Abstract
The effect of added ions (0.5 mM K + or 0.25 mM Ca 2+) on the critical overlap ( C*) and gelation ( C o′) concentrations for gellan, κ-carrageenan and alginate polysaccharides were investigated using steady shear rheometry. Both C* and C o′ decreased for all solutions with added salts, a trend more pronounced for gellan and alginate with added Ca 2+, and κ-carrageenan with added K +. Aggregation near the sol–gel transition was modeled as a percolation-type transition. In addition, the frequency dependence of the viscoelastic storage ( G′) and loss ( G″) moduli for bulk and localized areas within a 0.7% (w/w) gellan sol were measured using a controlled stress and oscillating magnetic bead rheometer, respectively. Flow behavior of the bulk was in the terminal and plateau relaxation regions of the viscoelastic spectrum, whereas localized behavior was in the plateau and rubber–glass transition regions.
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