Vapor-Crystal Phase Transition in Synthesis of Paracetamol Films by Vacuum Evaporation and Condensation

We report on the structural and technological investigations of the vapor-crystal phase transition during synthesis of paracetamol films of the monoclinic system by vacuum evaporation and condensation in the temperature range 220–320 K. The complex nature of the transformation accompanied by the formation of a gel-like phase is revealed. The results are interpreted using a model according to which the vapor-crystal phase transition is not a simple first-order phase transition, but is a nonlinear superposition of two phase transitions: a first-order transition with a change in density and a second-order phase transition with a change in ordering. Micrographs of the surface of the films are obtained at different phases of formation.