Effect of stabilizer on formation of "onionlike" multilayered polystyrene-block-poly(methyl methacrylate) particles

The effect of the kind of stabilizers on the formation of "onionlike" multilayered polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) particles was studied. The release of toluene from PS-b-PMMA/toluene droplets dispersed in aqueous medium resulted in the formation of onionlike multilayered structures in the particles for all stabilizers used. However, the surface composition of the particles was strongly affected by the kind of stabilizer. When sodium dodecyl sulfate (SDS) and poly(vinyl alcohol) (PVA) were used as stabilizers, the surface of the particles was occupied by PMMA phase. On the other hand, in the cases of Emulgen 911 (polyoxyethylene nonylphenyl ether) and Tween 80 (polyoxyethylene sorbitan monooleate) as stabilizers, the PS phase occupied the surfaces. These results for SDS, PVA, and Emulgen 911 are consistent with the surface layer of the PS-b-PMMA particles being occupied by the polymer phase, which gives a lower interfacial tension than that of another phase. However, in the case of Tween 80, interfacial tensions between water and toluene solutions of the polymer showed almost the same values making it impossible to predict the surface polymer phase.     

Blends of poly(epsilon-caprolactone) and intermediate molar mass polystyrene as Langmuir films at the air/water interface

Poly(epsilon-caprolactone)/polystyrene (PCL/PS) blends, where nonamphiphilic PS is glassy in the bulk state at the experimental temperature of 22.5 degrees C, are immiscible as Langmuir films at the air/water (A/W) interface. Surface pressure-area per monomer isotherm analyses indicate that the surface concentration of amphiphilic PCL is the only factor influencing the surface pressure below the collapse transition. For PS-rich blends, Brewster angle microscopy (BAM) studies at the A/W interface and atomic force microscopy studies on Langmuir-Schaefer films reveal that PS nanoparticle aggregates formed at very low surface pressures can form networks upon further compression. The morphologies seen in PS-rich blends (networklike rings) are consistent with a recent study of a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS), octaisobutyl-POSS, blended with amphiphilic poly(dimethylsiloxane), suggesting that the nonamphiphilic PS aggregates at the A/W interface produce domains with dipole densities that differ from that of pure PCL. In all composition regimes, the amphiphilic PCL phase tends to spread and form a continuous surface layer at the A/W interface, while simultaneously improving the dispersion of nonamphiphilic PS domains. During film expansion, BAM images show a gradual change in the surface morphology from highly continuous networklike structures (PS-rich blends) to broken ringlike structures (intermediate composition) to small discontinuous aggregates (PCL-rich blends). This study provides valuable information on the morphological evolution of semicrystalline PCL-based polymer blends confined in a "two-dimensional" geometry at the A/W interface and fundamental insight into the influence of microstructure (domain size, phase-separated structures, crystalline morphology, etc.) on the interfacial properties of blends as Langmuir films.     

THE NATURE OF COLLOID AND INTERFACE OF MISCIBLE PHASE SYSTEM IN ALKALINE-SURFACTANT COMBINATION FLOODING

Several representative systems of surfactant + alkaline combination flooding are chosen to study in this paper, these systems are characterized in two points: The first: oil is miscible with water only by reversing them five to ten times, this miscible process is close to spontaneous. Interfacial tension between oil and aqueous is ultra-low. The second: this type of systems is high dispersion and can be stabilized in a period of time. These systems are observed by inicroscopy, polarizing microscopy, microcalorimetry, laser particles analysis instrument and interfacial tension meter, it is found that small particles are main constituent and special liquid crystals distributed on the surface of small particles exist. Small particles and special liquid crystals are responsible for producing ultra-low interfacial tension. The middle phase microemulsion of sodium dodecylsulfate is studied. By comparing difference and similarity between middle phase microemulsion and miscible system, mechanisms of forming low interfacial tension in miscible system and middle phase microemulsion are discussed initially.     

The morphology of aerosol particles consisting of hydrophobic and hydrophilic phases: hydrocarbons, alcohols and fatty acids as the hydrophobic component

The morphology of bi-phase aerosol particles containing phase separated hydrophobic and hydrophilic components is considered, comparing simulations based on surface and interfacial tensions with measurements made by aerosol optical tweezers. The competition between the liquid phases adopting core-shell and partially engulfed configurations is considered for a range of organic compounds including saturated and unsaturated hydrocarbons, aromatics, alcohols, ketones, carboxylic acids, esters and amines. When the solubility of the organic component and the salting-out of the organic component to the surface by the presence of concentrated inorganic solutes in the aqueous phase are considered, it is concluded that the adoption of a partially engulfed structure predominates, with the organic component forming a surface lens. The aqueous surface can be assumed to be stabilised by a surface enriched in the organic component. The existence of acid-base equilibria can lead to the dissociation of organic surfactants and to significant lowering of the surface tension of the aqueous phase, further supporting the predominance of partially engulfed structures. Trends in morphology from experimental measurements and simulations are compared for mixed phased droplets in which the organic component is decane, 1-octanol or oleic acid with varying relative humidity. The consequences of partially engulfed structures for aerosol properties are considered.     

离子液体表/界面性质与结构

离子液体与气体、溶剂等物质组成的多相体系为吸收、萃取、两相催化等技术的发展提供了新的平台。离子液体的表/界面性质与结构是含离子液体多相体系的重要科学问题,可在介观尺度下显著影响多相体系反应和分离过程的效率。近年来,离子液体表/界面性质和结构的研究得到了广泛的关注。本文综述了离子液体及其与水、有机溶剂组成的混合物的表/界面张力及结构研究进展,介绍了现有的研究方法、研究对象与研究成果,归纳了离子液体及其混合物表/界面张力及结构的变化规律,分析了表/界面结构与表/界面张力之间的关系,探讨了离子液体表/界面研究存在的问题和未来的发展方向。     

Partition Coefficients and Interfacial Activity for Polar Components in Oil/Water Model Systems

Partition coefficients, surface tension, and interfacial tension for some polar organic components dissolved in oil/water model systems have been investigated. The systems consist of isooctane modeling the oil phase and of water solutions of NaCl and CaCl2 modeling the water phase. The organic compounds examined were 1-naphtoic acid, 5-indanol, and quinoline, all well-defined molecules known to be representative of polar components in crude oil. The dependence on pH, salinity, and ionic strength in the water phase was investigated. The surface tension and interfacial tension were also examined as a function of component concentration. The results show a connection between the distribution of the polar components and the interfacial tension. Correspondence between the partition coefficient and the pKa value for the components is also reported. For 1-naphtoic acid none of the two ionization forms of the molecule are found to be surface active in aqueous solution. For 5-indanol both forms are surface active, and for quinoline only the nonionic form of the molecule is found to be surface active. The results indicate that the aqueous phase is the one that governs the interfacial tension. Increasing salinity increases the concentration of the component in the oil phase and decreases the interfacial tension between the oil phase and the aqueous phase. The results are explained due to the "salting-out" effect and to changes in the electrostatics for the various systems. Copyright 1999 Academic Press.     

Finite-size effects in dissipative particle dynamics simulations

We have performed dissipative particle dynamics (DPD) simulations to evaluate the effect that finite size of transversal area has on stress anisotropy and interfacial tension. The simulations were carried out in one phase and two phases in parallelepiped cells. In one-phase simulations there is no finite-size effect on stress anisotropy when the simulation is performed using repulsive forces. However, an oscillatory function of stress anisotropy is found for attractive-repulsive interactions. In the case of liquid-liquid interfaces with repulsive interaction between molecules, there is only a small effect of surface area on interfacial tension when the simulations are performed using the Monte Carlo method at constant temperature and normal pressure. An important but artificial finite-size effect of interfacial area on surface tension is found in simulations in the canonical ensemble. Reliable results of interfacial tension from DPD simulations can be obtained using small systems, less than 2000 particles, when they interact exclusively with repulsive forces.     

Effect of charged colloidal particles on adsorption of surfactants at oil-water interface

A change of oil/water interfacial tension in the presence of cationic or anionic surfactants in an organic phase was observed due to the addition of charged fine solids in the aqueous phase. The charged fine solids in the aqueous phase adsorb surfactants diffused from the oil phase, thereby causing an increase in the bulk equilibrium surfactant concentration in the aqueous phase, governed by the Stern-Grahame equation. Consequently, surfactant adsorption at the oil-water interface increases, which was demonstrated from the measured reduction of the oil-water interfacial tension. The increased surfactant partition in the aqueous phase in the presence of the charged particles was confirmed by the measured decrease in the surface tension for the collected aqueous solution after solids removal, as compared with the cases without solids addition.     

Competitive adsorption of surfactants and hydrophilic silica particles at the oil-water interface: interfacial tension and contact angle studies

The effect of surfactants' type and concentration on the interfacial tension and contact angle in the presence of hydrophilic silica particles was investigated. Silica particles have been shown to have an antagonistic effect on interfacial tension and contact angle in the presence of both W/O and O/W surfactants. Silica particles, combined with W/O surfactant, have no effect on interfacial tension, which is only dictated by the surfactant concentration, while they strongly affect interfacial tension when combined with O/W surfactants. At low O/W surfactant, both particles and surfactant are adsorbed at the interface, modifying the interface structure. At higher concentration, interfacial tension is only dictated by the surfactant. By increasing the surfactant concentration, the contact angle that a drop of aqueous phase assumes on a glass substrate placed in oil media decreases or increases depending on whether the surfactant is of W/O or O/W type, respectively. This is due to the modification of the wettability of the glass by the oil or water induced by the surfactants. Regardless of the surfactant's type, the contact angle profile was dictated by both particles and surfactant at low surfactant concentration, whereas it is dictated by the surfactant only at high concentration.     

Erosion‐dependant continuity development in high viscosity ratio blends of very low interfacial tension

This work studies continuity development and cocontinuity in high viscosity ratio EPDM/PP blends. A very low interfacial tension (0.3 mN/m) between the blend components together with high viscosity ratios (11 and 17) result in a variety of unusual morphological features, including isolated nanometer diameter fibers, very large particles, partially coalesced particles, and numerous particles interconnected by fibers. This unique combination of morphologies leads the blend to a novel and stable cocontinuous structure of partially coalesced particles and particles interconnected by fibers. Compared with low to medium viscosity ratio EPDM/PP blends, these cocontinuous networks demonstrate early percolation thresholds, rapid continuity development, and attain cocontinuity at lower compositions of minor phase. The slow surface erosion of the high viscosity EPDM phase during melt blending is shown to be responsible for the generation of these unusual morphological structures. Typically the timescale for erosion phenomena are so small that they have defied study in the mixing environment itself and typical blend morphology studies almost always examine the final steady‐state morphology obtained after several minutes of mixing. The combination of very low interfacial tension and very high viscosity ratios of these EPDM/PP systems provide a unique opportunity to examine erosion phenomena persisting over longer time scales during melt mixing. We propose a new concentration‐dependant erosion mechanism that is based on particle collision–coalescence–separation dynamics. The proposed conceptual mechanism is shown to dramatically accelerate the erosion process and maintain cocontinuity over prolonged periods of mixing. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1919–1929, 2006     

Influence of Interfacial Tension on Seeded Calcium Carbonate Scale Precipitation: Effect of Adsorbed Asphaltenes

Clay particles with adsorbed asphaltenes, which are commonly found in produced water, have been used as seed particles during precipitation of calcium carbonate in order to determine whether such particles may influence the kinetics of precipitation. The results show that the presence of the adsorbed asphaltenes accelerates the precipitation, and there is also a significant difference between different types of adsorbed asphaltenes. The adsorption of asphaltenes at the seed surface leads to a significant increase in the interfacial tension between the seed surface and the aqueous solution, and calcium carbonate therefore precipitates at the seed surface in order to reduce this high interfacial tension.     

Metastable extension of the liquid-vapor phase equilibrium curve and surface tension

The method of molecular dynamics has been used to calculate the parameters of liquid-vapor phase equilibrium and the surface tension in a two-phase system of 4096 Lennard-Jones particles. Calculations have been made in a range from the triple point to near-critical temperature and also at temperatures below the triple point corresponding to the metastable equilibrium of a supercooled liquid and supersaturated vapor. To determine the surface tension, along with a mechanical approach a thermodynamic one has been used as well. The latter was based on calculation of the excess internal energy of an interfacial layer. It has been shown that in accuracy the thermodynamic approach is as good as the more sophisticated mechanical one. Low-temperature asymptotics of the phase-equilibrium curve and also of liquid and vapor spinodals have been considered in the Lennard-Jones and the van der Waals models. The behavior of the surface tension and the excess internal energy of an interfacial layer at T-->0 is discussed.     

Rheological parameters of protein interfacial layers as a criterion of the transition from stable emulsions to microemulsions

Proteins are considered as surface active substances. On the basis of experimentally measured rheological parameters of interfacial layers, protein accumulation at an interface between two immiscible liquids, isotherms of interfacial tension, accounting theoretical ideas elaborated for multicomponent systems, the formation of interfacial layers was referred to phase transition. The property of proteins to stabilise emulsions supposedly is connected with the formation of middle phases of lamellar structure. The correlation between elastic properties of interfacial layers and a phase transition of the middle phase upon addition of salts or lipids has been shown. Lipids being added as cosurfactants lead to the transition from lamellar to other structures, which does not provide emulsion stabilisation.     

Controlling phase distributions in macroporous composite materials through particle-stabilized foams

Aqueous foams stabilized by ceramic and thermoplastic polymeric particles provide a general method for producing novel porous materials because their extraordinary stability against disproportionation and drainage allows them to be dried and sintered into solid materials. Here, we report the different microstructures that can be obtained from liquid foams stabilized by binary mixtures of particles when the interfacial energies between the particles and the air-liquid interfaces are manipulated to promote either preferential or competitive self-assembly of the particles at the foam interface. Modification of the interfacial energies was accomplished through surface modification of the particles or by decreasing the surface tension of the aqueous phase. Materials derived from liquid foams stabilized by poly(vinylidene fluoride) (PVDF) and alumina (Al(2)O(3)) particles are investigated. However, as is shown, the method can be extended to other polymeric and ceramic particles and provides the possibility to manufacture a wide range of porous composite materials.     

Study of types and mixture ratio of organic solvent used to dissolve polymers for preparation of drug-containing PLGA microspheres

The effects of the types and the ratios of various organic solvents used as a mixtures to dissolve poly (lactide-co-glycolide) (PLGA) by using a solvent evaporation method, a technique used to prepare polymer particles, were carefully studied in order to investigate their advantages in developing drug delivery system (DDS) formulations for the prepared microspheres. The particle size and drug loading efficiency of drug-containing PLGA microspheres were found to be dependent on the types of solvent used due to the interfacial tension between the organic solvent and water phase. The drug loading efficiency of monodisperse microspheres prepared by using a membrane emulsification technique employing organic solvents and high interfacial tension for dissolving the PLGA was increased in a controlled manner. The organic solvents with high interfacial tension in the water phase used for the preparation of polymer particles by means of the solvent evaporation method were found to be suitable in terms of improvement in the properties of DDS formulations.     

Gas-liquid phase separation in oppositely charged colloids: stability and interfacial tension

We study the phase behavior and the interfacial tension of the screened Coulomb (Yukawa) restricted primitive model (YRPM) of oppositely charged hard spheres with diameter sigma using Monte Carlo simulations. We determine the gas-liquid and gas-solid phase transitions using free energy calculations and grand-canonical Monte Carlo simulations for varying inverse Debye screening length kappa. We find that the gas-liquid phase separation is stable for kappasigma相似文献   

Interfacial properties of emulsions stabilized with surfactant and nonsurfactant coated boehmite nanoparticles

The properties of emulsions stabilized with surface-modified boehmite particles of 26 and 8 nm in diameter have been investigated. The surface-modified particles were prepared by mixing aqueous dispersions of cationic boehmite particles with aqueous solutions of the surfactant p-dodecylbenzenesulfonic acid (DBSA) or the nonsurfactant p-toluenesulfonic acid (TSA). For the 26 nm particles, interfacial tension measurements indicate that p-dodecylbenzenesulfonic acid partitions between the particle surface and the oil-water interface, while p-toluenesulfonic acid remains on the particle surface. The partitioning of p-dodecylbenzenesulfonic acid supports the formation of emulsions, although in the absence of the particles the same surfactant concentration is not sufficient for emulsion stabilization. Due to the fast exchange kinetics, p-dodecylbenzenesulfonic acid is gradually replaced by particles. At equilibrium, the interfacial tension in the presence of the surface-modified particles is between the values for the pure particles and the pure surfactant solutions. However, the interfacial tension is independent of the surfactant concentration used in the preparation of the particles. Reducing the particle size to 8 nm leads to increased emulsion stability, and thus, the minimum particle concentration required to prepare stable emulsions was reduced to 0.1 g/L. However, above approximately 3.5 mmol/L of the sulfonic acids, the small particles dissolve slowly, and the emulsion stability is lost. This mechanism can be used to trigger the collapse of the emulsions.     

Interfacial dynamics and rheology of polymer-grafted nanoparticles at air-water and xylene-water interfaces

Particle-stabilized emulsions and foams offer a number of advantages over traditional surfactant-stabilized systems, most notably a greater stability against coalescence and coarsening. Nanoparticles are often less effective than micrometer-scale colloidal particles as stabilizers, but nanoparticles grafted with polymers can be particularly effective emulsifiers, stabilizing emulsions for long times at very low concentrations. In this work, we characterize the long-time and dynamic interfacial tension reduction by polymer-grafted nanoparticles adsorbing from suspension and the corresponding dilatational moduli for both xylene-water and air-water interfaces. The dilatational moduli at both types of interfaces are measured by a forced sinusoidal oscillation of the interface. Surface tension measurements at the air-water interface are interpreted with the aid of independent ellipsometry measurements of surface excess concentrations. The results suggest that the ability of polymer-grafted nanoparticles to produce significant surface and interfacial tension reductions and dilatational moduli at very low surface coverage is a key factor underlying their ability to stabilize Pickering emulsions at extremely low concentrations.     

Interfacial Molecular Imprinting in Nanoparticle-Stabilized Emulsions

A new interfacial nano and molecular imprinting approach is developed to prepare spherical molecularly imprinted polymers with well-controlled hierarchical structures. This method is based on Pickering emulsion polymerization using template-modified colloidal particles. The interfacial imprinting is carried out in particle-stabilized oil-in-water emulsions, where the molecular template is presented on the surface of silica nanoparticles during the polymerization of the monomer phase. After polymerization, the template-modified silica nanoparticles are removed from the new spherical particles to leave tiny indentations decorated with molecularly imprinted sites. The imprinted microspheres prepared using the new interfacial nano and molecular imprinting have very interesting features: a well-controlled hierarchical structure composed of large pores decorated with easily accessible molecular binding sites, group selectivity toward a series of chemicals having a common structural moiety (epitopes), and a hydrophilic surface that enables the MIPs to be used under aqueous conditions.