(42g) Direct Measurement of Diffusiophoretic Velocity of Colloidal Particles

Diffusiophoresis is the motion of a colloidal particle in a gradient of a solute with which the surface of the particle has an interaction. The measurement of the velocity of this motion is of importance to both fundamental studies as well as in applications such as sperm motility, chemotaxis, enhancement of mass-transfer, etc. Thus far, the diffusiophoretic velocity has not been directly measured and validated against theory without relying on some fitting parameter. We present a simple device and a principle to measure the velocity directly under a microscope. We also show that the measured velocity agrees reasonably with independent theoretical estimates.