(227x) 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.