FORMATION OF 2-DIMENSIONAL COLLOIDAL VOIDS, SOAP FROTHS, AND CLUSTERS

We report the observation of new pattern formation by spherical polyst yrene particles trapped at the air-water interface; namely, the format ion of two-dimensional void, soap-froth, and cluster structures. The f ormation of the soap-froth structure depends upon the initial surface concentration of particles. The void and soap-froth structures evolve with time. The clusters can be formed after deposition of the sample o r as a result of the evolution of the soap-froth structure. The experi mental observation can be explained in terms of a balance between elec trostatic repulsive and attractive interactions. An optimum cluster si ze can be obtained from an energy analysis of the system.