Characterization of pore size of trimethylol propane triacrylate (TMPTA) polymer foam by pulsed sputter coating and SEM analysis

This paper describes the production and characterisation of low density polymeric foams used by the Atomic Weapons Establishment (AWE) Plasma Physics programme. Production and preparation of such foam samples for characterisation by scanning electron microscopy (SEM) are described. Examining non-conductive low density foam specimens by conventional SEM requires sputter coating with a very thin layer of gold to prevent overcharging the sample. This paper describes modifications to this process, which have illustrated the destructive effects of the sputtering process on these foams. Optimum conditions to minimise foam damage during sputtering have been determined. Low-vacuum SEM in conjunction with a charge cascade detector which enables non-conductive samples to be directly imaged has been used to reduce the damage to fragile foams. These results are compared with those taken of samples coated under optimum sputtering conditions. Using sputter coating time trials and an absorbed electron (AE) detector, it was revealed that the pore size of TMPTA foam was in the region of 0.1 μm, i.e. an order of magnitude lower than reported previously. Some proposed damage mechanisms are also discussed.