Research Interests

Professor Prieve's research interests focus on the nature and measurement of colloidal forces and their effect on transport of colloidal particles. Applications include product formulation and solid-liquid separations.

Total Internal Reflection Microscopy We have developed a new experimental technique called Total Internal Reflection Microscopy (TIRM). Using TIRM we can monitor the separation distance between a single microscopic sphere (2 to 20 microns in diameter) immersed in an aqueous solution and a glass microscope slide as the sphere undergoes Brownian motion and interacts with the plate. When illuminated by an evanescent wave, the amount of light scattered by the sphere is exquisitely sensitive to the distance between the sphere and the plate. This allows us to detect changes in distance as small as a large molecule (one nanometer).
2-D assembly of colloidal particles on a/c electrodes D/C current normal to a planar electrode causes particles next to the electrode to aggregate as a result electroosmotic flow around the particles; reversing the polarity of the d/c field causes disaggregation. A/C current normal to the electrode can also cause aggregation if the frequency, amplitude and electrolyte are correctly chosen. Aggregation is one step in producing multilayered nanodeposits for photonic devices. Paul Sides and I are using TIRM to observe the motion of single particles normal to an electrode under the same conditions in which others have studied the tangential motion of ensembles. A major advantage of using single particles is that any model is axisymmetric; a second advantage is that no other technique is able to make these measurements.
Measurement of Colloidal Forces From a histogram of separation distances sampled by TIRM, we can determine the potential energy of the interaction between the sphere and the plate as a function of distance. Changes in potential energy can be detected which, again, are of molecular dimensions: a fraction of the thermal energy of single molecules. Because of its unique sensitivity, TIRM can be used to probe much weaker interactions than other techniques. Thus we have accurately measured the net bouyant weight of single particles (as small as 0.1 pN), double-layer (electrostatic) repulsion, retarded van der Waals attraction, depletion attraction (arises from nonadsorbing polymer), steric repulsion (arises from adsorbed polymer), the optical force exerted by a focussed laser, and unexpectedly long-range attraction between receptor-ligand pairs.
Measuring Charge on Flat Plate In water, a charged particle attracts ions of opposite charge, which accumulate near the surfaces to form a diffuse cloud.  The charge on microscopic particles is usually determined by measuring their terminal velocity in an electric field.  Determining the charge on a flat surface is more difficult.  By rotating a circular disk about its axis, we shear the ion cloud which generates a streaming current.  Conservation of charge induces a streaming potential profile in the bulk solution which can be measured and used to deduce the surface charge density.  We are working with Malvern Instruments (UK) to develop a commercial device to measure electrical properties of membranes, silicon wafers etc.

Electrostatic repulsion between particles in liquids of low dielectric constant

Electrostatic repulsion across water is quite well understood. A charged particle is surrounded by a cloud of counterions which make it appear electrically neutral from a distance. When two particles are close enough together for their clouds to overlap, repulsion is experienced which decays exponentially with separation (rather than the inverse-square expected from Coulomb's law); the decay length is the Debye length from the Debye-Huckel theory. Electrolytes tend to weakly dissociate in low-dielectric fluids like dodecane. Mechanisms of charging as well as electrostatic forces resulting from charge are much less well understood in nonaqueous media. These are quite important (for example) for display technology in which electric fields are used to turn pixels on and off.

Related sites:
Colloids, Polymers, and Surfaces Program
Complex Fluids Engineering

Representative Publications

DCP, "Changes in zeta potential caused by a dc electric current for thin double layers,"    Colloids and Surfaces A 250 , 67-77 (2004).

R.R. Dagastine, M.A. Bevan, L.R. White and D.C. Prieve, "Calculation of  Van der Waals Forces with Diffuse Coatings: Applications to Roughness and Adsorbed Polymers", J. Adhesion 80 , 365-394 (2004).

J.A. Fagan, P.J. Sides and DCP, "Vertical Motion of a Charged Colloidal Particle near an AC Polarized Electrode with a Nonuniform Potential Distribution: Theory and Experimental Evidence," Langmuir 20 , 4823-4834 (2004).

P.C. Odiachi and D.C. Prieve, "Removing the Effects of Additive Noise in TIRM Measurements," J. Colloid Interface Sci. 270 , 113-122 (2004).

S. Biggs, R.R.Dagastine and D.C.Prieve, "The Oscillatory Packing and Depletion of Polyelectrolyte Molecules at an Oxide-Water Interface," J. Phys. Chem. B 106 , 11557-11564 (2003).

M.A. Bevan and D.C. Prieve, "Hindered Diffusion of Colloidal Particles Very Near to a Wall: Revisited," J. Chem. Phys. 113 , 1228 (2000).

D. S. Sholl, M. Fenwick, E.S. Atman and D.C. Prieve, "Brownian Dynamic Simulation of the Motion of a Rigid Sphere in a Viscous Fluid Very Near a Wall," J. Chem. Phys. 113 , 9268 (2000).