High-Pressure Rheology of a Thermoreversible Protein Sol–Gel

Porcine gelatin gels were studied by in situ high pressure diffusing wave spectroscopy (HP-DWS) to measure the rheological effects of pressure and temperature on the sol–gel transition. Pressure-induced gelation occurs at temperatures above the ambient pressure gel transition temperature, suggesting that high pressure stabilizes the gel state. Using a transient network model, the elastic chain density is shown to follow a Barus-like scaling with applied pressure. The pressure-elasticity coefficients are significantly different for pressure-induced gels and compressed thermal gels, suggesting a competition exists between temperature-dependent hydrophobic interactions and pressure-dependent hydrogen bonding between gelatin chains. HP-DWS is used to map the pressure–temperature gel transition boundary, which shifts approximately 4 °C per 100 MPa. At higher pressures, the initial network at the critical gel condition exhibits a smaller fractal dimension and weaker gel strength. The implications of the results are discussed for other protein-based complex fluids and soft materials.