Thermal aging and reduced hydrophobic recovery of polydimethylsiloxane

Rapid prototyping of polydimethylsiloxane (PDMS) is frequently used to build microfluidic devices. PDMS is inherently hydrophobic; however, the surface can be temporarily rendered hydrophilic by exposing the surface to an oxygen plasma. Hydrophilic microchannels are sometimes advantageous over hydrophobic microchannels due to increased cell adhesion to hydrophilic surfaces or less air bubble trapping during filling with aqueous solution. However, the hydrophilic surface is unstable and low molecular weight (LMW) chains diffuse from the bulk of the PDMS and cover up the thermodynamically unstable surface. However, eliminating LMW species through thermal aging allows the hydrophilic surface to be more permanent.