Modelling the continuous relaxation time spectrum of aquous xanthan solutions using two commercial softwares

The continuous relaxation time spectrum\ua0was modelled from the mechanical spectrum\ua0of a xanthan aqueous solution both using the\ua0TA Instruments TRIOS\uae software, and with\ua0the rheology software IRIS\uae1. Two types of\ua0calculation were applied to obtain the\ua0relaxation modes since the software bundles\ua0used in this study base the calculation upon\ua0two different algorithms, named\ua0"parsimonious" as it models continuous\ua0relaxation spectra using a minimum number\ua0of modes to obtain continuous relaxation\ua0times2, and a nonlinear regularization method that provides a larger spectrum with\ua0several modes3. The results were overall\ua0comparable but slightly different for long\ua0relaxation times

Impact of Glucose on the Nanostructure and Mechanical Properties of Calcium-Alginate Hydrogels

Alginate is a polysaccharide obtained from brown seaweed that is widely used in food, pharmaceutical, and biotechnological applications due to its versatility as a viscosifier and gelling agent. Here, we investigated the influence of the addition of glucose on the structure and mechanical properties of alginate solutions and calcium-alginate hydrogels produced by internal gelation through crosslinking with Ca2+ . Using1H low-field nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS), we showed that alginate solutions at 1 wt % present structural hetero-geneities at local scale whose size increases with glucose concentration (15–45 wt %). Remarkably, the molecular conformation of alginate in the gels obtained from internal gelation by Ca2+ crosslinking is similar to that found in solution. The mechanical properties of the gels evidence an increase in gel strength and elasticity upon the addition of glucose. The fitting of mechanical properties to a poroelastic model shows that structural changes within solutions prior to gelation and the increase in solvent viscosity contribute to the gel strength. The nanostructure of the gels (at local scale, i.e., up to few hundreds of \uc5) remains unaltered by the presence of glucose up to 30 wt %. At 45 wt %, the permeability obtained by the poroelastic model decreases, and the Young’s modulus increases. We suggest that macro (rather than micro) structural changes lead to this behavior due to the creation of a network of denser zones of chains at 45 wt % glucose. Our study paves the way for the design of calcium-alginate hydrogels with controlled structure for food and pharmaceutical applications in which interactions with glucose are of relevance