Differences in particle sizes measured by cryo-sem and quasi-elastic light scattering in latex particles

Cryogenic-scanning electron microscopy has been well established as a technique for imaging microstructure detail in fluid systems, but has a major disadvantage in that microstructural detail in the nanometer scale becomes difficult to observe due to a combination of resolution effects in the SEM and the sample preparation steps employed during processing. Quasi-elastic light scattering, on the other hand, is a powerful investigative tool in the 10-1000 nm size range, but cannot accurately and reproducibly record data of particulate size distribution above 1 micron owing to an increased scattering. While cryo-SEM offers a direct visualization in a large depth of field, the QELS offers a better statistical averaging of distributions due to an increased path length. Particle size data generated by the two techniques agree very closely in the 400-900 nm size range for low viscosity, low vapour pressure samples such as dilute polystyrene latex. It can be concluded that results from particle size distributions are largely dependent on sample preparation methods and the technique employed to measure them and that the results generated by each technique are accurate only within a specific range of measurement, but improvements in sample preparation techniques and low dose imaging will yield better results. (C) 1998 Elsevier Science B.V.