Polystyrene spheres, dispersion

For our experiments we used a charge stabilized suspension of polystyrene spheres dispersed in ultrapure water (Batch No. PS-F-3390, Berlin Microparticles GmbH Germany). The diameter was determined by electron microscopy to be 590 nm. The size polydispersity was determined to be 5.8%. The particles are stabilized with CCX)H- and HSOq-groups and the effective charge was measured by conductivity to be Z = 3(XX) 100. For diluting of the stock solution to a definite volume fraction deionized water of a MilliQ water system was used. To adjust the salt concentration of the suspension NaCl was added to screen the interaction of the particles (typically 1 mM). 

Any fundamental study of the rheology of concentrated suspensions necessitates the use of simple systems of well-defined geometry and where the surface characteristics of the particles are well established. For that purpose well-characterized polymer particles of narrow size distribution are used in aqueous or non-aqueous systems. For interpretation of the rheological results, the inter-particle pair-potential must be well-defined and theories must be available for its calculation. The simplest system to consider is that where the pair potential may be represented by a hard sphere model. This, for example, is the case for polystyrene latex dispersions in organic solvents such as benzyl alcohol or cresol, whereby electrostatic interactions are well screened (1). Concentrated dispersions in non-polar media in which the particles are stabilized by a "built-in" stabilizer layer, may also be used, since the pair-potential can be represented by a hard-sphere interaction, where the hard sphere radius is given by the particles radius plus the adsorbed layer thickness. Systems of this type have been recently studied by Croucher and coworkers. (10,11) and Strivens (12). 

Fig. 10.15 The methods for capillary filling of nanotubes involves dispersal of the agent in a liquid capable of flowing into the nanotube followed by subsequent evaporation of the solvent to leave particles inside the tube. Nanotubes have been filled with polystyrene spheres and palladium nanocrystals using this method (Reprinted from Kim et al., 2005. With permission from American Chemical Society Reprinted from Tessonnier et al., 2005. With permission from Elsevier) (See Color Plates)...

Under the conditions of Example 5-23 the rubber phase of the end product shows an interesting micro-morphology. It consists of particles of 1-3 microns diameter into which polystyrene spheres with much lower diameters are dispersed. These included polystyrene spheres act as hard fillers and raise the elastic modulus of polybutadiene. As a consequence, HIPS with this micro-morphology has a higher impact resistance without loosing too much in stiffness and hardness. This special morphology can be visualized with transmission electron microscopy. A relevant TEM-picture obtained from a thin cut after straining with osmium tetroxide is shown in Sect. 2.3.4.14. 

One of the practical applications of dynamic light scattering involves the determination of particle sizes in media dispersed as dilute suspensions in a liquid phase. This aspect of dynamic light scattering is the focus here. Analysis of the scattering data will yield the translational diffusion constant D for a dilute aqueous suspension of polystyrene spheres, and this is directly related to the radius of the spheres. In addition, scattering will be studied from dilute skim milk, which reveals that a distribution of particle sizes exists for this system. 

Three of the experiments are completely new, and all make use of optical measurements. One involves a temperature study of the birefringence in a liquid crystal to determine the evolution of nematic order as one approaches the transition to an isotropic phase. The second uses dynamic laser light scattering from an aqueous dispersion of polystyrene spheres to determine the autocorrelation function that characterizes the size of these particles. The third is a study of the absorption and fluorescence spectra of CdSe nanocrystals (quantum dots) and involves modeling of these in terms of simple quantum mechanical concepts. 

Core-shell polystyrene-polyimide high performance particles have been successfully prepared by the dispersion copolymerization of styrene with vinyl-benzyltrimethyl ammonium chloride (VBAC) in an ethanol-water medium using an aromatic poly(amic acid) as stabilizer, followed by imidization with acetic anhydride [63]. Micron-sized monodisperse polystyrene spheres impregnated with polyimide prepolymer have also been prepared by the conventional dispersion polymerization of styrene in a mixed solvent of isopropanol/2-methoxyethanol in the presence of L-ascorbic acid as an antioxidant [64]. 

Problem 6.9 (Worked Example) You need to know if silica particles 20 pm in diameter with density 2 g/cm are likely to settle in an aqueous dispersion containing 10 M NaCl and 10% by volume of small, well-dispersed, 200-um-diametcr polystyrene spheres, each with a charge-... 

FIGURE 3.18 Frequency dependence of the relative dielectric increment of 265-nm radius polystyrene spheres in 0.1 nunol/1 KCl solution. Symbols experimental data soUd line classical calculation dashed line DSL calculation. In both calculations, the zeta potential used was the one best-fitting simultaneously electrophoretic mobility and dielectric dispersion data. 

This relates the polymer activity (which determines B2) to the colloid volume fraction at the spinodal. De Hek and Vrij [56] could give a good description of the phase line of mixtures of polystyrene chains plus small volume fractions of (hard-sphere like) octadecyl silica spheres dispersed in cyclohexane [109]. 

A thermochromic hydrogel based on Bragg reflection has been reported (16). The described system consists of crystalline colloidal arrays of monodisperse polystyrene spheres embedded in a poly(iV-isopropyl acrylamide) (PNIPAM) hydrogel, which was prepared by first dispersing highly charged and monodisperse... 

FIGURE 6. Test of dimensional analysis. Data on 40 vol.% dispersions of polystyrene spheres of four different particle sizes in media of three different viscosities (a) raw data of relative viscosity vs. shear stress for dispersions in benzyl alcohol (b) same data plotted as relative viscosity vs. dimensionless shear stress, together with data for dispersions in m-cresol and in water. 

Dekruif C.G., Vanlersel E.M.F., Vrij A., Russel W.B. Hard-sphere colloidal dispersions—Viscosity as a function of shear rate and volume fraction. J. Chem. Phys. 1985 83(9) 4717 725 Derooij R., Potanin A. A., Vandenende D., Mellema J. Steady shear viscosity of weakly aggregating polystyrene latex dispersions. J. Chem. Phys. 1993 99(11) 9213-9223 Derooij R., Vandenende D., Duits M.H.G., Mellema J. Elasticity of weakly aggregating polystyrene latex dispersions. Phys. Rev. E. 1994 49(4) 3038-3049 Derjaguin B.V., Landau L. Acta Physiocochim URSS. 1941 14 633-662... 

The experimental setup is shown schematically in Fig. 23(a). Uniformly sized microspheres with diametey ther 10, 25 or 96 pm, were dispersed in kerosene-based ferrofluid " and confined between two glass plates. The spacing between the plates were several times the diameter of the spheres. Two pairs of Helmholtz coils were used to produce two sinusoidal fields, H sinui t and H sin(w t+i/2) in the plane with amplitude H. The sample cell"(20x20 mm ) contained a very dilute dispersion of polystyrene spheres. This produces only a few pairs of spheres which were far apart and thus not interacting. The frequencies of the various modes were low (< Hz) and could easily be measured manually using a stop-watch. 

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