二氧化硅悬浮体的絮凝

微细颗粒的胶体二氧化硅广泛应用于橡胶工业、日用化学工业、无机材料工业等众多部门,它的专门用途不下千余种[1]．二氧化硅微细悬浮体是一种典型胶体分散体系,在其中加入大分子显的有机或无机絮凝剂,研究其絮凝规律,不但对研究絮凝现象的理论和实践有意义,而且有助于认识二氧化硅颗粒的表面性质和该分散体系的稳定性．1实验1·1材料和试剂二氧化硅（上海电化厂）：以燃烧法制得的）“品（白炭黑）,D＊T法测其比表面为7（）11。’·g‘．聚丙烯酸胺（＊＊M．广州南中塑料厂）：白色粉末状,用乙醇从水溶液中沉淀、提纯,粘度法测其…     

Dispersion of Silica Fines in Water-Ethanol Suspensions

The dispersion of silica fines in water-ethanol suspensions has been studied through the measurement of settling efficiency, wetting rate, zeta potential, and viscosity. The measurements were performed on two silica samples with mean volumetric diameters of 5.02 and 0.272 &mgr;m at different fractions of ethanol in water-ethanol suspensions. The results have demonstrated that the dispersion stability of the silica suspensions increased as the fraction of ethanol increased and reached to maximum at the fraction of 50%, followed by a decline. The stability was stronger in a pure ethanol suspension than in a pure water suspension. It was observed that the stability closely correlated with the lyophilicity of the particles, but was not predominated by the surface charge of the particles as predicted by the DLVO theory. Viscosity measurements have been used to estimate the solvation film thickness on silica particles immersed in water-ethanol suspensions, on the basis of Einstein's theory of the viscosity of dispersions. It was found that the solvation film thickness on silica fines in a water-ethanol (1 : 1) suspension is about double that in a pure water suspension and about 1.4-fold that in a pure ethanol suspension, respectively, which well explains the dispersion behaviors of the silica fines in the water-ethanol suspensions because a thicker solvation film will cause a stronger disjoining pressure to prevent the proximity of the particles. Copyright 2001 Academic Press.     

Effects of Fumed Silica on the Viscosity of Acrylic Latex System

Effects of fumed silica on the viscosity of acrylic latex system were studied by recording curves of the shear complex viscosity over shear rate and temperature and by measuring apparent viscosity with a variety of fumed silica concentrations at various steady angular velocities. Results show that the fumed silica obviously affects the shape and value of curves on the amplitude of complex viscosity versus either shear rate or temperature diagrams. Both dynamic and steady shear measurements illustrate a shear thinning phenomena for the acrylic latex filled with fumed silica. Dependence of the apparent viscosity on the fumed silica concentration can be satisfactorily modeled by the Krieger‐Dougherty expression. A fitted parameter that quantitatively describes the sensitivity of the effect of fumed silica on the acrylic latex system increases with angular velocity, but decreases with latex solid content.     

Viscosity Behaviors of Rapidly Curable Silica Sols

The viscosity behaviors of rapidly curable transparent silica aerogels, such as time at the onset point and the slope of viscosity increase, are investigated as functions of target density, water and catalyst content. Results were compared with the visually measured gel time. The effects of temperature and shear rate on the onset point and rate of the viscosity increase are also investigated with the selected samples. Experimental design and result analysis were also conducted using the Design of Experiment (DOE) method, and the Arrhenius relation was applied to predict the temperature dependence of viscosity. It is found that the target density and catalyst content played more important roles in determining gelation and viscosity behavior than water content did. As the target density increased, the gel time and the onset point appeared at significantly earlier times and the slope increased more rapidly, while there existed an optimum catalyst and water content for fast gelation and desirable viscosity behaviors. The temperature dependence of the viscosity behaviors of rapidly curable transparent silica sols can be expressed by the Arrhenius relation. The onset time of viscosity increase was little affected by the shear rate at a low shear rate range of up to 1.32 s⁻¹, and after that it linearly decreased with increasing shear rate, while the slope of viscosity increase continuously decreased with increasing shear rate. Overall, the viscosity measurement appears as a simple and reliable method for quantitatively measuring gel time, especially for the rapidly curable sol–gel process.     

Electrorheological Response and Structure Growth of Colloidal Silica Suspensions

The electrorheological response and structure growth of colloidal silica suspension was studied with in situ measurements of the shear stress, electric conductivity, and dielectric permittivity of the suspension. The measurements were carried out under steady and sweep shears after the application of an electric field of alternative current (100 Hz) using silica particles with a diameter of 630 nm and a water content of 4.5 wt%. The measurements of the conductivity enabled the detection of structure growth formed by particle aggregation and clarified that the development of the particle aggregation enlarged the dielectric permittivity and the shear stress. Hysteretic behavior observed in the electrorheological response was explained by considering structure growth of the particle aggregation. The correlation equation for the shear stress and the dielectric permittivity obtained in our previous work (1) was found to be applicable to the present results. Copyright 2001 Academic Press.     

Rheological Properties of Silica Particle Suspensions in Mineral Oil

The rheological properties of particles suspended in a non‐polar mineral oil have been investigated as a function of volume fraction of particles, particle size, surface properties and shear rate. Three different types of particles were investigated; glass microspheres, monodisperse silica particles and fumed silica. The suspensions showed shear thinning behavior at higher volume fractions, and the viscosity increased with decreasing particle size. The hydrophobic particles display lass shear thinning effects. The relative viscosity of all the suspensions was well fitted to the Krieger and Dougherty model.     

Influence of Monovalent Electrolytes on Rheological Properties of Gelled Colloidal Silica Suspensions

Rheological responses of the gelled (G) Snowtex 20 silica suspensions in the presence of LiCl, NaCl, and KCl have been investigated as functions of concentrations of silica and salt at pH 9.8 in terms of the Hofmeister series effect. The primary silica particle is isolated, and it is coagulated to form a gel above at 0.1, 0.3, and 0.5 M concentrations of LiCl, NaCl, and KCl, respectively, when the silica volume fraction φ is beyond 1.0%. The resulting G silica suspensions are classified into a strong‐link gel and their power‐law dependences of the critical strain as well as the storage modulus on the silica volume fraction were compared with the predictions by the fractal gel model. The resulting power‐law exponents of the critical strain are negative, this is in agreement with that predicted by the fractal model, and their magnitudes decrease with an increase in salt concentration, irrespective of the salt. Moreover, the magnitude of the power‐law exponent for the critical strain is well related to the Hofmeister series effect, namely it decreases in the order Li⁺, Na⁺, and K⁺, and the least hydrated K⁺ adsorbs in great enough in amount to create a less flexible network structure in the G silica suspension due to stronger attraction between the silica particles. Moreover, the stronger attraction, on the other hand, should be responsible for both the larger storage modulus and the higher power‐law exponent of the silica volume fraction dependence on the storage modulus. Therefore, the Hofmeister series effect is useful to understand the rheological properties of the G Snowtex 20 silica suspensions.     

Interaction of Quercetin with Highly Dispersed Silica in Aqueous Suspensions

The adsorption of a flavoanoid, quercetin, from water–ethanol solutions on the highly dispersed silica surface was investigated as a function of the ethanol and polyvinylpyrrolidone concentrations. Solvation effects of quercetin in the molecular and deprotonated forms and also in the adsorbed state were theoretically considered.     

Properties of Aqueous Suspensions of Highly Dispersed Silica in the Presence of Polyvinylpyrrolidone

The effect of polyvinylpyrrolidone (PVP) on stability, rheological, electrokinetic and electrophysical properties of aqueous dispersions of A-300 pyrogenic silica was studied. The suspensions were shown to be most stable at PVP concentrations in the range from 0.12 to 0.24 wt % that was provided by structure-related mechanical factors. In the presence of PVP, the value of -potential decreases, the ac conductivity increases, and rheological properties vary similarly to variations of oxide dispersity.     

SiO_2表面性质对LBG丙酮溶液体系粘度的影响

本文讨论了增塑剂、剪切速率、不同含量和不同表面性质的二氧化硅对LBG(一种偏氟乙烯和六氟丙烯共聚物 )的丙酮溶液粘度的影响机理     

Experimental Study on Viscosity of Colloidal Silica in Aqueous Electrolytic Solutions

The relative viscosity of colloidal silica dispersion in aqueous electrolytic solutions as the function of volume fraction of dry particles in the solutions has been experimentally determined in this work, in order to study the effects of pH and electrolytes (Na₂SO₄ and AlCl₃) on the hydration of the silica surfaces in the solutions. The results have shown that the maximum relative viscosity of the silica dispersion and the strongest hydration of the silica in aqueous solutions appeared at neutral pH, while the stronger the acidity and the alkalinity of the aqueous solution, the weaker the hydration. In the presence of the electrolytes (Na₂SO₄ and AlCl₃), the relative viscosity of the silica dispersion reduced and the hydration of the silica in aqueous solutions became weak. The higher the concentration of the electrolytes, the weaker the hydration, indicating that the destabilization of the colloidal silica dispersion in aqueous solutions might be realized through adding the high-valence electrolytes to weaken the hydration of the particle surfaces (hydration forces between the particles). Also, it has been shown that the negative zeta potentials of the colloidal silica in aqueous solutions greatly reduced in the presence of the electrolytes. Therefore, the high-valence electrolytes (Na₂SO₄ and AlCl₃) as the coagulant of colloidal silica in aqueous solutions might be originated from that the presence of the electrolytes simultaneously reduces the electrical double layer repulsive force and the hydration repulsive forces between the particles in aqueous solutions.     

Contribution of Steric Repulsion to Retention on an Octadecylsiloxane-Bonded Silica Stationary Phase in Reversed-Phase Liquid Chromatography

Plots of the retention factor against mobile phase composition were used to organize a varied group of solutes into three categories according to their retention mechanism on an octadecylsilioxane-bonded silica stationary phase, Ascentis ^TM C18, with acetonitrile-water and methanol-water mobile phase compositions containing 10–70% (v/v) organic solvent. The solutes in category 1 could be fit to a general retention model, Eq. (1), and exhibited normal retention behavior for the full composition range. The solutes in category 2 exhibited normal retention behavior at high organic solvent compositions with a discontinuity at low organic solvent mobile phase compositions. The solutes in category 3 exhibited a pronounced step or plateau in the middle region of the retention plots with a retention mechanism similar to category 1 at mobile phase compositions after the discontinuity and a different retention mechanism before the discontinuity. Selecting solutes and appropriate composition ranges from the three categories where a single retention mechanism was operative allowed modeling of the experimental retention factors using the solvation parameter model. These models were then used to predict retention factors for solutes excluded from the models. The overwhelming number of residual values, here defined as the difference between experimental and model predicted retention factors for the excluded solutes, could be explained by contributions from steric repulsion. The latter defined as the inability of solutes to fully insert themselves into the solvated stationary phase because of their size or conformation. Steric repulsion resulted in a systematic reduction in retention compared with predicted values for the fully inserted solute. The bonding density of the stationary phase; the type and composition of the mobile phase; and the size, conformation, type and number of functional groups on the solute are shown to affect the contribution of steric repulsion to the retention mechanism.     

Shear-Induced Changes in Rheological Reponses and Neutron Scattering Properties of Hydrophobic Silica Suspensions at Low Silica Concentrations

Rheological responses of hydrophobic fumed silica powders, whose surface silanol groups were modified by hexadecane, suspended in 1,4-dioxane at lower silica concentrations than 6.8 vol% have been investigated as a function of the silica concentration. Transient shear stress behavior before attaining the steady-state shear stress could be classified into three regimes as follows, irrespective of the silica concentration: at the lower shear rates than ca. 0.3 s^?1 a stress overshoot was observed, at the shear rate ranges from 0.3 to 30 s^?1 sustained oscillations in shear stresses were exhibited and these oscillations were first observed for the suspensions at the low particle concentrations, and beyond the shear rate of 30 s^?1 a sigmoid decrease of the shear stress with increasing time, that is, structural breakdown, was observed. At the steady state the silica suspensions showed shear thickening. Small angle neutron scattering (SANS) measurements of the silica suspension under shear flow provided that changes in the SANS intensities were well correlated with the shear thickening behavior. However, shear thinning behavior at higher shear rates did not cause any changes in the SANS intensities.     

Stability and Flow-Induced Flocculation of Fumed Silica Suspensions in Mixture of Water-Glycerol

A systematic investigation has been performed to relate the effect of glycerol composition to the rheological properties of aqueous suspensions of hydrophilic fumed silica at pH far from the isoelectric point. Steady state/dynamic rheology and electrophoresis measurements are compared to correlate the stability of the suspension with particle-particle and particle-solvent interactions. Although the extent of electrostatic stability is reduced by addition of glycerol, the rheological properties show a transition from a highly flocculated gel to stable dispersions containing no microstructures. This is attributed to a high degree of hydrogen-bonding between glycerol and the Aerosil surface silanol groups. Small dissociation of NaCl and particles reduce the effect of ion exchange and particle bridging mechanisms when the suspensions destabilise in the presence of glycerol. The high viscosity of glycerol is important with respect to the formation of a thick solvation layer around the particles. These parameters give rise to short-range, non-DLVO repulsive solvation forces, which stabilise the dispersion. At intermediate concentrations of glycerol (30–60 wt%) the apparent viscosity increase abruptly and irreversibly as both the extent and time of shearing are increased. The shear rate for the onset of the shear thickening is found to be retarded by decreasing the particle and salt concentration as well as by increasing the glycerol concentration. It is postulated that at intermediate glycerol concentration, where the height of the energy barrier is small, mechanical forces can activate the particles to overcome the energy barrier to enter the region where attractive forces dominate. Here, domination of the hydrodynamic forces to the colloidal forces under the shear results in formation of irreversible gels which does not relax to its initial condition.     

Electrostatic Retention Mechanism of 2,2'-Dihydroxyazobenzene-Metal chelates on Octadecylsilanized Silica Stationary Phase

The chelating agent 2,2'-dihydroxyazobenzene (DHAB), as shown in Fig. 1, was superior to the determination of trace metal ions by HPLC with ion-pair partition mode. Among the DHAB-metal chelates, only the cationic DHAB-aluminium 1:lchelate,[AIL]⁺, is fluorescent. Thus this chelate is expected to be applicable for selective and sensitive determination of aluminium ion by HPLC. However, the retention behavior of[AlL]⁺ on octadecylsilanized silica stationary phase was not well understood. The interaction between[A1L]⁺ and octadecylsilanized silica stationary phase has been investigated.     

The Effect of Composition of Water-Ethanol Solutions on Coagulation Kinetics of Amorphous Monodisperse Silica Suspensions

The effect of the composition of water-ethanol solutions on the coagulation kinetics of dilute amorphous monodisperse silica suspensions is studied using flow ultramicroscopy technique. It is found that the suspensions prepared by the addition of an aliquot of concentrated and stored for more than 20 days suspension of the aforementioned silica in 96% ethanol to water-ethanol mixtures containing 96–80 vol % of ethanol are stable with respect to aggregation. A decrease in the alcohol concentration in a system leads to an ultrafast coagulation, whose characteristic time (coagulation period) is much smaller than the value corresponding to the Smoluchowski theory of fast coagulation. It is established that the highest coagulation rate is observed for the suspensions containing 40 vol % of ethanol. Mechanisms of the aggregation stability and ultrafast coagulation of the studied suspensions are discussed.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 475–478.Original Russian Text Copyright © 2005 by Zhukov, Zavarovskaya, Chernoberezhskii.     

Aqueous Suspensions of Poly(ethylene Glycol)/Pyrocarbon/Fumed Silica

Aqueous suspensions of fumed silica and pyrocarbon/silica (CS) in the presence of dissolved poly(ethylene glycol) (PEG) were studied using (1)H NMR spectroscopy with freezing-out of bulk water and quantum chemical computations of the chemical shifts. The freezing effect for PEG/water is akin to that for low-molecular organics, as formation of solid phases of water (ice) and PEG occurs, and their mixture forms at the eutectic temperature. In the aqueous suspensions of fumed silica or CS, PEG molecules are localized at the solid-liquid interfaces and do not form the bulk solution even at large concentrations; however, the amount of bulk undisturbed water rises due to formation of the immobilized PEG layer. For such suspensions of silica or CS at a low amount of pyrocarbon (C(C)=4 wt%), there is a portion of the graph of the surface free energy (gamma(S)) increasing nearly linearly with the PEG concentration (C(PEG)); however, in the case of large C(C)=40 wt% in CS, a similar effect is not observed, as gamma(S) is maximal at low C(PEG)=0.1 wt%. Copyright 2001 Academic Press.     

Nucleation of Supramolecular Crystals in Suspensions of Monodispersed Spherical Silica Particles During Sedimentation

Growth of supramolecular crystals (SC) was studied during sedimentation in suspensions of monodisperse spherical silica particles (MSSP). The number of growth centers was found to decrease depending on the deionization of the dispersion. The process is accompanied by the corresponding enlargement of the crystals. The volume and surface components of the Gibbs energy of nucleation do not determine the probability of nucleation. The energy of electrostatic repulsion of ions covering structural units (SU), which exceeds the MSSP molecular gravitation, was the only parameter found to correlate with the number of crystallization centers.