솔젤법으로 제조된 고농도 실리카 입자 분산계의 유변학적 거동

Abstract

Monosized silica particles were synthesized using sol-gel method and rheological behaviors of the silica suspension at various concentrations were investigated experimentally. To stabilize the silica particles in organic solvent, the surface of particle was coated through the chemical adsorption of a silane coupling agent, γ-methacryloxypropyl triethoxysilane. The effects of the concentration on the rheological properties were examined for various dispersions of different volume fractions (φ) ranging from dilute (φ=0.05)to concentrated limit (φ=0.55). The coated silica particles possessed the so-called hard sphere characteristics and dispersion stability in an organic solvent with the aid of steric stabilization of the alkyl chain. When the suspensions had the volume concentration belowφ=0.25, they showed Newtonian behaviors like the medium solvent. On the other hand, non-Newtonian behavior such as shear thinning and high shear limiting viscosity were observed at the volume fraction above 0.25. These results were correlated satisfactorily with Krieger-Dougherty equation uptoφ=0.50. The highly concentrated dispersions above φ=0.50 exhibited an abrupt increase in viscosity, shear thinning and shear thickening behaviors. In particular, although the stable and fast viscous responses were observed below a critical shear rate (γcr at which shear thickening occurred, the rheological responses were unstable near or above γcr. However, these behaviors were reversible as confirmed by reversing successively the shear rate sweep tests.