Hierarchical cross-linking in physical alginate gels: a rheological and dynamic light scattering investigation

Abstract

We investigate the dynamics of alginate gels, an important class of biopolymer-based viscoelastic materials, by combining mechanical tests and non-conventional, time-resolved light scattering methods. Two relaxation modes are observed upon applying a compressive or shear stress. Dynamic light scattering and diffusive wave spectroscopy measurements reveal that these modes are associated with discontinuous rearrangement events that restructure the gel network via anomalous, non-diffusive microscopic dynamics. We show that these dynamics are due to 2 both thermal activation and internal stress stored during gelation and propose a scenario where a hierarchy of cross-links with different life times is responsible for the observed complex behavior. Measurements at various temperatures and sample ages are presented to support this scenario.

Coupling Space-Resolved Dynamic Light Scattering and Rheometry to Investigate Heterogeneous Flow and Nonaffine Dynamics in Glassy and Jammed Soft Matter

“…12 with sinc 2 = 1 (becauseγ = 0), and a slow, compressed exponential decay (t 1 = 1660 s and p = 1.16 > 1). These dynamics are consistent with the very slow compressed exponential relaxations reported for a variety of gels, with an exponent p ranging from 1.5 at low q down to p > ∼ 1 at large q [89][90][91][92][93][94][95]. These dynamics have been attributed to the relaxation of internal stress built up at gelation [89,96].…”

Single molecule investigation of the onset and minimum size of the calcium-mediated junction zone in alginate

“…We estimate a timeframe of several hundred milliseconds for the resolution of this stress in oligoG blocks up to 20 units in length. In the context of alginate gelation and the relaxation processes that contribute to the rheology of alginate gels this data provides molecular-level insight into the processes that govern the release of internal stresses, identified recently (Larobina & Cipelletti, 2013;Siviello, Greco, & Larobina, 2015) as a critical mechanism in alginate gel rheology.…”

“…Recently dynamic light scattering and direct mechanical analysis of alginate gels (Larobina & Cipelletti, 2013;Secchi, Roversi, Buzzaccaro, Piazza, & Piazza, 2013) has revealed the slow breaking of bonds during the relaxation of maturing alginate gels due to thermal activation and the relieving of internal stresses. These stresses arise when the formation of a crosslink by one section of a polymer constrains another part, leading to the breaking of crosslinks so that the tension may be relieved, as part of a two-stage process that takes up to thousands of seconds to resolve.…”

Relaxation processes in a lower disorder order transition diblock copolymer

“…This compressed exponential behavior has been observed for a variety of soft matter systems undergoing jamming transitions, which results in arrested solid like collective dynamics. [30][31][32] As the temperature surpasses the estimated temperature of the transition, the relaxation becomes diffusive with a clear q 2 dependence of 1/τ. The predominant mode in this regime, therefore, has the features of that predicted for incompressible block copolymers with some polydispersity, named in the literature as polydispersity or heterogeneity mode 12 and might be related to interdiffusion processes at the interphases.…”