Mechanochromic Fluorescent Probe Molecules for Damage Detection in Aerospace Polymers and Composites

Abstract

The detection of damage in aerospace composites can be improved by incorporation of mechanochromic fluorescent probe molecules into the polymers used in composite parts. This study focuses on a novel series of mechanochromic probes, AJNDE15 and AJNDE17, which are incorporated in structural epoxy resin DGEBA-DETA. Chapter 1 details the characterization of the DGEBA-DETA epoxy system used in this study. The important characteristics of DGEBA-DETA's response to mechanical loading will be discussed within the larger field of glassy amorphous polymer deformation. The mechanical, thermal, and chemical properties of DGEBA-DETA relevant to this work will be measured using standardized techniques and instrumentation. Chapters 2 and 3 focus on the mechanochromic probes AJNDE15 and AJNDE17 in the DGEBA-DETA system. Chapter 2 presents research designed to identify the mechanism through which the probes display mechanochromism. The possible mechanochromic mechanisms are introduced in a literature review. Research on these probes in DGEBA-DETA will be presented and discussed with respect to the possible mechanisms, and the mechanism that best fits the results will be identified as a mechanochemical reaction. Chapter 3 continues the analysis of the mechanochromism of the probes in DGEBA-DETA. The kinetics of the mechanochromic reaction will be studied and compared with the current understanding of glassy polymer deformation. Possible models for the molecular interactions responsible for mechanochromism in this system will be put forward. Research will be presented to evaluate the mechanochromism kinetics and for comparison with the behavior predicted by the models.