Streaming Potentials Arising Near a Rotating Disk in Doped Nonpolar Liquids

Streaming potentials arising near a rotating disk
in doped nonpolar liquids

AIChE Annual Meeting 2015, Salt Lake City, UT

Session 01J01 Poster Session: Fluid Mechanics (Area 1J)

Benjamin A. Yezer, Aditya S. Khair, Paul J. Sides and Dennis C. Prieve

Center for Complex Fluids Engineering

Department of Chemical Engineering

Carnegie Mellon University

Pittsburgh, PA 15213

When the solid-fluid interface bears a charge, fluid elements within a Debye length of the surface will acquire a net charge of opposite sign to that of the interface.  Any flow of these charged fluid elements creates an electric current.  In particular, the streaming potential is dependent on the outward radial flow, which is inertially driven by the centrifugal forces acting on the rotating fluid.  Radial convection of charge to edge of the disk must be conducted back through the electrically neutral bulk solution to the surface of the disk.  This back conduction is driven by a streaming potential profile which spontaneously arises in the bulk solution in order to satisfy conservation of charge.  At any point in the electrically neutral bulk solution, the streaming potential (relative to fluid far from the disk) is proportional to the 3/2 power of rotation rate.  From the proportionality constant, we can infer[1] the zeta potential of the solid-fluid interface which can be related to the charge density at the interface.  In recent studies[2], we have extended this method to porous disks and shown that streaming potential versus rotation speed can be used to infer the Darcy-law constant for the porous media as well as its zeta potential.  In this poster, we further extend the method to doped nonpolar liquids.  In particular, we have measured the streaming potentials developed by rotating a nonporous disk of silica, glass or a silicon wafer immersed in dodecane doped with OLOA 11000 [poly(isobutylene succinimide)].  These measurements are especially challenging because of the extremely low conductivity of these fluids and the absence of reversible electrodes.  We used a high-impedance electrometer with glassy-carbon sensors to detect streaming potential differences.  The response to changes in rotation speed was orders of magnitude slower than in aqueous solutions, but the 3/2 power dependence on rotation speed was confirmed.  The inferred zeta potentials compare favorably to results found using electrophoretic mobility of spheres constructed of similar material. 

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[1] P.J. Sides, J. Newman, J.D. Hoggard and D.C. Prieve, “Calculation of the Streaming Potential near a Rotating Disk,” Langmuir 2006 22, 9765-9769 (dx.doi.org/10.1021/la061041x). 

[2] D.C. Prieve and P.J. Sides, “Streaming Potential near a Rotating Porous Disk,” Langmuir 2014 30, 11197-11203 (dx.doi.org/10.1021/la5022092).