Fabrication of fine-pored polydimethylsiloxane using an isopropyl alcohol and water mixture for adjustable mechanical, optical, and thermal properties

Porous polydimethylsiloxane (PDMS) has garnered interest owing to its large inner surface area, high deformability, and lightweight, while possessing inherent properties, such as transparency, flexibility, cost-effectiveness, ease of fabrication, chemical/mechanical stability, and biocompatibility. For producing porous PDMS, gas foaming, sacrificial template, and emulsion template techniques have been used extensively. However, the aforementioned methods have difficulty in achieving submicron-sized inner pores, which is advantageous for improving flexibility and transparency. This study demonstrates a simple fabrication method for obtaining porous PDMS with fine pores partially down to the sub-micron scale. This is possible by the use of cheap, volatile, and easily accessible isopropyl alcohol (IPA) as a co-solvent in water and pre-PDMS emulsion. IPA shows an affinity towards both water and prepolymer, resulting in an increased distribution of small water particles inside PDMS before curing. These water particles evaporate while curing the prepolymer emulsion, thereby generating fine pores. The fine size and number density of pores are controlled by water and the added amount of IPA, resulting in adjustable mechanical, optical, and thermal properties of porous PDMS.