Densities of Poly(ethylene glycol) + Water Mixtures in the 298.15-328.15 K Temperature Range Ali Eliassi 1, * , Hamid Modarress 1 , G.Ali Mansoori 2 (1). Amir Kabir University of Technology (Tehran Polytechnique), Tehran, Iran (2). University of Illinois at Chicago (M/C 063), Chicago, Illinois, 60607-7052 Densities of aqueous solutions of poly(ethylene glycol) (PEG) have been measured at (300.15, 310.15, 313.15, 318.15, 323.15, and 328.15) K. The number-average molecular weights for PEG were 400, 4000, and 6000. The density data were fitted by a third-order polynomial with respect to mass fracton of the polymer at each temperature. Using the fitted polynomial expression and the Gibbs-Duhem equation, partial molar volumes of PEG and water for various mixtures were computed and reported. Introduction In recent years, aqueous polymer solutions have found widespread applications, mostly because of their use in two- phase aqueous systems for separation of biomolecular mixtures. Specially, solutions of poly(ethylene glycol) (PEG) in water has attracted much attention. These solutions have been used in biochemistry and biochemical engineering to separate and purify biological products, biomaterials, proteins, and enzymes from the complex mixtures in which they are produced (Albertsson, 1986; Mansoori and Ely, 1987; Hariri et al., 1989; Soane, 1992; Laurence, 1994). In some of the proposed models used for calculating the thermodynamic properties of (polymer + solvent) solutions, concentrations are expressed in terms of volume fractions. For example, in the application of the Flory-Huggins equation (Flory, 1941, 1953; Huggins, 1942), the volume fraction of components in solution is needed. To calculate volume fractions accurately, partial molar volumes should be known. Density of PEG solutions has been reported by other workers (Tawfik and Teja, 1989; Muller and Rasmussen, 1991; Gonzales-Tello et al., 1994; Mei et al., 1995), but the temperature ranges of their measurements were limited and also the molecular weight of PEG differed from our measurements. In this work, the densities of aqueous solutions of various PEGs with molecular weights of 400, 4000, and 6000 were measured in the temperature ranges from 300.15 to 328.15 K. The results of measurements were fitted to a third- order polynomial. With the application of the Gibbs- Duhem equation, the partial molar volumes of PEG and water were calculated. Experimental Section Materials. Poly(ethylene glycol)s with number average molecular weights of 400 (385-415), 4000 (3500-4500), and 6000 (5000-7000) manufactured by Merk were used in this study. The water used in making the solutions was double-distilled. Apparatus and Procedures. The solutions were pre- pared by mass, using an analytical balance with (0.1 mg accuracy (Shimadzu, model AEU 210). The density mea- surements were carried out using a 25 cm 3 glass pycnom- eter. The volume of the pycnometer was calibrated as a function of temperature using double-distilled water. The density of water was taken from Perry’s Chemical Engi- neering Handbook (Perry and Green, 1984). The density measurements were carried out at temperatures of (300.15, 310.15, 313.15, 318.15, 323.15, and 328.15) K. A constant temperature water bath was used to control the temper- ature to an accuracy of (0.1 K (Stork-Tronix, Type PZ:26- 4), and the accuracy of thermometer was (0.1 K. The reproducibility of density measurements was estimated to be (0.0002 g‚cm -3 . For measurement of density, the pycnometer was filled with the solution and immersed in the water bath. After thermal equilibrium was achieved, the pycnometer was removed from the bath and then cleaned and dried quickly. Densities were determined from measurements of the mass of the samples and the pycnometer volume. Results and Discussion Densities. The measured densities of solutions are listed in Tables 1-3. It is usual to express the density in terms of mass fraction according to the following equation (Gonzalez-Tello et al., 1994; Beg et al., 1995) where F is the density of the solution at the measured temperature, a, b, c, and d are coefficients of the polynomial in g‚cm -3 , and w is mass fraction of PEG in the solution. Values of coefficients a, b, c, and d are obtained by regression. These values along with the average percent of relative deviation (ARD %) are given in Tables 4-6. F/(g‚cm -3 ) ) a + bw + cw 2 + dw 3 (1) Journal of Chemical & Engineering Data Volume 43, Issue 5, Pages 719-721, 1998 ( * ). Corresponding Author; Present address: Iranian Research Organization for Science & Technology (IROST). E-mails: eliassi@irost.ir; alieliassi@yahoo.com 719 DOI: https://doi.org/10.1021/je970228a