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Title:A study of shape memory polymers and their usage in the development of directional dry adhesives
Author(s):Seo, John
Advisor(s):Kim, Seok
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:M.S.
Genre:Thesis
Subject(s):shape memory polymers
dry adhesives
microstructure
reversibility
directionality
Abstract:This thesis first introduces shape memory polymers and their unique phase-changing and recoverability properties. The underlying thermodynamic explanations along with their fundamental governing equations is presented. A few possible potential areas of interest for applications of this unique polymer are presented, but the one of particular interest is biomimetic dry adhesives. In this thesis, a shape memory polymer (SMP) surface with geometrically asymmetric micro-wedge array is fabricated as a reversible directional dry adhesive through a double exposure angled lithography technique. The unique shape fixing and recovery properties of SMPs and surface microstructuring enable highly reversible adhesion strength upon thermo-mechanical loading, and the tilted wedge geometry gives rise not only to its capability for varying adhesion strength based on loading direction, but also the reduction of strain energy input necessary to achieve contact area saturation with the opposing surface. To characterize the directional adhesion strength of the fabricated micro-wedge surface, adhesion tests are performed in the forward shear, backward shear, and normal directions based on the tilting direction of the micro-wedges. The adhesion strength is measured as a function of the applied preload for the three directions investigated, and is compared to a computational analysis by modeling the adhesive failure as the initiation of crack growth in linear elastic fracture mechanics. Additionally, reversibility is demonstrated by heating the micro-wedge surface above its T g , allowing the structure to recover its original shape after being deformed, resulting in almost zero adhesion strength. The adhesion tests demonstrate that the forward shear direction is capable of adhesion strengths that are greater than that of the backward shear direction by a factor of over 3, confirming its capability for directional adhesion. Finally, additional novel shapes are introduced, taking advantage of the angled exposure technique and properties of negative photoresist to "cleave" a unique wedge pattern based on the shape of the patterns on the photomask used in fabrication.
Issue Date:2016-07-19
Type:Thesis
URI:http://hdl.handle.net/2142/92867
Rights Information:Copyright 2016 John Seo
Date Available in IDEALS:2016-11-10
Date Deposited:2016-08


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