Direct visualization of microstructures in hydrophobically modified polyacrylamide aqueous solution by environmental scanning electron microscopy

Abstract

AbstractEnvironmental scanning electron microscopy (ESEM) is an improved technique which permits the observation of samples in their native state, requiring neither sample preparation nor surface coating, and so avoids losing the original characteristics of the observed specimens. By use of a differential pumping aperture system and a secondary electron detector, the environmental conditions in the sample chamber can be varied and accommodated to the properties of the samples. This newly developed technique is used in this work to characterize the microstructures of hydrophobically modified polyacrylamide (HMPAM) and its unmodified precursor in aqueous solution. The microstructures were directly visualized by sublimation of the ice in freeze‐dried samples. It is found that three‐dimensional network structures spread throughout the whole solution for both the modified and unmodified polymers when the polymer concentration is equal to or higher than the polymer critical association concentration (CAC); when the polymer concentration is below the CAC, a sparse network structure could be seen in the solutions of modified polymer, whereas no such phenomenon is found in unmodified polymer solutions. The network units of the microstructures in the solutions of modified polymer are displayed as regularly distributed hexagons, while those of unmodified polymer appear as irregular circles. The observed results are interpreted by a proposed association model.© 2002 Society of Chemical Industry