Improvements of an oscillatory squeezing flow rheometer for small elasticity measurements of liquids

Dilute dispersions and polymer solutions used as functional fluids or operation fluids are required to be controlled in an extremely high quality level in the semiconductor industry or MEMS (Micro Mechanical Electric System) devices, such as inkjet print heads and micro pumps. Many of the quality items depend on microscopic state of dispersion or solution stem from mutual interactions among the dispersed particles and solved polymers; hence, close investigations of these complex interactions are of great concern for developments of highly functional fluids and micro fluidic devices. Here, some great improvements are presented on a random oscillatory squeezing flow rheometer to detect subtle rheological properties arise as results of interactions between micro solid particles dispersed in liquids. To detect subtle elasticity within fundamentally viscous liquids, very small phase difference from the viscous response has to be measured, and for this reason effects from three major sources (sensor nonlinearity, nonlinear squeeze flow response, and instrument compliance) that give phase errors and noises as well as fluid inertia are completely compensated by data processing, achieving sensitivity for subtle dynamic modulus G′ to the extent of G′/G ∼0.001. As examples of the dilute dispersions, water dispersions of monodisperse acrylic latex were measured and detections of dynamic modulus G′ of 10−3 Pa at 100 Hz were demonstrated.