Ion-exchange>latexes

Polystyrene Latexes. The polystyrene latexes used were the mono-disperse LS-1102-A, LS-1103-A, and LS-1166-B (Dow Chemical Co.) with average particle diameters of 190, 400, and llOOnm, respectively. The latexes were cleaned by ion exchange with mixed Dcwex 50W-Dowex 1 resin (9). The double-distilled and deionized (DDI) water used had a conductivity of 4x10 ohm- cm-. The surface groups of the ion-exchanged latexes determined by conductometric titration (10) were strong-acid sulfates the surface charge densities were 1.35, 3.00 and 5.95 jiC/cm, respectively. 

One possibility is hydroxyl endgroups, which may be formed by a side reaction of sulfate ion-radicals to form hydroxyl radicals (9) or hydrolysis of the surface sulfate groups. To determine if hydroxyl groups were present, the ion-exchanged latexes were oxidized by heating with persulfate and 10 silver ion at 90°, then ion exchanged and titrated conductometrically to determine the carboxyl groups. Table II (9) shows that some sul-... 

Then, 300-500 ml latex was agitated slowly with an estimated 5-fold excess of resin (based on electrolyte and emulsifier concentrations), filtered, and titrated. This procedure was repeated until a constant charge was obtained. Ion exchange in batch was more efficient than ion exchange in columns. The effectiveness of the ion-exchange latex clean-up has been described in detail elsewhere (7-9). 

Figure 1. Conductometric Titration of Ion-Exchanged Latex A-2 with Sodium Hydroxide...

These results for the conductometric titration of ion-exchanged latex A-2 with sodium and barium hydroxides are similar to those obtained earlier (4) for acidified silver iodide sols. 

To interpret these data, let us assume that the 790X value for the ion-exchanged latex in electrolyte represents the actual diameter of the polystyrene particles, since the thickness of the double layer is minimized in this medium and no emulsifier is present. This value thus replaces the 822X value in Table IV for 0.1% Aerosol MA. Presumably, these particles are covered with a IbX-thick layer of emulsifier. If this represents a monolayer, the 854A-diameter of the original latex diluted in emulsifier solution is just 32X larger, suggesting that the particles of this sample are covered with a bimolecular layer of emulsifier. 

It is of interest to determine whether this large electroviscous effect observed in ion-exchanged latex A-2 is a primary effect, i.e., due to distortion of the electric field around the particle by the flow, or a secondary effect, i.e, due to double layer interaction (more detailed studies of electroviscous effects in latexes have been made by Stone-Masui and Watillon (40) and Wang (41)). Booth s treatment of the primary electroviscous effect (42), when applied to our results, accounts for only 1-5% of the observed increase in viscosity, depending upon the value selected for the zeta potential. Therefore, the secondary effect is predominant, as is also expected from the non-Newtonian viscosity behavior (see ref. 43). 

To obtain accurate measurements of a, the specific conductance of the ion-exchanged latexes was measured at different concentrations in a Washbum-type cell at 25 0.01°C. It was assumed that the electrolyte concentration of the ion-exchanged latexes was zero and that the conductance was due mainly to the counterions, the contribution of the charged particles to the conductance being 10% or less. Therefore, a is defined as the ratio of the measured conduc-... 

The surface charge densities were determined by conductometric titration of the ion-exchanged latexes with sodium hydroxide (1,2). The solids contents of the latexes were measured by drying 1.5-g samples to dryness on a hot plate. The latex mixtures are listed in Table II. The number ratios of small/large particles were calculated from the weight of polymer and the number average volumes determined by electron microscopy. 

Here we report experimental results in which both types of phenomena are observed. These experiments involve poly(/i-butyl methacrylate) [PBMA] latex films prepared from core-shell latex particles in which PBMA is the core polymer. One set of particles has a shell containing methacrylic acid [MAA] as a comonomer [P(BMA-ct -MAA)]. Films prepared from the ion-exchanged latex have a carboxylic-acid-group-rich phase as an interparticle membrane, whereas films prepared from the same particles at high pH form an ionomer phase in the membrane. These structures retard but do not prevent interparticle polymer diffusion. A second type of PBMA, prepared from a... 

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