Articles written in Bulletin of Materials Science

• Soft lithography meets self-organization: Some new developments in meso-patterning

This is a brief review of our recent and ongoing work on simple, rapid, room temperature, pressure- less and large area (∼ cm2) imprinting techniques for high fidelity meso-patterning of different types of polymer films. Examples include soft solid polymer films and surfaces like cross-linked polydimethylsiloxane (PDMS) and polyacrylamide (PAA) based hydrogels, thermoplastics like polystyrene (PS), polymethylmethacrylate (PMMA) etc both on planar and curved surfaces. These techniques address two key issues in imprinting:

attainment of large area conformal contact with the stamp, especially on curved surfaces, and

ease of stamp detachment without damage to the imprinted structures.

The key element of the method is the use of thin and flexible patterned foils that readily and rapidly come into complete conformal contact with soft polymer surfaces because of adhesive interfacial interactions. The conformal contact is established at all length scales by bending of the foil at scales larger than the feature size, in conjunction with the spontaneous deformations of the film surface on the scale of the features. Complex two-dimensional patterns could also be formed even by using a simple one-dimensional master by multiple imprinting. The technique can be particularly useful for the bulk nano applications requiring routine fabrication of templates, for example, in the study of confined chemistry phenomena, nanofluidics, bio-MEMS, micro-imprinting, optical coatings and controlled dewetting.

• Electrohydrodynamic instability: effect of rheological characteristics on the morphological evolution of liquid crystal–polymer interface

Electrohydrodynamic instability, in a polymer–air or polymer–polymer bilayer settings, gives rise to the formation of the orderedmicropillars or microwells at the initial planar interface. It is well known that the complex interplay amongthe controlling parameters, such as the intensity of the electrostatic field, film thickness, interfacial tension and dielectric constants of the layers determine the morphology of the interface. In this report, for the first time, experimentally it is shown that rheological property of the lower polymer layer [here, polydimethylsiloxane (PDMS)] has a significant influence on the morphological evolution.We probe the kinetic time scale of the evolution by inducing fast destabilization of the interface due to the high dielectric contrast between two layers (liquid crystal–PDMS) and reduced interfacial tension. At this time scale,it was demonstrated that micropillars are formed for thin viscoelastic ‘soft’ PDMS film, whereas microwells were observed for viscoelastic ‘hard’ film in similar settings. A transition from micropillar to microwell was observed for viscoelastic ‘soft’ film when the thickness of the film increased from $\sim$4 to 11 $\mu$m. Based on this observation, by controlling the rheological properties, different patterns were developed from similar templated PDMS substrates.

• Bulletin of Materials Science

Volume 45, 2022
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