A study on influence of surface roughness of flow cell on yield in α-gels

Abstract

We had examined the two type of the yield-like behavior in the α-gels, which are observed by the stress-ramp test in the stress-controlled rheometer. We called them the first yield and the second yield from a lower stress, respectively. The influence of the surface roughness of the flow cell in the yield-like behavior is examined in this study. The parallel plate made from the glass, the stainless steel and the glass with the sand-paper of the particles size #100 (Ra125) and #2000 (Ra20) are used in the experiments. The glass plates have the surface roughness in the order of a nanometer and the stainless plates are in the order of submicron scale. The first yield point, which is observed in the low shear stress, is affected by the surface roughness and the gap between the plates. The first yield stress measured by the glass plates is small and the first yield point is unclear compared with the results by the stainless plates. The stress difference between the upper plate and the under plate occurs clearly in the stainless plate in the different stress-ramp rate. It is considered that the uniform velocity distribution in the glass plate is formed and the shear-layer in the stainless plate gives the big influence to the flow field because it is formed stably at long intervals. On the other hand, the second yield point is influenced by the gap but not the surface roughness.