Abstract
Flow behavior of ten copolymer solutions of polyacrylonitrile and polymethyl methacrylate in concentrations up to 16% was studied at 30Β°C. with the use of capillaries of constant diameter but different lengths. The shear rate and shear stress range covered were up to 200,000 sec.^β1^ and 800,000 dynes/cm.^2^, respectively. A rheological model of the form log D = A~0~ + A~1~ (log Ο)^Ξ²^ + A~11~ (log Ο)^2Ξ²^ was employed in determining the inflection point of the flow curve by computer analysis. A marked dependence of the flow curve upon the lenghtβtoβdiameter ratio was observed when l/d ratio decreased to below 300. At shear rates above 50,000 sec.^β1^ the capillary βend effectβ corrections and the kinetic energy corrections were found to be large for the concentrated and dilute solutions, respectively. The flow curves were characterized in terms of the inflection point in accordance with the treatment of Schurz. An upper Newtonian viscosity Ξ·^*^ was observed at shear rates above 150,000 sec.^β1^. Up to a concentration of about 1%, the value of the upper Newtonian viscosity was such that the calculated Ξ·~sp~/C was essentially independent of C and equal to [Ξ·^*^] obtained by extrapolation to infinite dilution. The values of the heat of activation for viscous flow were found to be dependent upon the applied shear stress.