Surface properties of μm and sub-μm polydimethylsiloxane thin films after oxygen plasma treatment

Abstract

Polydimethylsiloxane (PDMS) is widely used in many areas of science due to its outstanding properties. The continuous expansion of its applications is evidenced by a large number of research studies dedicated to modifying this soft material, ultimately leading to tailored properties. These studies highlighted the important role of film thickness (in the range of a few micrometers to millimeters) on surface properties, including mechanical properties, wettability, and surface topography. In this work, we investigated these surface properties of pristine as well as oxygen plasma-treated PDMS, in a thickness range of submicrometer and micrometer. We explored the effects of film thickness, dilution ratio, and plasma treatment time on effective Young's modulus, surface topography (buckling structures), and wettability (hydrophobicity recovery) of the PDMS surfaces by conducting force–distance measurements, atomic force microscopy (AFM) and contact angle (CA) measurements, respectively, over a period of more than one month after the plasma treatment. The results of effective Young's modulus on pristine PDMS show a high correlation with the dilution ratio and no dependency on the thickness. The characterized waviness (λ) and amplitude (A) of the resulting buckling structures forming on the plasma-treated surfaces reveal a correlation with film thickness, which is not included in the theoretical predictions. The results of CAs show a faster recovery process for the advancing than for the receding condition, and uncover a high correlation with both film thickness and dilution ratio for short-time plasma treatment. Furthermore, the buckling structures as well as the hydrophobicity recovery process in this work revealed a significantly different domain in comparison to the studies in literature, where these properties of PDMS membranes with a thickness ranging from a few micrometers to a few millimeters have been investigated.