Model filled rubber. I: Effect of particle morphology on suspension rheology

Monodispersed polystyrene (PS) particles, crosslinked with divinylbenzene (DVB), were prepared by emulsifier-free emulsion polymerization. The colloidal-suspension rheology of a low-molecular-weight liquid polysulfide, which is used in commercial sealants, filled with these PS particles varying in size and particle-crosslink density, was studied. At low frequencies or shear rates, the dynamic moduli and viscosity increased as particle diameter decreased from 1.25 to 0.315 mu m or particle crosslink density increased from 0 to 5 mole% DVB. We suggest that particle-particle interactions are dominant and lead to the formation of clusters in the concentrated suspension. Rheological properties associated with network buildup in suspensions were most sensitively monitored by a kinetic-recovery experiment. The strength of, as well as the tendency for, cluster network formation in, the colloidal suspensions increases with decreasing particle size, and increasing particle-crosslink density, or decreasing surface roughness.