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Unformatted text preview: Nick Benzschawel Sarah Weinreis Chem 563 Sec 6 2/25/09 Experiment 46 Viscosity of Polymer Solutions Abstract The intrinsic viscosity of a solution of polyethylene glycol was determined by making measurements of different concentrations of the polymer in solution and using mathematical and graphical approaches to be 52.03 2.54 mL/g. This value was then used to determine the average molecular weight of the polymer in solution, which was 32620 10410 g/mol, and also to assess the quality of this measurement through comparison with the molecular weight of the pure polymer. Next, the viscosity data along with calculated and literature molecular weight values were used to evaluate the impact of solvent on polymer conformation and thus viscosity by determination and comparison of hydrodynamic radii of the polymer in solution ( 6.46(6.79) 10- 9 m) and the theoretical radius of the pure polymer ( 2.31 10- 9 m). Introduction The purpose of this experiment was to use viscosity measurements of the polymer polyethylene glycol made by the Ubbelohde viscometer to estimate the molecular weight and approximate size of the polymer in solution. This particular viscometer allowed fast, accurate measurement of solutions to be made independent of the total volume of solution. Seven total measurements were made: one using only water to determine the uncertainty in the viscometer, while the other six were made using different concentrations of polymer. Solutions of polymer were made by first adding 10mL of the solvent (water) and 10mL of the polymer and then adding water to make successive solutions. The intrinsic viscosity [ ] was determined through a series of viscosity calculations (e.g. relative viscosity ( r ), specific viscosity ( sp ), viscosity number ( n )) and then by plotting and performing a weight least squares fit of the viscosity number vs. concentration. This method was used to determine the intrinsic viscosity because it has been mathematically demonstrated that ] [ lim n = c , so extrapolation of this plot to where the concentration of polymer is zero (i.e. the y-intercept) should yield the intrinsic viscosity. Subsequent calculations of the molecular weight for the polymer in solution and hydrodynamic radius for both the pure polymer and polymer in solution were made to assess the quality of the measurements made and to verify important assumptions made during that data treatment e.g. that the polymer can be treated as a sphere (polymer with tightly bound solvent molecules). Data and Calculations To begin, concentration values for each concocted solution were generated. Further, error associated with these concentrations was also determined using an error analysis to reflect the successive dilution preparation utilized in the laboratory. Since successive dilutions were carried out using both 10mL and 25mL pipettes, which have different tolerances, 0.04 and 0.03, respectively, the total volume and associated error different tolerances, 0....
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