Date of Award

5-29-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Patrick T. Mather

Keywords

Polymeric Composites, Responsive (Smart) Materials, Self-Healing, Shape Memory

Subject Categories

Engineering

Abstract

Smart materials with the ability to respond to external stimulus have attracted tremendous attention in both academic institutions and industry. Such unique aspect of these materials make them great candidates to address current challenges in the world of Materials Science including those that no human intervention is a necessity. The objective of this dissertation is to employ different techniques to develop novel thermally and mechanically responsive polymeric composites for several industrial applications.

In Chapter 2, the curing kinetics and polymerization induced phase separation (PIPS) of an epoxy matrix with and without a semicrystalline thermoplastic was investigated. Same PIPS technique studied in this chapter was utilized in the following chapters to develop composites featuring triple shape memory and self-healing properties as we now describe.

In Chapter 3, we report an investigation into the preparation and characterization of shape memory assisted self-healing (SMASH) coatings utilizing shape memory (SM) response of a glassy amorphous epoxy matrix and rebonding the crack by a low melt-viscosity thermoplastic. Note that same materials and polymerization induced phase separation (PIPS) technique as in Chapter 2 was employed in this chapter.

Seeking to develop a simpler method to fabricate composites featuring SMASH, we successfully designed a setup for dual-electrospinning two immiscible polymers in

Chapter 5. Specifically Poly(vinyl acetate) (PVAc) and poly(ε-caprolactone) (PCL) solutions were dual-electrospun to fabricate composites featuring shape memory assisted self-healing (SMASH) and SM properties. The resulting material was capable of restoring its shape and mechanical properties with a simple thermal trigger.

Continuing on the subject of "Self-Healing", fiber reinforced composites (FRCs) in which the healing agent was encapsulated in polymeric fibers and released upon fracture were developed and studied in Chapter 4. Unique core-sheath fibers featuring stiff polyacrylonitrile (PAN) in the sheath and epoxy based self-healing agents in the core were fabricated by coaxial electrospinning. Upon damage, fibers break and the healing agent would flow to the damage site and polymerize to restore the mechanical properties of the composites. The proposed FRCs will lead to a cost-effective and much more durable composite structure capable of withstanding loads that would otherwise fail due to lack of proper reinforcement.

Chapter 6 then represents a novel strategy exploiting organic based layered double hydroxides (LDHs) to enhance mechanical and barrier properties of tire rubber-LDH composites. Pneumatic tires are composite structures inflated with pressurized gas to provide weight support, shock absorbance and traction transmission for an automotive. Therefore, developing tires that can hold inflation pressure for an extensive period of time is of great interest in auto industry. This was achieved by nano-exfoliation of the organic based LDHs in tire rubber. The relationship between microstructure and mechanical properties of such composites were investigated in this chapter.

In the case of "Shape Memory", Chapter 7 will focus on fabrication of triple shape memory composites featuring a semicrystalline thermoplastic and an amorphous epoxy. Such composites utilize polymerization induced phase separation (PIPS) (introduced in Chapter 2) and exhibit two distinct transition temperatures required for triple shape memory behavior. This study explores the relationships between the morphology of triple shape memory polymers and their shape memory characteristics.

Finally, Chapter 8 explores for the first time design, preparation, and characterization of triple shape memory polymeric foams that is open cell in nature and features a two phase, crosslinked SMP with a glass transition temperature of one phase at a temperature lower than a melting transition of the second phase. The soft materials were observed to feature high fidelity, repeatable triple shape behavior, characterized in compression and demonstrated for complex deployment by fixing a combination of foam compression and bending. We further explored the wettability of the foams, revealing composition-dependent behavior favorable for future work in biomedical investigations.

It is noteworthy that all the aforementioned materials and methods exhibit great potential for industrial applications considering their simplicity and low manufacturing costs. Beside, future work is required for each project some of which are listed at the end of each chapter.

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