Effect of Interfacial Adsorption on the Stability of Thin Polymer Films in a Solvent-induced Process

The stability of ultrathin polymer films plays a crucial role in their technological applications.Here,we systematically investigated the influence of interfacial adsorption in physical aging and the stability of thin polymer films in the solvent-induced process.We further identify the stability mechanism from the theory of thin film stability.Our results show that the aging temperature and film thickness can strongly influence the stability of thin PS films in acetone vapor.Physical aging can greatly improve the stability of thin polymer films when the aging temperature T_(aging1)>T_(g).A thinner PS film more quickly reaches a stable state via physical aging.At short aging time,the formation of the adsorbed layer can reduce the polar interaction;however,it slightly influences the stability of thin polymer films in the solvent-induced process.At later aging stage,the conformational rearrangement of the polymer chains induced by the interfacial effect at the aging temperature Taging1 plays an important role in stabilizing the thin polymer films.However,at T_(aging2)<T_(g),the process of physical aging slightly influences the stability of the thin polymer films.The formation of the adsorbed layer at Taging2 can reduce the short-range polar interaction of the thin film system and cannot suppress the instability of thin polymer films in the solvent-induced process.These results provide further insight into the stable mechanism of thin polymer films in the solvent-induced process.

Electrochemical study on adsorption behavior of surfactants at β-2CaO·SiO2/NaAlO2 interface

β-2CaO＇SiO2 was obtained with analytical grade reagents. Polyethylene glycol （PEG）, sodium polyacrylate （PAAS） and their mixture were used to inhibit the decomposition of β-2CaO·SiO2 in sodium aluminate solution. The potential of solid-liquid interface and the adsorption mechanism were studied by the methods of Zeta potential measurement and XPS. The results indicate that PEG and PAAS have synergistic effect on the inhibition of secondary reaction. The inhibitory effect is the best when the volume ratio of PAAS to PEG is 1：1 and the total concentration is 12.5 mg/L. PAAS adsorbs on the surface of β-2CaO-SiO2 by the formation of --COOCa coordinate bond, and the negative charge enters into Stem layer, which results in the decrease of particle potential and the obvious change of binding energy of Ca 2p, Si 2p and O Is. PEG only physically adsorbs on the surface ofβ-2CaO·SiO2, and had little effect on particle potential and binding energy of Ca 2p, Si 2p and O Is.

Wear behavior of SiC/PyC composite materials prepared by electromagnetic-field-assisted CVI

Silicon carbide/pyrolytic carbon (SiC/PyC) composite materials with excellent performance of self-lubrication and wear resistance were prepared on SiC substrates by electromagnetic-field-assisted chemical vapor infiltration (CVI). The composition and microstructure of the SiC/PyC materials were investigated in detail by XRD, SEM and EDS, etc. The effects of the deposition temperature on the section features and wear resistance of the SiC/PyC were studied. The results show that the PyC layers were deposited onto SiC substrates spontaneously at a lower deposition temperature. The SiC substrates deposited with PyC can significantly reduce the wear rate of the self-dual composite materials under dry sliding condition. The wear tests suggest that the SiC/PyC composite materials own a better wear resistance property when the deposition temperature is 800 °C, and the wear rate is about 64.6% of that without the deposition of PyC.

Hybrid surfactant-nanoparticles assisted CO_(2) foam flooding for improved foam stability:A review of principles and applications

Miscible carbon dioxide(CO_(2))flooding is a well-established and promising enhanced oil recovery(EOR)technique whereby residual oil is recovered by mixing with injected CO_(2)gas.However,CO_(2),being very light and less viscous than reservoir crude oil,results in inefficient sweep efficiency.Extensive research is ongoing to improve CO_(2)mobility control such as the development and generation of CO_(2)/water foams.The long-term stability of foam during the period of flooding is a known issue and must be considered during the design stage of any CO_(2)foam flooding project.The foam stability can be improved by adding surfactants as stabilizers,but surfactants generated foams have generally a shorter life because of an unstable interface.Furthermore,surfactants are prone to higher retention and chemical degradation in the porous media,particularly under harsh reservoir conditions.Research has shown that nanoparticles(NPs)can act as an excellent stabilizing agent for CO_(2)/water foams owing to their surface chemistry and high adsorption energy.The foams generated using NPs are more stable and provide better mobility control compared to surfactant-stabilized foams.One limitation of using NPs as foam stabilizers is their colloidal stability which limits the use of low-cost NPs.Combining surfactants and NPs for CO_(2)foam stabilization is a novel approach and has gained interest among researchers in recent years.Surfactants improve the dispersion of NPs in the aqueous phase and minimize particle aggregation.NPs on the other hand create a stable barrier at the CO_(2)/water interface with the help of surfactants,thus generating highly stable and viscous foams.This paper presents a comprehensive review of the basic principles and applications of stabilized CO_(2)foams.A brief overview of CO_(2)foam flooding is discussed first,followed by a review of standalone surfactant-stabilized and NPs-stabilized CO_(2)/water foams.The application of hybrid surfactant-NPs stabilized CO_(2)foams is then presented and areas requiring further investigation are highlighted.This review provides an insight into a novel approach to stabilize CO_(2)/water foams and the effectiveness of the method as proved by various studies.

Particles dispersion on fluid-liquid interfaces

This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. In this paper we show that motion of particles normal to the interface is inertia dominated; they oscillate vertically about their equilibrium position before coming to rest under viscous drag. This vertical motion of a particle causes a radially-outward lateral （secondary） flow on the interface that causes nearby particles to move away. The dispersion on a liquid-liquid interface, which is the primary focus of this study, was relatively weaker than on an air-liquid interface, and occurred over a longer period of time. When falling through an upper liquid the particles have a slower velocity than when falling through air because the liquid has a greater viscosity. Another difference for the liquid-liquid interface is that the separation of particles begins in the upper liquid before the particles reach the interface. The rate of dispersion depended on the size of the particles, the densities of the particle and liquids, the viscosities of the liquids involved, and the contact angle. For small particles, partial pinning and hysteresis of the three-phase contact line on the surface of the particle during adsorption on liquid-liquid interfaces was also important. The frequency of oscillation of particles about their floating equilibrium increased with decreasing particle size on both air-water and liquid-liquid interfaces, and the time to reach equilibrium decreased with decreasing particle size. These results are in agreement with our analysis.