Two-dimensional nano-periodic structures with thermoresponsive properties

Abstract

Two-dimensional nano-periodic structures with thermoresponsive properties in poly (N-isopropyl acrylamide) (PNIPAM) were fabricated via soft lithography. The polymers swell due to the hydrogen-bonds between polymer chain and water molecule below volume phase transition temperature (VPTT, 33 oC) whereas they shrink at elevated temperatures. This is because hydrogen-bonds became less favorable relative to polymer-polymer and water-water interactions in the solution of PNIPAM above VPTT. An elastic instability of cross-linked PNIPAM structures in a swollen state induces the change in the shape of the void regions of nanostructures from circular to oval. The shape transformations in nano-periodic structures can be important in a variety of fields such as tunable phononic crystals, photonic crystals and bioscaffolds for tissue engineering