Hydrophilic PDMS with a sandwich-like structure and no loss of mechanical properties and optical transparency

Polydimethylsiloxane (PDMS) has been widely utilized in many fields due to its excellent flexibility, good mechanical properties and optical transparency. However, the hydrophobicity of PDMS limits the extension of its applications in a wide variety of fields. In this work, a low-cost and simple method, namely the swelling/permeating (S/P) method, is used to hydrophilize PDMS. In the S/P process, cross-linked PDMS swelled in the toluene and then the amphipathic surfactant (Triton X-100, TX-100) diffused into the swollen PDMS. By controlling the TX-100 concentration in toluene and the permeating time, TX-100 was mainly in the skin layer of PDMS, forming a sandwich-like structure as was shown by XPS mapping. The water contact angle of the modified PDMS decreased to 46° and the obtained hydrophilicity was maintained for 3 months. The mechanical properties and optical transparency of the S/P-modified PDMS showed almost no degradation, while those of the hydrophilic modified PDMS obtained by mixing TX-100 clearly changed with increasing TX-100 content. Thus, the S/P method is a facile method that combines the advantages of both surface modification and blending; for this method, hydrophilic modification is carried out on the PDMS surface and the original mechanical and optical properties of PDMS are maintained.