Growth of preformed 3D nuclei in Langmuir monolayers below critical supersaturation

The features of the nucleation-growth process during the transformation of two-dimensional monolayer material into three-dimensional nuclei in supersa turated Langmuir monolayers of stearic acid are studied by a double surface pressure step technique. The first surface pressure step to a surface pres sure pi above the critical surface pressure (pi > pi(crit)) leads to the fo rmation of 3D nuclei according to a progressive nucleation process. 3D nucl ei preformed at different surface pressures under the condition pi > pi(cri t) are brought by a second surface pressure step into the region pi less th an or equal to pi(crit), where new nuclei cannot be formed. The nuclei pref ormed in the first compression step can grow as long as supersaturation exi sts. At the equilibrium surface pressure pi(e) the preformed nuclei cease t o grow. In the region pi(e) less than or equal to pi less than or equal to pi(crit), constant-surface-pressure relaxation occurs and is described by t he mechanism of instantaneous nucleation. The 2D-3D transformation process after the second step is determined by the number of nuclei and their growt h rate.