Hydrogels form a special class of form-stable, elastic materials that consist of a (polymer) network and a large amount of water. In this project you will use advanced nonlinear spectroscopic techniques to study biological hydrogels and supramolecular hydrogels. Biological hydrogels have a network formed by protein-polysaccharide chains, and typically contain 90-99% water. These hydrogels are ubiquitous in nature and perform important biological functions. Supramolecular hydrogels contain relatively small molecular components that reversibly assemble via hydrogen bonds and hydrophobic interactions into fibrils or bundels. Supramolecular hydrogels can already be form-stable and elastic while containing an astonishingly large amount (>99.9%) of water. As a result of the non-covalent nature of these interactions, supramolecular hydrogels are highly responsive to external stimuli like changes in temperature, pH, and exposure to light, thus allowing an easy control of their visco-elastic properties. For some supramolecular hydrogels, a small change in temperature already suffices to switch the state of the system between a liquid aqueous solution and a form-stable elastic hydrogel.

In this project you will study the molecular-scale structure and dynamics of the water and the polymer network of biological and supramolecular hydrogels, using femtosecond two-dimensional infrared spectroscopy and polarization-resolved femtosecond infrared spectroscopy. The obtained information will clarify how the macroscopic viscoelastic and responsive properties of hydrogels are determined by the structure and dynamics of the polymer network and the water molecules of the hydrogel.