In nature, the leaves of many plants exhibiting superhydrophobicity which have water contact angle greater than 150¡Æand low contact angle hysteresis are cleaned completely by a simple rain shower: rolling water droplets remove dirt and debris from their surfaces (self-cleaning). The unusual wetting characteristics of superhydrophobic surfaces are governed by both their surface chemistry and roughness on multiple scales. To fabricate such surfaces, we have proposed various methods, such as supramolecualr organosilane, layer-by-layer deposition method, texturing of metal surface, and micellization of block copolymer.
Surfaces with controlled anisotropic wettability have the advantage of limiting liquid flow to a desired direction, which has advantage potential applications in microfluidic devices, evaporation-driven formation of patterns and easy-clean coatings, etc. Anisotropic wetting behavior has been observed on one-dimensional patterned surfaces achieved either through chemical pattering or surface roughness. In nature, anisotropic wettability has been found on the rice leaf, and it has been mimicked by combining layer-by-layer assembly and the anisotropic wavy surface.
Self-assembled monolayers (SAMs) are molecularly thin films of supramolecules, which are excellent for the model study of investigating the adhesion behavior in nanometer-scale, i.e., nano-adhesion. Systematic research on the nano-adhesion behavior of SAMs of various structures is being performed using atomic force microscope (AFM) and Johnson-Kendall-Roberts (JKR) apparatus.
JKR apparatus is the instrument for evaluating the surface energy (¥ã) or intrinsic work of adhesion (W) between solid materials, which is based on contact mechanics. The excess deformation induced by interfacial attraction is mainly considered when measuring the change in contact area by applied load. We can obtain methodological advantages over conventional instruments such as contact angle meter, peel tester, etc. Intrinsic properties, such as W, are obtained by maintaining the contact in the equilibrium state during loading process. Non-equilibrium properties, such as effective adhesion energy (G), are also obtained by varying the unloading condition after contact, which gives us additional important information at the interface between the two materials. We expect this instrument can be applied in various fields such as nano-adhesion in self-assembled monolayers, adhesion of micro-particles, bio-interfacial adhesion, etc.
3.2 Polymer induced crystallization of amorphous CaCO3
Inspired by biomineralization process observed in seashell nacre, the biomimetic mineralization of calcium carbonate has received much attention in recent times. This, combined with a broader understanding of how organic molecules in biological systems affect the nucleation and growth of biominerals, has led to the design of new hybrid materials. Calcium carbonate is an attractive model mineral because its various crystal forms are easily recognizable, and its morphology has been the subject in biomineralization processes. We therefore have dealt with polymer-induced crystallization of ACC films and the sequential formation of CaCO3 structures assisted by the acidic polymer additives.