Electron Microscopy of Monodisperse Latexes

Abstract

A series of monodisperse polystyrene latexes has been prepared by carefully controlled emulsion polymerizations. The particle diameters of three of these latexes were determined by electron microscopy. The latex particles were dispersed on collodion membranes supported by copper grids. The microscopes had previously been calibrated with collodion replicas of a 30 000 line/inch diffraction grating. In general, the reproducibility of measurements from many photographic exposures was good; however, a few exposures yielded particle diameters considerably higher than the averages. An investigation of this technique indicated that: (1) polystyrene latex particle diameters (collodion membranes—copper grid supports) increased considerably on electron irradiation, (2) collodion diffraction grating replicas (copper grid supports) shrank slightly on electron irradiation, and (3) the magnification of the electron microscope varied slightly from exposure to exposure. It was found that variations of particle diameter resulting from the foregoing sources of error were negligible when the particles were dispersed directly on a silicon monoxide diffraction grating replica supported by a stainless steel grid. The particle diameters of the latexes determined in this manner ranged from 880 to 11 720 A. Many photographic exposures of each latex were used for these measurements. The monodispersity of the latex particles is evident from the small values of the standard deviations of the over-all particle-size distributions. The reproducibility of particle diameters determined from different exposures is evident from the small values of the standard deviations of the means of the exposure averages.