Journal of Colloid And Interface Science (v.325, #1)
Synthesis of ruthenium particles by photoreduction in polymer solutions
by Masafumi Harada; Saki Takahashi (pp. 1-6).
Colloidal dispersions of poly( N-vinyl-2-pyrrolidone)-protected ruthenium (Ru) particles have been synthesized by the photoreduction of Ru(III) ionic solutions in the presence of photo-activator such as benzophenone and benzoin. The size and the structure of the synthesized particles have been extensively investigated by UV–vis, transmission electron micrograph (TEM) and extended X-ray absorption fine structure (EXAFS). Metallic Ru particles with an average diameter of 1.3 nm were successfully synthesized in the presence of benzophenone, although mixtures of partly oxidized Ru particles and metallic Ru particles were synthesized in the presence of benzoin. Photoreduction of Ru(III) ionic precursors to Ru atoms was promoted by ketyl radicals, which is more efficiently generated by the photoirradiation of benzophenone than by that of benzoin. The photoirradiation of benzophenone in the Ru(III) ionic solutions is an efficient and convenient method to produce metallic Ru particles in polymer solutions rather than the refluxing and the hydrothermal method of ionic solutions of Ru.A TEM image of Ru particles produced from PVP aqueous ethanol solution in the presence of benzophenone by the photoreduction method, and the Fourier transforms of EXAFS of Ru K-edge for the Ru colloidal solutions before and after photoreduction.
Keywords: Colloidal dispersions; Ruthenium; Polymer-stabilized particles; Photoreduction; EXAFS
On the anatomy of the adsorption heat versus loading as a function of temperature and adsorbate for a graphitic surface
by D.D. Do; D. Nicholson; H.D. Do (pp. 7-22).
In this paper we review and classify the various patterns of isosteric heat versus loading for adsorption of gases on graphitised thermal carbon black at temperatures ranging from below the 3D triple point to temperatures above it, but less than the 3D critical point. We have identified the features of heat curve and highlighted the microscopic origin of these features. The patterns vary with temperature and with the relative strength of the fluid–fluid interaction and solid–fluid interaction. For simple adsorptives (by simple we meant there is no strong association between fluid particles), the heat curve is typified by fluid–fluid attraction and layering phenomena. For adsorptives showing strong association such as water, ammonia and methanol, the heat curve essentially begins below the condensation heat and then approaches it as loading is increased. This is mainly due to the strong hydrogen bonding in these fluids. A third group includes adsorptives such as benzene, where the heat curve is constant in the sub-monolayer coverage region (but is higher than the condensation heat) and then drops off to the condensation heat when higher layers are formed. The constant heat in the sub-monolayer region is due to the balance between the energy factor (from fluid–fluid interaction) and entropy factor (due to re-orientation of adsorbed molecules). Our proposed classification is supported by detailed GCMC simulations of various gases that have been reported in the literature, and we supplement these with new results for the adsorption of xenon on graphite to investigate in more detail the change in heat pattern with temperature. Xenon is chosen because of its high fluid–fluid interaction, allowing us to study the 2D-phase transition in the first as well as higher layers.Pattern of isosteric heat versus loading for adsorption of xenon on graphite at 90 K.
Keywords: Adsorption; Isosteric heat; Graphite; GCMC simulation; 2D-phase transition
Arsenate adsorption on ruthenium oxides: A spectroscopic and kinetic investigation
by Todd P. Luxton; Matthew J. Eick; Kirk G. Scheckel (pp. 23-30).
Arsenate adsorption on amorphous (RuO2⋅1.1H2O) and crystalline (RuO2) ruthenium oxides was evaluated using spectroscopic and kinetic methods to elucidate the adsorption mechanism. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local coordination environment of adsorbed arsenate. Additionally, pressure-jump (p-jump) relaxation spectroscopy was used to investigate the kinetics of arsenate adsorption/desorption on ruthenium oxides. Chemical relaxations resulting from the induced pressure change were monitored via electrical conductivity detection. EXAFS data were collected for two initial arsenate solution concentrations, 3 and 33 mM at pH 5. The collected spectra indicated a similar coordination environment for arsenate adsorbed to RuO2⋅1.1H2O for both arsenate concentrations. In contrast the EXAFS spectra of RuO2 indicated differences in the local coordination environments for the crystalline material with increasing arsenate concentration. Data analysis indicated that both mono- and bidentate surfaces complexes were present on both RuO2⋅1.1H2O and RuO2. Relaxation spectra from the pressure-jump experiments of both ruthenium oxides resulted in a double relaxation event. Based on the relaxation spectra, a two step reaction mechanism for arsenate adsorption is proposed resulting in the formation of a bidentate surface complex. Analysis of the kinetic and spectroscopic data suggested that while there were two relaxation events, arsenate adsorbed to ruthenium oxide surfaces through both mono- and bidentate surface complexes.Schematic representation of the proposed arsenate adsorption mechanism on ruthenium oxide.
Keywords: Adsorption; Arsenic; Ruthenium oxide; EXAFS; Pressure-jump relaxation
Lithium uptake in fixed-pH solution by ion sieves
by Lu Wang; Chang Gong Meng; Mei Han; Wei Ma (pp. 31-40).
In this study, Li+ uptake by ion sieves was studied in a fixed-pH aqueous phase using a pH 8.0 buffer solution of ammonia/ammonium chloride. Two different spinel-type manganese oxide ion sieves were used to investigate the effect of intrinsic properties of ion sieves on Li+ uptake. The effect of ionic strength was also considered for potential recovery of lithium from seawater and brine. The results of Li+ uptake indicated that the sorption isotherms fit the Langmuir model well. The uptake was found to obey a pseudo-second-order rate. The thermodynamic parameters,ΔG0,ΔH0, andΔS0, were calculated, and the results indicated that the Li+ uptake by both ion sieves was endothermic. The influence of ionic strength was mainly found on the kinetics of Li+ uptake. Moreover, the global reaction rate is probably controlled by both intraparticle diffusion and boundary layer diffusion, and the extent of control is greater for intraparticle diffusion than for boundary layer diffusion for Sieve-1; the reverse is for Sieve-2. Finally, Sieve-2, with high H content and small grain size, was proposed as a more suitable absorbent for recovery of lithium from seawater or brine.The Li+ uptake by two different lithium ion sieves was studied in pH 8.0 buffer solutions. Equilibrium were reached within 24 h.
Keywords: Lithium; Uptake; Ion sieve; Equilibrium; Kinetic
Equilibrium and heat of adsorption of diethyl phthalate on heterogeneous adsorbents
by Weiming Zhang; Zhengwen Xu; Bingcai Pan; Changhong Hong; Kun Jia; Peijuan Jiang; Qingjian Zhang; Bingjun Pan (pp. 41-47).
Removal of phthalate esters from water has been of considerable concern recently. In the present study, the adsorptive removal performance of diethyl phthalate (DEP) from water was investigated with the aminated polystyrene resin (NDA-101) and oxidized polystyrene resin (NDA-702). In addition, the commercial homogeneous polystyrene resin (XAD-4) and acrylic ester resin (Amberlite XAD-7) as well as coal-based granular activated carbon (AC-750) were chosen for comparison. The corresponding equilibrium isotherms are well described by the Freundlich equation and the adsorption capacities for DEP followed the order NDA-702 > NDA-101 > AC-750 > XAD-4 > XAD-7. Analysis of adsorption mechanisms suggested that these adsorbents spontaneously adsorb DEP molecules driven mainly by enthalpy change, and the adsorption process was derived by multiple adsorbent–adsorbate interactions such as hydrogen bonding, π– π stacking, and micropore filling. The information related to the adsorbent surface heterogeneity and the adsorbate–adsorbate interaction was obtained by Do's model. All the results indicate that heterogeneous resins NDA-702 and NDA-101 have excellent potential as an adsorption material for the removal of DEP from the contaminated water.The five resins exhibit different surface energy heterogeneities for the adsorption of DEP in aqueous solution and can be quantitatively described by Do's model.
Keywords: Adsorptive removal; DEP; Heterogeneous resin; Mechanism; Adsorbate–adsorbate interaction
Removal of Cd(II) from aqueous solutions using clarified sludge
by T.K. Naiya; A.K. Bhattacharya; S.K. Das (pp. 48-56).
Clarified sludge is a major waste generating during steel making process. In India and in most industrial countries, the use of clarified sludge as a road ballast and land filter has had a very long history. In present study, clarified sludge has been characterized and used for the removal of Cd(II) from aqueous solutions. The effect of pH, adsorbent dosage, adsorbate concentration, contact time and temperature on adsorption process was studied in batch experiments. Kinetics data were best described by pseudo-second order model. The effective diffusion co-efficient of Cd(II) is of the order of 10−11 m2/s. The maximum uptake was 36.23 mg/g. The adsorption data can be well described by Langmuir isotherm. The result of the equilibrium studies showed that the solution pH was the governing factor affecting the adsorption. Mass transfer analysis was also carried out for the adsorption process. The thermodynamic studies indicated that the adsorption was spontaneous and exothermic in nature. The sorption energy calculated from Dubinin–Radushkevich isotherm indicated that the adsorption process is chemical in nature. Desorption as well as the application studies were carried out considering the economic viewpoint of wastewater treatment plant operations.The experimental runs measuring the effect of pH on the batch adsorption of metal solution containing 10 mg/L of Cd(II) at 30 °C.
Keywords: Clarified sludge; Adsorption; Pseudo second order; Langmuir adsorption isotherm; Mass transfer analysis; Desorption
Modeling of the adsorption breakthrough behaviors of Pb2+ in a fixed bed of ETS-10 adsorbent
by Lu Lv; Yan Zhang; Kean Wang; Ajay K. Ray; X.S. Zhao (pp. 57-63).
On the basis of experimental breakthrough curves of lead ion adsorption on ETS-10 particles in a fixed-bed column, we simulated the breakthrough curves using the two-phase homogeneous diffusion model (TPHDM). Three important model parameters, namely the external mass-transfer coefficient (kf), effective intercrystal diffusivity (De), and axial dispersion coefficient (DL), were optimally found to be8.33×10−5 m/s,2.57×10−10 m2/s, and1.93×10−10 m2/s, respectively. A good agreement was observed between the numerical simulation and the experimental results. Sensitivity analysis revealed that the value ofDe dictates the model performance while the magnitude ofkf primarily affects the initial breakthrough point of the breakthrough curves.A two-phase homogeneous diffusion model (TPHDM) has been successfully used to describe and predict breakthrough curves for the fixed-bed sorption of lead ions onto microporous titanosilicate ETS-10 particles. Comparison of model simulation based on the optimized and estimated parametersDL,kf, andDe (C0=5.0 mM,us=2.33×10−4 m/s,dp=3.5×10−4 m).
Keywords: Microporous titanosilicate ETS-10; Two-phase homogeneous diffusion model; Heavy metal lead; Adsorption; Fixed-bed column
Application of water–activated carbon isotherm models to water adsorption isotherms of single-walled carbon nanotubes
by Pyoungchung Kim; Sandeep Agnihotri (pp. 64-73).
The objective of this study is to understand the interactions of water with novel nanocarbons by implementing semiempirical models that were developed to interpret adsorption isotherms of water in common carbonaceous adsorbents. Water adsorption isotherms were gravimetrically determined on several single-walled carbon nanotube (SWNT) and activated carbon samples. Each isotherm was fitted to the Dubinin–Serpinsky (DS) equation, the Dubinin–Astakov equation, the cooperative multimolecular sorption theory, and the Do and Do equations. The applicability of these models was evaluated by high correlation coefficients and the significance of fitting parameters, especially those that delineate the concentration of hydrophilic functional groups, micropore volume, and the size of water clusters. Samples were also characterized by spectroscopic and adsorption techniques, and properties complementary to those quantified by the fitting parameters were extracted from the data collected. The comparison of fitting parameters with sample characterization results was used as the methodology for selecting the most informative and the best-fitting model. We conclude that the Do equation, as modified by Marban et al., is the most suitable semiempirical equation for predicting from experimental isotherms alone the size of molecular clusters that facilitate adsorption in SWNTs, deconvoluting the experimental isotherms into two subisotherms: adsorption onto hydrophilic groups and filling of micropores, and quantifying the concentration of hydrophilic functional groups, as well as determining the micropore volume explored by water. With the exception of the DS equation, the application of other water isotherm models to SWNTs is not computationally tractable. The findings from this research should aid studies of water adsorption in SWNTs by molecular simulation, which remains the most popular tool for understanding the microscopic behavior of water in nanocarbons.
Keywords: Carbon nanotubes; Adsorption; Applications; Activated carbon; Surface science; Water; Clusters; Raman spectroscopy; Molecular simulation
Physicochemical study of amino-functionalized organosilicon cubes intercalated in montmorillonite clay: H-binding and metal uptake
by Georgia Balomenou; Panagiota Stathi; Apostolos Enotiadis; Dimitrios Gournis; Yiannis Deligiannakis (pp. 74-83).
Two organic-modified montmorillonite clays were prepared by embedding organosilanes bearing different chelating amino-functional groups [Apteos] (3-amino-propyltriethoxysilane), and [Edaptmos] (3-(2-aminoethylamino)propyltrimethoxysilane), in the interlayer space of a Zenith montmorillonite. XRD and FTIR spectroscopic data show that the amino organosilanes are intercalated into the interlamelar space forming cube-like structures bearing one polymanino tail at each cube apex. The intercalated cubes cause an increase of the interlayer spacing of the clay sheets by 6.6 Å in [Zenith–Apteos] and by 7.1 Å in [Zenith–Edaptmos]. The H-binding properties of the intercalated polyamino organosilanes were studied by potentiometric titration. The Cu-, Cd-, and Pb-binding capacity of [Zenith–Apteos] and [Zenith–Edaptmos] were evaluated in aqueous solution as a function of the pH. Both [Zenith–Apteos] and [Zenith–Edaptmos] showed improvement vs Zenith for metal binding in the order Cu > Pb > Cd. [Zenith–Edaptmos] showed the most important results vs Zenith. Theoretical analysis of the pH edge, achieved by a surface complexation model, shows that (a) the amino-functionalized cube-like structures constitute high affinity metal-binding sites; and (b) the metal ions are bound in a monodendate mode with the amino group of the cube, thus resulting in a maximization of metal-binding efficiency.Intercalation of amino-functionalized organosilicon cubes in montmorillonite clay enhances metal uptake.
Keywords: Montmorillonite; Zenith; Clay; SCM; Amino; Heavy metal; Cu; Cd; Pb; FITEQL; Organosilicon; Cubanes
Conformation of preadsorbed polyelectrolyte layers on silica studied by secondary adsorption of colloidal silica
by Lars-Erik Enarsson; Lars Wågberg (pp. 84-92).
The conformation of cationic polyelectrolytes preadsorbed on macroscopic silica surfaces was studied before and after addition of colloidal silica (CS) and compared to the fixation capacity of CS. The study included two polyelectrolytes of equal charge density, cationic polyacrylamide and cationic dextran. Adsorbed amounts were determined with stagnation point adsorption reflectometry (SPAR) and quartz crystal microgravimetry (QCM). Unsaturated layers of polyelectrolyte were formed in SPAR by stopping the adsorption at a fractional coverage relative to saturation adsorption. These layers were probed by secondary saturation adsorption of colloidal silica (CS). At low salt concentrations a high fractional coverage of polyelectrolyte was required to attain adsorption of CS, while significant adsorption of CS was found also for low fractional coverages of polyelectrolyte at salt concentrations above 10 mM NaCl. Saturation adsorption of cationic polyacrylamide (CPAM) and cationic dextran (Cdextran) onto the silica surface was found to be similar, while the secondary adsorption of CS was significantly higher onto preadsorbed CPAM compared with Cdextran. The QCM and SPAR data together indicated that the adsorbed layer of Cdextran was thinner than CPAM, and that a loose, expanded layer was formed after adsorption of CS on CPAM but not on Cdextran.
Keywords: Polyelectrolyte adsorption; Conformation; Cationic polyacrylamide; Cationic dextran; Colloidal silica; Nanoparticles; Reflectometry; Quartz crystal microbalance
Humic acid sorption onto a quartz sand surface: A kinetic study and insight into fractionation
by Aurélien Pitois; Liam G. Abrahamsen; Peter I. Ivanov; Nick D. Bryan (pp. 93-100).
A kinetic study of Aldrich humic acid sorption onto a quartz sand surface has revealed an initial rapid uptake of humic acid molecules followed by a much slower sorption. The humic acid molecular weight and chemical fractionation resulting from adsorption onto the simple quartz sand surface were investigated for the two kinetic steps by coupled asymmetric flow-field flow fractionation-UV/visible absorption spectrophotometry. The molecular weight distribution of residual humic acid in solution after adsorption deviated from the original molecular weight distribution, showing preferential adsorption of certain molecular weight components. This fractionation is different after the two kinetic steps. Humic acid molecules characterised by a molecular weight below 4800 Da and with a weight-average molecular weight ( Mw) of 1450 Da were adsorbed after the fast kinetic step, whereas humic acid molecules in the molecular weight range 1400–9200 Da and of Mw 3700 Da were adsorbed after the slower uptake. Therefore, the adsorption of low molecular weight humic components takes place initially, and is then followed by the adsorption of higher molecular weight components. Chemical adsorptive fractionation, investigated by studying the 253 nm/203 nm absorbance ratio over time, shows that aromatic components are preferentially adsorbed during the fast kinetic step. The fractionation pattern may be explained by the physicochemical characteristics of the Aldrich humic acid and the underlying sorption processes. The trend for the sorption kinetics of europium onto the quartz sand surface in the presence of humic acid is similar to that of the humic acid itself.The humic acid molecular weight and chemical fractionation resulting from adsorption onto the simple quartz sand surface were investigated by coupled asymmetric flow-field flow fractionation-UV/visible absorption spectrophotometry.
Keywords: Flow-field flow fractionation; Humic acid; Fractionation; Mineral surface; Quartz sand; Kinetics
Evolution of the surface polar character of pyrogenic silicas, with their grafting ratios by dimethylchlorosilane, studied by microcalorimetry
by Jean-Baptiste Donnet; Hassan Ridaoui; Henri Balard; Herbert Barthel; Torsten Gottschalk-Gaudig (pp. 101-106).
The interactions of water, hexamethyldisiloxane, and dodecane with pyrogenic silica samples, modified by a controlled partial silylation with dimethyldichlorosilane, were studied by microcalorimetry and wettability measurements. The samples, having a coverage ratio lower than dimethylsilyl (DMS) monolayer capacity (∼2.6 DMS/nm2), show a regular and linear decrease of their heat of immersion into water with the coverage ratio and correlate with the increase of residual silanol groups. Two critical coverage ratios were evidenced at about 25 and 50% of the DMS monolayer capacity, the grafted silica remaining hydrophilic, below 25% being strongly hydrophobic beyond. The heat of immersion into hexamethyldisiloxane decreases until 50% of the DMS monolayer whereas that of dodecane remains independent of the grafting ratio. This study demonstrates that the water/residual free silica surface plays the main role in the stabilization of the W/O Pickering's emulsions.Study of the influence of surface coverage ratio of fumed silica surfaces by dimethylsilyl grafts on their heat of immersion into water and wettability by water.
Keywords: Microcalorimetry; Wettability; Silica; Dimethyldichlorosilane; Water
Viscoelastic study of the adsorption of bovine serum albumin on gold and its dependence on pH
by V.B.C. Figueira; J.P. Jones (pp. 107-113).
Using a quartz crystal resonator system operating at 5 MHz the shear wave propagating properties of bovine serum albumin (BSA) have been monitored as it is adsorbed on a gold surface from a phosphate buffered saline (PBS) solution. Employing a 2-layer model for the combined BSA layer and PBS solution, the viscoelasticity of the BSA layer may be determined in real time as the adsorption on gold proceeds. The viscoelasticity is found to depend on the pH of the PBS solution and changes gradually over long times. It is suggested that at the low frequency of the measurement, large-scale molecular motions are being monitored which are a consequence of the structural changes in the protein molecules undergoing adsorption. Such low-frequency molecular motions are difficult to examine by any other technique. The results and their interpretation in viscoelastic terms demonstrate the considerable potential of the quartz crystal resonator system for assessing the stability of proteins on surfaces and their suitability as coatings for prosthetic materials.Adsorbed serum albumin molecules form a monolayer (a) which is assumed to be acoustically uniform (b). The viscosity (●) and elasticity (□) of the layer depend on the pH at formation (c).
Keywords: BSA; pH; QCM; Protein; Adsorption; Quartz crystal; Conformation
Structure of adsorbed layers of nitrophenoxy-tailed quaternary ammonium surfactants at the air/water interface studied by neutron reflection
by Xu Huang; Yilin Wang; Chuchuan Dong; Hsin-Hui Shen; R.K. Thomas (pp. 114-121).
The adsorbed layers of N, N, N-trimethyl-10-(4-nitrophenoxy)decylammonium bromide (ΦC10TAB) and N, N,N′,N′-tetramethyl- N,N′-bis[10-(4-nitrophenoxy)decyl]-1,6-hexanediammonium dibromide [(ΦC10)2C6] at the air/water interface have been studied by neutron reflection. The coverage of the surfactants was obtained over the concentration range from critical micelle concentration (CMC) to CMC/100. The area per ΦC10TAB molecule changes from50±3 to390±60 Å2 over this concentration range and the area per (ΦC10)2C6 molecule changes from139±3 to288±10 Å2. The overall thicknesses (single uniform layer) of the surfactant layers at CMC are about 19 and 16 Å for ΦC10TAB and (ΦC10)2C6 respectively. The distributions of the C10 chains show that the chains of both surfactants are tilted away from surface normal, with the tilt increasing in the outer part of the layer. The distribution of C10 chains in (ΦC10)2C6 is narrower than that in ΦC10TAB, indicating that the alkyl chains of (ΦC10)2C6 are more tilted. For both surfactants, the broad nitrophenoxy distribution may indicate significant positional disorder of the nitrophenoxy groups along the surface normal direction and their intermixing with alkyl chains in the adsorbed layer.The adsorption of N, N, N-trimethyl-10-(4-nitrophenoxy)decylammonium bromide (ΦC10TAB) and N, N,N′,N′-tetramethyl- N,N′-bis[10-(4-nitrophenoxy)decyl]-1,6-hexanediammonium dibromide [(ΦC10)2C6] at the air/water interface indicates significant tilt of the hydrophobic chains from the surface normal and substantial intermixing of alkyl chains with nitrophenoxy groups.
Keywords: Neutron reflection; Surface coverage; Adsorbed layer structure
Hysteresis and strain hardening in the creep response of a polyaniline ER fluid
by Piyanoot Hiamtup; Anuvat Sirivat; Alexander M. Jamieson (pp. 122-129).
The electrorheological creep response of PANI/silicone oil suspensions near the yield point is investigated using parallel plate rheometry. Controlled-stress, thixotropic loop experiments exhibit a pronounced hysteresis, from which we determined the static yield stress (σy(static)), as the stress where onset of flow occurs on the upward part of the loop, and a dynamic yield stress (σy(dynamic)), defined as the stress at which flow ceases on the downward part of the loop. The magnitude of the hysteresis, as characterized by the area under the loop, increases substantially with applied field strength and particle concentration, but decreases with increase of temperature. Consistent with literature data, the creep compliance shows an evolution from viscoelastic to viscoplastic to viscous flow behavior as the applied stress increases through the yield point. In the viscoplastic regime, the apparent equilibrium compliance,Jeapp, shows a discrete pre-yield transition to higher values, indicating a seemingly-enhanced ductility as the applied stress nears the yield point. Measurement of the static yield stress following these creep experiments suggests that the origin of this transition is a pronounced strain-hardening effect. We conclude that strain-hardening contributes to the hysteresis observed in the thixotropic loop test.The dependence of equilibrium creep compliance on the applied stress of polyaniline-based electrorheological fluid is displayed here at various temperatures. We propose that the creep compliance obeys the following relation:Jeapp=Je,oappexp(ασd2/kBT), where σ is the applied stress, d is the polyaniline particle size, and α is a constant.
Keywords: Electrorheology; Creep; Conductive polymer; Polyaniline
Transient interfacial tension of partially miscible polymers
by C. Tufano; G.W.M. Peters; P.D. Anderson; H.E.H. Meijer (pp. 130-140).
The interfacial tension of three different binary polymer blends has been measured as function of time by means of a pendent drop apparatus, at temperatures ranging from24°C to80°C. Three grades of polybutene (PB), differing in average molecular weight and polydispersity, are used as dispersed phase, the continuous phase is kept polydimethylsiloxane (PDMS), ensuring different asymmetry in molecular weight across the interface. The interfacial tension changes with time and, therefore, this polymer blends can not be considered fully immiscible. Changes in interfacial tension are attributed to the migration of low-molecular weight components from the source phase into the interphase and, from there, into the receiving phase. In the early stages of the experiments, just after the contact between the two phases has been established, the formation of an interphase occurs and the interfacial tension decreases with time. As time proceeds, the migration process slows down given the decrease in driving force which is the concentration gradient and, at the same time, molecules accumulated in the interphase start to migrate into the “infinite” matrix phase. A quasi-stationary state is found before depletion of the low-molecular weight fraction in the drop occurs and causes the interfacial tensionσ(t) to increase. The time required to reach the final stationary value,σstat, increases with molecular weight and is a function of temperature. Higher polydispersity leads to lowerσstat and a weaker dependence ofσstat on temperature is found. A model coupling the diffusion equation in the different regimes is applied in order to interpret the experimental results. Numerical solutions of the diffusion equation are proposed in the cases of a constant and a changing interphase thickness. In the latter case, the interphase is defined by tracking with time a fixed limiting concentration in the transient concentration profiles and the variations found inσ(t) are attributed to the changes in the interphase thickness. A discrete version of this continuous model is proposed and scaling arguments are reported in order to compare the results obtained with the predictions of the continuous model. The kinetic model as proposed by Shi et al. [T. Shi, V.E. Ziegler, I.C. Welge, L. An, B.A. Wolf, Macromolecules 37 (2007) 1591–1599] appears as a special case of the discrete model, when depletion is not taken into account. Using the models, time scales for the diffusion process can be derived, which fit the experimental results quite well.The transient interfacial tension for different temperature for a polybutene/polydimethylsiloxane (PB/PDMS) blend system caused by the migration of low-molecular weight components from the source into the receiving phase.
Keywords: Partial miscibility; Interfacial tension; Interphase
Polyether nanoparticles from covalently crosslinked copolymer micelles
by Maria Jamróz-Piegza; Wojciech Wałach; Andrzej Dworak; Barbara Trzebicka (pp. 141-148).
Double hydrophilic block copolymers poly(ethylene oxide)- b-polyglycidol were synthesized using living anionic polymerization. The polyglycidol blocks were made hydrophobic by the esterification of a part of hydroxyl groups with cinnamic acid, thus simultaneously attaching UV-sensitive double bonds to the polymer backbone. The block copolymers were found to spontaneously associate in aqueous solution forming well-defined micelles, where the corona of the micelles was formed of EO units and the cores consisted of hydrophobic glycidyl cinnanamate units. The critical micelle concentration was determined by light-scattering measurements and fluorescence spectroscopy. Stabilization of micelles was obtained by covalently crosslinking the cores of polyether micelles formed from amphiphilic block copolymers of the type poly(ethylene oxide)- b-poly(glycidol- co-glycidyl cinnamate) (denoted EO113- b-(Gl33- co-GlCA33− x)). To obtain stable nanoparticles double bonds of cinnamate units contained in core were crosslinked under UV irradiation. The kinetics of the stabilization process was investigated using SEC-MALLS and UV spectroscopy. The parameters of the micelles and nanogels were calculated from the light-scattering data.Stable nanoparticles were obtained by UV-induced dimerization of double bonds in poly(ethylene oxide)- b-poly(glycidol- co-glycidyl cinnamate) micelles. These polymeric nanoparticles may find application as novel carriers and agents for controlled release.
Keywords: Block copolymer; Self-assembly; Polymeric micelles; Micelle crosslinking; Nanogel
Facile preparation of superhydrophobic coatings by sol–gel processes
by Rosa Taurino; Elena Fabbri; Massimo Messori; Francesco Pilati; Doris Pospiech; Alla Synytska (pp. 149-156).
Different organic/inorganic compositions and deposition methods were used to prepare superhydrophobic surfaces using metal alkoxides and the sol–gel process. Both surface roughness and composition had to be adjusted in order to obtain very high contact angles and low contact angle hysteresis as a necessary requirement for superhydrophobicity. Multilayer samples with a fluorinated organic–inorganic top layer showed water contact angles of about 157° with low hysteresis (2°). Water drops rolled easily off their surface at a tilt angle as low as 4°.Superhydrophobic surfaces were prepared by a sol–gel process. Multilayer samples with a fluorinated organic–inorganic top layer showed water contact angles of 157° with low hysteresis (2°).
Keywords: Sol–gel process; Superhydrophobic surfaces; Ultrahydrophobic surfaces; Self-cleaning
Quartz crystal microbalance study of protein adsorption kinetics on poly(2-hydroxyethyl methacrylate)
by J.H. Teichroeb; J.A. Forrest; L.W. Jones; J. Chan; K. Dalton (pp. 157-164).
The interaction of macromolecules with artificial biomaterials may lead to potentially serious complications upon implantation into a biological environment. The interaction of one of the most widely used biomaterials, polyHEMA, with lysozyme, bovine serum albumin (BSA), and lactoferrin was investigated using quartz crystal microbalance (QCM). The concentration dependence of adsorption was measured for the aforementioned proteins individually as well as for lysozyme-BSA, and lysozyme–lactoferrin combinations. An extension of Voinova's viscoelastic model to n layers was used to create thickness–time graphs for adsorption. For each of lactoferrin and lysozyme, two distinctly different timescales of adsorption could be differentiated. However, the mechanisms of adsorption appeared to differ between the two. Negative dissipation shifts were measured for low concentrations of lysozyme, trending to positive dissipation at higher concentrations. This suggested that lysozyme was adsorbed initially into the matrix, stiffening the hydrogel, and later onto the surface of polyHEMA. Additionally, trials with commercial no-rub cleaning solutions indicated little added effectiveness over buffer solutions. Mixtures of proteins showed behaviour which differed in some cases from the simple combination of single protein adsorption experiments.
Keywords: Protein adsorption; PolyHEMA; Hydrogel; Ocular biomaterials
Effect of pH on deagglomeration and rheology/morphology of aqueous suspensions of goethite nanopowder
by Ping Ding; Andrzej W. Pacek (pp. 165-172).
The kinetics of deagglomeration in diluted suspensions of goethite nanopowder, as well as the rheology and morphology of the resulting suspensions, strongly depends on pH. At pH 3, nanopowder can be dispersed as separate nanoparticles, and the resulting suspension is Newtonian, with the viscosity only marginally higher than the viscosity of water. At pH between 5 and 12, nanoparticles tend to reaggregate and form weak aggregates/flocs. Morphology changes from a Newtonian suspension of primary nanoparticles to a non-Newtonian, shear-thinning suspension of large, porous, interconnected flocs with the yield stress reaching a maximum at an isoelectric point. The effect of pH on morphology and rheology is reversible, and as pH is reduced to 3, the suspension becomes Newtonian, with viscosity marginally higher than the viscosity of water. The rheological models based on DLVO theory do not allow prediction of the effect of pH on viscosity and yield stress, but the flow curves of goethite suspensions can be described by a fractal model with five adjustable parameters.At pH 3, dispersion of nanoparticles is Newtonian with the viscosity only marginally higher than the viscosity of water. At higher pH, large, porous aggregates form and dispersion becomes non-Newtonian. The effect of pH is reversible.
Keywords: Goethite nanoparticles; Aqueous suspensions; pH; Morphology; Rheology
Intrinsically stable dispersions of silicon nanoparticles
by A. Reindl; W. Peukert (pp. 173-178).
Stable suspensions of silicon nanoparticles (SiNP) were fabricated by dispersion in 1-butanol as well as ethanol without the application of an additive. In order to achieve an in-depth insight into the stabilizing mechanism, the particle–particle interactions need to be considered. In this respect the total interaction energy of the silicon nanoparticles in 1-butanol and ethanol was calculated for three model systems according to the DLVO theory: (1) two solid silicon spheres, (2) two spheres with a silicon core and an amorphous silicon dioxide shell, and (3) two spheres with a silicon core, an amorphous silicon dioxide shell and a monolayer of adsorbed solvent molecules. The results of the calculations are evaluated and discussed with regard to experimental data obtained by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), high resolution transmission electron microscopy (HRTEM), and zeta potential measurements.Schematic representation of the different model systems (left) used for calculating the total interaction energy of silicon nanoparticles dispersed in ethanol/1-butanol (right).
Keywords: Silicon nanoparticles; Stabilizing; Dispersing; DLVO theory; Core–shell
Microemulsion approach to neodymium, europium, and ytterbium oxide/hydroxide colloids—Effects of precursors and preparation parameters on particle size and crystallinity
by Christoph Rill; Matthias Bauer; Helmut Bertagnolli; Guido Kickelbick (pp. 179-186).
Colloids based on lanthanides or their oxides have a great potential in the areas of optical and magnetic materials. In this study the confined space of reverse micellar systems formed by water in cyclohexane was used to precipitate particles based on neodymium, europium, and ytterbium. The morphology and structural properties of the prepared colloids were determined by transmission electron microscopy, IR spectroscopy, and X-ray diffraction and absorption measurements. The size of the obtained systems as determined by dynamic light scattering ranged from a few nanometers to several hundreds of nanometers in diameter, depending on the reaction conditions. The employed surfactant was found to have a major influence on the particle size and morphology. In contrast to the ionic surfactants sodium dodecyl sulfate and cetyltrimethylammonium bromide, the nonionic surfactant Triton X-100 generally delivered very small and unagglomerated particles. The precursor counterion had a similar effect, depending on its ability to coordinate to the particle surface, and prevented particle growth and agglomeration. The influence of further parameters such as the pH of the aqueous starting solutions, the mixing methodology, and the preparation temperature was also investigated. Applying increased temperatures the particles exhibited a higher crystallinity, and at the same time the particle size was drastically increased.Various lanthanide salts were used as precursors for the precipitation of colloids in w/o microemulsions. A strong influence of the type of surfactant and counterion on the final particle size and morphology was observed.
Keywords: Colloids; Nanoparticles; Water-in-oil microemulsion; Lanthanide oxide; Dynamic light scattering
Insights into colloid-mediated trace element release at the soil/water interface
by Mathieu Pédrot; Aline Dia; Mélanie Davranche; Martine Bouhnik-Le Coz; Odile Henin; Gérard Gruau (pp. 187-197).
Organic or inorganic colloids play a major role in the mobilization of trace elements in soils and waters. Environmental physicochemical parameters (pH, redox potential, temperature, pressure, ionic strength, etc.) are the controlling factors of the colloidal mobilization. This study was dedicated to follow the colloid-mediated mobilization of trace elements through time at the soil/water interface by means of an experimental approach. Soil column experiments were carried out using percolating synthetic solutions. The percolated solutions were ultrafiltrated with various decreasing cutoff thresholds to separate the different colloidal phases in which the dissolved organic carbon and trace element concentrations were measured. The major results which stem from this study are the following: (i) The data can be divided into different groups of organic compounds (microbial metabolites, fulvic acids, humic acids) with regard to their respective aromaticity and molecular weight. (ii) Three groups of elements can be distinguished based on their relationships with the colloidal phases: the first one corresponds to the so-called “truly” dissolved group (Li, B, K, Na, Rb, Si, Mg, Sr, Ca, Mn, Ba, and V). The second one can be considered as an intermediate group (Cu, Cd, Co, and Ni), while the third group gathers Al, Cr, U, Mo, Pb, Ti, Th, Fe, and rare earth elements (REE) carried by the organic colloidal pool. (iii) The data demonstrate that the fulvic acids seem to be a major organic carrier phase for trace elements such as Cu, Cd, Co, and Ni. By contrast, the trace elements belonging to the so-called colloidal pool were mostly mobilized by humic acids containing iron nanoparticles. Lead, Ti, and U were mobilized by iron nanoparticles bound to these humic acids. Thus, humic substances allowed directly or indirectly a colloidal transport of many insoluble trace elements either by binding trace elements or by stabilizing a ferric carrier phase. (iv) Finally, the results demonstrated also that REE were mostly mobilized by humic substances. The REE normalized patterns showed a middle REE downward concavity. Therefore, as previously shown elsewhere humic substances are a major control of REE speciation and REE fractionation patterns as well since the humic substance/metal ratio was the key parameter controlling the REE pattern shape.The elemental distribution in the colloidal phase higher than 2 kDa is represented at the end of the column-mediated soil leaching experiment. Three different groups can be identified.
Keywords: Colloids; Trace elements; Humic substances; Rare earth elements; Leaching; Ultrafiltration
An excellent single-layered photoreceptor composed of oxotitanium phthalocyanine nanoparticles and an insulating resin
by Wei Chao; Xinran Zhang; Chao Xiao; Dejian Liang; Yuan Wang (pp. 198-202).
Photoconductive oxotitanium phthalocyanine (TiOPc) nanoparticles with an average diameter of 3.6 nm were successfully prepared. These nanoparticles could be well dispersed in organic solvents such as 1,2-dichloroethane to form a stable organic sol of solvent-stabilized TiOPc nanoparticles. An obvious size effect of TiOPc semiconductor was revealed by the UV–vis absorption spectroscopy measurements. Single-layered photoreceptors were prepared by coating colloidal solutions containing the C2H4Cl2-stabilized TiOPc nanoparticles and a polycarbonate (PC) resin onto aluminum plates. Optimum xerographic properties of the present photoreceptors were obtained on a photoreceptor containing 20 wt% of the TiOPc nanoparticles, which exhibited a photoconductive sensitivity (E1/2) of 0.54 μJ/cm2 and could be positively charged to 596 V.Photoconductive TiOPc nanoparticles with an average diameter of 3.6 nm were prepared and dispersed in polycarbonate films to fabricate single-layered photoreceptors with excellent xerographic properties in the positively charged model.
Keywords: Oxotitanium phthalocyanine; Nanoparticle; Photoconductivity; Organic photoreceptor
Temperature-programmed reduction study on carbon-supported platinum–gold alloy catalysts
by Kuan-Wen Wang; Chuin-Tih Yeh (pp. 203-206).
Alloy catalysts of Pt–Au/C with different Pt/Au ratios were prepared by the precipitation–deposition of metal chlorides and reduced by H2 at 470 K. The surface composition of alloy crystallites deposited on the prepared catalysts was characterized by a technique of temperature-programmed reduction (TPR). In the characterization, O2 was chemisorbed on the reduced catalysts and the chemisorbed O2 was reduced by TPR. A low-temperature routine (LT) in the temperature range between 120 and 430 K was used for the TPR characterization. Monometallic catalysts of Au/C and Pt/C showed a reduction peak in the LT-TPR at reduction temperature(Tr)=145 and 240 K, respectively.Tr from alloyed catalysts fell in the range and increased monotonously with their Pt/Au ratios. Interior Pt atoms in deposited alloy particles tended to segregate toward their surface during oxidation treatment at elevated temperatures.Peak temperatures in the temperature-programmed reduction of Pt xAu y/C varied with the surface composition of the alloy catalysts. Interior Pt atoms tended to segregate toward their surface during oxidation at 570 K.
Keywords: Platinum; Gold; Alloy; Temperature-programmed reduction; Redox treatment
High surface area nanoporous amorphous silica prepared by dodecanol assisted silica formate sol–gel approach
by Puyam S. Singh (pp. 207-214).
A simple polycondensation of monocarboxylic acids with silicon alkoxides led to transparent silica gels mainly comprised of silicate species of closed structures. This ‘sol–gel formic acid’ approach was modified by trapping an organic template (dodecanol) inside the silicate network during the polymerization process. Using this templating approach, porous silica of extremely high surface area, was produced in contrast to non-porous silica obtained by non-templating approach. TheSBET surface areas of the template assisted samples resulting from the entire pores were found to be up to 725 m2/g. The total pore volumes of the samples were in the range of 0.40–0.74 cc/g in which micropore volumes were about 0.15–0.25 cc/g; the porosity depending on the reactants molar ratios of dodecanol, silicon alkoxide and formic acid.Nanoporous silica withSBET surface area up to 725 m2/g using template assisted silica-formate approach is synthesized.
Keywords: Porous amorphous silica; Sol–gel; Organic templated formic acid approach
Permselectivity and microstructure of anion exchange membranes
by Xuan Tuan Le (pp. 215-222).
The water content, the ion exchange capacity, the transport number of counter-ion of the AMV and AMX anion exchange membranes were determined. The two-phase model (gel phase and interstitial phase) of structure microheterogeneity was validated by means of conductivity measurements. The chronopotentiometric results allowed us to affirm the overall surface homogeneity of the membranes. According to the two-phase model, the influence of the gel phase and the interstitial phase on the membrane permselectivity was discussed in detail. Majorities of co-ions exist in the interstitial phase, thus they have no influence on the transport of counter-ions in the gel phase. The determination of the KCl amount sorbed in the interstitial phase confirmed the existence of partition equilibrium between the interstitial phase and the external solution. Such partition equilibrium can be considered within the microheterogeneous model in order to represent the internal structure of the electromembranes.On the microstructural scale, the AMV and AMX homogeneous anion exchange membranes are described as two-phase systems: gel phase and interstitial phase with the volume fractionsf1 andf2, respectively. Increase in the volume of interstitial phase leads to a higher amount of KCl electrolyte found in the interstitial solution. Equilibrium partition between the external solution and the interstitial solution can be considered within the microheterogeneous model in order to represent the internal structure of the electro-membranes.
Keywords: Permselectivity; Electrolyte sorption; Donnan exclusion; Membrane conductivity; Two-phase model; Surface homogeneity
A comparison of spreading behaviors of Silwet L-77 on dry and wet lotus leaves
by Xiaolan Tang; Jinfeng Dong; Xuefeng Li (pp. 223-227).
Trisiloxane surfactants are widely used in pesticide applications as adjuvants to promote spray drop spreading on leaves. The efficacy of the spray is related to the wetting of plant surfaces. The surface (composite or wetted) formed by the liquid drop instantly contacting with the substrate is vital to the spreading. In this paper the spreading behaviors of surfactant solutions on dry and previous wet lotus leaf surfaces were studied. It was found that the drop spreading on the wet surface was obviously easier than on the dry surface, which was rational to the existence of water in the grooves of the wet surface. The spreading of Silwet L-77 aqueous drops on the wet lotus leaf surface is mainly controlled by the surface tension gradient along the air–liquid interface.Water modified wetting behavior on lotus leaf. It is clear that entrapped water has a significant effect on lotus wetting behavior.
Keywords: Lotus leaf; Silwet L-77; Spreading; Contact angle; Drop deposition
Hydrophobic monolayer preparation by Langmuir–Blodgett and chemical adsorption techniques
by Kristofer Paso; Ragne M.L. Helberg; Steinar Raaen; Johan Sjöblom (pp. 228-235).
Alkylsiloxane and perfluoroalkylsiloxane monolayers are prepared on siliceous surfaces using the techniques of Langmuir–Blodgett deposition and solid–liquid chemical adsorption. Acid-catalyzed hydrolysis and polycondensation reactions provide two-dimensional siloxane networks at the liquid–vapor interface, which can be compressed to mean molecular areas of ∼22 and ∼32 Å2 for pendent hydrocarbon and fluorocarbon chains, respectively. Subsequent Langmuir–Blodgett transfer onto glass substrates at moderate surface pressures leads to compact monolayers for single-component precursors, while mixed alkyl- and perfluoroalkylsilanes produce nonhomogeneous films characterized by transfer ratios greater than unity. As an alternate monolayer preparation technique, silane polymerization was performed directly on siliceous surfaces via a chemical adsorption mechanism. XPS analysis of a chemically adsorbed 1H,1H,2H,2H-perfluorodecylsiloxane film confirms a single adsorbed monolayer thickness in which the pendent fluoroalkyl chains align nonperpendicularly with respect to the surface. The surface free energy was determined to be 11.4 dyn cm−1 based on static contact angle measurements. AFM imaging shows the presence of surface defects due to oligomer deposition during the drying process. The use of solubilized trichloro-based silane coupling agents under anhydrous conditions is shown to produce surfaces with a minimal number of surface defects. The presence of undissolved silane material in the bulk solution significantly increases the number of surface defects.
Keywords: Fluorinated monolayer; Hydrolysis and condensation; Low-energy surface; Alkylsiloxane; Fluoroalkylsiloxane
Defining the different phases of premicellar aggregation using the photophysical changes of a surface-probing compound
by S. Syed Jaffer; M. Sowmiya; Subit K. Saha; Pradipta Purkayastha (pp. 236-242).
Photophysical changes of a cylindrical compound undergoing twisted intramolecular charge transfer may be used as a surface probe to study the different phases of premicellar aggregate formation. The probe molecule, trans-2-[4-(dimethylamino)styryl] benzothiazole (DMASBT), attaches itself to the premicellar and the micellar aggregates of cationic, anionic, and neutral surfactants in different orientations because of its dipolar nature in the excited state. The micelle formation is preceded by a few typical rearrangements of the surfactant molecules. These events need proper inspection that can only be done by compounds that sense environmental changes by residing in the vicinity of the surface of those aggregates. Steady-state and time-resolved fluorescence spectroscopy coupled with steady-state fluorescence anisotropy measurements serve as a very useful tool to monitor premicellar aggregate formation. The dipolar interaction of DMASBT with the surface of the aggregate and its extraordinary capability to sense the polarity of the environment make it a very efficient molecule to use for the purpose.Photophysical changes of trans-2-[4-(dimethylamino)styryl] benzothiazole, undergoing twisted intramolecular charge transfer, can be used as a surface probe to study the different phases of the premicellar aggregate formation.
Keywords: DMASBT; Photophysics; Premicellar aggregates; Fluorescence; Anisotropy
Solubilization of triglycerides in liquid crystals of nonionic surfactant
by Mohammad Mydul Alam; Dharmesh Varade; Kenji Aramaki (pp. 243-249).
The solubilization of triglycerides [1,2,3-tributanoylglycerol (TBG) and 1,2,3-trihexanoylglycerol (THG)] in water/octa(oxyethylene) dodecyl ether (C12EO8) systems has been investigated. Oil-induced changes in the structure of liquid crystals in water/C12EO8 system have been studied by optical observation and small-angle X-ray scattering (SAXS) measurements. In the water/C12EO8/oil systems, solubilization of THG and TBG induces a transition between H1 (hexagonal) and L α (lamellar) liquid crystals at high C12EO8 concentrations, whereas at low surfactant concentrations a H1–I1 (discontinuous micellar cubic phase) transition occurs. This anomalous behavior is attributed to the partitioning of solubilized oil in the micelles. At low surfactant concentrations THG is mainly solubilized into the hydrophobic cores of the surfactant micelles, indicating high swelling or low penetration tendency, resulting in a steep increase in the radius of the aggregates (rH), thereby inducing a rod–sphere transition. At high surfactant concentrations, THG is not mainly solubilized into the core but distributed between the palisade layer and the core of the aggregates. The TBG is considerably solubilized into the surfactant palisade layer, indicating a high penetration tendency, resulting in an increase in the effective cross-sectional area per surfactant molecule,as. The thermal stability of the I1 phase increases with the solubilization of THG into the aggregate cores. The percentage deviation of the experimental interlayer spacings (Pd) from complete swelling was also evaluated for different triglycerides in the H1 and L α phases or different surfactant concentrations. It is found that the penetration tendency of triglycerides could be used as a tuning parameter for I1 phase formation depending on the surfactant concentration and the molecular weight of the oil.The partitioning of triglycerides (THG) in micelles induces a hexagonal (H1)–cubic (I1) transition at low surfactant concentration but a hexagonal (H1)–lamellar (L α) transition at high surfactant concentration.
Keywords: Phase behavior; Triglyceride; Solubilization; Penetration; Swelling
Structure of biodiesel based bicontinuous microemulsions for environmentally compatible decontamination: A small angle neutron scattering and freeze fracture electron microscopy study
by S. Wellert; M. Karg; H. Imhof; A. Steppin; H.-J. Altmann; M. Dolle; A. Richardt; B. Tiersch; J. Koetz; A. Lapp; T. Hellweg (pp. 250-258).
Most toxic industrial chemicals and chemical warfare agents are hydrophobic and can only be solubilized in organic solvents. However, most reagents employed for the degradation of these toxic compounds can only be dissolved in water. Hence, microemulsions are auspicious media for the decontamination of a variety of chemical warfare agents and pesticides. They allow for the solubilization of both the lipophilic toxics and the hydrophilic reagent. Alkyl oligoglucosides and plant derived solvents like rapeseed methyl ester enable the formulation of environmentally compatible bicontinuous microemulsions. In the present article the phase behavior of such a microemulsion is studied and the bicontinuous phase is identified. Small angle neutron scattering (SANS) and freeze fracture electron microscopy (FFEM) measurements are used to characterize the structure of the bicontinuous phase and allow for an estimation of the total internal interface. Moreover, also the influence of the co-surfactant (1-pentanol) on the structural parameters of the bicontinuous phase is studied with SANS.Non-etched freeze fracture EM micrograph of a bicontinuous biodiesel/sugar surfactant microemulsion containing approximately equal amounts of oil and water.
Keywords: Decontamination; SANS; Microemulsion; Sugar surfactant; Phase behavior
Hydrophilic–lipophilic deviation (HLD) method for characterizing conventional and extended surfactants
by A. Witthayapanyanon; J.H. Harwell; D.A. Sabatini (pp. 259-266).
An accurate determination of the hydrophilic–lipophilic nature of surfactants plays an essential role in guiding the formulation of microemulsion with the goal of achieving low interfacial tension (IFT) and high solubilization. While several empirical models have been proposed as simple tools for predicting surfactant characteristics and microemulsion conditions, only a few of these models are fundamentally based yet convenient to use. In this work, the hydrophilic–lipophilic deviation (HLD) approach was used with mixed surfactant systems to determine the surfactant characteristic ( σ) and theσK parameter of conventional and extended surfactants. To our knowledge, this is the first time that the HLD index has been used to represent the hydrophilic–lipophilic behavior of extended surfactants. It was observed that inserting PO and/or EO groups in extended surfactants play a key role in altering σ values andσK values. Finally, the σ parameters found in this work were combined with the HLD equation and used to demonstrate its practical utility for guiding the optimum formulation (in this case, optimum salinity) for a microemulsion system.The hydrophilic–lipophilic deviation (HLD) approach using mixed surfactant systems was used in combination with microemulsion phase study to determine the hydrophilic–lipophilic characteristics of conventional and extended surfactants.
Keywords: Microemulsions; Hydrophilic–lipophilic balance; Extended surfactants; Hydrophilic–lipophilic deviation (HLD)
Effect of alcohol–water exchange and surface scanning on nanobubbles and the attraction between hydrophobic surfaces
by Marc A. Hampton; Bogdan C. Donose; Anh V. Nguyen (pp. 267-274).
Atomic force microscopy (AFM) was used to examine how different alcohols affect the hydrophobic attraction between a hydrophobic silica colloidal probe and a hydrophobic silica wafer. The experiments were performed in water and in water after rinsing alcohol (methanol, ethanol, or 1-propanol) throughout the AFM system. In all three cases the range of the attractive force increased after alcohol–water exchange, with 1-propanol showing the largest increase in range followed by ethanol and methanol. Additionally, experiments were performed before and after scanning the flat substrate with the colloidal probe. The range of the attractive force substantially increased with increasing scanning area. The attraction was explained by nanobubble bridging with a capillary force model with constant bridge volume proposed. The bridge volume (constant during each of the force curve measurements), contact angle and rupture distance were also determined for different scan sizes. The correlation between the rupture distance and bridge volume agreed with the available prediction.AFM tapping mode height image (5×5μm with 20 nm height scale) of octanol esterified silica in water after propanol–water exchange.
Keywords: Hydrophobic force; Alcohol; Nanobubble; Atomic force microscopy
Study of the influence of location of substitutions on the surface energy of dioctahedral smectites
by J.M. Douillard; S. Lantenois; B. Prelot; J. Zajac; M. Henry (pp. 275-281).
The surface energy of some clays belonging to the smectite group has been calculated starting from crystal structures and combining a partial charge model with the computation of the lattice energy. The dioctahedral smectites studied here include montmorillonite; beidellites; and nontronite. One of the differences between these clays is the location of the substitution in the octahedral sheet or in the tetrahedral one. Another is the possibility of vacancies in cis- or trans-octahedral positions. These locations and vacancies have an effect on the distortion of the crystal framework and therefore on the surface energy. Calculated surface energies of the solid samples increase in the order beidellites > montmorillonite > nontronite. The bond energy between the interlayer cation and the layer appears to follow the same order and to depend both on the nature of the most electropositive elements of the layer and on their location. The trends obtained provide elements for an analysis of data related to interlayer enlargement.In dioctahedral smectites, substitutions can occur in tetrahedral or octahedral positions and in cis- or trans-octahedral positions. A set of four idealized smectites has been built in order to represent the whole set of natural samples. The calculation of solid surface energy has been performed following a calculation, which uses the equalization of electronegativity method (partial charge calculation) and Ewald summation. The order of surface energy is as follows: cis-beidellite > cis– trans-beidellite > montmorillonite > nontronite. Two main reasons appear; the octahedral substitution increases the surface energy. Cis-substitutions have also an effect. However, Fe atoms decrease the surface energy.
Keywords: Solid surface energy; Montmorillonite; Beidellite; Nontronite; Dioctahedral smectite; Interlayer cation; Electronegativity; Lattice energy
Binding energies for alkane molecules on a carbon surface from gas–solid chromatography and molecular mechanics
by Thomas R. Rybolt; Christina E. Wells; Howard E. Thomas; Craig M. Goodwin; Jennifer L. Blakely; James D. Turner (pp. 282-286).
Gas–solid chromatography was used to determineB2s (gas–solid virial coefficient) values for 12 alkanes (10 branched and 2 cyclic) interacting with a carbon powder (Carbopack B, Supelco).B2s values were determined by multiple size variant injections within the temperature range of 393 to 623 K with each alkane measured at 5 or 6 different temperatures. The temperature variations of the gas–solid virial coefficients were used to find the experimental adsorption energy or binding energy values (E∗) for each alkane. A molecular mechanics based, rough-surface model was used to calculate the molecule–surface binding energy (Ecal∗) using augmented MM2 parameters. The surface model consisted of three parallel graphene layers with each layer containing 127 interconnected benzene rings and two separated nanostructures each containing 17 benzene rings arranged in a linear strip. As the parallel nanostructures are moved closer together, the surface roughness increases and molecule–surface interactions are enhanced. A comparison of the experimental and calculated binding energies showed excellent agreement with an average difference of 3.8%. Linear regressions ofE∗ versusEcal∗ for the current data set and a combined current and prior alkane data set both gave excellent correlations. For the combined data set with 18 linear, branched and cyclic alkanes; a linear regression ofE∗=0.9848Ecal∗ andr2=0.976 was obtained. The results indicate that alkane-surface binding energies may be calculated from MM2 parameters for some gas–solid systems.Binding energies were determined from molecular mechanics using a rough carbon surface model. These values compared well to experimental binding energies determined from gas chromatography.
Keywords: Adsorption; Henry's law; Alkane; Carbon surface; Virial coefficients; Gas–solid; Molecular mechanics; Adsorption energy; Binding energy; Molecule–surface
Heavy metal ion adsorption onto polypyrrole-impregnated porous carbon
by Moonjung Choi; Jyongsik Jang (pp. 287-289).
Polypyrrole-impregnated porous carbon was readily synthesized using vapor infiltration polymerization of pyrrole monomers. The results show that the functionalized polymer layer was successfully coated onto the pore surface of carbon without collapse of mesoporous structure. The modified porous carbon exhibited an improved complexation affinity for heavy metal ions such as mercury, lead, and silver ions due to the amine group of polypyrrole. The introduced polypyrrole layer could provide the surface modification to be applied for heavy metal ion adsorbents. Especially, polymer-impregnated porous carbon has an enhanced heavy metal ion uptake, which is 20 times higher than that of adsorbents with amine functional groups. Furthermore, the relationship between the coated polymer amount and surface area was also investigated in regard to adsorption capacity.The polypyrrole-impregnated porous carbon provided an excellent adsorbent toward for heavy metal ions with improved adsorption potential due to functional groups of polypyrrole and retained porous structure.
Keywords: Adsorption; Porous carbon; Polymer layer; Surface functionalization
Characterization of domain growth kinetics in a mixed perfluorocarbon-hydrocarbon Langmuir–Blodgett monolayer
by Shatha E. Qaqish; Matthew F. Paige (pp. 290-293).
The rate of domain growth in phase-separated, mixed Langmuir–Blodgett (LB) monolayers of arachidic acid, C19H39COOH (AA) and perfluorotetradecanoic acid, C13F27COOH (PA) was tracked via atomic force microscope measurements. The growth rate of domains comprised of phase-separated AA was consistent with that predicted by the Lifshitz–Slyozov model for diffusion-limited Ostwald ripening. In addition to Ostwald ripening, some evidence for domain coalescence was also observed when LB films were deposited under conditions of low temperature and short incubation times, though this tendency disappeared at higher deposition temperatures.Domain growth in phase-separated perfluorotetradecanoic/arachidic acid Langmuir–Blodgett films occurs via 2D Ostwald ripening and can be modeled using the Lifshitz–Slyozov relation.
Keywords: Langmuir–Blodgett film; Domain growth kinetics; Ostwald ripening; Phase-separation; Surface diffusion; Atomic force microscope; Arachidic acid; Perfluorotetradecanoic acid
Antibacterial behavior of transition-metals-decorated activated carbon fibers
by Byung-Joo Kim; Soo-Jin Park (pp. 297-299).
The antibacterial behavior of transition metals (Cu or Ag)-plated activated carbon fibers (ACFs) was investigated. The pore structure of the ACFs before and after metal electroplating was studied by N2/77 K isothermal adsorption. The antibacterial behavior against Staphylococcus aureus and Klebsiella pneumoniae was tested by a modified dilution method. As experimental results, the ACFs showed a decrease in specific surface area and micro- and total pore volume with increasing metal content. The antibacterial behavior of the ACFs was predominantly increased and showed over 99% against S. aureus as well as K. pneumoniae, attributed to the presence of metal nanoparticles in this system.All of metal-plated activated carbon fibers showed time-dependent curves in their erosion rates. It was found that erosion curves decreased rapidly in the initial time before they flattened.
Keywords: Activated carbon fibers; Antibacterial behavior; Electroplating; Washing resistance