OBSERVATIONS OF FIRST-ORDER LIQUID-TO-HEXATIC AND HEXATIC-TO-SOLID PHASE-TRANSITIONS IN A CONFINED COLLOID SUSPENSION

We have used digital video microscopy to study the equilibrium structu re of quasi-two-dimensional suspensions of sterically stabilized uncha rged polymethylmethacrylate spheres. Our experiments reveal the existe nce of an equilibrium hexatic phase as well as strongly first-order li quid-to-hexatic and hexatic-to-solid phase transitions. These observat ions are in agreement with the predictions of Bladon and Frenkel [Phys . Rev. Lett. 74, 2519 (1995)] for a confined colloid suspension in whi ch the pair interaction potential between particles has a hard core an d either a very short range attraction or a very short range step repu lsion.