Rotational magnetic particle microrheometry: The Newtonian case

A rotating sphere microrheometer, based on extensions of the work of Valber g [Valberg, P.A., "Magnetometry of Ingested Particles in Pulmonary Macro-Ph ages," Science 224, 513-516 (1984); Valberg, P.A., and H. A. Feldman, "Magn etic Particle Motions within Living Cells: Measurement of Cytoplasmic Visco sity and Motile Activity,'' Biophys. J. 52, 551-572 (1987)] and Edwards and Yeates [Edwards, P.A., and D. B. Yeates, Viscoelasticity of Biomaterials, Chap. 16, ACS Symposium Series, 489, edited by W. Glasser and H. Hatakeyama (Boston, MA, 1992)], was developed to rapidly (within 10 s) measure the rh eological properties of small ( similar to 10 CLL) quantities of highly vis cous (100-10 000 poise) fluids at small (10(-3) - 10(-1) Hz) rates of strai n. Previous experimental work was extended by the use of MQP-B(TM) 1.4-mu m -radius particles, which have extremely high coercivity and remanent magnet ic field, and in which rotation of magnetic domains within the particle doe s not occur. The microrheometer was tested with a series of Newtonian visco sity standards (100-10 000 poise) and found to accurately predict viscosity (error range 3%-9%). The effects of shape, size distribution, sedimentatio n, particle-particle magnetic interactions, and agglomeration were investig ated and found to be either negligible or easily determined. This microrheo meter can be used to determine the rheological properties of minute quantit ies of viscous fluids and may be applicable to the measurement of zero-shea r-rate viscosity of viscoelastic fluids. (C) 1999 The Society of Rheology. [S0148-6055(99)01803-9].