Quantified Measurements of Viscosity in The Bulk and In Pores, Using NMR Spin-lattice Relaxation in The Rotating Frame

Abstract

We present a novel method for the quantitative measurement of viscosity using spin-lock relaxation time (T1ρ) NMR. Recent work studying fast-field-cycling NMR on a set of oils of calibrated viscosity has demonstrated that T1 relaxation times measured across different rotational frequencies provide clear viscosity discrimination at lower frequencies. At frequencies above 2 MHz and at high viscosities, T1 is proportional to frequency, i.e., in the slow-motion regime. However, in the fast-motion regime, i.e., at low frequency and low viscosity, no frequency dependence is observed for bulk liquids. Here we extend this work to even lower rotational frequencies using the simpler technique of spin-lock T1ρ, and demonstrate that calibrated viscosities can be determined for both bulk liquids and liquids confined in pores. Particular cases examined to obtain calibrations in the bulk include high-viscosity oils and lower-viscosity sugar solutions. Subsequently, this calibration has been applied to a range of bulk liquids, including food oils, syrups and honeys. This approach was further extended to porous systems, enabling quantitative determination of oil and water viscosities in recovered geological rocks and naturally occurring oil and water in seeds.