Dielectric constant of polarizable,nonpolar fluids and suspensions

We study the dielectric constant of a polarizable, nonpolar fluid or suspension of spherical particles by use of a renormalized cluster expansion. The particles may have induced multipole moments of any order. We show that the Clausius-Mossotti formula results from a virtual overlap contribution. The corrections to the Clausius-Mossotti formula are expressed with the aid of a cluster expansion. The integrands of the cluster integrals are expressed in terms of two-body nodal connectors which incorporate all reflections between a pair of particles. We study the two- and three-body cluster integrals in some detail and show how these are related to the dielectric virial expansion and to the first term of the Kirkwood-Yvon expansion.     

Styrene heterophase radical polymerization in the presence of water-soluble polyvinylamides

Heterophase polymerization of styrene in the presence of poly-N-vinylamides of different structures as stabilizers was investigated. Optimal conditions for preparing of stable polystyrene suspensions with narrow size distribution and the factors affecting the diameter and size distributions of polymer particles were established.     

Metal particle adsorption and diffusion in a model polymer/metal composite system

We have developed a model polymer/metal composite system based on the adsorption of colloidal gold particles from a dilute aqueous suspension to the surface of poly(2-vinylpyr-idine) (PVP). Particle coverages and tracer diffusion coefficients for the particles within a PVP matrix phase were measured by Rutherford backscattering spectrometry. The adsorption process is quantitatively described by a diffusion-limited mechanism where gold particles irreversibly adsorb to the surface of the polymer film. Model dispersions produced in this way are excellent model systems for studying the fundamental properties of metal particle dispersions, since the particle size and the areal density of particles on the surface are well-controlled. Diffusion coefficients for the gold particles within PVP were also measured. The diffusion of the gold particles was found to be coupled to the bulk viscosity of the polymer, even though the size of the gold particles was only slightly larger than the mesh size of the entanglement network for PVP. © 1995 John Wiley & Sons, Inc.     

α-Fe粉体浓悬浮体系的制备及磁流变效应

报道使用价格低廉的还原铁粉制备磁性粒子浓悬浮体系 ,对体系磁流变效应进行研究 ,并研究了磁性颗粒尺寸和氧化物对悬浮体系力学性质及沉降稳定性的影响 .     

The elastic properties of sodium montmorillonite suspensions

Shear wave rigidity moduliG have been determined using a shear wave propagation technique for sodium montmorillonite suspensions. Measurements were made as a function of time at various values of pH, NaCl concentration (C) and solids concentration and the data used to estimateG _e the value of the modulus att=. The dependency ofG _e on pH,C and solids concentration is interpreted in terms of the mode of interaction between particles and the associated volume filling structure. The results suggest that whether a coagulated or dispersive structure develops in these suspensions depends not only on pH andC but also on the degree of delamination of the clay.     

ELECTRORHEOLOGICAL PROPERTIES OF TALC POWDER/SILICONE OIL SUSPENSIONS UNDER DC FIELDS

In this study, the electrorheological （ER） behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil （SO） medium was investigated. Sedimentation stabilities of suspensions （c = 5 wt%） prepared using these talc powder powders were determined to be 78 days. The ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. The shear stress of talc powder suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and showed a typical shear thinning non-Newtonian visco-elastic behavior. Effects of frequency on the ER activity of talc powder/SO system were also investigated.     

TEMPO-mediated surface oxidation of cellulose whiskers

Cellulose whiskers resulting from HCl acid hydrolysis of tunicin were subjected to TEMPO-mediated oxidation under various conditions and the extent of the resulting oxidation was characterized by Fourier-transform infrared spectroscopy (FT-IR), conductimetry, X-Ray diffraction analysis and transmission electron microscopy (TEM). With degree of oxidation of up to 0.1 the samples kept their initial morphological integrity and native crystallinity, but at their surface the hydroxymethyl groups were selectively converted to carboxylic groups, thus imparting a negative surface charge to the whiskers. When dispersed in water these oxidized whiskers did not flocculate and their suspensions appeared birefringent when viewed between cross polarizers, thus indicating a liquid crystalline behavior.     

Monitoring the absorption of organic vapors to a solid phase extraction medium applications to detection of trace volatile organic compounds by integration of solid phase absorbents with fiber optic Raman spectroscopy

By combining fiber optic Raman spectroscopy with a C-18 solid phase extraction medium, real time in situ detection of organic vapors is demonstrated. The response of the probe is fully reversible for benzene, trichloroethylene and carbon tetrachloride vapors. Because of the high degree of selectivity afforded by Raman spectroscopy, the composition of mixtures of the vapors can also be determined using the C-18 probe. The detection of ppm levels of benzene in water via headspace analysis using the C-18 probe is demonstrated.     

Numerical and approximate studies on the theoretical dielectric relaxation of colloidal suspensions in the time domain

In this work we show numerical calculations on the dielectric behavior of colloidal suspensions in the time domain. The theory elaborated by DeLacey and White ((1981) J Chem Soc Faraday Trans 2 77:2007–2039) for dilute suspensions in the frequency domain, will be the basis for the present study. The different contributions, and their relative importance, to the transient current density generated in the suspensions after the application of a step electric field, are calculated from the dielectric response function associated to the DeLacey and White's model. In particular, we analyze the conduction and absorption current densities in the transient states upon changing the concentration of the supporting electrolyte in the suspension. With the aim of characterizing the response of the suspension for short times, an approximation to the distribution function of relaxation times that best fits the dielectric model, is calculated. Finally, an exhaustive analysis of the behavior of the dielectric response function is carried out, together with a comparison with other models in the time domain.     

Effects of particle size on near-wall depletion in mono-dispersed colloidal suspensions

In this work we investigate the change in particle concentration near a solid boundary for colloidal dispersions in pressure driven flow, commonly referred to as wall depletion. In particular we determine the effect of Peclet number on the strength and spatial extent of the depleted layer. The change in concentration near the solid boundary is measured with attenuated total reflection infrared (ATR-IR) spectroscopy described previously (P.J.A. Hartman Kok et al., J. Rheol. 46 (2002) 481). The method is capable of measuring the concentration of particles at distances ranging from 0.2 to 1.0 mum from the boundary. The suspensions investigated consisted of mono-dispersed polystyrene particles in water. Particles of four different sizes were used, with radius, a, of 30, 54, 105, and 197 nm. (The ratio H/a was in the range 2500-17,000 with H being the height of the flow cell.) This enabled us to measure the wall depletion effect over a wide range of Peclet numbers, ranging from 0.01 to 45. We found that wall depletion was not significant for Peclet numbers smaller than unity. Estimates of the wall slip layer thickness obtained from rheological experiments were consistent with the results obtained by ATR-IR spectroscopy.