Date of Award

8-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Patrick T. Mather

Keywords

polymer coatings, polymer films, RPSM, self healing, shape memory, SMASH

Subject Categories

Mechanical Engineering

Abstract

My research aims to develop a novel approach that uses the shape memory (SM) effect to aid self healing (SH) polymeric systems that are able to simultaneously close and re-bond cracks with a single thermal stimulus. This new concept is termed shape memory assisted self healing (SMASH). Additionally, a new type of shape memory termed reversible plasticity shape memory (RPSM) was also developed where both the elastic and plastic deformation found after deformation completely recover upon a thermal stimulation. I aim to utilize a broad range of polymeric and composite systems that include a single phase semi-crystalline system, a single phase amorphous blend, and a combination of these two polymers in a composite elastomer system to prove the versatility of the SMASH and RPSM effects. Chapter 1 gives a polymer science background along with SM and SH material overview. Chapter 2 discusses the fabrication and analysis of miscible blends that show the SMASH and RPSM effect using a semi-crystalline polymer, poly(e-caprolactone) (PCL) to construct a SM PCL network (n-PCL) and PCL thermoplastic used as the SH agent (l-PCL). The PCL thermoplastic SH agent interpenetrated the n-PCL for form a single phase semi interpenetrating polymer network (SIPN). Films were made for testing to prove the SM and SH effects by varying the amount of SM network and SH agent to optimize both effects. Thermo-mechanical, tensile, and SH experiments were conducted to study the fixing, recovery and healing properties of the polymeric system. Chapter 3 focuses on a unique system for the fabrication of clear thin SMASH SIPN coatings that were developed for optical industrial applications. Here, an amorphous polymer composition, poly(tert-butyl acrylate) (poly(tBA)), was used in a blend of two forms, a network form for shape memory (n-tBA) and a linear form for self-healing (l-tBA), that, together, form a single phase SIPN. Thermal, thermo-mechanical, SM and SH scratch experiments were conducted to investigate both SM and SH mechanisms as influenced by the relative concentrations of n-tBA and l-tBA in the SIPN materials. Chapter 4 introduces for the first time an innovative smart polymeric soft material where aligned nanofibers are used to construct anisotropy embedded in an elastomeric matrix. This system, termed "Anisotropic Shape Memory Elastomeric Composite" (A-SMEC) was investigated for RPSM and SMASH properties. In addition, the anisotropic mechanical and shape memory properties were investigated and interpreted in light of the underlying structure. Chapter 5 builds upon the results of Chapter 4, presenting the fabrication and testing of laminated A-SMEC biomorphs that were designed to exploit anisotropic in RPSM behavior to yield predictably curled and twisted structures upon deformation. More specifically, the out-of-plane curvature and pitch were analyzed as a function of biomorph orientational lay-up. All polymeric systems described in this dissertation are examples of smart polymers that can be used to tailor mechanical performance while introducing new phenomena, such as self-healing, RPSM, and stretch-induced twisting. Chapter 6 discusses the conclusions followed by future work that are sub-sectioned for each chapter of the dissertation.

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Open Access

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