title: Kinetic appearance of first-order gas-liquid expanded and liquid expanded-liquid condensed phase transitions below the triple point.
abstract: Phase diagram of Gibbs monolayers of mixtures containing n-hexadecyl phosphate (n-HDP) and L-arginine (L-arg) at a molar ratio of 1:2 has been constructed by measuring surface-pressure-time (pi-t) isotherms with film balance and by observing monolayer morphology with Brewster angle microscopy (BAM). This phase diagram shows a triple point for gas (G), liquid expanded (LE), and liquid condensed (LC) phases at around 6.7 degrees C. Above this triple point, a first-order G-LE phase transition occurring at 0 surface pressure is followed by another first-order LE-LC phase transition taking place at a certain higher surface pressure that depends upon temperature. The BAM observation supports these results. Below the triple point, the pi-t measurements show only one first-order phase transition that should be G-LC. All of these findings are in agreement with the general phase diagram of the spread monolayers. However, the BAM observation at a temperature below the triple point shows that the thermodynamically allowed G-LC phase transition is, in fact, a combination of the G-LE and LE-LC phase transitions. The latter two-phase transitions are separated by time and not by the surface pressure, indicating that the G-LC phase transition is kinetically separated into these two-phase transitions. The position of the LE phase below the triple point in the phase diagram is along the phase boundary between the G and LC phases.
authors.affiliation: Venture Business Laboratory, Utsunomiya University, Yoto 7-1-2, Utsunomiya 321-8585, Japan.
authors.forename: Md Mufazzal
authors.initials: MM
authors.lastname: Hossain
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Iimura
authors.forename: Teiji
authors.initials: T
authors.lastname: Kato
mesh_terms: D005740:Gases / Q000737:chemistry*; D007700:Kinetics; D008853:Microscopy / Q000379:methods
chemical_list: D005740:Gases