Critical phenomena in thick films of a binary liquid mixture

Technical Report · Thu Jan 01 04:00:00 EST 1976

DOI:https://doi.org/10.2172/7208746· OSTI ID:7208746

Jacobs, D T

The first experimental data on the behavior of a critical system as it approaches two dimensionality are presented. Measurements of the bulk coexistence curve by use of refractive index techniques were done on the binary fluid mixture methanol--cyclohexane. These measurements gave the critical exponent ..beta.. = 0.326 +- 0.003, which agrees with recent Ising-model calculations. This same binary fluid mixture was then constrained between two highly reflective, optically flat pieces of fused silica in an interferometer. The critical temperature and coexistence curve were determined as the spacing between the flats was varied from 1 ..mu..m to 60 ..mu..m. The critical temperature was directly measured for spacings between 3 and 60 ..mu..m. It was found that, if the walls were close enough together (less than or equal to 6 ..mu..m), then the drops that form on phase separation would span the intervening space. The coexistence curves of these thick films (less than or equal to 6 ..mu..m) were determined from measurements of the difference in refractive index between the two phases that appeared as drops. It was found that the shift in the critical temperature as the spacing was varied followed a logarithmic dependence. Such a dependence is not expected from Scaling Theory for an Ising model, but is to be expected of systems with effectively infinite-range interactions. The coexistence curves for each spacing of the thick film indicated that the critical exponent ..beta.. was close to 0.5, which is the mean-field (infinite-range-interaction) value and not the two-dimensional Ising-model value of 0.125. The amplitude of the coexistence curves was found to vary with spacing as L/sup z/ with z in the range 0.6 ..-->.. 0.8. This was a much larger dependence than expected from the theory. 29 figures, 5 tables

• Research Organization: Colorado Univ., Boulder (USA). Dept. of Physics and Astrophysics
• OSTI ID: 7208746
• Report Number(s): COO-2203-7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ALCOHOLS
ALKANES
BINARY MIXTURES
CRITICAL TEMPERATURE
CRYSTAL MODELS
CYCLOALKANES
CYCLOHEXANE
DISPERSIONS
DISTANCE
FILMS
HYDROCARBONS
HYDROXY COMPOUNDS
INTERACTION RANGE
ISING MODEL
MATHEMATICAL MODELS
METHANOL
MIXTURES
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
REFRACTIVITY
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE