Determination of temperature dependent structure evolution by fast-Fourier transform at late stage spinodal decomposition in bicontinuous biopolymer mixtures

Abstract

The evolutions of the bicontinuous microstructures of aqueous phase separating gelatin/maltodextrin mixtures quenched to different end temperatures were determined by confocal laser scanning microscopy (CLSM). The growth of the bicontinuous microstructures was quantified by Fourier image analysis. Weighted least squares were applied in order to be able to use all the spectral information. The results of Fourier image analysis and weighted least squares were related to existing theories on coarsening. The mixtures were quenched from 60 °C to different end temperatures ranging between 10 °C and 37 °C and the concentration was held constant at 4.2 w/w % gelatin and 7.9 w/w % maltodextrin. The results showed that the mixture phase separated through spinodal decomposition at all temperatures. A crossover was found from structure growth governed by diffusion to structure growth governed by hydrodynamic flow. The results showed that the structure evolution at the beginning of the phase separation was temperature independent with a growth proportional to the time raised to one-third. After the crossover, the growth of the characteristic distance between the maltodextrin domains was temperature dependent with a growth proportional to the time raised to an exponent that varied from 0.75 to 1.58. It was found that the growth exponent increases with decreasing end temperature, i.e., increasing quench depth. The maximum intensity of the circularly averaged two-dimensional fast-Fourier transform of the CLSM micrographs was found to grow exponentially with time. The increases in the maximum intensity were proportional to the time raised to an exponent that varied from 1.98 to 4.97. It was found that this exponent increases with decreasing end temperature. Before the crossover, the relation between the growth exponent of the microstructure and the growth exponent of the maximum intensity, as compared with existing theories on coarsening, showed that the phase separation was in the intermediate or transitional stages of spinodal decomposition. Similarly, after the crossover, it was found that phase separation was in the late stages of spinodal decomposition. Furukawa master plots showed that the structure growth obeyed dynamical scaling and that the dimensionality of the growth was three, given off-critical conditions.