  A formula of steady shear viscosity is derived by introducing a model to
describe the dynamics of physically cross-linked network (physical gel), and
successfully analyzes the shear-thickening behavior observed in HEUR aqueous
solutions by Jenkins, Sileibi and El-Aasser. We take into account the effects
of looped chains at junctions which detach their one end from the junction as
the shear rate increases due to the collisions with other chains. This process
produces the weak and wide enhancement of the number of chains whose both ends
stick to the separate junctions (active chains) leading to the weak increase in
the shear viscosity. It is also shown that the nonlinear force sustained by
active chains induces the strong and sharp enhancement of the steady shear
viscosity.
