Dissertation
Scaling Reversible Adhesion in Synthetic and Biological Systems
(2013)
Abstract
Geckos and other insects have fascinated scientists and casual observers with their
ability to effortlessly climb up walls and across ceilings. This capability has inspired
high capacity, easy release synthetic adhesives, which have focused on mimicking the
fibrillar features found on the foot pads of these climbing organisms. However, without a
fundamental framework that connects biological and synthetic adhesives from
nanoscopic to macroscopic features, synthetic mimics have failed to perform favorably at
large contact areas. In this thesis, we present a scaling approach which leads to an
understanding of reversible adhesion in both synthetic and biological systems over
multiple length scales. We identify, under various loading scenarios, how geometry and
material properties control adhesion, and we apply this understanding to the development
of high capacity, easy release synthetic adhesive materials at macroscopic size scales.
Starting from basic fracture mechanics, our generalized scaling theory reveals
that the ratio of contact area to compliance in the loading direction, A/C, is the governing
scaling parameter for the force capacity of reversible adhesive interfaces. This scaling
theory is verified experimentally in both synthetic and biological adhesive systems, over
many orders of magnitude in size and adhesive force capacity (Chapter 2). This
understanding is applied to the development of gecko-like adhesive pads, consisting of
stiff, draping fabrics incorporated with thin elastomeric layers, which at macroscopic
sizes (contact areas of 100 cm2) exhibit force capacities on the order of 3000 N.
Significantly, this adhesive pad is non-patterned and completely smooth, demonstrating
that fibrillar features are not necessary to achieve high capacity, easy release adhesion at
macroscopic sizes and emphasizing the importance of subsurface anatomy in biological
adhesive systems (Chapter 2, Chapter 3).
We further extend the utility of the scaling theory under shear (Chapter 4) and
normal (Chapter 5) loading conditions and develop simple expressions for patterned and
non-patterned interfaces which describe experimental force capacity data as a function of
geometric parameters such as contact area, aspect ratio, and contact radius. These studies
provide guidance for the precise control of adhesion with enables the development of a
simple transfer printing technique controlled by geometric confinement (Chapter 6).
Force capacity data from each chapter, along with various literature data are collapsed
onto a master plot described by the A/C scaling parameter, with agreement over 15 orders
of magnitude in adhesive force capacity for synthetic and biological adhesives,
demonstrating the generality and robustness of the scaling theory (Chapter 7).
Disciplines
Publication Date
September, 2013
Degree
Doctor of Philosophy
Field of study
Polymer Science, Engineering
Department
Polymer Science and Engineering
Advisors
Alfred J. Crosby
Comments
© Copyright by Michael David Bartlett 2013. All Rights Reserved.
Citation Information
Michael D. Bartlett. "Scaling Reversible Adhesion in Synthetic and Biological Systems" (2013) Available at: http://works.bepress.com/michael-bartlett/20/