ABSTRACT
This chapter presents a background for the different kind of natural surfaces that demonstrate varied water contact angles (CAs). It discusses the classification schemes of the hydrophilic and hydrophobic surfaces along with their mathematical description and describes the laboratory-synthesised biomimetic nanostructured surfaces in light of the existing theories. 4.1 Introduction
Natural species show an excellent adaptability to their environments through the use of sophisticated material interfaces which are often beyond the visual or other common perceptions of human beings. There are many unique functions in different biological systems. For example, the self-cleaning property of lotus leaves [1], the waterwalking abilities of water striders and spiders [2], the directional
adhesion of butterfly wings [3], the anti-fogging functionality of the mosquito eyes [4], the anti-reflection of super-hydrophobic cicada wings [5], water collection observed in the desert beetle [6], spider silk [7], and also the antifouling or self-cleaning ability of fish scales [8] (Fig. 4.1) offer amazing designs for controlled and specific functionality. The functionality is accomplished through interaction of these natural surfaces with fluids (discussed in this
Figure 4.1 Multiscale structures in biological surfaces with special wettability. Several interesting wetting properties can be found in nature: (a) lotus leaf (Reprinted by permission from Macmillan Publishers Ltd.: Nature Materials, Ref. [1], Copyright 2003), (b) water strider legs (Reprinted by permission from Macmillan Publishers Ltd.: Nature, Ref. [9], Copyright 2005), (c) beetle shells (Reprinted by permission from Macmillan Publishers Ltd.: Nature, Ref. [10], Copyright 2003), (d) mosquito compound eyes (Reprinted with permission from Ref. [4]. Copyright © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim), (e) cicada wings (Reprinted with permission from Ref. [11]. Copyright 2004 American Chemical Society), (f) desert beetle (Reprinted by permission from Macmillan Publishers Ltd.: Nature, Ref. [6], Copyright 2001), (g) spider web (Reprinted by permission from Macmillan Publishers Ltd.: Nature, Ref. [7], Copyright 2010), (h) sandfish (Reprinted from Ref. [12], © 2008 Baumgartner et al.), (i) sucker of Octopus bimaculoides/bimaculatus (Reprinted from Ref. [13] by permission of Oxford University Press).
