Adsorption hysteresis and 2D phase nucleation of chloroform on graphite

The thermodynamic characterization of a chloroform (CHCl3) film adsorbed on (0001) graphite has been performed by means of isotherm measurements between 206.9 and 227.7 K. The isotherms exhibit two steps before bulk condensation. The first step is assigned to a monomolecular layer condensation, whose two-dimensional critical temperature is estimated to be 216 K. The second step measurement provides evidence of CHCl3 adsorptive properties very different from those classically observed in the formation of a second adsorbed layer. Slow adsorption kinetics and significant hysteresis in the second step domain for temperatures below 224.8 K are related to nucleation difficulties. A restructuration of the first adsorbed monolayer seems to be necessary in order to build a bilayer whose high stability results in unusually low relative pressures of the second steps of the isotherms.