Bio-inspired Micro and Nano-textured Self-cleaning and Antireflective Polymer Surfaces

Mattaparthi, S and Sharma, Chandra Shekhar (2019) Bio-inspired Micro and Nano-textured Self-cleaning and Antireflective Polymer Surfaces. PhD thesis, Indian institute of technology Hyderabad.

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Abstract

This thesis deals with the fabrication of superhydrophobic and antireflective polymeric surfaces. Inspired from Nature’s superhydrophobic and antireflective surfaces such as plant leaves and flower petals, we identified few commonly grown garden plants and climbers which also exhibit superhydrophobic and antireflective properties through their major organs such as leaves and flower petals. These plant-based functional properties majorly result from hierarchical surface morphology (structures ranging from milli-meter to nano-meter in length scale). This work aims to mimic these plant-based hierarchical surface morphology onto various polymer surfaces, which could possess not only similar surface structures but also to exhibit similar functional properties. We depicted a simple, inexpensive replica molding technique which comes under “soft-lithography” to replicate these diverse plant-based surface structures onto different polymeric materials such as polydimethylsiloxane (PDMS) and RF xerogel. In chapter 2, we describe the replication of Canna indica flower petal surface structures (possessing micron size surface structures) onto PDMS and RF xerogel polymer surfaces. Here we report the as-replicated polymer surfaces possessing surface structures exhibits not only extreme self-cleaning properties but also antireflective properties than planar surfaces of similar materials. We have also addressed a major scientific challenge which is hydrophilic to superhydrophobic transition. Followed by replication of micron size structures, in chapter 3, we took the challenge in replication of hierarchical structures (combination of micro and nanostructures) of different underside of leaves surface possessing superhydrophobic properties. Choosing underside of leaves as a template is important as there are many plants which show superhydrophobicity in under water conditions due to their underside leaf structure. Interestingly, we report these replicated polymer surfaces possessing hierarchical structures exhibit not only extraordinary superhydrophobic properties but also antireflective properties when compared to the replicated surfaces possessing micron-size structures and also planar surfaces of similar materials. We then extend our work in fabricating water pressure resist superhydrophobic surfaces as discussed in chapter 4. In this chapter, we report a case study on a porous surface and structured surface to identify the water pressure resist super hydrophobic surfaces. By again employing a soft lithography technique, we fabricated porous and structured surfaces using three different flower petals possessing various surface morphology. We address the most relevant issues in water pressure resist superhydrophobic surfaces such as drop impact and physical pressure over the water droplet with another surface. Interestingly, the fabricated polymer surface which possesses high cavity porosity exhibits extraordinary water pressure resist superhydrophobic properties than the structured and low cavity porous surfaces. In contrast to bio-mimicking, in chapter 5 we describe the fabrication of antireflective polymer surface by alternative routes such as using etched silicon surface as a template material and electrospinning. In summary, this thesis is all about fabrication of large area micro- and nano-textured surfaces in polymers that exhibit self-cleaning and anti-reflective properties with an aim to extend their application towards solar cells, optical displays in a haxsh environment.

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