1,2-propanediol and 1,3-propanediol homogeneous nucleation rates and phasetransitions in the new phase critical embryos

Nucleation rates of supersaturated vapors near the conditions for the criti cal line for each pair of 1,2- or 1,3-propanediol and carbon dioxide or sul fur hexafluoride at total system pressures of P=0.10, 0.20, and 0.30 MPa ha ve been measured in a flow diffusion chamber. Critical parameters, i.e., te mperatures and pressures, of the binary systems versus compositions were se miempirically evaluated. It was found experimentally that there is an area of parameters in the PTx phase diagram, for each pair of vapor and carrier gas investigated in the present research, for which critical embryo phase t ransitions of the first order take place (where P, T, and x are pressure, t emperature, and embryo composition, respectively). The nucleation rate surf ace singularity and a gap in the number of molecules in critical embryos re flect this area. Shifts of the phase transition temperatures can be initiat ed by increasing the pressure (or concentration) of the carrier gas. This b ehavior is peculiar for binary systems. It is well-known that no liquid-liq uid phase transitions can exist for a one-component system. At least a bina ry solution is required for liquid-liquid phase transitions. This means tha t vapor nucleation of the investigated substances in the carrier gas atmosp here can be considered as nucleation of a binary vapor-gas system. A schema tic diagram for the possible metastable vapor conditions is presented. On t he basis of our experimental results, one can assume that there exists a su rface describing the parameters related with a phase transition of the firs t order in critical embryos. This surface is located within the volume of t he possible vapor metastable conditions. (C) 2000 American Institute of Phy sics. [S0021-9606(00)70522-8].