Liquid Crystal Networks for Smart Biomimetic Micro/nano Structured Adhesives

Abstract

As modern technology demands for miniaturized structures with higher surface area to the volume ratio, the design and synthesis of materials with tailored surfaces is becoming more important. Moreover, some emerging technologies require materials with smart surface properties that can be controlled remotely, and work adaptively in “on” and “off” states when stimulated externally. Fascinating surface structures and adaptive functionalities that can be found in biological systems have provided great inspirations to researchers for fabrication of synthetic biomimetic assemblies. While the fabrication of materials with non-smart bio-inspired surface structures has been greatly accomplished, the mimicking of adaptive functionalities of the living systems is less investigated. Thus, there is a great zeal in developing materials with smart and adaptive biomimetic structured surfaces. The objective of this dissertation is to design and develop materials with smart biomimetic micro/nanostructured surfaces that can show desirable responses when remotely stimulated. First, an experimental study on the integration of a dissipative material (resembling the dissipative and wet nature of the tree frog toe pads) to an elastic fibrillar interface (resembling the dry and fibrillar nature of the gecko foot pads) is carried out. Accordingly, a new type of functionally graded adhesive is developed, which is composed of an array of elastic micropillars at the base, a thin elastic intermediate layer and a viscoelastic top layer. The results showed that the new proposed graded structure has remarkable adhesive properties in terms of pull-off force, work of adhesion, and structural integrity (i.e., inhibited cohesive failure). Second, muscle-driven actuation of biomimetic microfibrillar structures is achieved using integrative soft-lithography on a backing splayed liquid crystal elastomer or networks (LCEs/LCNs). Variation in the backing LCE layer thickness yields different modes of thermal deformation from a pure bend to a twist-bend. The muscular motion and dynamic self-cleaning of gecko toe pads are mimicked via this mechanism. Finally, the self-peeling of gecko toes is mimicked by the integration of film-terminated fibrillar adhesives to hybrid nematic LCN cantilevers. A soft gripper is developed based on the gecko-inspired attachment/detachment mechanism. Performance of the fabricated gripper for transportation of thin delicate objects is evaluated by the optimum mechanical strength of the LCN and the maximum size of the adhesive patch.