Determination of the true size of poly(vinyl chloride) latices by electron microscopy using a vertical shadowing technique

Abstract

Recently Davidson and Collins conclusively demonstrated that poly (vinyl chloride) (PVC) latices shrink about 20% in the beam of the transmission electron microscope. Furthermore, they suggested that particles smaller than about 0.05 μm would not be seen at all. Since the measurement of PVC latex particle sizes below 0.2 μm and especially below 0.1 μm still represents a problem, a transmission electron microscope sample preparation technique employing vertical shadowing was developed. In this technique the latex particles are shadowed using gold-palladium at an angle of 90° to the surface of the grid. Even though the particle shrinks in the electron beam, the circular shadow will still represent the original size. Ten PVC latex samples in the range 0.05 to 1.0 μm were examined using this technique and the diameters were found to be in good agreement with those obtained by other methods. The methods chosen for comparison were as follows: fractional creaming, Joyce Loebl Disc Centrifuge, Micromeritics Sedigraph, optical arrays, and Coulter Counter. Care must be taken to recognize the effect of agglomeration if good agreement between various methods is to be obtained.