Small-Angle Neutron Scattering Reveals Structural Hierarchy of Polymer– Nanoparticle Hydrogels

Self-assembled supramolecular materials formed through noncovalent interactions have found remarkable utility in applications ranging from drug delivery to wildfire management, owing to their extrudability and tunable properties. Determining the microstructure of these materials has been difficult due to their disordered and often metastable nature, hindering rational design. Here, we utilize contrast-matched small-angle neutron scattering to elucidate the microstructure of a supramolecular polymer–nanoparticle hydrogel composed of hydrophobically modified hydroxypropylmethylcellulose (HPMC) and core–shell polymeric nanoparticle crosslinkers. Scattering data for both components are successfully fit to distinct structural models across a range of formulations. We find that hydrophobically modified HPMC undergoes a disordered microphase separation in concentrated solutions, forming an incipient gel structure. The addition of nanoparticles induces the formation of a robust gel network formed via strong noncovalent polymer-nanoparticle interactions. The interaction expands the shell of the nanoparticles, which contributes to the gel structure by inducing particle jamming. These results leverage neutron scattering techniques to probe the structure of disordered, self-assembled hydrogels and enable future engineering and optimization of supramolecular materials.