Water content and guest size dictate the mechanical properties of cyclodextrin mediated hydrogels

In many natural and synthetic systems, quantifying the amount of water present within a material is crucial to understanding its mechanical properties. Furthermore, biological materials often rely on aqueous supramolecular interactions for both their structure and function. Therefore, studying the effect of water content in a simple, synthetic, supramolecular system is a good approach to gain further understanding about complex natural materials. We suggest that simple hydrogels cross-linked by inclusion complexes between cyclodextrin hosts and viologen-capped guest molecules are an excellent candidate for a model system. Herein we determine how modulating both the size of the viologen cap and the overall water content of the hydrogels effects the resultant mechanical properties. Tuning the stopper's steric bulk affects the kinetics of complexation, leading to distinct differences observed in the gel's rheological properties. Moreover, the influence of steric bulk on the tensile properties of the hydrogels changes depending on the water content and number of complexes that can form. Finally, small angle X-ray scattering was used to investigate the internal structure of the hydrogels and demonstrated that homogeneity depends on water content while the formation of distinct domains depends on the steric bulk of the stopper.