Enhanced Self-organized Dewetting of Ultrathin Polymer Films under Water-organic Solutions: Fabrication of Sub-micron Spherical Lens Arrays

Abstract

Field-induced self-organized patterning in ultrathin (< 100 nm) polymer films produces resolutions of the order of 10 {\mu}m or more because of the high energy penalty for the surface deformations on small scales. We propose here a very simple but versatile method to fabricate sub-micron (~100 nm) ordered and tunable polymeric structures by self-organized room temperature dewetting of ultrathin polystyrene films by minimizing the surface tension limitation. We illustrate this technique by fabricating sub-micron lens arrays of tunable curvature. This is achieved by switching to controlled room temperature dewetting under an optimal mix of water, acetone and methyl-ethyl ketone (MEK). Organic solvents used decrease the glass transition temperature, greatly decrease the interfacial tension, intensify the field and increase the contact angle/aspect ratio of the resulting tunable nano-structures, without a concurrent solubilization of PS owing to water being the majority phase in the outside mixture.