Liquid thin films generate intriguing flow regimes and under specific conditions, lead to disintegration and de-wetting with the formation structures of submicron feature size. This concept has been well utilized as a non-lithographic route for creating meso-scale structures, where the structures can be ordered by guiding the instability pathway using a template. We show that patterns present on the surface of a polymer thin film (polystyrene) on a flat substrate can result in an ordered dewetted morphology under certain conditions. The pre-patterned polymer thin film undergoes pattern directed rupture along the thinnest parts of the film when the initial local thickness over these zones (hrm) is reduced to a limiting thickness (hlim = 10 nm). In addition, depending on the periodicity of the imprinted patterns, the wavelength of instability corresponding to hrm must be lower than the width of the patterned grooves (ls). A morphology phase diagram is constructed which indicates a transition from the surface tension induced flattening to the ordered pattern directed rupture. The versatility of this technique is in its ability to form myriad of aligned meso-patterns starting from a simple grating structure on the film surface. We further extend this concept to polystyrene-poly(methylmethacrylate) bilayers with a patterned polymer-polymer interface, where the instability is more complex due to coupled deformation of multiple, confined interfaces. This leads to creation of exotic patterns such as submerged, embedded and core shell structures, which are beyond the capability of standard lithography methods. The morphology of the evolving patterns is controlled by several parameters including the initial film thickness (hF), pre-pattern amplitude (hst), duration of solvent vapor exposure and wettability of the stamp used for pre-patterning the film. The evolution can be interrupted at any intermediate stage thereby achieving patterns on demand, which are well ordered as well as significantly miniaturized as compared to features obtained from dewetting of a flat film of same initial thickness.
1. N. Bhandaru, P. S. Goohpattader, D. Faruqui, R. Mukherjee, and A. Sharma, Langmuir 31, 3203−3214 (2015).
2. N. Bhandaru, A. Das, R. Mukherjee, Nanoscale 8, 1073-1087 (2016).
5:00 PM–7:00 PM Apr 23, 2019 (US - Arizona)
PCC North, 300 Level, Exhibit Hall C-E