Domenico Larobina is a researcher at the Institute of Polymers, Composites, and Biomaterials – National Research Council of Italy in Naples. Within his current research visit to Montpellier financed by the LabEx NUMEV, Dr Larobina will give a seminar on his research activity on the rheological properties of biomaterials on Thursday 18 November 2021 at 10 am, at the Laboratoire Charles Coulomb (L2C). More information on the L2C website.
Aging represent a limiting factor in the performances of soft-solid-based products and devices. Many efforts have been devoted to understand the microscopic origin of this long-term behavior in physical gels. In this contribution, we investigate macromolecular physical gels (strontium alginates) at different aging times, combining linear stress relaxation and dynamic light scattering. Stress relaxation shows two-step decay, with an early logarithmic decay followed by a stretched exponential behavior. Two characteristic times can be identified, which increase as distinct power laws of the gel age. The DLS clearly displays anomalous microscopic dynamics, with compressed exponential decay of autocorrelation functions and ballistic wavelength dependence of the decay time. The comparison between rheology and DLS allows for the identification of two dynamic correlation lengths: λ_o and λ_s(fig. 1a). The former (λ_o) is roughly constant with the aging time, while the latter (λ_s) increases linearly with t_w. Overall, rheological and DLS data allow us to attribute the observed mechanical decay to two different mechanisms occurring in our macromolecular physical gel. The first, visible at early-to-medium times, is ascribed to local rearrangements in the gel network (on length scale smaller than the pore size). The second, which occurs at long times, results from collective rearrangements involving an increasing number of pores, and is related to gel syneresis and aging.