A model is developed in which the theory of deterministic chaos for the interface layer is used to treat both homophase and heterophase fluctuations of density (volume) and the fluctuations of pressure, whose duration increases as the critical point is approached. This approach, based on the transition from continuous differential equations to mappings, leads to a number of important consequences in theoretical analysis of high-temperature processes of evaporation and condensation, including the loss of information on the initial conditions, the alternation, and the presence of branching points on bifurcation diagrams.