Viscosity measuring method

Abstract

A method for measuring the average viscosity of a test fluid uses calibrated magnetic nanoparticles, with certain chosen hydrodynamic diameters and actual lateral dimensions (e.g. diameters), that are mixed into a small volume of the test fluid and a single magnetic relaxation curve measurement to provide data for viscosity determination. The distribution of hydrodynamic particle sizes of an ensemble of magnetic nanoparticles that are magnetically blocked at room temperature can be determined. Modifications of the method can be used to determine the distribution of viscosities in a complex fluid at the sub-microscopic level providing a novel type of viscosity measurement.

1 .- 10 . (canceled) 
     
     
         12 . A method of determining distribution of hydrodynamic particle sizes of magnetic nanoparticles by relaxometry measurement, comprising introducing magnetic nanoparticles having a particle lateral dimension selected large enough to reduce or eliminate Neel relaxation effects on the relaxometry measurement into a control fluid, subjecting the control fluid to a magnetic field pulse, and measuring a relaxation curve, which is the sum of one or more single exponential decays, for the nanoparticles in the control fluid, and using the measured relaxation curve to determine distribution of relaxation time constants, which are proportional to the distribution of hydrodynamic particle diameters. 
     
     
         13 . The method of  claim 12  wherein each magnetic nanoparticle has an actual diameter selected large enough to reduce or eliminate Neel relaxation effects on the relaxometry measurement. 
     
     
         14 . A method of determining distribution of viscosity values of a test fluid by relaxometry measurement, comprising determining a distribution of hydrodynamic particle diameters of magnetic nanoparticles introduced in a control fluid according to  claim 12 , introducing the magnetic nanoparticles in the test fluid, subjecting the test fluid to a magnetic field pulse, and measuring the relaxation curve, which is the sum of one or more single exponential decays, of the nanoparticles in the test fluid, and determining a distribution of decay time constants from the measured relaxation curve from which decay time constants a distribution of viscosity values can be determined. 
     
     
         15 . (canceled) 
     
     
         16 . A method of determining distribution of viscosity values of a test fluid by relaxometry measurement, comprising determining a distribution of hydrodynamic particle diameters of magnetic nanoparticles introduced in a control fluid according to  claim 12 , introducing the magnetic nanoparticles in the test fluid, subjecting the test fluid to a magnetic field pulse, and measuring the relaxation curve, which is the sum of one or more single exponential decays, of the nanoparticles in the test fluid, and determining a distribution of decay time constants from the measured relaxation curve from which decay time constants a distribution of viscosity values can be determined, including determining the distribution of viscosities by analyzing the distribution of time constants by inverse Laplace transformation.