Cryo-SEM of particulate suspensions

Abstract

Advances in particulate coatings for paper products and high-density recording media require an understanding of orientation, clustering, and cluster aggregation of submicron particles suspended in high volume fractions in liquid. Particles for paper coatings are typically platelets; for magnetic coatings, acicular, tabular, or compact metal oxide or composite grains. One goal is to visualize the dynamic microstructures behind the rheological properties of these suspensions.Fixation of liquid calls for cryo-techniques. Replication for TEM examination is difficult because clusters and cluster aggregates adhere to carbon support films in such a way as to interfere with imaging and even disrupt replicas. The best technique we have found is cryo-SEM with freeze-fracture and deep etching.A procedure similar to that for freeze-fracture replication for TEM was used. For each sample, a small drop was flattened between two copper sheets (Balzers BU 012 056-T and BU 012 054-T).