Scanning electric potential microscopy (SEPM) together with noncontact AFM images were obtained from the surfaces of two latex films: the first is a self-arrayed poly(styrene-co-hydroxyethyl methacrylate) macrocrystal, while the other is a thin film formed by coagulation of polystyrene particles at the latex liquid surface, under exposure to chloroform vapor. In both cases, large electric potential differences are detected by the microscope probe between adjacent domains in the films. Domains with positive or negative potentials reach a few hundred nanometers in size. These dielectric films are thus mosaics of electrically charged domains, and their electroneutrality is only observed at the macroscopic level.

Particles of a poly[styrene-co-(2-hydroxyethyl methacrylate)] latex were prepared and examined by electron spectroscopy imaging (ESI), using an energy-filtered transmission electron microscope (EFTEM). Both whole particles and thin ultramicrotomed sections were examined, in the brightfield and energy-loss modes. The following elemental distributions were determined, for the larger particles in the latex: (i) C is rather uniformly distributed throughout the raspberry-like latex particles; (ii) O is also distributed throughout the particles but with significant fluctuations from point to point, and it is more concentrated in the vicinity of the particle surfaces; (iii) S distribution resembles that of C, but it is absent from the particle-particle contact areas; (iv) K is mostly found in a thin outer particle layer. Elemental distribution patterns in the smaller particles are different: these have a higher O/C ratio, and K is dispersed in the bulk of the particles. The main conclusions are as follows: hydrophobic and hydrophilic domains are distributed throughout the particles; negative charges are trapped in the particle bulk, and countercations are dispersed in the bulk (small particles) or concentrated at the surfaces (large particles); these results are consistent with particle formation by homogeneous nucleation, following previous work by the Fitch and Okubo groups.S0743-7463(97)01167-0 CCC: $15.00