Viscosity of colloidal suspensions
- Interfaculty Reactor Institute, Delft University of Technology, 2629 JB Delft (The Netherlands)
- The Rockefeller University, New York, New York 10021 (United States)
Simple expressions are given for the Newtonian viscosity {eta}{sub N}({phi}) as well as the viscoelastic behavior of the viscosity {eta}({phi},{omega}) of neutral monodisperse hard-sphere colloidal suspensions as a function of volume fraction {phi} and frequency {omega} over the {ital entire} fluid range, i.e., for volume fractions 0{lt}{phi}{lt}0.55. These expressions are based on an approximate theory that considers the viscosity as composed as the sum of two relevant physical processes: {eta}({phi},{omega})={eta}{sub {infinity}}({phi})+{eta}{sub cd}({phi},{omega}), where {eta}{sub {infinity}}({phi})={eta}{sub 0}{chi}({phi}) is the infinite frequency (or very short time) viscosity, with {eta}{sub 0} the solvent viscosity, {chi}({phi}) the equilibrium hard-sphere radial distribution function at contact, and {eta}{sub cd}({phi},{omega}) the contribution due to the diffusion of the colloidal particles out of cages formed by their neighbors, on the P{acute e}clet time scale {tau}{sub P}, the dominant physical process in concentrated colloidal suspensions. The Newtonian viscosity {eta}{sub N}({phi})={eta}({phi},{omega}=0) agrees very well with the extensive experiments of van der Werff {ital et al.}, [Phys. Rev. A {bold 39}, 795 (1989); J. Rheol. {bold 33}, 421 (1989)] and others. Also, the asymptotic behavior for large {omega} is of the form {eta}{sub {infinity}}({phi})+{eta}{sub 0}A({phi})({omega}{tau}{sub P}){sup {minus}1/2}, in agreement with these experiments, but the theoretical coefficient A({phi}) differs by a constant factor 2/{chi}({phi}) from the exact coefficient, computed from the Green-Kubo formula for {eta}({phi},{omega}). This still enables us to predict for practical purposes the viscoelastic behavior of monodisperse spherical colloidal suspensions for all volume fractions by a simple time rescaling. {copyright} {ital 1997} {ital The American Physical Society}
- OSTI ID:
- 505232
- Journal Information:
- Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, Vol. 55, Issue 3; Other Information: PBD: Mar 1997
- Country of Publication:
- United States
- Language:
- English
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