Journal of Colloid And Interface Science (v.370, #1)
Effect of kaolinite, silica fines and pH on transport of polymer-modified zero valent iron nano-particles in heterogeneous porous media
by Hye-Jin Kim; Tanapon Phenrat; Robert D. Tilton; Gregory V. Lowry (pp. 1-10).
Display Omitted► At pH<7 anionic polyelectrolyte coated NZVI aggregates and deposition increases. ► Surface charge heterogeneity on sand and clay particles increased deposition of NZVI. ► Pre-adsorbing polyelectrolyte on sand and clay and decreases deposition.Polymer coatings on nano-sized remediation agents and subsurface heterogeneity will affect their transport, likely in a pH-dependent manner. The effect of pH on the aggregation of polymer-coated nanoscale zerovalent iron (nZVI) and its deposition onto sand and clay (kaolinite) surfaces was studied. nZVI coatings included a high molecular weight (90kg/mol) strong polyanion, poly(methacrylic acid)-b-(methy methacrylate)-b-(styrenesulfonate) (PMAA-PMMA-PSS) and a low molecular weight (2.5kg/mol) weak polyanion, polyaspartate. Aggregation and deposition increased with decreasing pH for both polyelectrolytes. The extent was greater for the low MW polyaspartate coated nZVI. Enhanced deposition at lower pH was indicated because the elutability of polyaspartate-modified hematite (which did not aggregate) also decreased at lower pH. The greater deposition onto clay minerals compared to similar sized silica fines is attributed to charge heterogeneity on clay mineral surfaces, which is sensitive to pH. Heteroaggregation between kaolinite particles and nZVI over the pH range 6–8 confirmed this assertion. Excess unadsorbed polyelectrolyte in solution (100mg/L) enhanced the transport of modified nZVI by minimizing aggregation and deposition onto sand and clay. These results indicate that site physical and chemical heterogeneity must be considered when designing an nZVI emplacement strategy.
Keywords: Environmental nanotechnology; Nanoparticle heteroaggregation; Exposure assessment; Nanoparticle transport; Surface modified nanoparticle; Nanoparticle coatings
Vapor detection enabled by self-assembled colloidal photonic crystals
by Hongta Yang; Peng Jiang; Bin Jiang (pp. 11-18).
Display Omitted► Self-assembled colloidal photonic crystals enable reversible vapor detection. ► Diffraction peak shift is linear with vapor partial pressure for various vapors. ► A new full-peak analysis technique has been developed to improve sensitivity. ► Optical simulation agrees well with experimental results. ► A modified Kelvin equation works for a wide range of vapor partial pressures.Here we report the sensitive and reversible detection of vapors by using self-assembled colloidal photonic crystals. The condensation of various vapors in the interstitials of silica colloidal photonic crystals leads to red-shift and amplitude reduction of optical stop bands. A linear relationship between wavelength shift and vapor partial pressure has been observed for a variety of vapors including ethanol, water, and toluene. Importantly, the sensitivity of colloidal photonic crystal-based vapor detectors can be improved by nearly two orders of magnitude by using a new full-peak analysis technique that takes advantage of the manifest amplitude reduction of optical stop bands during vapor condensation. Optical simulation based on a scalar-wave approximation model shows that the predicted optical responses during vapor condensation in colloidal photonic crystals agree well with experimental results. The condensation of vapors between submicrometer-scale microspheres, a topic that has received little examination, has also been investigated by both experiments and theoretical calculations. Predictions based on a modified Kelvin equation match with the experiments for a wide range of vapor partial pressures.
Keywords: Photonic crystals; Self-assembly; Vapor condensation; Bragg diffraction; Vapor detection
Guest controlled aggregation of amphiphilic sulfonatomethylated calixresorcinarenes in aqueous solutions
by Victor V. Syakaev; Ella Kh. Kazakova; Julia E. Morozova; Yana V. Shalaeva; Shamil K. Latypov; Alexander I. Konovalov (pp. 19-26).
Display Omitted► NMR study of aggregation of amphiphilic calixarenes and different guests is present. ► The ‘head-to-tail’ aggregation unusual for amphiphilic calixarenes is observed. ► The binding of guest molecules by ‘head-to-tail’ packed aggregates is more efficient. ► The structural control of the guest inclusion into capsule is shown. ► Lifetime of incapsulated methylviologen cation-radical ca.14-fold increases.Supramolecular nanoaggregates formed through the association of amphiphilic sulfonatomethylated calixresorcinarenes with different substituents on the lower rim (methyl, pentyl, heptyl) and number of aromatic, aliphatic, and cationic guests differing in their shapes and sizes were investigated in aqueous solution by various NMR techniques (1H, 2D NOESY, FT-PGSE). It was shown that slight variations of the alkyl chain length on the lower rim of calixresorcinarenes dramatically change their aggregation behavior. Unlike the other calixresorcinarenes studied, the “head-to-tail” packing mode is observed for calixresorcinarene with pentyl moieties on the lower rim, which is unusual for amphiphilic calixarene aggregates. This calixresorcinarene demonstrates the stronger binding capacity toward the guest molecules due to their encapsulation into the capsule-like aggregate subunits. The guest–host complexation modifies the properties of both components, with the size of the resulted colloid particles being controlled by the guest nature.
Keywords: Self-assembly; Supramolecular; Calixarene; Hydrophobic effect; Molecular capsules; NMR spectroscopy
Optimized solvent-exchange synthesis method for C60 colloidal dispersions
by Randall D. Maples; Martha E. Hilburn; Befrika S. Murdianti; Rangika S. Hikkaduwa Koralege; Jason S. Williams; Satish I. Kuriyavar; Kevin D. Ausman (pp. 27-31).
Display Omitted► Solvent exchange method for aqueous colloidal fullerene synthesis optimized for 75nm particles. ► Colloidal particle size control demonstrated over the range 75–210nm. ► Residual organic solvent content below detection limits.An existing solvent exchange method used to produce aqueous suspensions of fullerene C60 aggregates ( nC60) using the solvents toluene, tetrahydrofuran, acetone, and water, has been optimized for producing 75nm diameter particles. Numerous synthesis parameters were evaluated for their effects on colloid yield and particle size distribution. Varying the relative volumes used of the intermediate solvents relative to the initial toluene volume allowed the controlled tuning of the resulting particle size up to a diameter of 210nm. The resulting suspensions produced 10–20ppm concentrations and reduced the residual organic solvents to less than the detection limit of 1ppm.
Keywords: n; C; 60; Fullerene; C; 60; TTA/; n; C; 60; C; 60; colloid; Fullerene water systemAbbreviations; C; 60; buckminsterfullerene; n; C; 60; colloidal aggregates of C; 60; THF; tetrahydrofuran; TTA; toluene/tetrahydrofuran/acetone/water solvent exchange method; DLS; dynamic light scattering; PDI; polydispersity index; SPME; solid-phase microextraction; HPLC; high performance liquid chromatography; TEM; transmission electron microscopy/micrograph; FWHM; full-width half-maximum
Influence of surface functionalization via chemical oxidation on the properties of carbon nanotubes
by Jiuling Chen; Qinghai Chen; Qing Ma (pp. 32-38).
Display Omitted► Difference between oxidants in the formed groups was compared in the details. ► Difference in surface hydrophilicity and pHPZC of CNTs was compared. ► Promoting effect of carboxyls on Pd–Pt/CNTs was investigated.The surface of carbon nanotubes (CNTs) was functionalized in different chemical oxidants, hydrogen peroxide, mixed concentrated HNO3/H2SO4 and acidic KMnO4 solution. The influences on the properties of CNTs were systematically investigated, such as the structure, the kinds and the contents of the formed surface oxygen-containing functional groups, the pHPZC values and the surface hydrophilicity using XRD, HREM, FTIR and chemical titration. The results show that the kinds and the contents of the surface oxygen-containing groups are dependent on the functionalization methods. The formation of the oxygen-containing groups can decrease pHPZC values and improve surface hydrophilicity of CNTs. The dispersion of the supported Pd–Pt particles on the functionalized CNTs and their catalytic activity in the profile reaction of naphthalene hydrogenation to tetralin are both promoted due to the presence of these oxygen-containing groups.
Keywords: Carbon nanotubes; Surface functionalization; Oxygen-containing functional groups; Chemical oxidization; Surface hydrophilicity
Gravitational compression dynamics of charged colloidal crystals
by Masako Murai; Tohru Okuzono; Masaaki Yamamoto; Akiko Toyotama; Junpei Yamanaka (pp. 39-45).
Display Omitted► We examine the compression of charged colloidal silica crystals under gravity. ► The Bragg diffractions from the crystal lattice are monitored using spectroscopy. ► Time evolutions of the sedimentation profiles are determined. ► Numerical simulations are performed based on a continuum model. ► The numerical results agree well with the experimental data at high ionic strength.We examine the compression of charged colloidal crystals under the influence of gravitational force by monitoring the spatiotemporal variations of Bragg diffraction from the crystal lattice. We use the dilute aqueous dispersions of colloidal silica particles (diameter=216nm, charge number=733, a particle volume fraction ϕ=0.06) in the presence of 5–15μM sodium chloride. The sedimentation profiles of the colloidal crystals along the crystal height are determined by in situ fiber optics reflection spectroscopy. The time evolutions of the sedimentation profiles are calculated by numerical simulations based on a phenomenological continuum model that explicitly incorporates the electrostatic interparticle interactions. The simulation results correctly describe the experiments at sufficiently high ionic strength.
Keywords: Silica colloid; Charged colloidal crystal; Gravitational compression; Sedimentation kinetics
Gold nanoparticle deposition on Si by destabilising gold colloid with HF
by A.J. O’Reilly; C. Francis; N.J. Quitoriano (pp. 46-50).
Display Omitted► Deposition of commercial gold colloid onto hydrogen-terminated silicon. ► Deposition of catalysts for epitaxial nanowire growth. ► Deposition controlled by time and concentration. ► Agglomeration controlled by time and particle size. ► Multiple depositions increase deposition density.Gold nanoparticles from commercially available colloids were deposited onto a hydrogen-terminated silicon substrate without the use of a polyelectrolyte linker by the addition of HF acid. The deposition density was shown to be controlled over three orders of magnitude by varying the colloid concentration, and finer control is achieved by varying the deposition time. In order to minimise agglomeration, however, we show that deposition times should be minimised since nanoparticle agglomeration increases rapidly over the first 2min after the addition of HF. To increase nanoparticle density without increasing agglomeration, we show that successive depositions of short times linearly increase the deposition density without increasing the agglomeration of nanoparticles.
Keywords: Gold colloid; Nanoparticle; Deposition; Agglomeration; Silicon
Novel LaBO3 hollow nanospheres of size 34±2nm templated by polymeric micelles
by Manickam Sasidharan; Nanda Gunawardhana; Hom Nath Luitel; Toshiyuki Yokoi; Masamichi Inoue; Shin-ichi Yusa; Takanori Watari; Masaki Yoshio; Takashi Tatsumi; Kenichi Nakashima (pp. 51-57).
Display Omitted► Poly(styrene- b-acrylic acid- b-ethylene oxide) forms micelles with core– shell– corona architecture. ► The shell block with COO− ions effectively produce LaBO3 hollow nanospheres under mild conditions. ► The LaBO3 hollow nanosphere is reported for the first time using soft template of polymeric micelles. ► Till date no methods are available for synthesis of LaBO3 hollow nanospheres. ► The LaBO3 hollow nanosphere exhibit high charge/discharge cycling performance in lithium-ion rechargeable batteries.Novel lanthanum borate (LaBO3) hollow nanospheres of size 34±2nm have been reported for the first time by soft-template self-assembly process. Poly(styrene- b-acrylic acid- b-ethylene oxide) (PS-PAA-PEO) micelle with core– shell– corona architecture serves as an efficient soft template for fabrication of LaBO3 hollow particles using sodium borohydride (NaBH4) and LaCl3⋅7H2O as the precursors. In this template, the PS block ( core) acts as a template of the void space of hollow particle, the anionic PAA block ( shell) serves as reaction field for metal ion interactions, and the PEO block ( corona) stabilizes the polymer/lanthana composite particles. The PS-PAA-PEO micelles and the resulting LaBO3 hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray diffraction, magic angle spinning-nuclear magnetic resonance (11B MAS NMR), energy dispersive X-ray analysis, thermal analyses, Fourier transform infra red spectroscopy, and nitrogen adsorption/desorption analyses. The nitrogen adsorption/desorption analyses and TEM observation of the hollow particles confirmed the presence of disordered mesopores in the LaBO3 shell domain. The solid state11B MAS NMR spectra of LaBO3 hollow nanospheres revealed that the shell part contains both trigonal and tetrahedral boron species. The LaBO3 hollow particles were applied to anode materials in lithium-ion rechargeable batteries (LIBs). The hollow particles exhibited high coulombic efficiency and charge–discharge cycling capacities of up to 100 cycles in the LIBs.
Keywords: LaBO; 3; Hollow nanospheres; Triblock copolymer; Micelles; Lithium-ion battery
Elaboration of chitosan-coated nanoparticles loaded with curcumin for mucoadhesive applications
by Letícia Mazzarino; Christophe Travelet; Sonia Ortega-Murillo; Issei Otsuka; Isabelle Pignot-Paintrand; Elenara Lemos-Senna; Redouane Borsali (pp. 58-66).
Display Omitted► Chitosan-coated nanoparticles loaded with curcumin were successfully prepared. ► Changes in size and zeta potential confirmed their decoration with chitosan. ► Light scattering studies showed monodisperse distributions of the nanoparticles. ► All the studied systems showed high encapsulation efficiency (99%). ► Strong interaction of chitosan-coated nanoparticles with bovine submaxillary mucin.Polycaprolactone (PCL) nanoparticles decorated with a mucoadhesive polysaccharide chitosan (CS) containing curcumin were developed aiming the buccal delivery of this drug. These nanoparticles were prepared by the nanoprecipitation method using different molar masses and concentrations of chitosan and concentrations of triblock surfactant poloxamer (PEO–PPO–PEO), in order to optimize the preparation conditions. Chitosan-coated nanoparticles showed positive surface charge and a mean particle radius ranging between 114 and 125nm, confirming the decoration of the nanoparticles with the mucoadhesive polymer, through hydrogen bonds between ether and amino groups from PEO and CS, respectively. Dynamic Light Scattering (DLS) studies at different scattering angles and concentrations have shown that the nanoparticles are monodisperse (polydispersity indices were lower than 0.3). The nanoparticle systems were also examined with Nanoparticle Tracking Analysis (NTA), and the results were in good agreement with those obtained by DLS. Colloidal systems showed mean drug content about 460μg/mL and encapsulation efficiency higher than 99%. Finally, when coated with chitosan, these nanoparticles show a great ability to interact with mucin indicating also their suitability for mucoadhesive applications.
Keywords: Polysaccharide coating; Chitosan-coated nanoparticles; Mucoadhesive nanoparticles; Curcumin; Dynamic Light Scattering (DLS); Nanoparticle Tracking Analysis (NTA)
pH induced swelling of PVP microgel particles – A first order phase transition?
by Joseph Patrick Cook; David Jason Riley (pp. 67-72).
Display Omitted► Microgels can be simply treated by considering the osmotic pressure for a particle. ► The Maxwell construction can extend the model across the full pH range. ► The swelling is predicted to occur at a pH lower than the p Ka of the polymer.The pH-induced swelling of poly(2-vinylpyridine) microgel particles was studied using dynamic light scattering. The increase in particle diameter with decreasing pH was modeled using a well-established thermodynamic model for microgel swelling. The Maxwell construction was applied to extend the model and yield a prediction for a pH-responsive microgel across the entire pH range. The model predicts a first order phase transition for polymer–solvent combinations with a Flory interaction parameter, χ, greater than a critical value χc. The modified theory compared favorably to the dynamic light scattering data for the hydrodynamic diameter of microgel particles based on 2-vinylpyridine at different pH values. In particular, the swelling transition is both predicted theoretically and observed experimentally to occur at a pH lower than the p Ka of the polymer.
Keywords: Microgel; Poly(2-vinylpyridine); Phase transition; Light scattering; pH
Temperature and emulsifier concentration effects on gallic acid distribution in a model food emulsion
by Sonia Losada-Barreiro; Verónica Sánchez-Paz; Carlos Bravo-Díaz; Fátima Paiva-Martins; Laurence S. Romsted (pp. 73-79).
Display Omitted► We analyzed the effects of emulsifier and T on the distribution of gallic acid in food-grade emulsions. ► The concentration of gallic acid, GA, in the oil region is effectively zero. ► At least 40% of the total GA is located in the interfacial region of the emulsion. ► The thermodynamic parameters for the GA transfer were determined.We determined the effects of emulsifier concentration and temperature on the distribution of gallic acid (GA) in a food-grade emulsion composed of 1:9 vol:vol stripped corn oil, acidic water and Tween 20. The distribution of GA can be defined by the partition constant between the aqueous and the interfacial regions,PWI, which was determined by using a kinetic method and the pseudophase kinetic model. OncePWI is known, determining the distribution of GA is straightforward. Our results show that at least 40% of the total GA is located in the interfacial region of the emulsion at 0.005 volume fraction of Tween 20, and this percentage increases to ca. 85% of the total GA at 0.04 volume fraction of Tween 20. The variation ofPWI with the temperature was used to estimate the thermodynamic parameters for the GA transfer from the aqueous to the interfacial region of the emulsion and the activation parameters for the reaction between 16-ArN2+ and GA in the interfacial region. The free energy of transfer from the aqueous to the interfacial region,ΔGT0,W→I, is negative, the enthalpy of transfer is small and negative, but the entropy of transfer is large and positive. Our results demonstrate that the partitioning of GA in acidic emulsions between aqueous and interfacial regions depends primarily on droplet concentration and is only slightly dependent on temperature.
Keywords: Gallic acid; Oil-in-water emulsions; Partition constants; Kinetics; Pseudophase model; Antioxidant distribution; Emulsions; Pseudophase kinetic model; Arenediazonium ions
Zwitterionic heterogemini surfactants containing ammonium and carboxylate headgroups 2: Aggregation behavior studied by SANS, DLS, and cryo-TEM
by Kanae Nyuta; Tomokazu Yoshimura; Koji Tsuchiya; Hideki Sakai; Masahiko Abe; Hiroki Iwase (pp. 80-85).
Display Omitted► Aggregation of heterogemini surfactant aggregates in solution was investigated using SANS, DLS, and cryo-TEM. ► Aggregation behavior was influenced by hydrocarbon chain length and surfactant concentration. ► These surfactants exhibit unique behavior such as transitions spherical micelle→rod-like micelle→rod-like micelle+vesicle→vesicle. ► The membrane structure of vesicles was found to be interdigitated bilayers.The aggregation behavior in aqueous solution of zwitterionic heterogemini surfactants, N, N-dimethyl- N-[2-( N′-alkyl- N′- β-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2C nAmCa, in which n represents hydrocarbon chain lengths of 8, 10, 12, and 14), with nonidentical headgroups containing ammonium and carboxylate was investigated through small-angle neutron scattering (SANS), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) techniques. We found that the aggregation behavior of 2C nAmCa strongly depended on the hydrocarbon chain length and the surfactant concentration. 2C8AmCa forms spherical micelles with radius of approximately 2nm in solution. 2C10AmCa forms rod-like micelles at low concentration in the solution, and the structure changes to vesicles with increasing concentration. The membrane thickness of the vesicle is independent of the surfactant concentration. Aggregation shape transitions were also observed for 2C12AmCa. In addition, it appears that the vesicles of 2C12AmCa coexist with the rod-like micelles at a wide range of surfactant concentrations. Interestingly, 2C14AmCa forms vesicles with averaged membrane thickness of 2.32nm in solution, even at the extremely low concentration of 10 times the cmc. Thus, it was concluded that 2C nAmCa exhibits unique aggregation behavior, such as the formation of spherical micelle→rod-like micelle→rod-like micelle+vesicle (coexistence)→vesicle with increasing hydrocarbon chain length and surfactant concentration. We also found that the membrane structure is an interdigitated bilayer when the vesicles are formed. This formation of interdigitated structures is related to the origins of the effective properties of 2C nAmCa in solution.
Keywords: Gemini surfactant; Aggregation behavior; Small-angle neutron scattering; Dynamic light scattering; Cryogenic transmission electron microscopy
Aggregation and adsorption behavior of low concentration aqueous solutions of hexadecyltrimethylammonium ortho, meta, and parafluorobenzoate
by G. Landázuri; J. Alvarez; F. Carvajal; E.R. Macías; A. González-Álvarez; E.P. Schulz; M. Frechero; J.L. Rodríguez; R. Minardi; P.C. Schulz; J.F.A. Soltero (pp. 86-93).
Display Omitted► Solution properties of fluorobenzoic acids (FBAs) were studied. ► Micellization of hexadecyltrimethylammonium fluorobenzoates (HTAFBs) was studied. ► The position of the fluorine atom in the counterion strongly affects these properties. ► Experimental results were explained via computational simulation.The aggregation properties of 2-, 3-, and 4-fluorobenzoic acids (2FBA, 3FBA, and 4FBA, respectively) and their salts with hexadecyltrimethylammonium cations (HTA2FB, HTA3FB, and HTA4FB) in water were studied with a battery of techniques. Their activity at the air/solution interface has been also studied. The position of the fluorine atom in the acid affected the solubility, adsorption, and aggregation in the pure acids solutions. The 4FBA is less water soluble, more hydrophobic, and has the lower critical aggregation concentration of the three isomers. The behavior of the HTA2FB compound in aqueous solution is different from that of HTA3FB and HTA4FB. The critical micelle concentration, critical concentration for sphere-to-rod-like micelle transition, and Krafft point of HTA3FB and HTA4FB are lower than those of the other surfactant but their surface activities are higher. The differences between the HTA2FB and the other two surfactants have been explained on the basis of the regular solution theory of mixed micelles and in light of the analysis of the hydration shell of the acids through molecular dynamic simulations. The results of the present work suggest that the different behaviors are due to a combination of different dehydration tendencies and the steric possibility of inclusion of the counterions in the micelle palisade layer. The formation of rod-like micelles by HTA2FB, while the tetradecyltrimethylammonium 2-fluorobenzoate only forms spherical aggregates, is explained on the basis of the packing parameter. The mentioned factors are complementary to others presented in literature. These conditions may be used in the rational design of micelles by means of molecular dynamics simulations, reducing the trial-and-error approach used to date.
Keywords: Fluorobenzoic acids; Hexadecyltrimethylammonium fluorobenzoates; Critical micelle concentration; Krafft point; Molecular dynamic simulation; Mixed micelles
Properties of aqueous solutions of hydrophobically modified polyethylene imines in the absence and presence of sodium dodecylsulfate
by Ismael C. Bellettini; Leandro G. Nandi; Renato Eising; Josiel B. Domingos; Vanderlei G. Machado; Edson Minatti (pp. 94-101).
Display Omitted► Polyethylene imines with pendant alkyl groups show pronounced surface activity. ► Polyelectrolyte hydrophobicity can be tuned by increasing the alkyl chain length. ► Hydrophobic polyethylene imines interact strongly with sodium dodecylsulfate (SDS). ► At high c(SDS), polyethylene imines form aggregated and random-coil polymer chains.Four modified hyperbranched polyethylene imines (PEIs) were synthesized by means of the alkylation of PEI. SAXS, viscosity, surface tension, and pyrene fluorescence emission were then used as techniques to examine the conformation and aggregation of the modified PEIs in aqueous solution, in the absence and presence of sodium dodecylsulfate (SDS). Analysis of the SAXS data showed that the radius of gyration decreases with an increase in the alkyl chain length of the polymer, while the viscosity data indicated a decrease in the intrinsic viscosity under the same conditions. The nonmodified PEI was not surface active, while the hydrophobically modified samples showed pronounced surface activity and the presence of hydrophobic domains. On addition of SDS, the onset of the formation of polymer–surfactant complexes was determined, indicating a decrease in the critical aggregate concentration with an increase in the alkyl chain length of the polymer backbone.
Keywords: Polyelectrolyte; Intrinsic viscosity; Polymer–surfactant interactions; Pyrene fluorescence; Hydrophobic effect; Polyethylene imine
A model for monomer and micellar concentrations in surfactant solutions: Application to conductivity, NMR, diffusion, and surface tension data
by Wajih Al-Soufi; Lucas Piñeiro; Mercedes Novo (pp. 102-110).
Display Omitted► An empirical analytical model for surfactant concentrations near the cmc is presented. ► Conductivity, surface tension, NMR shift, and self-diffusion data are well reproduced. ► A method for the robust analytic determination of the cmc of micellar solutions. ► Functions for standard nonlinear (global) regression of surfactant data are given. ► No need for premicellar species in order to reproduce the transition around the cmc.An empirical model for the concentrations of monomeric and micellized surfactants in solution is presented as a consistent approach for the quantitative analysis of data obtained with different experimental techniques from surfactant solutions. The concentration model provides an objective definition of the critical micelle concentration ( cmc) and yields precise and well defined values of derived physical parameters. The use of a general concentration model eliminates subjective graphical procedures, reduces methodological differences, and thus allows one to compare directly the results of different techniques or to perform global fits. The application and validity of the model are demonstrated with electrical conductivity, surface tension, NMR chemical shift, and self-diffusion coefficient data for the surfactants SDS, CTAB, DTAB, and LAS. In all cases, the derived models yield excellent fits of the data. It is also shown that there is no need to assume the existence of different premicellar species in order to explain the chemical shifts and self-diffusion coefficients of SDS as claimed recently by some authors.
Keywords: Surfactants; Micelles; Critical micelle concentration; Concentration model; Data analysis
Surface properties of Gemini surfactants with pyrrolidinium head groups
by Bo Cai; Xuefeng Li; Yi Yang; Jinfeng Dong (pp. 111-116).
Display Omitted► Pyrrolidinium Gemini surfactants were synthesized and characterized. ► Gemini surfactants with heterocyclic head groups have superior surface activity compared to traditional analogues. ► The mechanism of micellization varies as a function of the chain length.Gemini surfactants C n-4- nPB (where n represents the alkyl chain length of 10, 12, 14 and 16) were synthesized and characterized. Their surface activity, thermodynamic properties, and aggregation behavior were investigated by means of surface tension, electrical conductivity, and steady-state fluorescence. It was found that the Gemini surfactants C n-4- nPB have superior surface activity to their corresponding monomer surfactants C nMPB as expected. Additionally, these compounds have lower cmc and surface tension in comparison with conventional cationic Gemini surfactants m-4- m. Thermodynamic parameters(ΔGm0,ΔHm0,TΔSm0) show that the micellization is an entropy driven process with shorter hydrophobic chain lengths but instead is enthalpy driven for longer hydrophobic chain lengths. The effect of the hydrophobic alkyl chain length and the addition of inorganic salt NaBr on the surface activity and micellization are in line with the conventional cationic Gemini surfactants.
Keywords: Gemini surfactant; Heterocyclic head group; Pyrrolidinium; Micellization; Thermodynamics
Bioinspired Au/TiO2 photocatalyst derived from butterfly wing ( Papilio Paris)
by Jianjun Chen; Huilan Su; Fang Song; Won-Jin Moon; Yang-Soo Kim; Di Zhang (pp. 117-123).
Display Omitted► Contrive superior Au/TiO2 photocatalyst with admirable nano-structures and ingredient. ► Introduce butterfly wings template into a facile sol–gel technique for Au/TiO2. ► Biomorphic Au/TiO2 possesses superior photocatalytic activity. ► Show a shortcut for the design of functional materials and devices.The reticular hierarchical structure of butterfly wings ( Papilio Paris) is introduced as template for Au/TiO2 photocatalyst by depositing the Au nanoparticles on TiO2 matrix, which is carried out by a water–ethanol sol–gel procedure combined with subsequent calcination. The obtained Au/TiO2 nanocomposites present the reticular hierarchical structure of butterfly wings, and Au nanoparticles with an average size of 7nm are homogeneously dispersed in TiO2 substrate. Benefiting from such unique reticular hierarchical structure and composition, the biomorphic Au/TiO2 exhibits high-harvesting capability and presents superior photocatalytic activity. Especially, the biomorphic Au/TiO2 at the nominal content of gold to titanium of 8wt% shows the highest photocatalytic activity and can completely decompose methyl orange within 80min, which is obviously higher than that of commercial Degussa P25 powders.
Keywords: Au/TiO; 2; nanocomposites; Photocatalyst; Butterfly wings; Bioinspired
Electron transfer studies of redox probes in bovine milk
by S. Shrikrishnan; V. Lakshminarayanan (pp. 124-131).
Display Omitted► Milk has nearly 150mM of electro-active species. ► It has been demonstrated as an electrolytic medium without any supporting electrolyte. ► Found to sustain redox reactions in the absence of a supporting electrolyte. ► Cyclic voltammetry and impedance studies reveal the role of milk components in redox reactions. ► Electrochemical techniques can be used as potent tools for milk quality analysis.In this work, we show that milk can act as an electrolytic medium to study electrochemical processes in the absence of any supporting electrolyte. The electron transfer properties of three different redox systems in bovine homogenized whole milk, skimmed milk, and reconstituted milk powder have been studied by cyclic voltammetry and impedance spectroscopy using a three-electrode system with a gold disk working electrode, a platinum sheet counter electrode, and a standard calomel reference electrode. It has been shown that the milk incredibly sustains the redox reactions in the absence of any supporting electrolyte and the electrochemical responses are comparable to those obtained when the same reactions were carried out in standard solvent preparations containing supporting electrolytes. The study clearly demonstrates the potential of developing new innovative techniques based on the intricate concepts of electrochemistry to study various aspects of milk that may help in the development of analytical sensors for the diary industry.
Keywords: Homogenized milk; Skimmed milk; Reconstituted milk powder; Milk Fat Globule Membrane (MFGM); Casein micelle; Cyclic voltammetry; Impedance spectroscopy
Controllable synthesis and visible-light-responsive photocatalytic activity of Bi2WO6 fluffy microsphere with hierarchical architecture
by Hui Huang; Hongfeng Chen; Yang Xia; Xinyong Tao; Yongping Gan; Xianxian Weng; Wenkui Zhang (pp. 132-138).
Display Omitted► Various morphologies of Bi2WO6 are synthesized via a simple hydrothermal route without surfactant and template. ► The samples with hierarchical structure assembled of many nanosheets. ► The fluffy microsphere-like sample exhibits excellent photodegradation efficiency (99% in 20min).Bismuth tungstate (Bi2WO6) has attracted great research interest as an important visible-light-responsive photocatalyst. In this paper, we report a facile hydrothermal route for the shape-controlled synthesis of micro/nanostructured Bi2WO6, without adding surfactants or templates. The results show that various morphologies of Bi2WO6 including coralloid spherical particles, packed nanosheets, fluffy microspheres, and plates can be obtained by adjusting the pH values of the precursors. The as-prepared porous fluffy microspheres with a hierarchical architecture synthesized at pH 8 exhibit the highest photocatalytic activity for the degradation of Rhodamine (RhB) under visible light irradiation. The photodegradation efficiency reaches as high as 99% within 20min irradiation. This enhanced photocatalytic activity can be attributed to the unique porous structure and high BET surface area of fluffy microspheres with hierarchical architecture.
Keywords: Hydrothermal; Photocatalyst; Bi; 2; WO; 6; Fluffy microsphere
Point of zero potential of single-crystal electrode/inert electrolyte interface
by Piotr Zarzycki; Tajana Preočanin (pp. 139-143).
Display Omitted► Electrostatic characteristics of specific crystal faces from non-hysteretic titration. ► Surface reconstruction increases the number of sites with high proton affinity. ► Halide ions preferentially adsorbed on silver halide surfaces.Most of the environmentally important processes occur at the specific hydrated mineral faces. Their rates and mechanisms are in part controlled by the interfacial electrostatics, which can be quantitatively described by the point of zero potential (PZP). Unfortunately, the PZP value of specific crystal face is very difficult to be experimentally determined. Here we show that PZP can be extracted from a single-crystal electrode potentiometric titration, assuming the stable electrochemical cell resistivity and lack of specific electrolyte ions sorption. Our method is based on determining a common intersection point of the electrochemical cell electromotive force at various ionic strengths, and it is illustrated for a few selected surfaces of rutile, hematite, silver chloride, and bromide monocrystals. In the case of metal oxides, we have observed the higher PZP values than those theoretically predicted using the MultiSite Complexation Model (MUSIC), that is, 8.4 for (001) hematite (MUSIC-predicted ∼6), 8.7 for (110) rutile (MUSIC-predicted ∼6), and about 7 for (001) rutile (MUSIC-predicted 6.6). In the case of silver halides, the order of estimated PZP values (6.4 for AgCl<6.5 for AgBr) agrees well with sequence estimated from the silver halide solubility products; however, the halide anions (Cl−, Br−) are attracted toward surface much stronger than the Ag+ cations. The observed PZPs sequence and strong anions affinity toward silver halide surface can be correlated with ions hydration energies. Presented approach is the complementary one to the hysteresis method reported previously [P. Zarzycki, S. Chatman, T. Preočanin, K.M. Rosso, Langmuir 27 (2011) 7986–7990]. A unique experimental characterization of specific crystal faces provided by these two methods is essential in deeper understanding of environmentally important processes, including migration of heavy and radioactive ions in soils and groundwaters.
Keywords: Single-crystal electrode; Point of zero potential; Common intersection point; Point of zero salt effect; Surface potential; Rutile; Hematite; Silver bromide; Silver chloride
Hydrothermal synthesis of CuO micro-/nanostructures and their applications in the oxidative degradation of methylene blue and non-enzymatic sensing of glucose/H2O2
by M.U. Anu Prathap; Balwinder Kaur; Rajendra Srivastava (pp. 144-154).
Display Omitted► Morphologically controlled green synthetic route for CuO has been developed. ► Amino acids-/citric acid-/tartaric acid-assisted synthetic route has been developed. ► Materials were used as catalysts in the oxidative degradation of methylene blue. ► Materials were used for non-enzymatic sensing of glucose and H2O2. ► Nanostructured CuO exhibited higher electrocatalytic activity than CuO.In this paper, we report on the amino acids-/citric acid-/tartaric acid-assisted morphologically controlled hydrothermal synthesis of micro-/nanostructured crystalline copper oxides (CuO). These oxides were characterized by means of X-ray diffraction, nitrogen sorption, scanning electron microscopy, Fourier transform infrared, and UV–visible spectroscopy. The surface area of metal oxides depends on the amino acid used in the synthesis. The formation mechanisms were proposed based on the experimental results, which show that amino acid/citric acid/tartaric acid and hydrothermal time play an important role in tuning the morphology and structure of CuO. The catalytic activity of as-synthesized CuO was demonstrated by catalytic oxidation of methylene blue in the presence of hydrogen peroxide (H2O2). CuO synthesized using tyrosine was found to be the best catalyst compared to a variety of CuO synthesized in this study. CuO (synthesized in this study)-modified electrodes were used for the construction of non-enzymatic sensors, which displayed excellent electrocatalytic response for the detection of H2O2 and glucose compared to conventional CuO. The high electrocatalytic response observed for the CuO synthesized using tyrosine can be correlated with the large surface area, which enhances the accessibility of H2O2/glucose molecule to the active site that results in high observed current. The methodology adopted in the present study provides a new platform for the fabrication of CuO-based high-performance glucose and other biosensors.
Keywords: Copper oxide; Amino acid-assisted synthesis; Glucose sensing; H; 2; O; 2; sensing; Methylene blue degradation
Evaporation of a sessile droplet: Inside the coffee stain
by Guillaume Berteloot; Anna Hoang; Adrian Daerr; H. Pirouz Kavehpour; Francois Lequeux; Laurent Limat (pp. 155-161).
Display Omitted► Two phases in the growth of a colloidal deposit have been observed using microscopy. ► The first phase has been modeled using a simple model. ► The deposit displays patterns of lines at 45° from the deposition line.We have investigated experimentally, for the first time at microscopic level, the growth of the deposit left around a drop of colloids drying on a solid surface (“coffee stain effect”). Direct observations show that there are several distinct phases of growth, the later ones exhibiting surprising pattern formations with spatial modulation of the deposit. In addition, fluorescence reveals that the initial growth phase is governed by a single length scale, increasing with time ast23. We show that this exponent is a direct consequence of the divergence of evaporation near contact line evidenced by Deegan et al. We propose a simple ballistic model that allows us to calculate both this exponent and the prefactor, in agreement with yet available more complex descriptions. This model also opens the possibility to include effects neglected up to now.
Keywords: Colloids; Evaporation; Deposition; Coffee stain
The production and verification of pristine semi-fluorinated thiol monolayers on gold
by Kym Ford; Bronwyn J. Battersby; Barry J. Wood; Ian R. Gentle (pp. 162-169).
Display Omitted► We present a simple and efficient method for producing high-quality self-assembled monolayers. ► SAMs produced in this way show almost no sign of adventitious species. ► These results will have wide-ranging applicability to the production of many types of SAM.The presence of adventitious contamination of self-assembled monolayers (SAMs) is a well-known phenomenon that is often overlooked or underestimated in the literature. Herein, we demonstrate that it is possible to produce pristine self-assembled monolayers (SAMs) on gold surfaces that are devoid of adventitious species. The chemical purity or the pristine quality of the SAM was verified by the experimental relative atomic ratios measured by X-ray photoelectron spectroscopy (XPS) of all elements including carbon and corresponded to within 5% of the stoichiometric ratios. Perfluoro-octyl-thiolate (F8) was used as a model compound in this study, where monolayers were assembled from solutions of an acetylated F8 precursor. Quantitative elemental characterization of the acetylated F8 precursor by cold-stage XPS provided valuable reference data for the analysis of the subsequent SAMs. Comprehensive analysis of high-resolution XPS C 1s spectra proved to be essential for establishing the purity of the SAMs, since the peaks of the adventitious species were easily distinguished from those of the F8. Analyses of deliberately contaminated F8 SAMs showed that the adventitious species persisted during the process of self-assembly and therefore co-existed with the SAM in the interfacial region. The work also established that even a lengthy deposition time of 18h was incapable of displacing the adventitious species present at the interface.
Keywords: Semi-fluorinated; Thiol; Self-assembled monolayer; XPS; Adventitious species; Perfluoro-octyl-thioacetate
Coverage-dependent morphology of PEGylated lysozyme layers adsorbed on silica
by Sheetal S. Pai; Frank Heinrich; Adam L. Canady; Todd M. Przybycien; Robert D. Tilton (pp. 170-175).
Display Omitted► Neutron reflection to study mono-PEG-lysozyme adsorption at silica/water interface. ► Two surface concentrations on both sides of a transition in adsorption isotherm. ► Low surface concentration: high PEG volume occupancy of surface proximal region. ► High surface concentration: PEG chains extend further into solution. ► Findings provide opportunities for design of chromatographic separation protocols.Neutron reflection was used to characterize the adsorbed layer structure for lysozyme conjugated at the N-terminus with a single perdeuterated methoxy poly(ethylene glycol) (PEG) chain at the silica/water interface. Adsorbed layers were produced with two different surface concentrations corresponding to opposite sides of a pronounced transition in the adsorption isotherm for mono-PEGylated lysozyme. The transition was previously ascribed, on the basis of less direct characterization by normal force measurements, to a change in the distribution of the conjugated PEG chain segments in the interfacial region in response to lateral repulsions (S.M. Daly, T.M. Przybycien, R.D. Tilton, Langmuir 21 (2005) 1328–1337). Neutron reflectivity was measured for both surface concentrations using three different sets of neutron scattering length density contrast conditions, and models for the distribution of PEG and lysozyme content in the layers were obtained by simultaneous regression of all contrast condition data sets. This analysis indicated that the surface proximal volume is occupied almost equally by PEG and lysozyme at the low surface concentration, while at the higher surface concentration PEG is preferentially shifted away from the surface, with all lysozyme remaining in the surface proximal region. The distal regions of the high surface concentration layer contain only PEG, consistent with the previous interpretation of normal force measurements.
Keywords: Poly(ethylene glycol); Lysozyme; PEGylation; Neutron reflectivity; Protein adsorption; Polymer conformation; Silica
Unusual trend of increasing selectivity and decreasing flux with decreasing thickness in pervaporation separation of ethanol/water mixtures using sodium alginate blend membranes
by Eoin J. Flynn; Donal Keane; Justin D. Holmes; Michael A. Morris (pp. 176-182).
Display Omitted► Mechanically stable sodium alginate based membrane with high flux and selectivity. ► Reduced relaxational effects through control of glass composition of membrane. ► Increased selectivity of membrane as thickness decreases. ► Increased crosslinking of membrane polymer as thickness decreases due to longer periods of solvent evaporation. ► Results in increased hydrophobicity of membrane as thickness decreases which explains improved selectivity.Pervaporation membranes were produced comprising a 4:1 sodium-alginate:poly(vinyl-alcohol) polymer blend selective layer with a plasticizing agent (glycerol). Membranes were supported on a poly(acrylonitrile) mesoporous support layer and non-woven fabric base. Pervaporation separation of ethanol/water mixtures was carefully followed as a function of film thickness and time. It was found, contrary to what might be expected from literature, that these films showed increased selectivity and decreased flux as film thickness was reduced. It is argued that the morphology and structure of the polymer blend changes with thickness and that these structural changes define the efficiency of the separation in these conditions.
Keywords: Selectivity; Flux; Sodium-alginate; Pervaporation; Glass transition temperature
Surface tension and adsorption kinetics of amphiphiles in aqueous solutions: The role of carbon chain length and temperature
by Abdolhamid Firooz; P. Chen (pp. 183-191).
Display Omitted► Effects of carbon chain length and temperature were studied on adsorption kinetics. ► Surface tensions were found to decrease with temperature from 10°C to 35°C. ► Adsorption from vapor phase was much more important than that from liquid phase. ► Adsorption rate constants were increased with temperature and carbon chain length. ► Equilibrium constants were increased with temperature and carbon chain length.The effects of carbon chain length and temperature were investigated on adsorption kinetics and surface tension of a group of slightly volatile, short carbon chain molecules: 1-octanol, 1-hexanol, and 1-butanol. Experiments were performed in a closed chamber where simultaneous adsorption from both sides of the vapor/liquid interface was considered. The dynamic (time dependent) and steady-state surface tensions were found to decrease with temperature ranging from 10°C to 35°C. It was shown that, at the final steady-state, the effect of adsorption from the vapor phase was much more important than that from the liquid phase especially for short carbon chain molecules (e.g., 1-butanol). The modified Langmuir equation of state and modified kinetic transfer equation, which account for adsorption from both sides of a vapor/liquid interface, were used to model the experimental data of the steady-state and dynamic surface tension, respectively. Modeling results showed that the equilibrium constants and adsorption rate constants were increased with temperature and carbon chain length. The maximum surface concentration showed a decrease with temperature and an increase with carbon chain length. Some variations in the fitting parameters were observed in the dynamic modeling. These variations may be due to the experimental errors or the limitations of the proposed model.
Keywords: Surface tension; Adsorption kinetics; Amphiphiles; Carbon chain length; Temperature; Axisymmetric drop shape analysis (ADSA) method
Neutron reflectivity study of substrate surface chemistry effects on supported phospholipid bilayer formation on(112¯0) sapphire
by Timothy A. Oleson; Nita Sahai; David J. Wesolowski; Joseph A. Dura; Charles F. Majkrzak; Anthony J. Giuffre (pp. 192-200).
Display Omitted► Phospholipid bilayer coverage on sapphire varies with pH, ionic strength ( I) and Ca2+. ► Nearly full coverage observed with positive surface charge on sapphire and low I. ► Trends of increasing coverage agree with previous results using Al2O3 particles. ► Lipid (DPPC) bilayers observed on sapphire for the first time by neutron reflection.Oxide-supported phospholipid bilayers (SPBs) used as biomimetic membranes are significant for a broad range of applications including improvement of biomedical devices and biosensors, and in understanding biomineralization processes and the possible role of mineral surfaces in the evolution of pre-biotic membranes. Continuous-coverage and/or stacked SPBs retain properties (e.g., fluidity) more similar to native biological membranes, which is desirable for most applications. Using neutron reflectivity, we examined the role of oxide surface charge (by varying pH and ionic strength) and of divalent Ca2+ in controlling surface coverage and potential stacking of dipalmitoylphosphatidylcholine (DPPC) bilayers on the(112¯0) face of sapphire (α-Al2O3). Nearly full bilayers were formed at low to neutral pH, when the sapphire surface is positively charged, and at low ionic strength ( I=15mM NaCl). Coverage decreased at higher pH, close to the isoelectric point of sapphire, and also at high I⩾210mM, or with addition of 2mM Ca2+. The latter two effects are not additive, suggesting that Ca2+ mitigates the effect of higher I. These trends agree with previous results for phospholipid adsorption on α-Al2O3 particles determined by adsorption isotherms and on single-crystal(101¯0) sapphire by atomic force microscopy, suggesting consistency of oxide surface chemistry-dependent effects across experimental techniques.
Keywords: Supported phospholipid bilayer; Dipalmitoylphosphatidylcholine; Oxide; Alumina; Adsorption; Surface coverage