Replication and Compression of Surface Structures with Polydimethylsiloxane Elastomer

This paper describes simple classroom demonstrations and laboratory experiments based on properties of polydimethylsiloxane (PDMS). PDMS is a colorless, transparent elastomer. Spheres cast from PDMS can be cross-linked to varying extents to affect their rigidity, as seen in their ability to bounce when dropped. PDMS recently has been used by Whitesides et al. to replicate submicron-scale patterns by casting a negative relief image from a master template, and to progressively reduce the dimensions of these patterns through cycles based on mechanical compression. Curing PDMS in contact with features pressed into aluminum foil transfers the foil features to the elastomer. The raised surface features of the resulting cured PDMS block can transfer ink images to paper in a fashion that is similar to microcontact printing processes. Stretching or compressing the block will alter the dimensions of the transferred image. Curing PDMS in contact with the microscopic features on optical transform slides can transfer the slide features to the elastomer. The feature spacings, altered by stretching or compressing the elastomer, can be determined through the optical transform experiment. Moreover, when the elastomer is suitably compressed, the features, now with reduced dimensions, can be transferred first to an epoxy resin and then to a new sample of PDMS, representing a cycle that can lead to progressively reduced feature spacings.