Volumetric interpretation of viscosity for concentrated and dilute sugar solutions

Abstract

Viscosities of aqueous sugar solutions are shown to correlate with free volume and molar volume, a principle advanced by Hildebrand for pure simple liquids. Here, the ultrahigh viscosity range (a > lo4 mPa.s) is examined for the fist time for small-molecule solutions, using new data on a noncrystallizing sugar mixture under conditions of temperature (20 < T < 80 "C) and concentration (mole fraction x > 0.4) where glassy behavior is approached.The WLF equation, based on free volume concepts and used widely with polymers, is found to characterize ~(7') extremely well. Two parameters are employed, the glass transition temperature Tg(x) and the glass viscosity ~~( 2 ) ; proposals are advanced for estimating vg in terms of molar volumes of the components. For dilute solutions ( x < 0.3) at 20 "C, a low-viscosity regime, average molar volume proves to be sufficient information to predict q(x) for the six solute systems evaluated. IntroductionThe temperature dependence of viscosity, V, for simple liquids received a major interpretive clarification when Hildebrand and co-workers1i2 showed that it correlates

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

“…White and Cakebread [65] described various physical defects in frozen and dehydrated foods stored above T g . Caking of amorphous powders, stickiness, collapse, crystallization, and aroma loss have been described as temperature/time/water content-dependent phenomena occurring above a collapse temperature [66][67][68][69]. Acceleration of these phenomena is the result of the decreased viscosity and consequent increase in mobility, when a system transforms from the glassy (below T g ) to the rubbery (above T g ) state [8].…”

“…The WLF equation [68,69] relates the η at T to the η g at T g , as a function of the difference between T and T g , as follows: (4) As discussed in Sections 2.2 and 2.4, in a cryoconcentrated system, T m ' represents the "mobility temperature" at which the constrains due to solute mobility are overcome during warming. It represents the temperature at which the diffusion of solute in the maximally freeze-concentrated system can occur in a practical experimental time frame, and is an appropriate reference temperature (instead of T g ) to use in the WLF equation in this kind of systems for estimating solute diffusion and reaction rates at subfreezing temperatures above T m ' [201].…”

Biological glasses: nature's way to preserve life

“…In many glass-forming substances, melting of the glass results in a dramatic increase in translational and rotational motion (Soesanto and Williams, 1981;Roozen et al, 1991;Steffen et al, 1992;Blackburn et al, 1996;Deppe et al, 1996;Champion et al, 1997;Hemminga and Van den Dries, 1998;Van den Dries et al, 1998a). It has been known for a long time that stabilisation of many macromolecules is greatly enhanced by the presence of aqueous glasses.…”

“…Several models have been developed which describe the kinetics of viscosity or molecular mobility for glass-forming substances above T g (Perez, 1994). The Williams-Landel-Ferry (WLF) equation (eqn 0.2) is an often used model in foodpolymer science to predict the effect of increasing temperature on relative relaxation times above T g (Williams et al, 1955;Ferry, 1980;Soesanto and Williams, 1981;Chan et al, 1986;Roos and Karel., 1991;Steffen et al, 1992;Champion etal., 1997), where C x and C 2 are system-dependent coefficients (Ferry, 1980), and a T is defined as the ratio of the relaxation phenomenon at T to the relaxation at the reference temperature T ref . This empirical equation was originally derived from the free volume interpretation of the glass transition.…”

“…Average values for the WLF coefficients (C^ 17.44 and C 2 =51.6) were calculated by Williams et al General Introduction (1955) using the available values for many synthetic polymers. The universal constants have been shown to also apply to molten glucose (Williams et al, 1955), amorphous glucose-water systems (Chan et al, 1986), amorphous sucrose and lactose powders at low moisture (Roos and Karel, 1991), and concentrated solutions of mixed sugars (Soesanto and Williams, 1981).…”