Articles written in Bulletin of Materials Science

    • Hydrophobic recovery of cross-linked polydimethylsiloxane films and its consequence in soft nano patterning


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      Cross-linked polydimethylsiloxane (PDMS) films and surfaces obtained by thermal cross-linking of commercially available Sylgard 184 are widely utilized in many areas of science, due to superior thermal stability, low dielectric constant, transparency and biocompatibility. Cross-linked PDMS surfaces are weakly hydrophobic and several experiments, particularly the ones that utilize capillary-driven microscale flow require the modulation of the surface wettability. A well-known strategy to achieve the same is by exposing the Sylgard 184 surface to UV/ozone (UVO) treatment at room temperature. Depending on the duration of exposure, the wettability drops from hydrophobic to a nearcompletewetting (water contact angle $\sim$10$^{\circ}$), due to the formation of a surface oxide layer. However, under normal atmospheric conditions, these surfaces recover their hydrophobicity over a period of time due to diffusive migration of the uncrosslinked oligomers to the surface, and formation of a hydrophobic dimethyl silicone layer. We explore the hydrophobic recovery process as a function of cross-linker concentration and UVO exposure time and show how a partially or fully recovered PDMS stamp may influence subsequent nanopatterning, including the possible creation of features with different morphology using a single stamp.

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