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Leveraging the state of absorbed moisture within a polymer network to identify physical and chemical features of the host material is predicated upon a clear understanding of the interaction between the polymer and a penetrant water molecule; an understanding that has remained elusive. Recent work has revealed that a novel damage detection method that exploits the very low baseline levels of water typically found in polymer matrix composites (PMC) may be a valuable tool in the composite NDE arsenal, provided that a clear understanding of polymer–water interaction can be obtained. Precise detection, location, and possible quantification of the extent of damage can be performed by characterizing the physical and chemical states of moisture present in an in-service PMC. Composite structures have a locally elevated dielectric constant near the damage sites due to a higher fraction of bulk (“free”) water, which has a higher dielectric constant when compared to water molecules bound to the polymer network through secondary bonding interactions. In this study, we aim to get a clear atomistic scale picture of the interactions which drive the dielectric signature variations necessary for tracking damage. Molecular Dynamics (MD) simulations were used to explore the effect of temperature on the state of moisture in two epoxy matrices with identical chemical constituents but different morphologies. The motivation was to understand whether higher polarity binds a greater fraction of moisture even at higher temperatures, leading to suppressed dielectric activity. Consequently, the influence of secondary bonding interactions was investigated to understand the impact of temperature on the absorbed water molecules in a composite epoxy matrix. 

Dendrimers are globular, multi-functional, monodisperse macromolecules with perfect structure fidelity. Their architecture is composed of a series of branched polymeric arms, composed within “wedges”, that emanate from a central core. Their structure contains a high density of functional groups located at their periphery, referred to as the “outer shell”. Due to their globular structure, it is assumed that the relative “size” of a dendrimer does not fluctuate greatly between solvents. This may be due to the inability of the branched arms, or wedges, to significantly expand or collapse (comparative to analogous linear polymers) owing to steric barriers from branching, especially at higher generations. In contrast, it is expected that a linear polymer, of similar molecular weight to a dendrimer analog, would have a greater degree of size variation dependent on solvent-polymer interactions. This stems from its innate flexibility and greater conformational flexibility. For this investigation, analogous dendritic and linear bis-MPA polyesters as well as poly(caprolactone) (PCL) were analyzed using size-measuring techniques including gel permeation chromatography (GPC) and diffusion ordered spectroscopy-nuclear magnetic resonance (DOSY- 1 H NMR).