Effect of Sticker Clustering on Dynamics of Associative Polymer Networks

Recent studies of associative networks have explored chain architectures with stickers clustered in groups along the chain, enhancing strength and toughness. Here, we provide microscopic insight into the effect of sticker clustering in associative networks by combining experiment and coarse-grained modeling, comparing networks with stickers randomly distributed along the chain versus stickers clustered on the chain ends. Small-angle neutron scattering of a model hydrogel based on metal-coordinate bonds shows an increase in large-scale density fluctuations in networks with clustered stickers, which correlates with slower stress relaxation due to the cooperative effect of multiple bonds. However, sticker clustering results in faster self-diffusion of the network-forming chains, despite the slower relaxation. Brownian dynamics simulations demonstrate key changes to the network topology caused by the clustered stickers, particularly an enhancement in loop defects, which increase the rate of chain hopping and overall self-diffusivity on large length scales. These studies highlight the strong effects of sticker clustering on the structure and dynamics of associative networks on different length scales, providing handles for design.