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

  • Author / Creator
    Walid, Khaled B
  • 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.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.