confined Impinging Jets Reactor (CIJR) were characterized by Dynamic Light Scattering, Zeta potential measurements and Scanning Electronic Microscopy. Results clearly show the strong effect of mixing on the particle size distribution and how mixing must be controlled in order to obtain a product with particular characteristics. Eventually the measured thermodynamic and kinetic parameters are used to interpret the obtained experimental data.PCL mean particle size(dm) versus the flow rate (FR) forMw=14,000, initial polymer concentrationscPCL0=10 mg/ml and for water to acetone flow rate ratio W/A = 1 (□), W/A = 2 (○), W/A = 3 (▵), W/A = 4 (▿).
Keywords: Nanoparticles; Solvent displacement; Poly-; ε; -caprolactone; Drug delivery; Particle size distribution; Mixing
Interaction of mineral surfaces with simple organic molecules by diffuse reflectance IR spectroscopy (DRIFT)
by Joan E. Thomas; Michael J. Kelley (pp. 516-526).
The adsorption of simple organic molecules to mineral surfaces was investigated by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and by solution chemical analysis. Salicylic acid, myristic acid or octacosane were deposited from water or hexane onto γ-alumina and kaolinite, and examined without evacuation or blending with KBr. The DRIFTS results replicated those from ATR-IR, where available, supporting the validity of DRIFTS as a versatile and convenient alternative to ATR. Results were obtained for coverage as low as 0.02 molecules/nm2. Monolayer coverage on γ-alumina was determined from spectra as 0.7 molecules/nm2 for salicylic acid, confirmed by solution analysis, and 2 molecules/nm2 for myristic acid. Spectral features of salicylic acid deposited on γ-alumina from hexane were not distinguishable from those deposited from water. In almost all cases, spectral features associated with the carboxyl moiety were substantially altered, indicating a significant role in the adsorption mechanism. Adsorption of salicylic acid from hexane onto kaolinite was also as carboxylate, but myristic acid showed both carboxylate and carbonyl. The results from using hexane as solvent compared to water suggest that surface-adsorbed hydroxyl and molecular water, present on mineral oxides under ambient conditions, may be a key determinant of the adsorbate architecture.DRIFT IR shows that salicylic acid loading on alumina saturates (above) at a fixed value, corresponding to about 0.7 molecules/nm2 (lower), in agreement with solution depletion measurements: (×) phenolicOH 1263 cm−1, (♦)COO 1281 cm−1.
Keywords: Infrared spectroscopy; DRIFTS; Oxide minerals; Adsorption; Carboxylic acids; Surface water
In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions
by M.M. Dávila-Jiménez; M.P. Elizalde-González; J. Mattusch; P. Morgenstern; M.A. Pérez-Cruz; Y. Reyes-Ortega; R. Wennrich; H. Yee-Madeira (pp. 527-536).
Adsorption methods have been developed for the removal of arsenic from solution motivated by the adverse health effects of this naturally occurring element. Iron exchanged natural zeolites are promising materials for this application. In this study we introduced iron species into a clinoptilolite-rich zeolitic tuff by the liquid exchange method using different organic and inorganic iron salts after pretreatment with NaCl and quantified the iron content in all trials by XRF spectroscopy. The materials were characterized by XRD, FTIR, FTIR-DR, UV–vis, cyclic voltammetry, ESR and Mössbauer spectroscopies before and after adsorption of arsenite and arsenate. The reached iron load in the sample T+Fe was %Fe2O3—2.462,nFe/nAl=0.19,nSi/nFe=30.9 using FeCl3, whereby the iron leachability was 0.1–0.2%. The introduced iron corresponded to four coordinated species with tetrahedral geometry, primarily low spin ferric iron adsorbing almost 12 μg g−1 arsenite (99% removal) from a 360 μgAs(III) L−1 and 6 μg g−1 arsenate from a 230 μgAs(V) L−1. Adsorption of arsenite and arsenate reached practically a plateau atnFe/nSi=0.1 in the series of exchanged tuffs. The oxidation of arsenite to arsenate in the solution in contact with iron modified tuff during adsorption was observed by speciation. The reduction of ferric iron to ferrous iron could be detected in the electrochemical system comprising an iron-clinoptilolite impregnated electrode and was not observed in the dried tuff after adsorption.Introduction of iron into a clinoptilolite-rich zeolitic tuff was optimized using FeCl3 and pretreatment with NaCl. Characterization by in situ XRF spectroscopy assessed that adsorption of arsenite and arsenate reached a plateau atnFe/nSi=0.1.
Keywords: Clinoptilolite; Iron modification; Arsenic adsorption; Mössbauer spectroscopy; ESR spectroscopy; Zeolite impregnated electrode
Electrocatalytic oxidation of ethylene glycol on Pt and Pt–Ru nanoparticles modified multi-walled carbon nanotubes
by Vaithilingam Selvaraj; Mari Vinoba; Muthukaruppan Alagar (pp. 537-544).
The synthesis and characterization of catalysts based on nanomaterials, supported on multi-walled carbon nanotubes (CNT) for ethylene glycol (EG) oxidation is investigated. Platinum (Pt) and platinum–ruthenium (Pt–Ru) nanoparticles are deposited on surface-oxidized multi-walled carbon nanotubes [Pt/CNT; Pt–Ru/CNT] by the aqueous solution reduction of the corresponding metal salts with glycerol. The electrocatalytic properties of the modified electrodes for oxidation of ethylene glycol in acidic solution have been studied by cyclic voltammetry (CV), and excellent activity is observed. This may be attributed to the small particle size of the metal nanoparticles, the efficacy of carbon nanotubes acting as good catalyst support and uniform dispersion of nanoparticles on CNT surfaces. The nature of the resulting nanoparticles decorated multiwalled carbon nanotubes are characterized by scanning electron microscopy (SEM) and transmission electron microscopic (TEM) analysis. The cyclic voltammetry response indicates that Pt–Ru/CNT catalyst displays a higher performance than Pt/CNT, which may be due to the efficiency of the nature of Ru species in Pt–Ru systems. The fabricated Pt and Pt–Ru nanoparticles decorated CNT electrodes shows better catalytic performance towards ethylene glycol oxidation than the corresponding nanoparticles decorated carbon electrodes, demonstrating that it is more promising for use in fuel cells.TEM images of nanoparticles decorated MWCNT obtained by glycerol as reducing agent.
Keywords: Multi-walled carbon nanotubes (CNT); Ethylene glycol (EG) oxidation; Pt nanoparticles; Pt–Ru nanoparticles; Fuel cells
Interface synthesis of mesoporous MnO2 and its electrochemical capacitive behaviors
by C.Z. Changzhou Yuan; Bo Gao; L.H. Linghao Su; X.G. Xiaogang Zhang (pp. 545-550).
Mesoporous MnO2 has been synthesized by means of a novel, facile, and template-free method by virtue of a soft interface between CCl4 and H2O without any surfactants or organometallic precursors or ligands. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy analysis, scanning electron microscopy, and an ASAP2010 autoadsorption analyzer were applied to investigate the composition and microstructure of the as-synthesized MnO2. The structure characterizations indicated a good mesoporous structure for as-prepared MnO2 with an adsorption average pore diameter of 9.7 nm, mesoporous volume of 0.58 cm3 g−1, and Brunauer–Emmett–Teller specific surface area of 239 m2 g−1. Electrochemical properties of the mesoporous MnO2 were elucidated by cyclic voltammograms, galvanostatic charge–discharge, and electrochemical impedance spectroscopy in 1 M Na2SO4 electrolyte. Electrochemical data analysis demonstrated that as-synthesized MnO2 had good capacitive behavior due to its unique mesoporous structure. A specific capacitance of ca. 220 F g−1 could still be delivered for the mesoporous MnO2 even at a scan rate of 100 mV s−1.Mesoporous MnO2 with good electrochemical performance has been synthesized by means of a facile and template-free method by virtue of soft interface between CCl4 and H2O.
Keywords: Mesoporous MnO; 2; CCl; 4; /H; 2; O soft interface; Template free; Electrochemical capacitance
Microscopic approach for the identification of cationic membrane fouling during cheddar cheese whey electroacidification
by F. Lin Teng Shee; P. Angers; L. Bazinet (pp. 551-557).
This is the first time that fouling of cation-exchange membranes during cheddar cheese whey electroacidification with bipolar membranes is reported. A mineral fouling was observed only on the cationic membrane side in contact with the base. The deposit was identified as magnesium hydroxide and this fouling was more important on the cation-exchange membrane situated close to the cathode. Little deposit was formed after six electroacidification runs, but on long time, the buildup of fouling film would lead after many electroacidifications to an important decrease of the system efficiency. Since, fouling of permselective membranes represents one of the major issues in electrodialytic processes, this result will be the basis for the determination of cleaning conditions allowing the prevention of such a fouling.Fouling of cationic membrane used in electroacidification with bipolar membranes of whey was idendified as magnesium hydroxide, with magnesium from whey, and hydroxyl ions from water dissociation.
Keywords: Electroacidification; Cationic membranes; Fouling
Adsorption of bulky molecules of nonylphenol ethoxylate on ordered mesoporous carbons
by Xun Yuan; Wei Xing; Shu-Ping Zhuo; Weijiang Si; Xiuli Gao; Zhaohui Han; Zi-Feng Yan (pp. 558-565).
Ordered mesoporous carbons (OMCs) with varying pore sizes were prepared using ordered mesoporous silica SBA-15 as hard templates. The OMCs possess abundant mesopores with narrow pore size distribution, on which the adsorption behavior of bulky molecules of nonylphenol ethoxylate (NPE) were investigated. The isotherms of NPE on OMCs can be fitted by Langmuir adsorption model, evidenced by the adsorption data. The surface area of the pores larger than 1.5 nm is a crucial factor to the adsorption capacity of NPE, whereas the most probable pore diameter of OMCs is crucial to the adsorption rate of NPE. The adsorption temperature has more significant effects on adsorption rate than the adsorption capacity. Theoretical studies show that the adsorption kinetics of NPE on OMCs can be depicted with the pseudo-second-order kinetic model. In addition, thermodynamic parameters of adsorption were evaluated based on the equilibrium constants related to the equilibrium of adsorption at different temperatures.Adsorption isotherms of NPE over ordered mesoporous carbons.
Keywords: Adsorption; Bulky molecule; Mesoporous carbon; Mesoporous silica; Adsorption isotherm; Adsorption kinetics
Plasma treatments of PET meshes for fuel–water separation applications
by Stefano Zanini; Paola Massini; Marco Mietta; Elisa Grimoldi; Claudia Riccardi (pp. 566-571).
Sulphur hexafluoride (SF6) plasma treatments and hexamethyl disiloxane (HMDSO) plasma polymerisation were performed on poly(ethylene terephthalate) (PET) meshes and the resulting wettability against liquids having very different surface tensions were investigated at the light of a possible use of the materials in the fuel/water separation technology. Surface modification of the meshes owing to HMDSO plasma polymerisation followed by SF6 plasma treatment was also investigated. Hydrophobic performances were characterised refining the conventional Wilhelmy dynamic contact angle (DCA) technique, using several reference solutions having the surface tension values between 20–72 mN/m. Measurements of the water intrusion pressure (WIP) of the treated samples were also performed. Surface modifications on the plasma treated meshes were investigated by means of Fourier-transform infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. SF6 and HMDSO plasma treatments decrease the surface energy of the PET meshes, lowering the liquid surface tension at which the wettable/unwettable transition occurs and increasing the WIP. Moreover, an increase in hydrophobic performances was achieved with HMDSO plasma polymerisation followed by SF6 plasma treatment.The chemical modifications and the wettability against liquids having different surface tensions of SF6 and HMDSO plasma treated PET meshes were investigated.
Keywords: PACS; 81.65.-B; 52.77.DQ; 52.80.PIPlasma treatments; PECVD; Fuel–water separation; Wilhelmy method; Water intrusion pressure
Micellization and interfacial behavior of binary and ternary mixtures of model cationic and nonionic surfactants in aqueous NaCl medium
by Aijaz Ahmad Dar; Ghulam Mohammad Rather; Soumen Ghosh; Akhil Ranjan Das (pp. 572-581).
Mixed micelle formation and interfacial properties of aqueous binary and ternary combinations of hexadecyltrimethylammonium bromide (C16Br), hexadecylbenzyldimethylammonium chloride (C16BzCl) and polyoxyethylene (20) cetyl ether (Brij58) at 25 °C in 30 mM aqueous NaCl have been studied in detail employing tensiometric and fluorimetric techniques. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameters and free energy of micellization have been estimated using the theoretical approaches of Clint, Rosen, Rubingh, Blankschtein et al., Rubingh–Holland and Maeda. A comprehensive account of the comparative performance of these models on the selected cationic–cationic–nonionic surfactant mixtures at constant ionic strength has been presented. The Blankschtein model predicted lower synergism than from Rubingh's method because it neglects the contribution due to steric interaction between surfactant head groups of different sizes and charges. Free energy of micellization calculated using Maeda's approach, which employs interaction parameter and micellar mole fraction from Rubingh's model as inputs, shows good correlation with that calculated from commonly used phase separation model. The present study also reveals that the modified Rubingh–Holland method along with the Rosen's model can be applied to analyze the interfacial characteristics of ternary surfactant mixtures with a fair degree of success thereby widening the domain of applicability of this model.Comparison of experimental critical micelle concentration of C16Br, C16BzCl and Brij58 in their various ternary combinations using Clint's, Blankschtein's, and Rubingh–Holland formulations.
Keywords: Mixed micelle formation; Mixed monolayer formation; Micropolarity; Aggregation number; Rubingh–Holland
Extruded vesicles of dioctadecyldimethylammonium bromide and chloride investigated by light scattering and cryogenic transmission electron microscopy
by António Lopes; Katarina Edwards; Eloi Feitosa (pp. 582-588).
Combined dynamic and static light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM) were used to investigate extruded cationic vesicles of dioctadecyldimethylammonium chloride and bromide (DODAX, X being Cl− or Br−). In salt-free dispersions the mean hydrodynamic diameter,Dh, and the weight average molecular weight,Mw, are larger for DODAB than for DODAC vesicles, and bothDh andMw increase with the diameter ( ϕ) of the extrusion filter. NaCl (NaBr) decreases (increases) the DODAB (DODAC) vesicle size, reflecting the general trend of DODAB to assemble as larger vesicles than DODAC. The polydispersity index is lower than 0.25, indicating the dispersions are rather polydisperse. Cryo-TEM micrographs show that the smaller vesicles are spherical while the larger ones are oblong or faceted, and the vesicle samples are fairly polydisperse in size and morphology. They also indicate that the vesicle size increases with ϕ and DODAB assembles as larger vesicles than DODAC. Lens-shaped vesicles were observed in the extruded preparations. Both light scattering and cryo-TEM indicate that the vesicle size is larger or smaller than ϕ when ϕ is smaller or larger than the optimalϕ∗≈200 nm.Cryo-TEM image of DODAB extruded vesicles.
Keywords: DODAB; DODAC; Cationic vesicle; Extruded vesicle; Lens-shaped vesicle; Light scattering; Cryo-TEM
Synergistic effects in mixtures of oppositely charged surfactants as calculated from the Poisson–Boltzmann theory: A comparison between theoretical predictions and experiments
by L. Magnus Bergström; Tobias Bramer (pp. 589-595).
Critical micelle concentrations in mixtures of an anionic surfactant and a cationic amphiphilic drug have been investigated using a model-independent procedure to quantify observed synergistic effects. Experimental results were compared with a theory based on the Poisson–Boltzmann mean field approximation of a charged interface with a diffuse layer of counterions. Explicit expressions for the activity coefficients from which the critical micelle concentration can be calculated and quantitatively predicted have been derived and excellent agreement between experimental data and theory was obtained. As a result, we demonstrate that it is possible to rationalize and predict the magnitude of synergism in mixtures of oppositely charged surfactants in the presence of added salt.Comparison between experiments and a theory based on the Poisson–Boltzmann mean field approximation shows that it is possible to rationalize and predict the magnitude of synergistic effects in mixtures of oppositely charged surfactants in the presence of added salt.
Keywords: Surfactants; Catanionic mixtures; Critical micelle concentration; Synergistic effects; Micelles; Vesicles; Solubilization
Wormlike micelles in mixed amino acid-based anionic/nonionic surfactant systems
by Rekha Goswami Shrestha; Lok Kumar Shrestha; Kenji Aramaki (pp. 596-604).
We present the formation of viscoelastic wormlike micelles in mixed amino acid-based anionic and nonionic surfactants in aqueous systems in the absence of salt. N-Dodecylglutamic acid (designated as LAD) has a higher Krafft temperature; however, on neutralization with alkaline amino acidl-lysine, it forms micelles and the solution behaves like a Newtonian fluid at 25 °C. Addition of tri(oxyethylene) monododecyl ether (C12EO3) and tri(oxyethylene) monotetradecyl ether (C14EO3) to the dilute aqueous solution of the LAD–lysine induces one-dimensional micellar growth. With increasing C12EO3 or C14EO3 concentration, the solution viscosity increases gradually, but after a certain concentration, the elongated micelles entangle forming a rigid network of wormlike micelles and the solution viscosity increases tremendously. Thus formed wormlike micelles show a viscoelastic character and follow the Maxwell model. Tri(oxyethylene) monohexadecyl ether (C16EO3), on the other hand, could not form wormlike micelles, although the solution viscosity increases too. The micelles become elongated; however, they do not appear to form a rigid network of wormlike micelles in the case of C16EO3. Rheological measurements have shown that zero shear viscosity (η0) increases with the C12EO3 concentration gradually at first and then sharply, and finally decreases before phase separation. However, no such maximum in theη0 plot is observed with the C14EO3. Theη0 increases monotonously with the C14EO3 concentration till phase separation. In studies of the effect of temperature on the wormlike micellar behavior it has been found that theη0 decays exponentially with temperature, following an Arrehenius behavior and at sufficiently higher temperatures the solutions follow a Newtonian behavior. The flow activation energy calculated from the slope of logη0 versus1/T plot is very close to the value reported for typical wormlike micelles. Finally, we also present the effect of neutralization degree of lysine on the rheology and phase behavior. The formation of wormlike micelles is confirmed by the Maxwell model fit to the experimental rheological data and by Cole–Cole plots.
Keywords: Amino acid surfactants; Nonionic surfactant; Phase behavior; Wormlike micelles; Rheology; Viscoelastic solutions
Reversed micelle formation in a model liquid–liquid extraction system
by Fuqiang Guo; Hongfei Li; Zhifeng Zhang; Shulan Meng; Deqian Li (pp. 605-610).
The formation of reversed micelles and the roles of extractant and extracted complexes were investigated in the Cyanex923/ n-heptane/H2SO4 system. Interfacial tension ( γ), electrical conductivity ( κ), and water content measurements showed that Cyanex923 had a tendency to self-assemble, forming reversed micelles. The changes in electrical conductivity with concentration of H2SO4 in the organic phase (CH2SO4,o) exhibited an S-type curve: a correlation was found between the change in electrical conductivity and the water content as a function ofCH2SO4,o. The changes of electrical conductivity were mainly induced by the components and microstructure in the organic phase, while the conversion of extracted complex also resulted in the changes of components and microstructure in the organic phase. Fourier transform infrared (FTIR) spectroscopy and dynamic light scattering (DLS) were used to characterize the organic phases and sizes of the reversed micelles, respectively. The extractant and extracted complexes, such as Cyanex923⋅H2SO4, were involved in the formation of reversed micelles.
Keywords: Reversed micelle; Cyanex923; Liquid–liquid extraction system; Interfacial tension; Electrical conductivity
Light-sensitive lamellar phases
by Aihua Zou; Julian Eastoe; Kevin Mutch; Paul Wyatt; Günther Scherf; Otto Glatter; Isabelle Grillo (pp. 611-616).
Light sensitive lamellar (L α) phases have been generated in glycerol/water mixtures from blends of an inert ABA tri-block co-polymer (dimethylsiloxane-polyethylenoxide, (EO)15–(PDMS)15–(EO)15), and a photodestructible anionic surfactant C6PAS (sodium 4-hexylphenylazosulfonate). These L α systems have been formulated in a 6/4 glycerol/water (v/v) mixed solvent. Rheology, small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS) and dynamic light scattering (DLS) have been used to characterize the change in phase behavior and structure after the incorporated C6PAS is selectively degraded by UV light incident on the L α phases. The ABA co-polymer alone forms weakly structured lamellar mesophases, which are stabilized by thermal fluctuations and characterized by low shear moduli (L α phase-A). Addition of C6PAS (10 mM) introduces charge stabilization, generating more ordered and stiffer L α systems (L α phase-B). After UV irradiation (Hg lamp) of the L α-B phases, and subsequent degradation of the ionic C6PAS, the results of rheological and scattering studies are consistent with an irreversible change back to L α phase-A type systems. These formulations display a novel transition between electrostatically- and thermally-stabilized lamellae, which may be controlled by incident UV light.SANS measurements of photosurfactant/block co-polymer lamellar phases in a mixed glycerol/water solvent. (a) L α-A phase without photosurfactant C6PAS; (b) L α-B phase with 10 mM C6PAS before UV irradiation; (c) the L α-B′ system after 60 min UV irradiation to destroy the photosurfactant.
Keywords: L; α; phases; Light-triggered systems; SAXS; SANS
Electrical charging of a conducting water droplet in a dielectric fluid on the electrode surface
by Yong-Mi Jung; Hyun-Chang Oh; In Seok Kang (pp. 617-623).
It has been conceived that a charged droplet driven by Coulombic force can be used as a droplet-based microreactor. As a basic research for such applications, electrical charging of a conducting water droplet is studied experimentally. The effects of electric field, medium viscosity, and droplet size are investigated. It is found that the amount of electrical charging increases with the droplet size and the electric field. However, the medium viscosity does not have a significant effect in the range of the present study. A scaling law is derived from the experimental results. Unlike the case of a perfect conductor, the estimated amount of electrical charge (Qest) of a water droplet is proportional to the 1.59 power of the droplet radius ( R) and the 1.33 power of the electric field strength ( E). (For a spherical perfect conductor, Q is proportional toR2 and E.) In order to understand these differences, numerical simulations are performed for the idealized droplets of perfect conductor. Comparison of the numerical and experimental results suggests that the differences are mainly due to incomplete charging of a water droplet resulted from the combined effect of electrochemical reaction at electrode and the relatively low conductivity of water.A sequence of photographs that shows the motion and deformation of a water droplet near the electrode.
Keywords: Charging; Coulombic force; Dielectric fluid; Charged conducting droplet
Drug and surfactant transport in Cyclosporine A and Brij 98 laden p-HEMA hydrogels
by Yash Kapoor; Anuj Chauhan (pp. 624-633).
Surfactants are commonly incorporated into hydrogels to increase solute loading and attenuate the release rates. In this paper we focus on understanding and modeling the mechanisms of both surfactant and drug transport in hydrogels. Specifically, we focus on Brij 98 as the surfactant, Cyclosporine A (CyA) as the hydrophobic drug, and poly-hydroxy ethyl methacrylate (p-HEMA) as the polymer. The models developed here are validated by experiments conducted with gels of different thicknesses and surfactant loadings. Also the model is compared with prior experimental studies in literature. The model predicts that the percentage surfactant as well as drug release scales as 1/(surfactant loading)0.5, and thus a four fold increase in surfactant loading leads to a two fold reduction in percentage release for both drug and surfactant at a given time. The models for the surfactant and drug release are fitted to the experimental data to obtain values of1.44×10−14m2/s for CyA diffusivity and 414.4 for the partition coefficient between drug concentration inside the micelle and that in the gel. These models can be very helpful in tuning the drug release rates from hydrogels by controlling the surfactant concentration. The results also show that Brij 98 loaded p-HEMA exhibit an extended release of CyA and so contact lenses made with this material can be used for extended ocular delivery of CyA, which is an immunosuppressant drug commonly used for treatment of various ocular ailments.A schematic of transport from surfactant laden hydrogel. Region I represents the depletion zone with no micelles because the surfactant concentration is below the critical aggregation concentration. Region II contains surfactant aggregates along with free surfactant.
Keywords: Cyclosporine A; p-HEMA; Transport; Model; Micelles; Aggregation; Brij 98
Diffusiophoresis and electrophoresis of a charged sphere perpendicular to two plane walls
by Yu C. Chang; Huan J. Keh (pp. 634-653).
The problem of diffusiophoretic and electrophoretic motions of a dielectric spherical particle in an electrolyte solution situated at an arbitrary position between two infinite parallel plane walls is studied theoretically in the quasisteady limit of negligible Peclet and Reynolds numbers. The applied electrolyte concentration gradient or electric field is uniform and perpendicular to the plane walls. The electric double layer at the particle surface is assumed to be thin relative to the particle radius and to the particle–wall gap widths, but the polarization effect of the diffuse ions in the double layer is incorporated. To solve the conservative equations, the general solution is constructed from the fundamental solutions in both cylindrical and spherical coordinates. The boundary conditions are enforced first at the plane walls by the Hankel transforms and then on the particle surface by a collocation technique. Numerical results for the diffusiophoretic and electrophoretic velocities of the particle relative to those of a particle under identical conditions in an unbounded solution are presented for various cases. The collocation results agree well with the approximate analytical solutions obtained by using a method of reflections. The presence of the walls can reduce or enhance the particle velocity, depending on the properties of the particle–solution system and the relative particle–wall separation distances. The boundary effects on diffusiophoresis and electrophoresis of a particle normal to two plane walls are found to be quite significant and complicated, and generally stronger than those parallel to the confining walls.The problem of diffusiophoretic and electrophoretic motions of a dielectric spherical particle with a thin but polarized electric double layer in an electrolyte solution perpendicular to two parallel plane walls at an arbitrary position between them is studied theoretically.
Keywords: Diffusiophoresis; Electrophoresis; Boundary effects; Thin but polarized double layer
Synthesis of poly( N-isopropylacrylamide)- b-poly(2-vinylpyridine) block copolymers via RAFT polymerization and micellization behavior in aqueous solution
by Jianguo Zeng; Keyu Shi; Yuying Zhang; Xuehui Sun; Lin Deng; Xianzhi Guo; Zongjie Du; Baolong Zhang (pp. 654-659).
Poly( N-isopropylacrylamide)- b-poly(2-vinylpyridine) (PNIPAM- b-P2VP) block copolymers were synthesized for the first time via reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of S-1-dodecyl-S′-(a,a′-dimethyl-a″-acetic acid)trithiocarbonate as chain transfer agent (CTA) and2,2′-azobis(isobutyronitrile) as initiator. Both pH- and thermo-induced micellization behavior of the PNIPAM59- b-P2VP102 block copolymer in dilute aqueous solution was investigated by pyrene fluorescence, dynamic and static light scattering, transmission electron microscopy and1H NMR. The results show that the critical aggregation pH value of the block copolymer is around 5 and the critical aggregation temperature of the block copolymer is around 42 °C. A reversible transition between P2VP-core and PNIPAM-core micelles can be observed through an intermediate unimer state in aqueous solution.Schematic representation of the ‘schizophrenic’ micellization of the PNIPAM59- b-P2VP102 block copolymer in aqueous solution.
Keywords: RAFT polymerization; pH-responsive; Thermo-responsive; ‘Schizophrenic’ micellization
Modeling the surface charge evolution of spherical nanoparticles by considering dielectric discontinuity effects at the solid/electrolyte solution interface
by Marianne Seijo; Serge Ulrich; Montserrat Filella; Jacques Buffle; Serge Stoll (pp. 660-668).
It is well known that the electrostatic repulsions between charges on neighboring sites decrease the effective charge at the surface of a charged nanoparticle (NP). However, the situation is more complex close to a dielectric discontinuity, since charged sites are interacting not only with their neighbors but also with their own image charges and the image charges of all neighbors. Titrating site positions, solution ionic concentration, dielectric discontinuity effects, and surface charge variations with pH are investigated here using a grand canonical Monte Carlo method. A Tanford and Kirkwood approach is used to calculate the interaction potentials between the discrete charged sites. Homogeneous, heterogeneous, and patch site distributions are considered to reproduce the various titrating site distributions at the solid/solution interface of spherical NPs. By considering Coulomb, salt, and image charges effects, results show that for different ionic concentrations, modifications of the dielectric constant of NPs having homogeneous and heterogeneous site distributions have little effect on their charging process. Thus, the reaction field, due to the presence of image charges, fully counterbalances the Coulomb interactions. This is not the case for patch distributions, where Coulomb interactions are not completely counterbalanced by the reaction field. Application of the present model to pyrogenic silica is also performed and comparison is made with published experimental data of titration curves at various ionic concentrations.Effects of pH and site distribution on the charging process of spherical nanoparticles.
Keywords: Nanoparticle surface charge; Nanoparticle titration curves; Monte Carlo simulations; Tanford and Kirkwood model; Dielectric discontinuity
Unusual behavior of PEG/PPG/Pluronic interfaces studied by a spinning drop tensiometer
by Jeffrey D. Martin; Sachin S. Velankar (pp. 669-674).
The effects of surfactants on the interfacial tension driven retraction of elongated drops were studied in a spinning drop tensiometer. Experiments were conducted on polypropylene glycol (PPG) drops suspended in polyethylene glycol (PEG), with Pluronic block copolymers as surfactants. Two unusual observations are reported here. In the first, initially-elongated drops generated at high rotational speed were allowed to retract by reducing the rotational speed. Pluronic-laden drops would not retract completely, but would instead maintain strongly nonspherical shapes indefinitely. We attribute such “nonretraction” to an interfacial yield stress induced by the Pluronic surfactant. In the second, drops being heated while spinning at a constant speed would elongate sharply at some temperature, and subsequently breakup. Such “autoextension” and breakup indicate complex nonmonotonic changes in interfacial tension with time during heating. We propose that autoextension occurs because at low temperature, interfacially-adsorbed surfactant is crystallized and hence trapped at the interface at a concentration far above equilibrium.Surfactant-laden drops show nonspherical shapes, likely indicating that the interface has a small yield stress. Heating sometimes causes a large increase in interfacial area, indicating that the surfactant can be trapped at the interface at a concentration above equilibrium.
Keywords: Interfacial tension; Interfacial viscoelasticity; Pluronic; Interfacial crystallization; Interfacial yield stress; Nonspherical drops
Node contribution to the permeability of liquid foams
by O. Pitois; N. Louvet; E. Lorenceau; F. Rouyer (pp. 675-677).
This paper deals with the drainage of liquid foams. The liquid velocity is known to be related to viscous dissipation occurring within the elements of the liquid network, i.e. the channels and the nodes. When compared together, available values for the hydrodynamic resistance of a foam node appear to span over more than one order of magnitude. To clarify this point, we propose an alternative experimental method to estimate the value of this parameter. In contrast to previous experimental work performed on the foam scale, the node resistance is not treated as a fitting parameter, but instead it is measured directly on the microscopic scale. The results allow a consistent range of values to emerge for this parameter.Study of a single foam node connected to four Plateau borders.
Keywords: Hydrodynamic resistance; Drainage; Permeability; Plateau border; Vertex
Microviscosity of hydrophobically modified hydroxyethyl cellulose aqueous solutions
by G.Q. Guangqiang Zhao; Shing Bor Chen (pp. 678-680).
The microviscosity of hydrophobically modified hydroxyethyl cellulose (HMHEC) aqueous solutions is experimentally determined by conductometry with added ions as probe. Compared to its bulk viscosity, the microviscosity of HMHEC solution could be lower by four orders of magnitude. Since the electric conductivity reduction of added NaCl is almost the same for HMHEC and its unmodified counterpart at an equal weight concentration, one can conclude that the hydrophobic modification for the polymer hardly has any effect on the solution's microviscosity.
Keywords: Microviscosity; Associative polymer; Conductivity; Ions; Gel