Small angle X-ray scattering (SAXS) is a powerful tool for detecting mesoscale features present in self-assembled supramolecular structures. Furthermore, SAXS can be used to investigate molecular level changes in the supramolecular assembly in response to an external stimulus, lending significant insight into the development of stimulus-responsive materials.  In this work a physically cross-linked supramolecular hydrogel scaffold is developed from a novel poly(ethylene glycol)-poly(MTC-benzyl ester) triblock copolymer. SAXS spectra of this class of materials show a correlation peak that corresponds to a feature size of 25 to 30 nm.  The location of this correlation peak is dependent on the molecular weight of both the poly(ethylene glycol) segment and the poly(MTC-benzyl ester) segment.  The PEG-poly(MTC-benzyl ester) material was incorporated into a series of covalently cross-linked thermoresponsive pNIPAAm hydrogels of varied cross-link densities to form a semi-interpenetrated network (semi-IPN). SAXS was used to determine if the nanoscale scattering feature present in single network gels was affected by forcing the collapse of the pNIPAAm gel scaffold. SAXS spectra of the semi-IPNs taken at ambient temperatures the semi-IPN did not show a correlation peak, however, after forcing the collapse of the pNIPAAm scaffold by elevating the temperature to 37�C the 25 nm scattering feature appears. Control samples of pNIPAAm hydrogel networks did not show a scattering feature at either ambient or elevated temperatures, indicating that the scattering feature is attributed to the interactions of the pNIPAAm scaffold and the PEG-poly(MTC-benzyl ester). This work contributes to the understanding of molecular-level changes that occur in stimulus responsive and topologically constrained hydrogel networks.

Small-angle X-ray scattering of self-assembled hydrogels in topologically constrained systems

248th National Meeting (2014)

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