Influence of gellan gum concentration on the dynamic viscoelasticity and transient flow of fluid gels

Start-up at the inception of shear and flow interrupted experiments were carried out to illustrate the transient flow properties and thixotropic recovery of low-acyl gellan gum fluid gels prepared by a low-energy mechanical treatment. Small amplitude oscillatory shear tests were conducted to illustrate the rheological response under non-destructive conditions. Confocal laser scanning microscopy revealed the occurrence of a dispersion of gel-like domains in a continuous phase. Rheological methods were used to check that the samples characterised were free of thermo-mechanical history effects prior starting the transient flow tests. Start-up shear flow experiments at 10 s−1 resulted in a nearly instantaneous sharp rise of viscosity until a peak value was reached before it dropped following a sum of two first-order kinetic equations. The kinetic coefficients as well as the relative fall in viscosity were found to increase with gellan concentration. The equilibrium modulus as well as the peak and steady-state viscosities scaled with the gellan concentration following a power law equation with a characteristic exponent of about 2.0. Conversely, the degree of thixotropic recovery after a rest time of 10 s went down as gellan concentration increased, emphasising the need to balance both effects when formulating gellan fluid gels as stabilisers. The results obtained do a better job of highlighting the importance of peak viscosity than steady-state viscosity when data for pump selection and calculation are required.

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► We prepare low-acyl gellan gum fluid gels by a low-energy mechanical treatment.
► CSLM shows fluid gels are dispersions of gel-like domains in an aqueous phase.
► The influence of gellan concentration on mechanical spectra of fluid gels is studied.
► Start-up tests avoiding pre-shear were used to model thixotropic viscosity decay.
► Flow interrupted tests illustrated the concentration dependence on viscosity recovery.