Oscillatory rheometric tracing of dextran crosslinking reaction in aqueous semidilute solutions – Effects of formulation on the gelation properties

Rheological characteristics evolved during chemical gelation of semidilute dextran solutions are reported at different temperatures, levels of epichlorohydrin (ECH as a cross-linker), polymer concentration, and amount of catalyst i.e., NaOH. Increasing temperature, cross-linker, polymer and NaOH concentrations, all lead to faster gelation. Gelation at higher temperatures resulted in weaker incipient gels, whereas higher ECH addition or increasing polymer concentration gave rise to higher values of the gel strength parameter S. The results disclosed that for all systems the gelation process proceeds over a long time, and both the complex viscosity and the power law exponent reveal that solid-like gel structures are formed in the post-gel region. These results clearly show that the rheological characteristics of the incipient dextran hydrogels can be tuned by changing the conditions of temperature, polymer and cross-linker concentration, as well as the amount of catalyst.