Experimental Study on the Constant Speed Squeezing Flow of Polymer Solutions : Measurement of Forces generated in and after the Approaching motion

Transmitting forces were measured during the time when a upper spherical surface was approaching to a lower flat plate at a constant speed and after the movement of the upper surface was stopped. The forces measured for glycerin and PEO solutions were predicted by the theory of viscous fluids. In the case of Separan solutions, however, overshoot of the force was seen at the inception of the squeezing motion and the maximum in magnitude was about 1.5 times larger than the force estimated with the viscous stress. This trend agrees well with those of the stress overshoot in simple shear flows. After the squeezing motion was stopped, the clearance between two surfaces was observed to slowly decrease because of the spring back of the load cell attached to the lower plate. At this stage, the larger transmitting force was maintained for the Separan solution than that for the viscous fluids. This result is considered to be related to the stress relaxation.