Bulk superhydrophobic

The purpose of this chapter is to deal with the surface modification of cellulose fibres in order to provide them with specific functionalities, so that they can play determining roles in such applications as reinforcing elements for composite materials, self-contained composite structures, anti-pollution aids, hybrid materials, superhydrophobic surfaces and conductive and magnetic materials. Other types of surface modifications, such as those associated with dying or the manufacture of chromosorb, enzymatic and ion-exchange supports, fall outside the scope of this review. Within the structure of this book, this chapter constitutes in many ways a bridge between the chemistry associated with bulk modification treated in Chapter 16 and the processing and properties of composite materials in Chapter 19, with the addition of more specific aspects. 

Figure 9.2 Due to the high contact angle and low hysteresis, liquid droplets easily roll off superhydrophobic surfaces. However, damage to the surface often leads to an increased contact angle hysteresis and, consequently, droplets stick to the surface, (a) A hydrophobic surface coating on a roughness pattern may get easily worn off, and hydrophilic bulk material will be exposed as a result, (b) If the roughness features are fabricated of hydrophobic material, wear will not introduce hydrophilic pinning sites [22].

Figure 9.17 Field emission scanning electron microscope images of the bulk material at low (a) and high (b) magnification (c) water droplets exhibit spherical shape on the surface of the bulk material (d) mirror-like phenomenon can be observed on the bulk material submerged in water and (e) optical image and contact angle profile of the water droplet placed on the abraded bulk material. Bottom schematic illustration of a bulk material which can still sustain its superhydrophobicity after mechanical abrasion because of the low surface energy microstructures extending throughout its volume. Reproduced from [87,88] with permission of The Royal Society of Chemistry.

Properties that bulk materials never show merge at the nanoscale such as conductor-insulator transition, dilute magnetism, Dirac-Fermi polarons, catalytic conversion and enhancement, superhydrophobicity, superfluidity, super lubricity, and supersolidity. 

Size reduction-induced polarization happens in compounds containing N, O, and F and metals with the outermost s-orbit filled with unpaired electrons like Ag, Au, Rh, while happens not to metals with such s-orbit that is empty or filled with paired electrons, such as Pt and Co. Such polarization of substance at the nanoscale creates properties that the bulk counterpart never demonstrates such as the dilute magnetism, catalysis, superhydrophobicity, fluidity, lubricity, as will be addressed in later section. 

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