title: Nanoliter droplet viscometer with additive-free operation.
abstract: Measurement of a solution's viscosity is an important analytic technique for a variety of applications including medical diagnosis, pharmaceutical development, and industrial processing. The use of droplet-based (e.g., water-in-oil) microfluidics for viscosity measurements allows nanoliter-scale sample volumes to be used, much smaller than those either in standard macro-scale rheometers or in single-phase microfluidic viscometers. By observing the flow rate of a sample plug driven by a controlled pressure through an abrupt constriction, we achieve accurate and precise measurement of the plug viscosity without addition of labels or tracer particles. Sample plugs in our device geometry had a volume of ~30 nL, and measurements had an average error of 6.6% with an average relative standard deviation of 2.8%. We tested glycerol-based samples with viscosities as high as 101 mPa s, with the only limitation on samples being that their viscosity should be higher than that of the continuous oil phase.
authors.affiliation: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Livak-Dahl
authors.forename: Jaesung
authors.initials: J
authors.lastname: Lee
authors.forename: Mark A
authors.initials: MA
authors.lastname: Burns
mesh_terms: D004867:Equipment Design; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation* / Q000379:methods; D036103:Nanotechnology; D009821:Oils / Q000737:chemistry; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D009821:Oils; D014867:Water