Probe of multiparticle colloidal interactions in a 2D cage
Abstract
We have studied multiparticle interactions between 0.6 μm diameter highly charged polystyrene spheres (PS) trapped in ion-exchanged water between two glass plates 2.5 μm apart. A diffractive optical element was used to create an adjustable-spacing, square array of 64 optical tweezers (plus a tweezer formed from the undiffracted beam). When the spacing between the tweezer locations is small enough, PS spheres trapped in the tweezer array form a 2D cage of fixed charge spheres for spheres free to move outside the optical trap locations. The freely moving spheres are trapped in the third dimension by the glass plates of the cell. Sphere positions as a function of time were determined using digital video microscopy, enabling the determination of the 2D cage potential energy contours. The measured potential energy contours were compared with that due to a superposition of four DLVO potentials from the spheres in the optical traps. Our measurements at all tweezer separations from 2.5-3.5 μm were consistent with a DLVO interaction potential with a screening length of 0.255 ±0.05 μm and a renormalized charge Z=24000e.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2000
- Bibcode:
- 2000APS..MARP30003S