Controlling the size of replicable polydimethylsiloxane (PDMS) molds/stamps using a stepwise thermal shrinkage process

We demonstrate, for the first time, the size-controllability of replicable three-dimensional polydimethylsiloxane (PDMS) molds/stamps using a stepwise shrinkage effect in a repeated heat treatment process. Various microstructures were heated in ambient nitrogen gas to study the temperature effect on the thermal shrinkage of PDMS. The ramped heat-up and cool-down speeds of the temperature in ambient nitrogen gas were 10 degrees C/min to various maximum temperatures and 2 degrees C/min to room temperature, respectively. The three-dimensional shape of the PDMS structure was observed and measured with a scanning laser microscope. The shrinkage ratios of the PDMS samples heated to 300, 500, and 700 degrees C were approximately 10%, 13%, and 24%, respectively. There were small variations in shrinkage, which depended on the micropattern dimensions. The higher temperatures, such as 500 and 700 degrees C, were not optimum for the sequential replica molding process, because of locally cracked and bent shapes as well as increased surface roughness. Therefore, we generated and replicated PDMS molds/stamps using a 300 degrees C multi-step heat treatment process. During the multi-step heat treatment process, the microstructures became narrower and deeper, which may have been caused by differences in the thermal capacity within the embossed micropatterns region, the PDMS structure, and the curing process of the initial PDMS structure. Thus, the structure width decreased as the depth of the samples increased. (C) 2010 Elsevier B.V. All rights reserved.