Rheological properties of PDMS filled with CaCo 3 : The effect of filler particle size and concentration

The effects of filler particle size and concentration on the rheological properties of hydroxyl terminated polydimethylsiloxane (HO‐PDMS) filled with calcium carbonate (CaCO 3 ) were investigated by an advanced rheometric expansion system (ARES). The Casson model was used to describe the relationship between shear stress and shear rate for steady‐state measurement. Micron‐CaCO 3 could not afford the CaCO 3 /HO‐PDMS suspensions obvious shear thinning behavior and a yield stress high enough, whereas nano‐CaCO 3 could provide the suspensions with remarkable shear thinning behavior and high yield stress. Incorporation of nano‐CaCO 3 into HO‐PDMS resulted in the transformation of HO‐PDMS from a mainly viscous material to a mainly elastic material. With increasing nano‐CaCO 3 content, shear thinning behavior of nano‐CaCO 3 /HO‐PDMS suspensions became more obvious. Remarkable yield stress was observed in nano‐CaCO 3 /HO‐PDMS suspensions with high filler content, and increased with increasing nano‐CaCO 3 content. The degree of thixotropy was quantitatively determined using a thixotropic loop method. It was found that nano‐CaCO 3 favored more the buildup of filler network structure in the suspensions than micron‐CaCO 3 at the same weight fraction. Furthermore, increasing nano‐CaCO 3 content accelerated the establishment of filler network structure in the nano‐CaCO 3 /HO‐PDMS suspensions. An overshoot phenomenon was observed in the nano‐CaCO 3 /HO‐PDMS suspensions at high shear rates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3395–3401, 2006