Noncovalent Intermolecular Forces in Complex Fluids: Correlating the Multiscale Dynamic Influence of Forces on H-Bonds and Viscoelastic Behavior of Gelatin Hydrogel

The material properties of hydrogels have conventionally relied on chemical modifications of biopolymers. However, polymeric complex fluid interactions and intermolecular forces also contribute to the diverse characteristics of hydrogels. Entanglements within polymer chains facilitate energy dissipation, thereby enabling the broad practical applications of hydrogels. The modifications in H-bond network of the polymer can shed light on enhancing the viscoelastic properties of hydrogels. H-bonds and viscoelasticity, controlled by noncovalent intermolecular forces are two parameters of primary importance in physically cross-linked hydrogels that can directly influence their material properties. Salts and plasticizers impart electrostatic and van der Waals forces, respectively, and directly or indirectly affect the H-bonds in the hydrogel polymer network. These forces exhibit their effects at different length scales, i.e., atomic, nano, micro, and macroscale. Hence, selectively analyzing the forces at a multiscale level is crucial for determining the relationship between H-bonds and the viscoelasticity of hydrogels. This study considers gelatin-based hydrogels with different plasticizers and salts to analyze the impact of noncovalent intermolecular forces. The plasticizer and salt interactions vary on the multiscale according to their plasticizing effects and screening potential, respectively. MD simulations along with ATR/FTIR spectroscopy (atomic-scale), and scattering (nanoscale) as well as rheological analysis (macro-scale) were corroborated with each other to elucidate the proportionality between H-bonds and viscoelasticity.