Surface energy tailoring of glass by contact printed PDMS

A simple contact printing method to modulate the surface wettability of glass employing poly(dimethyl)siloxane (PDMS) mold was investigated. PDMS is a well known material in microfluidics and soft lithography for biomedical applications, being easy to process, low cost, biocompatible and transparent. Moreover its wettability can be tuned, by the exposure to oxygen plasma, UV-ozone or chemical oxidant solutions, or by surface functionalization. Unfortunately the effects of these treatments are not so stable in time. In this work a method to modify the surface energy (SE) of PDMS by changing its composition is proposed. Different mixing ratios (polymer base/curing agent) are analyzed evidencing that SE decreases while increasing the content of the polymer base, permanently modifying the surface behavior. As a thin layer of PDMS can be transferred to glass surfaces by contact printing, it is possible to locally change the wettability of glass simply patterning PDMS. In this work a SE patterning technique for glass surfaces by PDMS transfer is proposed. The technological process is based on the fabrication of PDMS molds by lift-off technique using Laser Direct Writing (LDW) lithography to process commercial photoresist. The transferring process for structures having a width of 10 μm was studied for a chosen PDMS composition, analyzing the surface energy of the patterned thin film by contact angle (CA) measurements.