Off-campus UMass Amherst users: To download campus access dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Dissertations that have an embargo placed on them will not be available to anyone until the embargo expires.

Author ORCID Identifier

https://orcid.org/0000-0002-4054-9028

Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Ryan C. Hayward

Subject Categories

Polymer and Organic Materials

Abstract

This thesis broadly aims to examine how different surface instability modes compete with each other across various length scales and to apply the resulting fundamental understanding to enable switchable liquid/gas permeation and electrical sensing devices. To this end, Chapter 2 describes a new model for the crease nucleation and growth phenomenon. There have been discrepancies between experiments and theories in critical strains of creasing, especially for systems with high elastocapillary number. In this chapter, we resolved the discrepancy by verifying our new model, which properly takes the surface tension effects into account. Chapter 3 describes acceleration induced surface instabilities. Although wrinkling frequently appears in a bilayer system, it has rarely been observed in a single layer system. In this chapter, we demonstrated rotational acceleration induced wrinkling instabilities on the surface of a single layer gel. Chapter 4 discusses the interplay between surface instability modes originating from a patterned bilayer with characteristic length-scales comparable to those of the instability modes. While applications, such as flexible electronics, have surfaces with in-plane heterogeneity (e.g. metal electrode patterns on PDMS), a fundamental understanding of surface instabilities with in-plane heterogeneity have not been understood well. In this chapter, we successfully controlled critical strains, locations, and types of surface instabilities by changing the micro-pattern geometries, leading to a rich set of surface topographies composed of multiple surface instability modes. Chapter 5 describes the effects of geometrical singularities in the form of notch structures on the development of surface morphology under compression. Although creasing leads to reversible surface self-contact, its applications are limited partly due to the large activation strain required for the crease formation and the difficulties in controlling crease position. In this chapter, reversible surface self-contact was induced by the stress concentration associated with notch structures, and mechanically gated electrical switches with small and tunable activation strains and high on/off ratios were demonstrated. Chapter 6 discusses the fabrication of devices for switchable liquid/gas permeation and electrical sensing and their performance. Devices consisting of large active area surfaces with impermeable conductive patterns were fabricated, which enabled switchable liquid/gas permeation and electrical resistivity under mechanical compression.

Available for download on Sunday, May 10, 2020

Share

COinS