Forensics of Polymer Networks

Polymer networks intertwine many aspects of our lives from consumer goods to biological tissues. It is now well understood that their mechanical response is a result of convolution of distinct structural parameters: chemical composition, strand conformation, and network topology. Unfortunately, since the discovery of rubber vulcanization by Charles Goodyear in 1839, the internal organization of networks has remained a sealed “black box”, due to inability of modern techniques to characterize crosslinked systems in details once they are formed. This long-standing problem of polymer science is addressed by developing a forensic-style method based on the analysis of a network non-linear response to deformation. This methodology provides information about strand degree of polymerization between crosslinks, contribution of loops and entanglements in network elasticity as well as fraction of stress-supporting strands. Application of the developed framework to networks with trapped entanglements highlights a transition from crosslink- to entanglement-controlled network elasticity with increasing degree of polymerization of network strands between crosslinks and illustrates how specific feature of this transition manifested in changes of entanglement and structural shear moduli characterizing different modes of network deformation. For networks with comb and bottlebrush strands, it allows to establish dependence of their Kuhn length on molecular architecture. Furthermore, the decoded structural information enables classification of different network types according to the effectiveness of stress distribution between strands and quality control to evaluate human error in network synthesis.