Superhydrophobicity from biomedical to environmental applications

Abstract

Superhydrophobicity is a unique interfacial phenomenon in which water is highly repelled by a solid surface, as a result of the surface’s special architecture and chemistry. High water repellence is desirable for versatile practical applications, such as production of self-cleaning, anti-fogging, water-proofing, or anti-fouling materials. Superhydrophobic surfaces have, therefore, drawn a lot of attention, especially in the last two decades. This thesis aims to investigate superhydrophobic surfaces and powders, with particular emphasize on novel practical applications of such materials. Moreover, research on Liquid Marbles, as drops of liquid enwrapped in highly hydrophobic powder, will be presented as a closely related phenomenon. Two distinct research pathways have been pursued and the outcome is discussed in two parts; The first part includes four chapters, consisting of the research on properties and applications of liquid marbles. Liquid Marbles have been subject to numerous studies in the past decade. However, to exploit their unique properties in practical applications, such as preparation of micro- and bio microreactors is seldom studied. Micro- bioreactors made of liquid marbles are hence explored in this part, as powerful means for conducting diagnostic assays, biochemical reactions, and 3D cell spheroid culture. The idea of using liquid marble microreactors is then further extended, by using liquid marbles for gas detection purposes. This part is then concluded with a discussion on an important property of liquid marbles known as liquid marble’s surface tension. Clear understanding and experimental determination of liquid marble’s surface tension is of high importance, especially in design and fabrication of microreactors, as well as their accessories, such as micropumps made of liquid marbles. Subsequently, the second part of this thesis discusses the fabrication and characterization of environmentally friendly superhydrophobic surfaces and powders. Fabrication of superhydrophobic paper, via a facile two-step method and by using cellulose nanofibers as binder, is firstly reported in this part. Next, preparation and characterization of superhydrophobic and oleophilic precipitated calcium carbonate (PCC) powder is discussed and the powder is introduced as environmentally friendly oil sorbent, which can absorb low surface tension liquids such as crude oil out of water, hence can be used in oil spill clean-ups. Superhydrophobic surfaces and liquid marbles are both emerging areas of science and engineering. This thesis aims to provide a better understanding of their unique interfacial phenomena, and to enlighten few significant possibilities these phenomena can offer in a wide range of areas, from biomedical to environmental applications.