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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2015

Month Degree Awarded

September

First Advisor

Alfred J. Crosby

Subject Categories

Mechanics of Materials | Polymer and Organic Materials

Abstract

Wrinkling has been employed by many organisms to form unique topography, such as fingerprints, gut villi, and surface of flower petal cells. The wavy wrinkle structure provides friction enhancement, surface area increase, optical, and wetting properties improvement. Inspired by Nature, scientists have created wrinkles synthetically and proposed numerous uses for them. However, wrinkling surfaces encounters limitations on achieving massive area and high amplitude-to-wavelength ratio (aspect ratio).

The three phase contact line wrinkling technique creates well-defined wrinkles in a continuous fashion, and has great potential to scale-up for massive production. In addition to the velocity dependent adhesion force, we find the film deformed by the surface tension also contributes to the wrinkle amplitude and pattern. We refine the contact line mechanics with the material properties for the wrinkle aspect ratio and the pattern. (Chapter 2)

It has been known the aspect ratio of wrinkles is a function of the square root of applied strain until the wrinkling transitions into the strain localization modes. The localization modes, e.g. folding, have very different topographical structures and distinct properties to the wrinkles, and are undesired for wrinkling applications. This restricts the aspect ratio of the wrinkles reported in literature to be less than 0.3, limiting the functionalities of the wrinkling surfaces. To understand the transition to the localization mode, we create inhomogeneous wrinkled surfaces that have alternating flat and wrinkling regions, and study the distribution of applied global strain. We find that the distribution of the applied strain is neither localized nor homogenized by the initial inhomogeneity. (Chapter 3)

We further explore the limitation of the aspect ratio. In this thesis, delaying the localization transition to larger strains is the main strategy to access high aspect ratio wrinkles. We use two approaches to influence the onset of the strain localization. The first approach is the substrate prestretch, a practical method as it is also popular to create wrinkles. The amount of prestretch is found to delay localizations, and appropriate material properties are selected to avoid surface fractures. (Chapter 4) The second approach demonstrated a concept inspired from living organisms, which stabilizes wrinkles by reducing the stress. We rearranging the crosslinking network to minimize the traction forces during the growth of aspect ratio. This is described by the reduction of the strain energy in the substrate. (Chapter 5) These approaches allow us to achieve an aspect ratio three times larger (0.9) than that reported previously in the literature.

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