Rheology and application of thermoreversible polymer networks based on the Diels-Alder cycloaddition

Sheridan, Richard James

Graduate Thesis Or Dissertation

Rheology and application of thermoreversible polymer networks based on the Diels-Alder cycloaddition Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/3j3332456

Abstract

A model thermoreversible network based on the Diels-Alder cycloaddition reaction was synthesized. These materials exhibit extreme changes in material properties near a critical temperature. The model network was used to test theoretical predictions of viscoelasticity near this critical temperature. The resulting data supported the theory and allowed for the description of the complex process of stress relaxation in transient networks to be written in terms of a simple linear scaling relationship. To use the scaling relationship, we revisited earlier work on externally triggered healing, in which the thermal reactivity of the material could be activated by self-limited RF hysteresis heating. This composite of chromium(IV) dioxide particles suspended in the model Diels-Alder material was used to demonstrate their ability to be readily tailored to applications that are constrained by factors not related directly to the polymer, such as the Curie temperature of CrO2. We demonstrated the effect of composition on fracture healing, showing that more highly crosslinked materials take longer to recover strength after fracture. To bring some of the temporal and spatial control of optical curing techniques to thermally activated systems, we developed a robust custom nanoparticle to serve as a durable photothermal chromophore. The particle was designed to efficiently convert laser light into heat while maintaining surface plasmon resonance and colloidal behavior even in the high temperature, poor solubility environment of a Diels-Alder network. We observed a unique reaction to laser irradiation, in the formation of bumps at the location of exposure. We demonstrated substantial control over the height of these features by varying the time and intensity of the laser exposure, and investigated the cause of feature formation.

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