The flow behaviors of rod-like polymer solutions were investigated. Hydroxypropyl cellulose was chosen as a polymer sample. The stress-optical rule was confirmed in the semi-dilute region. However, the polydispersity (Mw/Mn=7.2) of polymer affects the validity of stress-optical rule.
In the polydispersed system, the rotational diffusivity played an important role. Since a long rod-like molecule showed a lower rotational diffusivity, it oriented in the low shear rate than a short rod-like molecule did. As a result the optical measurements were more sensitive in the low shear rate than in the high shear rate. The concentration region that the stress-optical rule was not applied, the stress-optical coefficient decreased with shear rate.
The birefringence increased and the orientation angle decreased with concentration and shear rate. The birefringence depended on not only concentration but also molecular weight(the length of rod).
In this research the stress-optical rule was confirmed to be applicable to the solution with the mass fraction of 1.5% to 5%, but at the mass fraction of 7.5% the stress-optical coefficient decreased with shear rate. The stress-optical rule was not confirmed in the solution of 7.5% mass fraction.