Electrorheological behavior of low filled suspensions of highly anisometric montmorillonite particles

The electrorheological (ER) behavior of modified montmorillonite (MMT) suspensions in polydimethylsiloxane is studied. As established by rotational viscometry, the samples with a dispersed phase concentration from 1 to 8 wt % reveal viscous Newtonian behavior and dramatically change their properties to elastic when electric field is applied. The rheological characteristics of the suspensions over 0–7 kV mm⁻¹ range of electric field strengths are also studied. Novel X-ray diffraction method is developed to evaluate the suspension of the filler in a siloxane medium and to calculate the degree of its exfoliation. The dependence of exfoliation degree, dielectric, and ER characteristics on the type of modifier in the MMT structure is considered. Based on the obtained data, a new model of system behavior with the various types of fillers is proposed and the prospects of utilizing MMT as a filler for ER fluids are demonstrated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47678.     

Effects of pH and temperature on the sorption of sodium dodecyl sulfate by cellulose acetate/polyaniline blend membranes

Cellulose acetate/polyaniline (PANi) blends show a selective response to the presence of sodium dodecyl sulfate (SDS). Such detection can be monitored by visible absorption spectroscopy. In this article, we show how this is dependent on the pH and temperature. At pH 2, the redshift of the maximum absorbance wavelength of blend films is essentially dependent on hydrochloric acid; however, at pH 3, this effect clearly decreases, and at pH values between 4 and 6, the alteration of the blend color depends only on SDS. The selective detection of SDS is faster with a higher percentage of PANi in the blend. At 25°C, the mechanism of sorption is essentially Fickian for short times, but this changes at higher temperatures, and at temperatures of 40°C and higher, the sorption kinetics show an initial time lag in which no visible response from the blend to SDS is detected. The response rate of blends to SDS detection increases with the temperature and PANi content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Colloidal transport phenomena in dynamic,pulsating porous materials

We study the transport phenomena of colloidal particles embedded within a moving array of obstacles that mimics a dynamic, time-varying porous material. While colloidal transport in an array of stationary obstacles (“passive” porous media) has been well studied, we lack the fundamental understanding of colloidal diffusion in a nonequilibrium porous environment. We combine Taylor dispersion theory, Brownian dynamics simulations, and optical tweezer experiments to study the transport of tracer colloidal particles in an oscillating lattice of obstacles. We discover that the dispersion of tracer particles is a nonmonotonic function of oscillation frequency and exhibits a maximum that exceeds the Stokes–Einstein–Sutherland diffusivity in the absence of obstacles. By solving the Smoluchowski equation using a generalized dispersion framework, we demonstrate that the enhanced transport of the tracers depends critically on both the direct interparticle interactions with the obstacles and the fluid-mediated, hydrodynamic interactions generated by the moving obstacles.     

天然土壤胶体对U(Ⅵ)迁移的影响

以石英砂为填充介质,采用动态柱实验方法研究了某中低放处置场地表土壤胶体对U(Ⅵ)在石英砂柱中迁移行为的影响,并结合静态批式实验探究了土壤胶体对U(Ⅵ)迁移的影响机制。结果表明,当U(Ⅵ)进样质量浓度从1.0 mg/L增大至5.0 mg/L时,U(Ⅵ)在石英砂柱中的穿透速率显著增大,且达到洗脱平衡时所需淋洗液的体积从250 PVs(孔隙体积)增大至400 PVs。与U(Ⅵ)相比,土壤胶体在石英砂柱内迁移较快,这可能是由于土壤胶体与石英砂之间相互作用较弱所致。土壤胶体与U(Ⅵ)共存体系中,U(Ⅵ)的迁移速率明显增大,而土壤胶体迁移速率无显著变化,表明共存体系中U(Ⅵ)的迁移行为主要受土壤胶体所控制。静态吸附实验表明,在石英砂-U(Ⅵ)二元体系中,pH≈6.0时石英砂对U(Ⅵ)的吸附率最大,而在胶体-石英砂-U(Ⅵ)三元体系中,U(Ⅵ)主要在土壤胶体表面发生吸附。本研究所用土壤中胶体的质量分数仅约占0.04%,但可吸附20%U(Ⅵ)(初始质量浓度为5.0 mg/L);由此可见,土壤胶体可与U(Ⅵ)发生强的相互作用,进而对U(Ⅵ)在真实环境体系中的吸附、迁移和扩散等行为产生至关重要的影响。     

坝址渗水析出物及其潜在影响研究

坝址析出物是伴随渗水而出现的，对大坝安全运行具有潜在的不利影响。采用现场调查、取样多手段测试等方法，对此进行综合分析与评价。按照出露位置，可分为坝基及坝体析出物两类。其形成机理包括溶解—沉淀作用、还原—氧化—絮凝作用、浸析作用等。坝址析出物的潜在影响反映在对岩体的渗透稳定性、对帷幕体的防渗时效性以及对坝体结构的耐久性等方面；不同成因的析出物具有不同的潜在影响程度：化学成因者多限于微观方面，而物理成因者则在一定阶段可显现在宏观方面。在实际工作中，应加强对具有物理成因或化学—物理双重成因一类析出物的监测。     

Gelation—A review

This paper reviews the modern ideas on the process of gelation which have arisen from the analogy between gelation and percolation. The basic features which are common to all types of gels, colloidal or polymeric systems are first recalled; then after a simplified presentation of the percolation model, a few examples illustrating these concepts are chosen (for chemical gelation, a copolymerisation reaction and for physical gelation, the gelatin sol-gel transition). In conclusion, electron micrographs of gel networks (gelatin gel and an inorganic gel of thorium phosphate) are shown, which reveal the great diversity and complexity of the structures.     

A new route for the preparation of cyano‐containing poly(N‐isopropylacrylamide) microgel latex for specific immobilization of antibodies

A prepolymerization process was used to prepare functionalized poly(N‐isopropylacrylamide) latexes with surface cyano groups. The functionalized latexes prepared were characterized by FTIR, ¹H NMR, scanning electron microscopy and quasi‐elastic light scattering. In addition, the polymerization conversion and the water‐soluble polymer amounts were quantified. The polymerization conversions were found to be above 80% with 5–14 wt% of water soluble polymer formation. The immobilization of antibody (immunoglobulin) onto such cyano‐containing thermally sensitive particles, suggests the feasibility of specific dipole–dipole interactions between the cyano and hydroxyl functional groups from particle and antibody, respectively. Copyright © 2004 Society of Chemical Industry     

Aqueous Dispersion and Slip Casting of Boron Carbide Powder: Effect of pH and Oxygen Content

The effect of pH and oxygen content on the zeta potential, viscosity, and casting performance of fine (>3 μm) boron carbide powder is presented. X-ray photoelectron spectroscopy of the powder revealed a surface layer of adsorbed water and oxides of boron and carbon. The soluble boric acid impurity was removed by washing the powder with water or alcohols. Electrophoresis indicated that the B₄C surface was negatively charged in water above pH 1, but the presence of dissolved boric acid suppressed the zeta potential at high pH. Stable, low-viscosity dispersions of >30 vol% solids were prepared and slip cast at pH >6, but boric acid was destabilizing for dispersions prepared above pH 7. The green density of slip-cast parts was more reproducible and about 3% to 5% higher for washed powders than for high-oxygen-content powders.