Helium ion microscopy based wall thickness and surface roughness analysis of polymer foams obtained from high internal phase emulsion

• Published in: Ultramicroscopy 2014-04, Vol.139, p.13-19
• Main Authors: Rodenburg, C., Viswanathan, P., Jepson, M.A.E., Liu, X., Battaglia, G.
• Format: Article
• Language: English
• Subjects: Helium - chemistry; Ions - chemistry; Microscopy - methods; Polymers - chemistry; Surface Properties
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2014.01.004

Due to their wide range of applications, porous polymers obtained from high internal phase emulsions have been widely studied using scanning electron microscopy. However, due to their lack of electrical conductivity, quantitative information of wall thicknesses and surface roughness, which are of particular interest to tissue engineering, has not been obtained. Here, Helium Ion Microscopy is used to examine uncoated polymer foams and some very strong but unexpected contrast is observed, the origin of which is established here. Based on this analysis, a method for the measurement of wall thickness variations and wall roughness measurements has been developed, based on the modeling of Helium ion transmission. The results presented here indicate that within the walls of the void structure there exist small features with height variations of ~30nm and wall thickness variations from ~100nm to larger 340nm in regions surrounding interconnecting windows within the structure. The suggested imaging method is applicable to other porous carbon based structures with wall thicknesses in the range of 40–340nm. •The first helium ion microscopy image of uncoated structures formed from HIPEs is presented.•Unusually high contrast features that change with accelerating voltage are observed.•The origin of the observed contrast is determined to be mass thickness contrast.•A new method for quantitative wall thickness variation/roughness measurements is demonstrated.