Fabrication of Polymer Surfaces with Varying Roughness and Its Effect on Anti-Reflective Properties

Killada, S (2014) Fabrication of Polymer Surfaces with Varying Roughness and Its Effect on Anti-Reflective Properties. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

Any real surface is rough at some length scale. Surface roughness plays an important role in various physical properties including light scattering phenomenon. In first part of the work, we have chosen electrospun nanofibers mat first time to the best of our knowledge, as a model polymer surface of varying roughness. We have varied the surface roughness by electrospinning cellulose acetate based nanomaterials, like only beads to fibers. Spin coated thin film was considered as a reference sample. Cellulose acetate was an obvious choice for selection of polymer due to its low refractive index, 1.47. Surface morphology and roughness of prepared samples was characterized using scanning electron microscopy (SEM) and 3-D non contact optical profiler. Optical properties were characterized using by measuring specular reflectance/transmittance in the visible spectral range by using UV-VIS spectrophotometer. These results showed that cellulose acetate surfaces with only beads morphology show near zero reflection (< 0.1%) for a wide range of wavelength. For only beads as well as only fibers morphology, cellulose acetate surfaces showed <0.16% reflection while varying the angle of incidence of light from 30º to 75º while transmittance was also reduced to less than 5%. Further we have chosen PS-b-PMMA block copolymer (BCP) and fabricated rough and porous surfaces by inducing phase separation using solvent/non-solvent exchange. We have shown that by choosing different combinations of solvent/non-solvents, we can vary the surface roughness at nanoscale. These rough BCP surfaces were further tested for their optical properties and results confirmed broadband and omnidirectional near-zero reflection behavior for these surfaces as well. Finally nano and micro scale rough surfaces as fabricated in this work due to their anti-reflective nature may find potential applications in solar panels, marines, optical displays etc.

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