Effect of sputter coating on the observation of polymeric membrane structure

In the present work, the effect of sputter coating, a step for preparing SE M specimen, on the observation of polymeric membrane structure was investig ated by using AFM to examine the difference in membrane structure before an d after sputter coating. It was observed that the sputtering process can pr oduce coatings made up of distinguished particles. The size of the particle s is on the same order of that of nodules (20 nm), which are believed by ma ny as a basic structure of polymeric membranes. Hence, the sputter coating could affect the judgement if nodules exist in a system and influence the d etermination of the size of nodules. In addition, it was found that, for th ree PMMA membranes studied in this work, the surface is not uniform but con sists of a lot of protrusions, which is believed to be aggregations of poly mer (nodules). For membrane surfaces with small crevices among protrusions, it seems that the protrusions receive more coatings than the crevices duri ng coating process, resulting in larger surface protrusions after sputter c oating. On the other hand, for membrane surfaces with large crevices among protrusions, the crevices would be filled with the coating material, result ing in smaller crevices after sputter coating. The results indicate that on e should be careful in using SEM to investigate the fine polymeric structur e such as nodules because the coating process could influence the fine stru cture.