Particle Deposition on Microporous Membranes Can Be
Enhanced or Reduced by Salt Gradients
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Abstract
Colloidal particle deposition on
membranes is a continuing scientific
and technological challenge. In this paper we examine the role of
a previously unexplored phenomenondiffusiophoretic particle
transport toward a membranein relation to fouling. Diffusiophoresis
is an electrokinetic transport mechanism that arises in salt gradients,
especially when the ions have different diffusion coefficients. Through
experiments conducted with salt diffusing across microdialysis membranes,
with no advection, we show experimentally that diffusiophoresis induces
colloidal deposition on the surface of microporous surfaces. We used
transient salt (NaCl, KCl, LiCl) gradients and fundamental electrokinetic
modeling to assess the role of diffusiophoresis in colloidal fouling.
Based on (i) difference in diffusion coefficients of ions, (ii) zeta
potential on the particles, and (iii) ionic gradient applied across
the walls of the membrane, colloidal fouling could be both quantitatively
and qualitatively predicted. Our understanding enabled us to stop
particle deposition by adding calcium carbonate outside the membrane,
which generates a stronger electric field in a direction opposite
to that created by salt diffusing from the membrane. We propose that
accounting for this diffusiophoretic mode of particle deposition is
important in understanding membrane fouling