Nanoscale Mobility of Aqueous Polyacrylic Acid in Dental Restorative Cements.

: Hydrogen dynamics in a time range from hundreds of femtoseconds (fs) to nanoseconds (ns) can be directly analyzed using neutron spectroscopy, where information on the inelastic and quasi-elastic scattering, hereafter INS and QENS, can be obtained. In this study, we applied these techniques to understand how the nanoscale mobility of the aqueous solution of polyacrylic acid (PAA) used in conventional Glass Ionomer Cements (GIC) changes under confinement. Combining the spectroscopic analysis with calorimetric results we were able to separate distinct motions within the liquid and in the GIC's. The QENS analysis revealed that the self diffusion translational motion identified in the liquid is also visible in the GIC. However, as a result of the formation of the cement matrix and its setting, both translational diffusion and residence time differed from the PAA solution. When comparing the local diffusion obtained for the selected GIC, the only noticeable difference was observed for the slow dynamics associated to the polymer chain. Additionally, over short-term ageing, progressive water binding to the polymer chain occurred in one of the investigated GIC. Finally, a considerable change in the density of the GIC without progressive water binding indicates an increased polymer crosslinking. Taken together, our results suggest that accurate and deep understanding of polymer-water binding, polymer crosslinking as well as material density changes occurring during the maturation process GIC are necessary for development of advanced dental restorative materials.