Self-Cleaning Properties Arising from Hierarchical Structures

SELF-CLEANING PROPERTIES ARISING FROM HIERARCHICAL STRUCTURES 

Order Species Structural Morphology Water Contact Angles (°) 

The superhydrophobicity of an insect wing surface and its ability to selfclean are very important factors that contribute to an insect s ability to survive. The nanoarray structures present on the surfaces of some insect wings such as those of the cicada and dragonfly afford the insect antireflective properties, which can assist in protecting them from attack from predators (Watson et al., 2008). The superhydrophobic and self-cleaning properties can assist to keep their surfaces clean and free from contaminants that may 

Since Barthlott and Neinhuis first reported the lotus effect, the lotus has become the archetype surface for superhydrophobicity and self-cleaning abilities (Barthlott and Neinhuis, 1997). For centuries the lotus has been known as symbol of purity in many Asian religions. For over a decade, this purity has become a phenomenon within the scientific community, with many studies having been performed with a view to determining the mechanism responsible for their self-cleaning ability. 

Unique Superhydrophobic Surfaces Superhydrophobic Surfaces with a High Adhesive Force 

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Superhydrophobicity arises from the combination of hierarchical surface structures and low surface energy materials. When superhydrophobicity is combined with the ability to self-clean, we witness surfaces that can perform multiple functions (fung and Bhushan, 2006 Bhushan et al., 2009 Yan et al., 2011). To achieve these properties, the presence of multiscale or hierarchical structures on naturally hydrophobic materials is required (Nosonovsky and Bhushan, 2005 Verho et al., 2012 Papadopoulos et al., 2013). Nosonovsky and Bhushan determined that a composite interface... 

Surfaces that possess directionally dependent or anisotropic superhydropho-bicity have been the subject of a number of studies due to their potential application in microfluidic devices, their ability to form evaporation-driven surface patterns, and their potential to form coatings that are readily cleaned (Higgins and Jones, 2000 Liu et al., 2006, 2010). Anisotropic superhydro-phobicity has been observed on the surfaces of a number of plants and insects, including rice leaves and butterfly wings (Figure 5). These surfaces were found to exhibit properties associated with anisotropic hydropho-bicity, these being low water drag, superhydrophobicity, and the abihty to self-clean (Bixler and Bhushan, 2012, 2013), properties that arise from the unique hierarchical structures present on the surface (Bixler and Bhushan, 2013). 

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