The concept of micro-rheology was introduced for describing particles motion in non-Newtonian liquids. This motion depends not only on viscosity of the basic liquid but also on the dimensions of the additives molecules that make liquid non-Newtonian. If particle size is much less than dimensions of this additives, then particles freely swim between them and experience only low viscosity of the basic liquid, which is usually Newtonian. If particles are large, then they experience macro-viscosity that can be orders of magnitude larger than viscosity of the basic liquid.There are several publications presenting various details of this concept for variety of systems:
- Mason Weitz (1995).Physical Review Letters74:7.
- Crocker, John C. and Valentine, M. T. and Weeks, Eric R. and Gisler, T. and Kaplan, P. D. and Yodh, A. G. and Weitz, D. A. (2000). “Two-Point Microrheology of Inhomogeneous Soft Materials”.Physical Review Letters 85(4): 888–891Bibcode:2000PhRvL..85..888Cdoi
- Bhosale, P.S. and Berg, J.C. “Acoustic spectroscopy of Colloids Dispersed in a Polymer Gel System”, Langmuir, 26 (18), pp. 14423-14426 (2010)
- Dukhin, A.S. and Goetz, P.J. “Method for determining particle size distribution and structural properties of concentrated dispersions”, US Patent 6,910,367 (2005)
Acoustic spectroscopy offers very simple way of measuring micro-viscosity that particles experience moving in particular non-Newtonian liquid. Attenuation frequency spectra depends on particle size and viscosity. If p[article size is known, then we can fit experimentally measured spectra with unknown viscosity number. This method is accomplished in the software of Models DT-1202 and DT-100