Nonlinear rheology of concentrated spherical silica suspensions: 3. Concentration dependence

@article{citeulike:2178429, abstract = {Nonlinear rheology was examined for concentrated suspensions of spherical silica particles (with radius of 40 nm) in viscous media, 2.27/1 (wt/wt) ethylene glycol/glycerol mixture and pure ethylene glycol. The particles were randomly and isotropically dispersed in the media in the quiescent state, and their effective volume fraction \&\#123eff ranged from 0.36 to 0.59. For small strains, the particles exhibited linear relaxation of the Brownian stress \&\#134B due to their diffusion. For large step strains \&\#110, the nonlinear relaxation modulus G(t,\&\#110) exhibited strong damping and obeyed the time-strain separability. This damping was related to \&\#110-insensitivity of strain-induced anisotropy in the particle distribution that resulted in decreases of \&\#134B/\&\#110. The damping became stronger for larger \&\#123eff. This \&\#123eff dependence was related to a hard-core volume effect, i.e., strain-induced collision of the particles that is enhanced for larger \&\#123eff. Under steady/transient shear flow, the particles exhibited thinning and thickening at low and high \&\#110\&\#163, respectively. The thinning behavior was well described by a BKZ constitutive equation using the G(t,\&\#110) data and attributable to decreases of a Brownian contribution, \&\#134B/\&\#110\&\#163. The thickening behavior, not described by this equation, was related to dynamic clustering of the particles and corresponding enhancement of the hydrodynamic stress at high \&\#110\&\#163. In this thickening regime, the viscosity growth \&\#109+ after start-up of flow was scaled with a strain \&\#110\&\#163t. Specifically, critical strains \&\#110d and \&\#110s for the onset of thickening and achievement of the steadily thickened state were independent of \&\#110\&\#163 but decreased with increasing \&\#123eff. This \&\#123eff dependence was again related to the hard-core volume effect, flow-induced collision of the particles enhanced for larger \&\#123eff.}, author = {Watanabe, Hiroshi and Yao, Ming-Long and Osaki, Kunihiro and Shikata, Toshiyuki and Niwa, Hirokazu and Morishima, Yotaro }, citeulike-article-id = {2178429}, doi = {10.1007/s003970050151}, journal = {Rheologica Acta}, keywords = {colloid, experience, suspension}, month = {May}, number = {1}, pages = {2--13}, posted-at = {2007-12-29 02:52:06}, priority = {2}, title = {Nonlinear rheology of concentrated spherical silica suspensions: 3. Concentration dependence}, url = {http://dx.doi.org/10.1007/s003970050151}, volume = {38}, year = {1999} }

TY - JOUR ID - citeulike:2178429 L3 - citeulike-article-id:2178429 TI - Nonlinear rheology of concentrated spherical silica suspensions: 3. Concentration dependence JF - Rheologica Acta VL - 38 IS - 1 SP - 2 EP - 13 N2 - Nonlinear rheology was examined for concentrated suspensions of spherical silica particles (with radius of 40 nm) in viscous media, 2.27/1 (wt/wt) ethylene glycol/glycerol mixture and pure ethylene glycol. The particles were randomly and isotropically dispersed in the media in the quiescent state, and their effective volume fraction &#123eff ranged from 0.36 to 0.59. For small strains, the particles exhibited linear relaxation of the Brownian stress &#134B due to their diffusion. For large step strains &#110, the nonlinear relaxation modulus G(t,&#110) exhibited strong damping and obeyed the time-strain separability. This damping was related to &#110-insensitivity of strain-induced anisotropy in the particle distribution that resulted in decreases of &#134B/&#110. The damping became stronger for larger &#123eff. This &#123eff dependence was related to a hard-core volume effect, i.e., strain-induced collision of the particles that is enhanced for larger &#123eff. Under steady/transient shear flow, the particles exhibited thinning and thickening at low and high &#110&#163, respectively. The thinning behavior was well described by a BKZ constitutive equation using the G(t,&#110) data and attributable to decreases of a Brownian contribution, &#134B/&#110&#163. The thickening behavior, not described by this equation, was related to dynamic clustering of the particles and corresponding enhancement of the hydrodynamic stress at high &#110&#163. In this thickening regime, the viscosity growth &#109+ after start-up of flow was scaled with a strain &#110&#163t. Specifically, critical strains &#110d and &#110s for the onset of thickening and achievement of the steadily thickened state were independent of &#110&#163 but decreased with increasing &#123eff. This &#123eff dependence was again related to the hard-core volume effect, flow-induced collision of the particles enhanced for larger &#123eff. KW - colloid KW - experience KW - suspension AU - Watanabe, Hiroshi AU - Yao, Ming-Long AU - Osaki, Kunihiro AU - Shikata, Toshiyuki AU - Niwa, Hirokazu AU - Morishima, Yotaro PY - 1999/05/12/ UR - http://dx.doi.org/10.1007/s003970050151 ER -