Predicting the temporal wetting of porous, surfactant-added polydimethylsiloxane (PDMS)

Diverse surface/bulk treatments have been introduced to overcome the interfacial limitations of pristine (or untreated) PDMS, thus extending the possible applications of PDMS in micro/nano device development. Despite of extensive efforts, the temporal wetting change of PDMS induced by surface/bulk treatments still remains incompletely understood. We prepared 3 kinds of physicochemically treated PDMS blocks using widely used surface/bulk treatments-3D interconnected pore network formation, biocompatible surfactant (i.e., Silwet L-77) addition, and combination of both. Their wetting nature was characterized by measuring the time profile of water contact angle. A 3D interconnected pore network formation produced a time-invariant decrease in PDMS wettability; a surfactant addition increased the PDMS wettability in a time-variant way; a combination of pore network formation and surfactant addition had a combined effect. The measurement led to the successful development of a model for predicting the temporal wetting change in PDMS caused by variances in pore size and surfactant concentration. The accuracy of our model was verified by comparing experimental results with model predictions. This model will result in better understanding of polymer interface.