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The Newtonian viscosity of concentrated stabilized dispersions: Comparisons with the hard sphere fluid
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UNSPECIFIED. (2004) The Newtonian viscosity of concentrated stabilized dispersions: Comparisons with the hard sphere fluid. JOURNAL OF RHEOLOGY, 48 (1). pp. 223248. ISSN 01486055
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Official URL: http://dx.doi.org/10.1122/1.1634986
Abstract
The Newtonian shear viscosity, eta(S), of nearhardsphere colloidal particle liquids from many sources at various packing fractions is compared with that of the pure hard sphere fluid which can be calculated essentially exactly by molecular dynamics, MD, computer simulations. The experimental relative viscosities for the colloidal systems, eta(S) / eta(0) , where eta(0) is the viscosity of the solvent, generally lie in between two curves formed from the hardsphere data, namely, eta(S) / eta(B) as an upper bound and the inverse selfdiffusion coefficient, DB /D, as the lower bound, where eta(B) and DB are the Boltzmann transport coefficients accurate at low densities. Brownian dynamics simulation values of eta(S) / eta(0) and D0 / DL where DL is the longtime selfdiffusion coefficient are close to this lower bound which indicates that Brownian motion alone without hydrodynamic interactions underestimates the viscosity of the system. Hydrodynamic effects increase the viscosity closer to the pure hardsphere curve obtained by MD. The ratio, D0 / DL obtained from the experimental data increases slightly more rapidly than eta(S) / eta(L) at high packing fractions. There is a nearlinear relationship between the inverse viscosity (fluidity) and selfdiffusion coefficient with inverse packing fraction for the hardsphere fluid, the former proposed by Dymond (1974). This analytic form accounts reasonably well for the corresponding quantities of the colloidal systems as well. We analyzed the values of the relative viscosities at 50% packing fraction. We conclude that the value is similar to 40 for the pure hard sphere fluid itself from recent molecular dynamics simulations by of Sigurgeirsson and Heyes (2003), and probably similar to 25+/5 from experiments on real nearhard sphere colloids (although the experimental scatter is quite large), and similar to 10 by Brownian dynamics computer simulations. For the long time selfdiffusion coefficient the ratio is similar to 40+/10 for experimental colloidal systems, and similar to 10 from simulation by molecular dynamics and Brownian dynamics. The infinite frequency shear viscosity has a ratio similar to 10 and the shorttime selfdiffusion coefficient ratio is similar to 4, both of which are somewhat lower than their longtime counterparts. The shear viscosity at finite shear rates in the second Newtonian plateau typically lies in between the values of the Newtonian viscosity and the infinite frequency viscosity (i.e., similar to 15+/5). (C) 2004 The Society of Rheology.
Item Type:  Journal Article  

Subjects:  T Technology > TJ Mechanical engineering and machinery  
Journal or Publication Title:  JOURNAL OF RHEOLOGY  
Publisher:  JOURNAL OF RHEOLOGY AMER INST PHYSICS  
ISSN:  01486055  
Official Date:  January 2004  
Dates: 


Volume:  48  
Number:  1  
Number of Pages:  26  
Page Range:  pp. 223248  
Identifier:  10.1122/1.1634986  
Publication Status:  Published  
URI:  http://wrap.warwick.ac.uk/id/eprint/8893 
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