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Mechanical Evaluation Methods For Polymer And Composite Systems, Donna Theresa Wrublewski

Open Access Dissertations

This dissertation describes the development and application of various mechanical characterization techniques to four types of polymer composite materials. The composite nature of these materials ranges from molecular to macro-scale, as do the size scales probed by the techniques chosen. The two main goals of this work are to evaluate the suitability of existing characterization methods to new composite materials (and augment the methods as needed), and to use these methods to determine optimal composite system parameters to maximize the desired mechanical response. Chapter 2 employs nondestructive ultrasonic spectroscopy for characterizing the stiffness response of both micron-scale woven composites and …

Self-Nucleated Crystallization Of A Branched Polypropylene, Dhwaihi Alotaibi

Masters Theses 1911 - February 2014

Long chain branched polypropylene (LCBPP) crystallizes rapidly and with high nucleation density. The origin of this fast crystallization process is not well understood. It has been attributed to its complicated molecular architecture. In this research, we explore isothermal crystallization of LCBPP, 5%LCBPP and linear polypropylene (LPP) through rheological, thermal, microscopy and optical measurements at different experimental temperatures. The time resolved mechanical spectroscopy technique was used to predict the liquid-to-solid transition (gel point) at different crystallization temperatures (supercooling rates) in order to understand the structure during the crystallization process.

The crystallization process of LCBPP was completed in time scale less …

Room Temperature Magnetic Materials From Nanostructured Diblock Copolymers, Zoha M. Al-Badri, Raghavendra R. Maddikeri, Yongping Zha, Hitesh D. Thaker, Priyanka Dobriyal, Raja Shunmugam, Thomas P. Russell, Gregory N. Tew

Gregory N. Tew

Nanostructured magnetic materials are important for many advanced applications. Consequently, new methods for their fabrication are critical. However, coupling self-assembly to the generation of magnetic materials in a simple, straight-forward manner has remained elusive. Although several approaches have been considered, most have multiple processing steps, thus diminishing their use of self-assembly to influence magnetic properties. Here we develop novel block copolymers that are preprogrammed with the necessary chemical information to microphase separate and deliver room temperature ferromagnetic properties following a simple heat treatment. The importance of the nanostructured confinement is demonstrated by comparison with the parent homopolymer, which provides only …

Depletion Versus Deflection: How Membrane Bending Can Influence Adhesion, Jin Nam, Maria Santore

Maria Santore

During depletion-driven vesicle adhesion, a stiff membrane’s resistance to bending at fixed tension prevents contact angle equilibrium and vesicle spreading over an opposing vesicle, while more flexible vesicles partially engulf opposing vesicles. Estimates of the bending cost associated with the spreading contact line, relative to the adhesion energy, were consistent with the observed spreading or lack of spreading for the flexible and stiff membranes, respectively, and predicted a lag time sometimes preceding spreading.

Synthesis Of Hydrogels Via Ring-Opening Metathesis Polymerization: Factors Affecting Gelation, Gregory N. Tew, Ahmad E. Madkour, Joshua M. Grolman

Gregory N. Tew

Ring-opening metathesis polymerization (ROMP) was used to synthesize hydrogels via copolymerization of a diamine monomer 3 and a novel cross-linker 5 using Grubbs' third generation catalyst as initiator. Reactions were performed at two different monomer concentrations and at various initial molar ratios of cross-linker to initiator. At low monomer concentration, gelation occurred at initial cross-linker to initiator ratios of 1.5 and greater, which decreased to values of 1.05 and greater when increasing the monomer concentration. This result is in agreement with the Flory–Stockmayer theory. The gel yield and swelling properties were also found to be dependent on the cross-linker to …