(294e) Polymer Nanofibrillar Structures for Bioinspired Smart Adhesives

Various micro/nano-structures in nature have been motivating extensive efforts to mimic their unique capabilities in such properties as wettability, adhesion, and optical properties. Among these, geckos, which exhibit amazing capability of climbing on various surfaces, evolved the advanced concept of adhesion, that is, strong adhesion with directionality and reversibility. Since the adhesion mechanism of gecko is revealed to be mostly due to van der Waals forces, great efforts have been paid to synthesize the micro/nano-fibrillar structures from various materials, mainly carbon nanotubes and polymers. Polymers usually have a strong merit of small preload over carbon nanotube, and soft polymers such as elastic rubber have been mainly considered due to their high adhesion and ease of fabrication. However, stiffer materials with micro/nano-fibrillar structures are more desirable for repeatable adhesion with minimal contamination, as in the case of real gecko. More recently, there have been several reports on successful adhesion from stiff polymer such as polyethylene and polypropylene. Although there have been numerous reports on the synthetic gecko-like structures, many fundamental and practical issues remain. For example, systematic studies on the effect of material stiffness or the surface energy are still required. With this background, we have focused on the synthesis of nanofibrillar surfaces from stiff polymers with well-controlled nanostructures such as diameter, length and density. We have successfully developed the fabrication process based on simple wet chemistry in order to overcome disadvantages from photolithography-based techniques such as high cost, energy and time-consuming processes. Well-defined Si-nanowire templates are fabricated by metal-assisted electroless etching combined with colloidal techniques, and with subsequent nanomolding, polymer nanofibrillar structures are successfully achieved over large areas (centimeter scale) using polyethylene and polypropylene. In this way, optimum geometrical conditions for achieving best performance in adhesion/friction on various surfaces are systematically investigated and will be reported.