Counting primary loops in polymer gels

Huaxing Zhou a, Jiyeon Woo a, Alexandra M. Cok a, Muzhou Wang b, Bradley D. Olsen b, and Jeremiah A. Johnson a,1Departments of a Chemistry and b
Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved October 9, 2012 (received for review July 31, 2012)

Much of our fundamental knowledge related to polymer networks is

built on an assumption of ideal end-linked network structure. Real

networks invariably possess topological imperfections that negatively affect mechanical properties; modifications of classical network theories have been developed to account for these defects.

Despite decades of effort, there are no known experimental protocols for precise quantification of even the simplest topological

network imperfections: primary loops. Here we present a simple

conceptual framework that enables primary loop quantification in

polymeric materials. We apply this framework to measure the

fraction of primary loop junctions in trifunctional PEG-based hydrogels. We anticipate that the concepts described here will open new

avenues of theoretical and experimental research related to polymer

network structure.