TEMPERATURE CONTROLLED DISPERSION OF POLY(N-ISOPROPYL ACRYLAMIDE) TREATED SILICA CLUSTERS LUCIANA BAVA, DONALD L. FEKE* DEPARTMENT OF CHEMICAL ENGINEERING, CASE WESTERN RESERVE UNIVERSITY , CLEVELAND, OH ICA MANAS-ZLOCZOWER, STUART J. ROWAN DEPARTMENT OF MACROMOLECULAR SCIENCE, CASE WESTERN RESERVE UNIVERSITY , CLEVELAND, OH ABSTRACT The dispersion of particle agglomerates is affected by the presence of any chemical additives incorporated within the agglomerate structure. Traditional additives change the particle-particle and particle-matrix interactions to a degree that depends primarily on the chemical nature of the additive and its concentration within the agglomerate. A new gen- eration of additives, based on polymeric systems that respond to external stimuli, allows the adjustment of interparticle interactions by manipulating the variable to which the additive is responsive. In this study, dispersion tests in simple shear flow are used to examine the effect of a thermally responsive additive, poly(N-isopropyl acrylamide) (PNIPAM), on the dispersion behavior of silica agglomerates. The temperature sensitivity of the dispersion mechanisms and kinetics for sil- ica clusters treated with either linear or crosslinked PNIPAM has been examined. INTRODUCTION The properties of filled materials are strongly affected by the degree of dispersion of fine- particle agglomerates into the polymeric matrix or processing media. Therefore, understanding and controlling dispersive mixing is of great importance in many industrial applications includ- ing rubber/filler systems. Conventionally, dispersion has been controlled and enhanced by opti- mizing the factors that directly affect the counterbalance of forces that result in dispersion: cohe- sive and hydrodynamic forces. While the hydrodynamic forces depend on the viscosity of the dispersing fluid, the flow dynamics (steady versus unsteady) and the rate of shear, 1-2 the cohe- sive strength of the agglomerate has its origins in interparticle forces of various origins (e.g., van der Waals, electrostatic). Cohesive forces also depend on the agglomerate morphology (porosity and packing structure), solid material properties (Hamaker constant and material density) and primary particles and/or aggregate sizes. 4-10 In addition, the nature and extent of the interfacial interactions between the solid and the fluid play a relevant role by determining the transmission of hydrodynamic force on the agglomerate surface as well as the infiltration of the host medium into the particle cluster. This infiltration can cause rearrangement of the packing structure and formation of liquid bridges which alter not only the cohesive forces acting within the cluster, but also the manner in which the hydrodynamic stress is transmitted from the external dispersing media to the cluster. 3,10-11 Secondary species such as binders are commonly used to alter the clus- ter cohesive forces as well as the interfacial interactions between the solid and liquid. 12 The focus of this study is to investigate the use of polymeric additives/binders that are responsive to external stimuli to control dispersion behavior. By manipulating the stimulus to which the polymer responds, interparticle interactions (and therefore cluster cohesivity) can be affected. Thermo-responsive materials are being widely studied because of their large variation in properties in response to small temperature variation. One class of thermoresponsive polymer is that which exhibits a lower critical solution temperature (LCST) in aqueous environments. Below this temperature the polymer is hydrophilic and soluble in water, while above this tem- 809 * Corresponding author. Ph: 216-368-4389; Fax: 216-368-3016; email: donald.feke@case.edu