Polystyrene latex particles with

Serizawa and Akashi [95] analyzed the monolayer adsorption of polystyrene latex particles with cationic polyvinylamine grafted on their surface, while Serizawa et al. [96,97] used commercial anionic latex particles. Both types of particles were adsorbed on polyelectrolyte-coated substrates previously prepared by alternating adsorption of cationic and anionic polyelectrolytes such as polyallylamine hydrochloride (PAH) and polystyrene sulfonate sodium salt (PSS) according to the method described by Decher [164]. Using... 

Figure 2. Variation of electrophoretic mobility in distilled water with pH for polystyrene latex particles with different surface groups (1) 520 sulfate (2) 520 carboxyl (3) 520 hydroxyl (4) LS-1010-E sulfate (5) LS-1010-E hydroxyl.

In order to test the model used here, calculated values of the limiting free polymer concentration 0 at which phase separation occurs are compared with the experimental data [6] on the aqueous dispersions of polystyrene latex particles with adsorbed polyethylene oxide and with polyethylene oxide as the free polymer. Since no information is available regarding the thickness of the adsorbed layer, the values used by Vincent et al. [6] in their theoretical calculations are adopted. Table 1 compares the experimental values of the limiting volume fraction of the free polymer with our calculated values for two different molecular weights of the free polymer. The simple model used here gives reasonably good agreement with the experimental values. 

Swelling of polystyrene latex particles with styrene. The swelling ratios and the corresponding interfacial tensions for the different-size latexes with added anionic surfactants Aerosol MA and sodium dodecyl sulfate are listed in Table II. Those values obtained with added nonionic surfactant Triton X-100 and polymeric surfactant polyvinyl pyrrolidone are listed in Table III. Figure 1 compares theoretical curves from Model I with all of the experimental data. It is found that a curve corresponding to Xmp = 0.35 fits the data best. Therefore, a semi-empirical... 

The magnetic polystyrene latex particles with diameter of 120 nm were covered by PNIPA gel layer. The mPS latex prepared according to the procedure described previously was strongly stirred at 60 °C and kept under N2 atmosphere for 1 h. Then, 0.05 g APS and 0.5 mL 1 M NIPA solution were added to the mPS latex and the reaction mixture was stirred at 60 °C for more than 1 h. Then, 0.5 mL 1 M NIPA solution and 0.36 mL 0.1 M BA solution were added. After 2 h, 0.5 mL 1 M NIPA solution and 0.36 mL 0.1 M BA solution were added again to the mixture. This mixture was stirred 60 °C for more than 2 h under N2 atmosphere. Figure 9 shows the structure of the core-shell microsphere in dry state. 

The parameter Ej j lkTh s been used in estimating the adhesion of polystyrene latex particles with a diameter of 0.28-0.34 fxm [170]. Adhesion occurs when max/ 10-... 

Fig. 1.17 Micrograph taken 25 min after mixing polystyrene latex particles with 370 mg/L sodium polyacrylate. Picture reprinted from A. Kose and S. Hachisu, J. Colloid Interface Sci., 55 487, 1976, with permission from Elsevier...

It is now important to calculate the stress exerted by the particles. This stress is equal to aApgfZ. For polystyrene latex particles with radius 1.55 pm and density 1.05 g cm , this stress is equal to 1.6 x 10 Pa. Such stress is lower than the critical stress for most EH EC solutions. In this case, one would expect a correlation between the settling velocity and the zero shear viscosity. This is illustrated in Chapter 7, whereby v/a is plotted versus 7(0). A linear relationship between log( /a ) and log 7(0) is obtained, with a slope of —1, over three decades of viscosity. This indicated that the settling rate is proportional to [7(0)] . Thus, the settling rate of isolated spheres in non-Newtonian (pseudo-plastic) polymer solutions is determined by the zero shear viscosity in which the particles are suspended. As discussed in Chapter 7, on rheological measurements, determination of the zero shear viscosity is not straightforward and requires the use of constant stress rheometers. 

For a brush on a flat surface, the attached chain is confined to a cylindrical volume of radius D/2 and height A. If the individual chains of the brush are attached to a spherical core (as is the case with nanoparticles), then the volume accessible to each chain increases and the polymer chains have an increased freedom to move laterally resulting in a smaller thickness A. This is schematically illustrated in Fig. 2.28 which shows the difference between particles with high surface curvature (Fig. 2.28 (a)) and that for a surface with low surface curvature (Fig. 2.28 (b)). The curvature effect was illustrated for PEG and poloxamer block copolymers using polystyrene latex particles with different sizes. An increase in the layer thickness with increasing particle radius was observed. 

The particles studied [22,23] were monodisperse, surfactant-free spherical polystyrene latex particles with sulfate groups on the surface. When these groups are fuUy ionized in water, the particles have a surface charge density of around 8 /xC cm , equivalent to 1 sulfate group per 2 nm. Unless otherwise stated, the particle diameter was 2.6 /u.m. 

From knowledge (or assumption) of interparticle interactions within a monolayer, it is possible to obtain a theoretical surface equation of state (i.e., a relationship between the surface pressure and the area available to particles in the monolayer) that can be compared with the experimental tt-A curves. The state of charge of a polystyrene latex particle (with sulfate groups at its surface) is illustrated in Fig. 19. In the aqueous phase, an asymmetrical double layer is set up that leads to a net dipole normal to the interface. The magnitude of this dipole is expected to depend on the concentration of the inert electrolyte (e.g., NaCl) in the aqueous subphase, and the dipoles lead to lateral repulsion between particles. The sulfate groups also carry permanent dipoles, and this leads to a net dipole normal to the interface within the oil phase and hence to another contribution to lateral repulsion. It turns... 

Paine et al. [99] tried different stabilizers [i.e., hydroxy propylcellulose, poly(N-vinylpyrollidone), and poly(acrylic acid)] in the dispersion polymerization of styrene initiated with AIBN in the ethanol medium. The direct observation of the stained thin sections of the particles by transmission electron microscopy showed the existence of stabilizer layer in 10-20 nm thickness on the surface of the polystyrene particles. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results supported the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents. 

A very similar effect of the surface concentration on the conformation of adsorbed macromolecules was observed by Cohen Stuart et al. [25] who studied the diffusion of the polystyrene latex particles in aqueous solutions of PEO by photon-correlation spectroscopy. The thickness of the hydrodynamic layer 8 (nm) calculated from the loss of the particle diffusivity was low at low coverage but showed a steep increase as the adsorbed amount exceeded a certain threshold. Concretely, 8 increased from 40 to 170 nm when the surface concentration of PEO rose from 1.0 to 1.5 mg/m2. This character of the dependence is consistent with the calculations made by the authors [25] according to the theory developed by Scheutjens and Fleer [10,12] which predicts a similar variation of the hydrodynamic layer thickness of adsorbed polymer with coverage. The dominant contribution to this thickness comes from long tails which extend far into the solution. 

TABLE 1 Characteristic Properties of Core-Shell Latex Particles with Polystyrene Core... 

Studies on orthokinetic flocculation (shear flow dominating over Brownian motion) show a more ambiguous picture. Both rate increases (9,10) and decreases (11,12) compared with orthokinetic coagulation have been observed. Gregory (12) treated polymer adsorption as a collision process and used Smoluchowski theory to predict that the adsorption step may become rate limiting in orthokinetic flocculation. Qualitative evidence to this effect was found for flocculation of polystyrene latex, particle diameter 1.68 pm, in laminar tube flow. Furthermore, pretreatment of half of the latex with polymer resulted in collision efficiencies that were more than twice as high as for coagulation. 

Figure 8.14 CLSM images showing the initial development of the microstructure of a phase-separated mixed biopolymer system (25.5 wt% sugar, 31.4 wt% glucose syrup, 7 wt% gelatin, and 4 wt% oxidized starch pH = 5.2, low ionic strength) containing 0.7 wt% polystyrene latex particles (d32 = 0.3 pm). The sample was quenched from 90 to 1 °C, held at 1 °C for 10 min, heated to 40 °C at 6 °C min-1, and observed at 40 °C for various times (a) 2 min, (b) 4 min, (c) 8 min, and (d) 16 min. White regions are rich in colloidal particles. Reproduced from Firoozmand et ai (2009) with permission.

FIG. 13.4 Stereo pairs of colloidal dispersions generated using computer simulations, (a) Polystyrene latex particles at a volume fraction of 0.13 with a surface potential of 50 mV. The 1 1 electrolyte concentration is 10 7 mol/cm3. The structure shown is near crystallization. (The solid-black and solid-gray particles are in the back and in the front, respectively, in the three-dimensional view.) (b) A small increase in the surface potential changes the structure to face-centered cubic crystals. (Redrawn with permission from Hunter 1989.)... 

Garvey et al.85) made a similar sedimentation study on poly(vinyl alcohol) adsorbed on polystyrene latex particles. Adsorbance of the polymer was also measured. Both the thickness of the adsorbed layer and the adsorbance increased linearly with the square root of the molecular weight. The volume occupied by a polymer molecule in the adsorbed layer was approximately equal to that of the effective hydrodynamic sphere in bulk solution. However, the measured values of LH were greater than the hydrodynamic diameters of the polymer coils in solution. Thus, it may be concluded that adsorbed poly(vinyl alcohol) assumes a conformation elongated in the direction normal to the surface. 

Experimental data are generally not in accord with the theoretical prediction in equation (8.21) regarding particle size96,196,204. For example, Ottewill and Shaw204 found no systematic variation in d log W/d log c for a number of monodispersed carboxylated polystyrene latex dispersions with the particle radius ranging from 30 nm to 200 nm. This problem still remains unresolved. 

Figure 14. Changes in stability of an anionic polystyrene latex (particle diameter = 52.7 nm) admixed with a cationic latex (particle diameter = 43.4 nm). N+ and N. = the number concentration of the cationic and anionic latices, respectively (-A-) 10 3 mol dm 3 sodium chloride solution (-O-) 2 X 10 3 mol dm 3 sodium...

Earlier work (3) has shown that cleaned monodisperse polystyrene latexes stabilized with surface sulfate (and perhaps a few hydroxyl) groups an be used as model colloids. For example, the distribution of H ions in the electric double layer as determined by conductometric titration has been correlated with the particle diameter determined by ultracentrifugation (3). The conductometric titration gives two measures of the concentration of H+ ions the initial conductance of the latex and the amount of base required for neutralization. The number of H+ ions determined by conductance is always smaller than the number determined by titration. This difference is attributed to the distribution of the H+ ions in the electric double layer those closest to the particle surface contribute least to the overall conductance. This distribution is expressed as the apparent degree of dissociation a, which is defined as the ratio H+ ions... 

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