The rheological behavior of poly(ethylene glycol) of 1500 g·mol −1 (PEG1500) aqueous solutions with various polymer concentrations (w = 0.05, 0.10, 0.15, 0.20 and 0.25) was studied at different temperatures (T = 283.15, 288.15, 293.15, 298.15 and 303.15) K. The analyses were carried out considering shear rates ranging from (20 to 350) s −1 , using a cone-and-plate rheometer under controlled stress and temperature. Classical rheological models (Newton, Bingham, Power Law, Casson, and Herschel−Bulkley) were tested. The Power Law model was shown suitable to mathematically represent the rheological behavior of these solutions. Well-adjusted empirical models were derived for consistency index variations in function of temperature (Arrheniustype model; R 2 > 0.96), polymer concentration (exponential model; R 2 > 0.99) or the combination of both (R 2 > 0.99). Additionally, linear models were used to represent the variations of behavior index in the functions of temperature (R 2 > 0.83) and concentration (R 2 > 0.87).
■ INTRODUCTIONKnowledge of rheological properties of polymers in aqueous solution is necessary for the design of equipment used in the chemical and biochemical industry. 1 Such properties affect fluid behavior when polymeric solutions are submitted to shear conditions, for example, during pumping and transport through pipelines. Therefore, accurate rheological data for solutions of biotechnologically relevant polymers are essential tools to industries or academic laboratories working in the bioseparation fields. 1−3 Poly(ethylene glycol) [HO−CH 2 −CH 2 −(O−CH 2 −CH 2 ) n−1 − OH], commonly known as PEG or PEO, consists of nonbranched polymers, normally soluble in water and in various organic solvents. In general, their solubilities, as well as the rheology of the resulting solutions, are markedly influenced by type of solvent, polymer molar mass, dissolved polymer concentration, and temperature of the medium. 4 Among other technological applications, PEGs of a wide range of molar masses, mixed with other polymers or inorganic compounds (mainly salts), are often employed to obtain aqueous two-phase system (ATPS) used as partitioning systems for biomolecules. 5−13 In such systems, the rheological characteristics of the dissolved polymers affect both the time of phase separation before equilibrium is reached and the speed of displacement of solutes within the polymer-rich phase in partitioning experiments.Despite the recognized technological importance of PEGs, the number of studies available in the literature addressing the rheological behavior of these polymers is quite small. 14−21 In most of these studies, either PEG melts or solutions exhibited a non-Newtonian behavior, meaning that their viscosities do not remain constant as the velocity gradient varies. Commonly, the viscosity of these fluids decreases as the shear rate increases; that is, they present a shear thinning (pseudoplastic) behavior. 22 Simpled stated, this can be attributed to the fact that under shear conditions an alignment of the nonbranc...