Date of Award

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Materials Science and Engineering

Committee Member

Dr. Philip J. Brown

Committee Member

Dr. Olin Thompson Mefford, IV

Committee Member

Dr. Vincent Blouin

Committee Member

Dr. William Pennington

Abstract

This work investigated and characterized the structure-property relationship of a polyurethane-based block copolymer and the thermal energy storage properties obtained through the solid-to-solid phase transition of a PCM polyol polymer that undergoes a thermal transition at low temperatures. The chemical and physical factors that influence or dictated the microphase separation between the urethane “hard” segment block and the polyol “soft” segment block of conventional polyurethanes how the resulting changes in phase morphology effects the crystallization behavior of the “soft” component, which in this dissertation is analogous to the PCM polymer component was analyzed. Theurethane HS group behaves as a cross-link and restricts PCM polymer chain mobility, thereby the PCM can no longer translate freely and instead exhibits a solid-to-solid phase transition. The introduction of HS cross-link exhibits a behavior known as the HS chain-end effect, in which HS constrictions cause the PCM polymer to become partially crystalline. The extent to which PCM crystallization is limited by the HS chain end effect can vary depending on HS structural factors, such molecular architecture and HS composition. The HS chain end effect was quantified for the following HS structural variables; HS cross-link nature, diisocyanate molecular geometry, HS chain length to characterize and compare how each factor limits PEG PCM polymer crystallization. By doing so in a systematic manner, the optimal configuration for an effective PU-SSPCM can be determined. To examine HS cross-link nature, an analogous linear and a non-linear PU-SSPCM polymer, were compared to determine differences in final thermal energy storage properties. The effects of diisocyanate molecular geometry was investigated by comparing the thermal energy storage properties of a series of PU-SSPCMs varied only by its diisocyanate component. The considered diisocyanates were selected based on specific structural moieties that affect the structural regularity, rigidity, and symmetry of the HS. The chain length of the hard segment component influence on thermal energy storage properties was also investigated by varying the proportions of urethane HS concentration and PCM polymer concentrations. HS cross-link nature, the HS diisocyanate component, and HS chain length are considered chemical level factors since they can be controlled during synthesis. On the physical level, the possibility of a connection between the degree of phase separation and thermal energy storage properties were explored. This relationship was investigated by measuring thermal energy storage properties of PU-SSPCMs with a high, medium, and low degree of phase separation. Varying HS crystallization by cooling rates from a homogeneous melt state was used to obtain different levels of phase separation. Thermal energy storage properties were measured using Differential Scanning Calorimetry experiments. Supplemental information about the chemical structure of the synthesized polyurethane-based solid-to-solid phase change materials (PU-SSPCM) was analyzed by FTIR analysis techniques. The phase morphology and the degree of phase separation prevalent in the prepared samples was characterized by FTIR, TGA, and DSC techniques.

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