Monitoring molecular diffusion of sucrose in xanthan solutions using ultrasonic velocity measurements

Measurements of the velocity of ultrasound through a sample as a function of diffusion distance were used to study molecular diffusion of sugars through biopolymer solutions. A1 wt% xanthan solution was prepared which consisted of a lower layer containing no sucrose, and an upper layer containing sucrose (10, 20, 30, or 40 wt%). The velocity of ultrasound through the biopolymer solutions was measured as a function of sample height and time, and then converted into sucrose concentration-distance profiles using an empirical calibration curve. The translational diffusion coefficient of the sucrose in the upper and lower layers was determined by fitting the experimental data to a Fickian diffusion model. The measured diffusion coefficients were in reasonable agreement with published values for sucrose in aqueous solutions in the absence of xanthan, which suggests the biopolymer had little influence on molecular diffusion.