Shape memory polymers as direct contact dry adhesives for transfer printing and general use

Adhesive;Micromanufacturing;Transfer printing;Bioinspired;Shape memory;Polymer;Dry adhesive

Eisenhaure, Jeffrey D

关键词: Adhesive;    Micromanufacturing;    Transfer printing;    Bioinspired;    Shape memory;    Polymer;    Dry adhesive;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/99291/EISENHAURE-DISSERTATION-2017.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

For most diminutive life on Earth, control over external adhesive forces is crucial for survival. As humans, we pay little notice because at our scale inertial forces typically overwhelm adhesive forces by a wide margin. Nonetheless, the study and development of dry adhesives, which rely on ubiquitous intermolecular attractions to repeatedly form and break attachment to their adherends, have garnered substantial interest in recent decades. High performance artificial dry adhesives may unlock the door for many exciting new technologies from nanoscale manufacturing to wall climbing robots, but thus far the challenges have proven substantial and few successful commercial applications have come to fruition.This dissertation represents an initial investigation into the benefits and potential limitations of developing shape memory polymer (SMP)-based dry adhesives. Prior to the presentation of experimental results, a review of the current state of dry adhesive knowledge including both theory, observations of the natural world, and lessons learned by other researchers in their attempts to develop a wide variety of synthetic dry adhesives is provided. It is concluded that dry adhesives fundamentally function through careful control of elastic energy, an idea that is very well suited to explore using SMPs which offer a large change in compliance across their thermal transition temperature. Thermoset epoxy SMPs are identified as an ideal choice for the investigation due to their mechanical strength, chemical resistance, manufacturability and convenient glass transitions among other features. The dry adhesive performance of a selected SMP is first evaluated for the purpose of microscale transfer printing, wherein micro-objects are assembled through precise control of adhesive surface forces. Significant benefits over existing solutions in terms of maximum adhesive strength during loading (~7 MPa), minimum strength for release (~0 MPa), and process versatility are confirmed, culminating in demonstrations of several challenging assemblies. The increase in adhesive strength is explained by invoking arguments from linear fracture mechanics and considering the dramatic compliance change experienced by the SMP between bond and load events. Advanced methods of heating and meaningful steps towards commercial-scale parallel printing processes are demonstrated.The suitability of SMP for larger-scale applications is considered next. Strength rivaling or exceeding known alternatives is demonstrated, showing adhesion exceeding 2 MPa for 6 mm diameter adhesives while retaining excellent releasability through the use of microstructuring. A method of internally heating the SMP by adding conductive carbon nanoparticles is explored, including quantitative analyses of conductivity and the SMP composite's storage and loss moduli. The resulting flexible and conductive bi-layer SMP adhesive supports load while attached to surfaces of varied curvature. Variations on the SMP formula have their adhesive and mechanical properties tested, and are used to produce a self-contained SMP prototype wall-hanging adhesive.