Evaluating Epoxy Cure And Adhesion Strength Through Single-Sided Nmr Measurements Of Molecular Mobility

Commonly used in aerospace, automotive, marine, defense, electronic, and manufacturing industries, epoxy adhesives offer advantages over mechanical joints by providing stronger and/or more flexible bonds, more uniform stress distribution, low shrinkage, and lightweight connections between materials. Determination of curing kinetics and properties of interfaces between epoxy and inorganic substrates provides insight that is useful for quality control and defect detection for such applications. Single-sided NMR provides a nondestructive and inexpensive method for probing epoxy materials and spatially resolving the decay of spin-lattice and spin-spin relaxation times (T1 and T2) during and after curing of epoxy resins onto substrates. In this thesis, we report the use of single-sided NMR for both characterizing the strength of adhesion between epoxy and inorganic substrates and monitoring the cure of epoxy at various temperatures. Multi-dimensional T1 –T2 measurements were performed to correlate with changes in surface energies that provide insight on the chemical adhesion of various epoxy samples. Furthermore, we used NMR measurements to monitor in-situ room-temperature and heat curing of epoxy to probe reductions in molecular mobility throughout the curing process. NMR relaxation properties were correlated with DSC data for comparison of the cure extent and cure rates. Our results show the efficacy of single-sided NMR measurements for studying curing, the extent of cure, adhesion strength of epoxies, and interphase phenomena