Light-Scattering Characterization of Polyvinyl Acetate Latex Films

Abstract

Light scattering from solid films of polyvinyl acetate latices was studied as a function of particle size distribution, surfactant and stabilizer content, as well as temperature of film formation. The two basic structural parameters from the Debye-Bueche theory were obtained: 〈η2〉, the mean square fluctuation in dielectric constant, and a, the average distance between fluctuations. It was shown that 〈η2〉 was due only to density fluctuations and increased with polyvinyl alcohol stabilizer content. Generally, increasing the temperature of film formation also caused 〈η2〉 to increase. When stabilizer was present the a parameter was of the same order of magnitude as the particle diameter. Over the range of film-forming temperatures, a was relatively constant for a given latex sample. For two of the four systems studied a distinct maximum in the angular scattering was observed. By means of surface replication and electron microscopy, observed packing periodicities in the films could be correlated with the first-order spacings calculated for the angular maxima from the Bragg equation. The data indicate that 〈η2〉 is a useful measure of latex film texture. The polymeric stabilizer seems to form a continuous matrix in which particles are embedded. It is a major factor determining film heterogeneity.