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Design and Manufacture of Anisotropic Dry Adhesives for MEMS Compatible Pick and Place Open Access


Other title
Oligomer Transfer
Thermoplastic Elastomer
van der Waals
Dry Adhesive
Type of item
Degree grantor
University of Alberta
Author or creator
Walid, Khaled B
Supervisor and department
Sameoto, Dan (Mechanical Engineering)
Examining committee member and department
Daneshmand, Mojgan (Electrial and Computer Engineering)
Ayranci, Cagri (Mechanical Engineering)
Department of Mechanical Engineering

Date accepted
Graduation date
Master of Science
Degree level
Directionality or anisotropy is one of the benchmark properties of gecko adhesion, allowing geckos to adhere strongly to a surface and detach easily with little effort. Geckos achieve anisotropy by means of intricate micro-nano hierarchical structures on its feet, which is very difficult to mimic in synthetic versions. This work demonstrates that directionality can be induced on otherwise isotropic mushroom shaped fibers simply by incorporating a defect on the edges of the cap surface in a 2-step photolithography process, thus taking advantage of what is usually considered as an undesirable effect. A hypothesis based on linear beam theory is presented to explain the phenomena of defect-dependent adhesion of cylindrical fibers, and the hypothesis is confirmed with finite element analysis on mushroom shaped fibers and empirical data. The adhesion strength and directionality of the fibers were found to depend on the shape, position and size of the defect which could be tailored based on the application of the adhesive. Synthetic dry adhesives are commonly manufactured by a casting method using thermoset polymers such as polydimethylsiloxane (PDMS) and polyurethane, a procedure which has drawbacks such as long processing times, requirement of a vacuum, and relatively expensive base materials. Styrene-ethylene/butylene-styrene (SEBS) thermoplastic elastomer is introduced in this work as an alternative material for the manufacturing of mushroom-shaped adhesive fibers. Surface contamination tests using X-ray Photoelectron Spectroscopy (XPS) reveals that the SEBS thermoplastic elastomers are less likely to transfer oligomers upon contact with a die surface compared to polydimethylsiloxane (PDMS) and polyurethane, thus rendering this material more suitable for sensitive gecko adhesive applications such as MEMS pick and place. With a comparable adhesion strength, along with the added advantages of much faster manufacturing using thermo-compression molding, scalability, less expensive and non-toxic raw materials, thermoplastic elastomers appear to be better suited for large scale manufacturing of these bio-mimetic adhesives.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
W. B. Khaled and D. Sameoto. Fabrication and characterization of thermoplastic elastomer dry adhesives with high strength and low contamination. ACS Appl. Mater. Interfaces 2014. Available:
. B. Khaled and D. Sameoto. Anisotropic dry adhesive via cap defects. Bioinspiration & Biomimetics, 8(4), 044002, 2013. Available:
. B. Khaled and D. Sameoto. Manufacture of mushroom shaped dry adhesives by thermo-compression molding of thermoplastic elastomers. Proceedings of the Annual Meeting of the Adhesion Society, 2014. Available at:
. B. Khaled and D. Sameoto. The Deliberate Defect: A Facile Method for Mass Manufacture of Anisotropic Dry Adhesives. Proceedings of the Annual Meeting of the Adhesion Society, 2013, Available at:

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