Gel setting of hybrid carrageenan solutions under steady shear

Abstract

We study the gel formation under steady shear and the final gel properties of hybrid-carrageenan solutions in NaCl and KCl, with a systematic comparison with kappa- and iota-carrageenan solutions. For high enough shear rates corresponding to homogeneous flow, the structural development of the gels is overall the same for the different salts and carrageenans, and shows the following features: (a) helices are formed during cooling and the onset of formation is not affected by the flow; (b) the flow-induced orientation of structures results in the shear thinning behaviour of the cooling fluids; (c) structural orientation is locked upon the gel setting which takes place immediately after flow cessation and results in a significantly weaker gel elasticity, longer gel structural build-up, a shift of the spectrum of gel relaxation times to longer times, and in the eventual birefringence of films obtained from dried gels. A new phenomenological model that contemplates all experimental results is proposed.