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Langmuir 1995,11, 4665-4672 4665 Pattern Formation in Nonaqueous Colloidal Dispersions
 

Summary: Langmuir 1995,11, 4665-4672 4665
Pattern Formation in Nonaqueous Colloidal Dispersions
via Electrohydrodynamic Flow
M. Trau, S. Sankaran, D. A. Saville, and I. A. Aksay*
Department of Chemical Engineering and Princeton Materials Institute, Princeton University,
Princeton, New Jersey 08544-5263
Received March 24, 1995. In Final Form: July 31, 1995@
We describea new electrohydrodynamicphenomenonobservedin inhomogeneous,nonaqueouscolloidal
dispersionswith a spatiallyvaryingparticlenumberconcentration. In the presenceof an external electric
field, the dielectric constant and conductivity gradients in these systems engender fluid motion which
results in the formation of patterned colloidal structures: columns, disks, and other more complicated
structures. Other workers found similar effects in high conductivity systems, where the particles are
dispersed in water with dissolved electrolyte. Our experimentalresults with barium titanate dispersed
in low conductivity,apolar liquidsindicatethat electricalforcesdue to free charge and dielectricconstant
variations each play a role in inducing flow. This pattern forming phenomenon differs from previously
observed field-induced pattern formation in colloidal dispersions (e.g., colloidal string formation in
electrorheologicaland ferrofluids)largely as a result of the inducedfluidflow. A mathematical model has
been developed which predicts, qualitatively, the initial flow patterns encountered in our system. The
theorymay alsohelp explainthe formationof more complicatedfield-inducedparticlemorphologieswhich
have been reported in aqueous and nonaqueous media as well as the observation of dispersion band

  

Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University

 

Collections: Materials Science