Research On Gecko-inspired Dry Adhesion Arrays Based On Micro-nano Structure System

Geckos can walk freely on the walls, ceilings and any other surfaces, which attracted the focus of the researchers in recent years. The climbing ability of geckos is attributed to fibrillar arrays, consisting of stiff, hydrophobicβ-keratin which covers the bottom of gecko's feet. Such high dry adhesion between the feet and surfaces originates from Vander Waals forces. To mimic gecko foot hairs, surface design parameters such as pillar size, shape, elastic modulus, or tilt angle need to be considered. To simulate the materials with microstructure has a high practical value. Mussels have a special adhesion to surface in the water. The amazing ability of adhesion is due to a kind of proteins in mussels that is dopamine (DOPA). Either natural or synthetic DOPA has an excellent adhesion. The higher content of the DOPA has a greater adhesion. Dopamine-modified microarrays have an ability of adhesion in a wet environment. It can broaden the application of the microarrays by the modification of dopamine-polymer.In the first chapter, we reviewed the development of bio-mimick gecko and generalize the mechanism of the adhesion and detachment. In addition, we introduced the preparation of the gecko-inspired arrays by different methods and different materials. In the last, we introduced the main methods of the adhesion measurement.In the second chapter, we introduced the fabrication technology of the micro/nano polymer arrays and designed a platform to investigate the macro adhesion of the fabricated arrays. Atomic force microscope(AFM) was utilized to measure the micro adhesion of the arrays. 3,4-dihydroxy-ι-phenylalanine(DOPA) was synthesized and then was modified to the polyurethane polymer arrays. The experimental result shows that the dopamine-modified microarrays can enhance the adhesion of the, also have an ability of adhesion in a wet environment. We have also discussed the mechanism of the modification and adhesion of the arrays.In the last chapter, segmented polyurethane (PU) was utilized to fabricate micro arrays by the porous polydimethyl siloxane (PDMS) membrane molding method. We fabricated a series of segmented PU from 4, 4'- diphenylmethane diisocyanate (MDI), Polyoxytertramethylene Glycol (PTMG) (Mn = 1000), with 1, 4– butanediol (BDO) as the chain extender. We studied the influence of the elastic modulus on the gecko-inspired dry adhesion by regulating the elastic modulus of bulk polyurethane combined with changing the size of microarrays. By varying the ratios of hard and soft segments of the bulk PU and changing the radius of the PU arrays, regulation of the elastic modulus of PU micro arrays is achieved to realize the modulation of the dry adhesion. The properties of the micro arrays, such as the elastic modulus and adhesion were investigated by Triboindenter. The study demonstrates that bulk surfaces show the highest effective modulus, with similar values at around 175 MPa and decreasing the arrays radius causes a significant decrease in E, down to 0.62 MPa. The corresponding adhesion experiment shows that decrease of the elastic modulus can enhance the adhesion which is consistent with the recent theoretical models.