Effect of silica particles on vortex dynamics in a micro-contraction channel flow of poly(ethylene oxide) solutions

The effect of silica particles in poly(ethylene oxide) (PEO) solutions on both the rheological properties and vortex dynamics under a micro-contraction channel flow was investigated. Although most materials used in industry are not only polymeric solutions or melts but also the suspensions consisting of particles as well as polymers, studies on the interaction between particle-polymer and their vortex behaviors under contraction flow are rare. The effect of silica particles was demonstrated in comparisons between PEO solutions and silica/PEO suspensions. The addition of 1.0 wt% of silica particles decreased the vortex size and delayed the formation of a lip vortex and a subsequent corner vortex. As the silica concentration increased, the vortex size increased and the flow rate at which the lip vortex and corner vortex formed decreased. The vortex behavior inside the micro-contraction channel was related more to the storage modulus than to the viscosity. The storage modulus also decreased initially and then increased with the silica concentration, similar to the vortex size. The decreases in the vortex size and the storage modulus were due to the adsorption of polymers onto the silica particles. The storage modulus increased with an increase in the silica concentration when the amount of free polymer was kept nearly constant. The same tendency was observed when the suspension was supplied with additional polymers corresponding to the amount of adsorbed polymer.