Adsorption of trichloroethene at the vapor/water interface.

Abstract

Aqueous solution surface tension (pressure) as a function of vapor-phase trichloroethene (TCE) pressure isotherms were measured at atmospheric pressure at 287.2, 291.2, 297.2, 303.2, and 315.2 K using a flow-through vapor adsorption method. Solute (i.e., TCE)-induced surface tension variations were quantified using Axisymmetric Drop Shape Analysis-Profile (ADSA-P); vapor-phase TCE pressures were measured using automated gas chromatograph analysis. Surface tension reductions of 5-10% from neat water at saturated TCE vapor pressure were noted. Measured surface tension (pressure) isotherms were used to estimate vapor/water interface adsorption as a function of vapor-phase TCE pressure using the Gibbs relative interface excess (i.e., adsorption) equation and a nonideal two-dimensional equation of state. Complete isothermal adsorption profiles were nonlinear, with accelerated adsorption at increasing vapor-phase TCE pressures. Comparison to other studies of adsorption at infinite dilution (i.e., linear partitioning) and corresponding to thermodynamics (i.e., ideal equilibrium standard molar free energy, enthalpy, and entropy change) indicate good agreement. Estimates of TCE planar surface area were used to calculate the fraction of monolayer coverage at the vapor/water interface as a function of vapor-phase TCE pressure, which approached a maximum of 0.6-0.75 at saturated vapor pressure.