Investigation of the nodular microstructure of selected silsesquioxane and epoxy thermosetting resins

The role of the nodular microstructure in the failure of thermosetting resins is unknown. The goal of the research presented here is to determine the mechanisms by which the nodular microstructure affects failure of thermosetting resins.; Epoxy samples were fractured in tension and characterized for fractal dimension, nodular size, and toughness. Samples of epoxy resins have been shown in this work to have a relationship between nodular size and toughness. Two compositions were chosen to study the effect of strain rate and nodule size on toughness and a structural parameter, a0. Additionally fractal dimensional increment was measured using two separate techniques, Flaw to Mirror ratio (F-M), and Slit-Island contours. The fractal dimensional increment for slit-island contours was calculated using two similar algorithms; by hand, and with the aid of software.; It was shown through the course of this work that nodule size does not directly relate to toughness. Additionally, it was also shown that the epoxy resins characterized for this research are not structurally homogenous. It is believed that the inhomogeneities in the structure can be related to a 0.; Silsesquioxanes were synthesized using a novel two phase reaction. Samples were characterized for molecular weight and structure using matrix assisted laser desorption and ionization (MALDI) and silicon-29 nuclear magnetic resonance (Si-29 NMR). Additionally samples were characterized during growth using an Ubbelohde viscometer to characterize the growth processes of the two phase reaction. It was found that as the temperature of the growth phase synthesis increases, the viscosity of the polymer decreases; this is contrary to what one would normally expect in polymer condensation reactions. This result is due to immiscible two phase nature of the reaction process.; Additional experiments were performed to inquire about the role of the organic group on nodular size. It was hypothesized that nodule size is dependent on the difference in surface energy between the nodule and the free energy of the solution. Organically different silsesquioxanes and different solvents were used to investigate this hypothesis.