• NANDINI BHANDARU

Articles written in Bulletin of Materials Science

• Solvo-selective imprinting of a thin polymer blend film for creating multi-length scale patterns

Controlling and spatial ordering of the phase separation in ultra-thin polymer-blend films is a viable approach to create complex surface structures with unique properties. This study reports a facile solvo-selective patterning techniquein a phase-separated polymer blend thin film comprising of immiscible polymers polystyrene (PS) and poly(methylmethacrylate) (PMMA). The pattern replication was achieved using capillary force lithography by imprinting the blendfilms with cross-linked polydimethylsiloxane stamp with grating patterns. The replication was done in the presence of 1-chloropentane or acetic acid vapours, which are selective solvents for PS and PMMA, respectively. This engenderedcapillary flow of only one phase while the domains of the second phase remain rigid. Depending on the initial as-cast morphology of the film which is a function of the relative proportion of PS and PMMA, a variety of structures wereobtained by combining the phase-separated domains with the structure imposed by the stamp. This method can be considered as a simple, one-step technique for creating hierarchical patterns that are likely to find applications inmodulating properties of soft surfaces.

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

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.

• # Bulletin of Materials Science

Volume 43, 2020
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020