Wednesday, 21 June 2006 - 11:50 AM
Eng Ctr 151 (University of Colorado at Boulder)

Surface Properties of Sugar Solutions

Mina Hoorfar1, Zdenka Policova2, Michael L. Hair2, A. Wilhelm Neumann2, and J. Adin Mann Jr.1. (1) Case Western Reserve University, Cleveland, OH, (2) University of Toronto, Toronto, ON, Canada

Reports in the literature suggest that sugars such as dextrose and sucrose increase the surface tension of water. The effect was interpreted as a depletion of the solute molecules at the water-air interface. This effect is scrutinized through accurate measurement of the surface tension of aqueous solutions of three sugars, i.e. dextrose, fructose and sucrose, at different concentrations. An automated drop shape technique called axisymmetric drop shape analysis (ADSA) was used to determine the surface tension. The results show that the effect of sugar on the surface tension of water is more complicated than the unsubstantiated interpretation reported in the literature. The surface tension of sucrose solutions at low concentrations (i.e. up to 5 wt.%) is near that of water, but as the concentration increases the surface tension increases even above the surface tension of water. For dextrose and fructose, the pattern is different. For the concentrations lower than 5 wt.%, the surface tension of the aqueous solutions of dextrose and fructose decreases continuously with increasing concentration (the effect is more pronounced for dextrose). Then, the surface tension increases above the surface tension of water (similar to sucrose solutions) for higher concentrations. To gain better insight into these patterns, we present our surface tension data as a function of the chemical potential obtained for each sugar solutions; the activity coefficient values are known at different concentrations. As a result, a rigorous interpretation is provided for the surface properties of these aqueous solutions by taking into account the non-ideal solution behavior.

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