Multifunctional Superhydrophobic Nanoparticle Coatings for Cellulose-based Substrates by Liquid Flame Spray

Abstract

Wettability of a solid surface by a liquid plays an important role in several phenomena and applications, for example in adhesion, printing, and coating. Especially, wetting of rough surfaces has attracted a great scientific interest in recent decades. Superhydrophobic surfaces, which possess extraordinary water repellency properties due to their low surface energy chemistry and specific nano- and microscale roughness, are of particular interest due to the great variety of potential applications ranging from self-cleaning surfaces to microfluidic devices. Another driving force for the extensive scientific work on superhydrophobicity has been a desire for detailed understanding of wetting phenomena on different types of superhydrophobic surfaces, for example on natural superhydrophobic surfaces of lotus leaves where easy mobility of water droplets results in self-cleaning effect, rose petals where water droplets firmly adhere to the surface, and butterfly wings which possess directional water droplet adhesion.

This thesis work reviews recent aspects on different modes of superhydrophobicity and explores a variety of functional anti-wetting/wetting properties on both natural and artificial superhydrophobic surfaces. In addition, fabrication techniques, properties, and potential applications of superhydrophobic surfaces and coatings are examined with focus on cellulose-based substrate materials on which an extensive literature survey is executed. In recent years, a great number of different approaches ranging from simple one-step methods to sophisticated multi-step procedures to fabricate superhydrophobic coatings on cellulose-based substrate materials such as cotton or paper have been reported. Potential applications for the cellulose-based superhydrophobic materials vary from water- and stain-repellent, self-cleaning and breathable clothing to cheap and disposable lab-on-a-chip devices.

The experimental section of this work focuses on fabrication of functional superhydrophobic and superhydrophilic nanoparticle coatings on cellulose-based substrate materials by liquid flame spray (LFS) and examination of the coating properties. LFS proved itself straightforward and versatile one-step method to fabricate broad range of functional nanoparticle coatings on various substrate materials in an atmospheric roll-to-roll process. It has established itself among the most potential candidates for large-scale production of superhydrophobic coatings on affordable cellulose-based substrates.