Characterizing dynamic heterogeneities in degrading polymer gels

Understanding degradation of hydrogels is critical for a range of applications. In particular, photo-controlled bond scission permits localized control of gel properties. We focus on hydrogels formed by end-linking of four-arm polyethylene glycol precursors and characterize structural and dynamical heterogeneities in these gels during photodegradation. We use our recently developed dissipative particle dynamics framework that captures bonds scission and diffusion of degraded fragments at the mesoscale. This approach allows us to model behavior of the highly non-ideal degrading network without making a-priori assumptions typically made in continuum theories regarding network deformations. To quantify spatial fluctuations in local dynamic behavior, we calculate the self-part of van-Hove correlation function for the network junctions and reactive end groups. We demonstrate strong deviations from the Gaussian fit during the degradation and quantify variations in non-Gaussian character with the proximity to the reverse gel point. The proposed framework allows one to characterize spatial and dynamic heterogeneities and quantify spatial fluctuations in local dynamics of these highly non-ideal systems.