Question

1. An aqueous polymer solution has a relative viscosity of 1.375 at 25 Celsius. What is the absolute viscosity of the solution? What is the specific viscosity of the solution?
2. If the intrinsic viscosity of an aqueous PEG solution is 0.200, what is the estimated molecular weight of the solute?

Answer 1

1)

Given relative viscosity = 1.375 at 25 deg C

The viscosity of water at 25 deg C = 0.89 mPa-s

We know that relative viscosity = absolute viscosity / viscosity of solvent

      Therefore   1.375 = absolute viscosity / 0.89

              absolute viscosity = 1.375 x 0.89 mPa-s

                                          = 1.224 mPa-s

Specific viscosity = absolute viscosity -1

                         = 1.224 -1

                          = 0.224 mPa-s

Thus the absolute viscosity and specific viscosity of the given polymer are 1.224 mPa-s and 0.224 mPa-s respectively.

2)

Intrinsic viscosity and molecular wt of polymer are related by Mark-Hauwink equation

        intrinsic viscosity = k M^alpha

                       for PEG solution k = 1.56 x 10^-3

                                              alpha = 0.5

                        0.200 = 1.56 x 10^-3 x M^0.5

                                   M^0.5 =[ 0.2 / 1.56 ] x 10³

                                 = 128.2

                          M = 128.2² = 16435

Thus the estimated molecular wt of the solute is 16435