Suspensions of polystyrene spheres

Measured extinction spectra for aqueous suspensions of polystyrene spheres—the light scatterer s old friend—are shown in Fig. 11.19. Water is transparent only between about 0.2 and 1.3 jam, which limits measurements to this interval. These curves were obtained with a Cary 14R spectrophotometer, a commonly available double-beam instrument which automatically adjusts for changing light intensity during a wavelength scan and plots a continuous, high-resolution curve of optical density. To reproduce the fine structure faithfully, the curves were traced exactly as they were plotted by the instru-... 

Kigure 11.19 Measured extinction by aqueous suspensions of polystyrene spheres with three different mean diameters. 

The comparisons presented in Figures 7 and 8, show that the RY closure relation works better than HNC, PYand RMSA, for the two kinds of systems with repulsive interactions here considered. Before the introduction of the RY approximation, the picture was that HNC and PY were better approximations to describe the static structure of systems with repulsive long-range and hard-sphere interactions, respectively. The RMSA approximation, however, has been used extensively in the comparison with experimental data for the static structure of aqueous suspensions of polystyrene spheres, mainly because it has an analytical solution even for mixtures [36]. 

FIG. 9 Illustration of particle concentration fluctuations. The figure shows the same picture of the quasi-two-dimensional suspension of polystyrene spheres shown in Fig. 1, but with the total area divided in small cells. Here one can see that the local particle concentration varies from cell to cell due to thermal fluctuations. 

Now, let us look at Fig. 13. Here, the static structure factor of a three-dimensional homogeneous suspension of polystyrene spheres of diameter 94 nm is shown. The particles volume fraction is 0 = 2.0 x 10 4. Experimental data from static light scattering (closed circles) are compared with computer simulation (Monte Carlo) results (symbol x) and theoretical predictions (lines) obtained from the Ornstein-Zernike equation and different closure relations. The computer simulations and the theoretical calculations where carried out assuming that the interaction between the... 

FIG. 15 Two-dimensional radial distribution function g(r) of quasi-two-dimensional aqueous suspensions of polystyrene spheres, measured by digital video microscopy. Adapted from Carbajal-Tinoco et al. [42]. 

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. 

Watkins et al. [223] studied suspensions of polystyrene spheres in forced laminar flow of oil. Maximum improvements of 40 percent were observed. 

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). 

Reduced viscosity versus reduced shear stress for suspensions of polystyrene spheres, = 0.50, solid line, in water, open circles, in benzyl alcohol solid circles, m-cresol. Replotted from Krieger (1972). 

Deggelmann, M., Palberg, T., Hagenbuchle, M., Maire, E., Krause, R., Graf, C., Weber, R., Electrokinetic Properties of Aqueous Suspensions of Polystyrene Spheres in the Gas and Liquid-like Phase, 4 Colloid Interface Sci., 1991, 143, 318-326. 

Our experiments are typically carried out at DNA concentrations of 20-50 /ig/ml with 1 ethidium per 300 bp, so that depolarization by excitation transfer is negligible.(18) The sample is excited with 575-nm light, and the fluorescence is detected at 630, 640, or 645 nm. Less than one fluorescent photon is detected for every 100 laser shots. The instrument response function e(t) is determined using 575-nm incident light scattered from a suspension of polystyrene latex spheres. 

FIG. 2.1 Sedimentation field flow fractionation (SdFFF) (a) an illustration of the concentration profile and elutant velocity profile in an FFF chamber and (b) a schematic representation of an SdFFF apparatus and of the separation of particles in the flow channel. A typical fractionation obtained through SdFFF using a polydispersed suspension of polystyrene latex spheres is also shown. (Adapted from Giddings 1991.)... 

FIG. 2 Two-dimensional colloidal crystal formed by a single layer of polystyrene spheres of diameter 3 /mi. The particles are initially suspended in water. The crystal is formed by confining the suspension between two glass plates and reducing the separation until it equals the diameter of particles. Here, one can see some typical features of crystals such as defects, fractures and vacancies. 

Replicas of these slides were prepared immediately after the contact angle measurements were completed. Saturated monolayers were expected to be stable, but rearrangement in incomplete monolayers, or in monolayers incorporating appreciable amounts of solvent, was considered a definite possibility [2]. Just before the specimen was placed in the evaporator, a water suspension of polystyrene latex spheres of about 0.09-micron diameter was sprayed onto the monolayered surface with a nebulizer. The presence of a sphere in the micrograph allows quick differentiation between holes in a nearly complete film and islands of acid molecules rising above the substrate surface. The spheres... 

Some experimental viscosity results on dilute suspensions of rigid spheres x, glass 5 fim in zinc iodide glycerin (Manley and Mason, 1954) O. polystyrene aqueous latices, 0.42, 0.87 /xm (Saunders, 1961) v. low shear rate, and A, high shear rate limits for nonaqueous polystyrene latices, 0.16-0.43 urn (Krieger, 1972). 

An important step in tire progress of colloid science was tire development of monodisperse polymer latex suspensions in tire 1950s. These are prepared by emulsion polymerization, which is nowadays also carried out industrially on a large scale for many different polymers. Perhaps tire best-studied colloidal model system is tliat of polystyrene (PS) latex [9]. This is prepared with a hydrophilic group (such as sulphate) at tire end of each molecule. In water tliis produces well defined spheres witli a number of end groups at tire surface, which (partly) ionize to... 

Fig. 6.12. A Typical CARS signal trajectory revealing the particle number fluctuations of 110-nm polystyrene spheres undergoing free Brownian diffusion in water. The epi-detected CARS contrast arises from the breathing vibration of the benzene rings at 1003cm 1. B Measured CARS intensity autocorrelation function for an aqueous suspension of 200-nm polystyrene spheres at a Raman shift of 3050 cm-1 where aromatic C-H stretch vibrations reside. The corresponding translational diffusion time, td, of 20 ms is indicated. (Panel B courtesy of Andreas Zumbusch, adapted from [162])...

The validity of Einstein s equation has been confirmed experimentally for dilute suspensions (0 < c 0.02) of glass spheres, certain spores and fungi, polystyrene particles, etc., in the presence of sufficient electrolyte to eliminate charge effects. 

FIG. 1 Quasi-two-dimensional suspension in the fluid-like phase. The system is formed by polystyrene spheres of diameter 0.5 /glass plates separated by a distance of twice the diameter of the particles. 

As discussed earlier (see Secs. II and VI), for polystyrene spheres in water the DLVO pair potential provides an expression for the effective interparticle interaction that, with an appropriate renormalization of the charge, accounts for the main features of the structure of 3D homogeneous suspensions. One might think that the DLVO potential should be a good assumption under most circumstances. This, however, turns out to be the case at least for the systems being considered here. Then the question is, how to measure the effective pair potential One way to do it is described here in some detail. For sufficiently dilute suspensions, one can resort to the low concentration approximation to obtain the pair potential directly from the measured radial distribution functions, i.e.,... 

Sample Preparation. The polystyrene spheres to be used should be monodis-perse with a particle radius i of about 50 nm, although any size in the range i = 30 to 100 nm is suitable. Such nanospheres are available commercially as aqueous latex suspensions with 1% to 10% PS by weight. A small amount of this latex suspension should be diluted 100- to 1000-fold. Using a microsyringe, take 0.1 mL from the PS stock, deliver this into a rinsed dilution bottle, and then add 10 mL of a hltered lO-mM solution of NaCl or other 1 1 electrolyte. The purpose of this electrolyte is to partially suppress coulombic interactions (electrostatic double-layer repulsion) that can influence the diffusion constant and lead to R values that are artificially high by —10%. The electrolyte solution should be prepared from distilled water and stored at room temperature. Before use, it must be hltered through a suitable membrane (0.1-jum pore size) to remove dust particles. Avoidance of dust is cracial, and capped dilution bottles should be used. 

FIGURE 12.10 Reduced torque versus strain following flow reversal for hard sphere suspension of various concentrations. Polystyrene spheres 45 pm in diameter in silicone oil. Taken from Gadala-Maria and Acrivos [34]. 

Fig. 9. Echo attenuation function E q, ) as a function of q for a close-packed suspension of 9.870 im polystyrene spheres surrounded by water. The times A are 10 ms (circles), 20 ms (solid circles), 20 ms (squares), and 40 ms (solid squares). The solid lines represent fits using Eq. (110) for which the parameters are a = 3.0 /xm, b = 10.7 /xm, f = 0.1 /xm, and [Reproduced by permission from Coy and Callaghan, 1994.]...

Figure 6.29 Zero-shear relative viscosity versus particle volume fraction for aqueous suspensions of charged polystyrene spheres (a = 34 nm) in 5 x lO " M NaCl ( ) (Buscall et al. 1982a). The line is calculated by using Eq. (6-66) for the viscosity, with 0eff given by Eq. (6-64), and d ff by Eq. (6-67a) or (6-67b). The potential 1T(/ ) is given by Eq. (6-58) or (6-59) with k given by Eq. (6-61) the constant K is 0.10, and is in the range 50-90 mV. (From Buscall 1991, reproduced with permission of the Royal Society of Chemistry.)...

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