Impact of Sol Molecular Weight and Architecture On the Mechanical Performance and Toughness of Polymeric Gels

The implementation of polymer gels into many practical applications is limited by their relatively poor mechanical performance and toughness. For a particular network cross-link density, the mechanical properties of the gel are largely dependent on the solvent quality and loading. In this report, we investigate the impact of the non-reactive soluble material (sol) molecular weight on the mechanical properties of the gel. Sols with a molecular weight near or below the molecular weight of entanglement (MW_ENT) produce a change in the modulus that follows theoretical scaling laws. Sols with a molecular weight higher than the MW_ENT exhibit a similar modulus to lower molecular weight sols at low strain rates but strain harden at higher strain rates. The deviation from the theoretical behavior occurs at timescales consistent with the sol reptation times. As a result, sol loading, sol molecular weight, and crack velocity have a dramatic influence on the fracture toughness of the gel. We anticipate that using branched sols will increase the reptation times, shifting the toughness-crack velocity curve to lower strain rates, and provide sufficient toughness to be implemented into a wide range of practical applications.