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SUMMARY:Diffusion and viscosity in complex liquids at all length scales - 
 Prof. Robert Holyst (University of Warsaw\, Poland)
DTSTART:20100924T110000Z
DTEND:20100924T120000Z
UID:TALK25337@talks.cam.ac.uk
CONTACT:Dr Mark Miller
DESCRIPTION:Water-based polymer solutions appear in a wide variety of syst
 ems and industrial processes and products (e.g. biological cells\, food pr
 oduction processes\, paints\, and personal care products). Their viscosity
  can be larger by several orders of magnitude than that of water. However\
 , because water is the dominant fraction in these solutions\, small object
 s of sub-nanometer size should experience only the viscosity of water whil
 e diffusing in the solutions. On the other hand\, large objects\, much gre
 ater than the polymer size\, should experience the large macro-viscosity o
 f the solution. It follows immediately that the coefficient of viscosity d
 epends on the length-scale at which it is probed: viscosity should change 
 from the value for water at the nano-scale to a large macro-viscosity at t
 he macroscale. A number of questions are still open in this context: what 
 is the length-scale for which we observe a crossover from nanoviscosity to
  macroviscosity? What is the relation between nanoviscosity determined fro
 m the diffusion of nanoprobes and macroviscosity measured by standard rheo
 meters? Is the Stokes–Sutherland-Einstein relation valid for nanoprobe d
 iffusion in polymer solutions? Using fluorescence correlation spectroscopy
  (FCS)\, photon correlation spectroscopy (PCS)\, capillary electrophoresis
  (CE)\, NMR\, SANS and rheology data\, we show how the viscosity changes f
 rom the value for water at the molecular scale to the large macroviscosity
  in complex liquids. We determined the viscosity experienced by nanoprobes
  (of sizes from 0.28 to 190 nm) in PEG (flexible polymer) solutions\, aque
 ous micellar solution of hexaethylene-glycol-monododecyl-ether (C12E6 – 
 nonionic surfactant) and fd virus solutions and  determined the  scaling l
 aws relating nanoviscosity to the macroviscosity.  In polymer solutions th
 e crossover length scale is set by the radius of gyration and in micellar 
 solutions by the length of micelles.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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