Diffracted X-Ray Tracking for Analysis of Heterogeneity of Hydrogels

Diffracted X-ray tracking (DXT) was applied to evaluate spatial heterogeneities in polyacrylamide gel networks. Diffraction spots from the (111) planes of gold nanocrystals (GNPs) encapsulated in the gels exhibited temporal motion during time-resolved X-ray diffraction measurements using a quasi-monochromatic X-ray beam. This observation indicates that the GNPs undergo rotational motion within the gel matrix. An analysis of the diffraction spot trajectories revealed that the rotational diffusion coefficient of GNPs in homogeneous gels follows a single Gaussian distribution, whereas that of heterogeneous PAAm gels, with regions of varying cross-linking density, is described by a bimodal distribution. These findings demonstrate that DXT is a powerful technique for analyzing polymer network heterogeneity.