Correlated twoparticle diffusion in dense colloidal suspensions at early times: Theory and comparison to experiment.
 Citation data:

Physical review. E, Statistical, nonlinear, and soft matter physics, ISSN: 15502376, Vol: 92, Issue: 5, Page: 052304
 Publication Year:
 2015
 Repository URL:
 http://scholarworks.unist.ac.kr/handle/201301/17911
 PMID:
 26651692
 DOI:
 10.1103/physreve.92.052304
 Author(s):
 Publisher(s):
 Tags:
 Physics and Astronomy; Mathematics; HYDRODYNAMIC INTERACTIONS; CONCENTRATED SUSPENSION; COOPERATIVE DYNAMICS; SPHERES; LIQUIDS; MICRORHEOLOGY; SCATTERING; PARTICLES; NEUTRONS; EQUATION
article description
The spatially resolved diffusive dynamic cross correlations of a pair of colloids in dense quasitwodimensional monolayers of identical particles are studied experimentally and theoretically at early times where motion is Fickian. In very dense systems where strong oscillatory equilibrium packing correlations are present, we find an exponential decay of the dynamic cross correlations on small and intermediate length scales. At large separations where structure becomes random, an apparent power law decay with an exponent of approximately 2.2 is observed. For a moderately dense suspension where local structural correlations are essentially absent, this same apparent power law decay is observed over all probed interparticle separations. A microscopic nonhydrodynamic theory is constructed for the dynamic cross correlations which is based on interparticle frictional effects and effective structural forces. Hydrodynamics enters only via setting the very shorttime singleparticle selfdiffusion constant. Noadjustableparameter quantitative predictions of the theory for the dynamic cross correlations are in good agreement with experiment over all length scales. The origin of the longrange apparent power law is the influence of the constraint of fixed interparticle separation on the amplitude of the mean square force exerted on the two tagged particles by the surrounding fluid. The theory is extended to study highpackingfraction 3D hard sphere fluids. The same pattern of an oscillatory exponential form of the dynamic cross correlation function is predicted in the structural regime, but the longrange tail decays faster than in monolayers with an exponent of 3.