I'm working on sodium alginate and xanthan gum to make a gel. The xanthan gum is working well and has good viscosity, however, with the addition of alginate, the viscosity is decreasing. I'm confused why is it so.
You observe a sudden viscosity drop on addition of sodium alginate to xanthan. This is probably due to phase separation between these unlike polymers on mixing. This phenomenon is caused by the fact that the entropy of mixing is strongly depressed in polymer mixtures because of the connectedness between monomers, as compared to monomer mixtures. As a consequence, miscibility decreases with increasing molar mass. Effects of mixing on the rheology of xanthan-alginate-water systems are displayed in the added file, together with pictures of the phase diagram and morphology of the phase-separated system.
In order to obtain homogeneous gels you have to remain within the monophasic region by manipulating polymer concentration, molar mass, and maybe temperature. The question is then whether your system viscosity is within the requested range.
The Google Scholar search page in the added file shows that the full PhD thesis of this research is freely available as PDF.
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