Water permeation through Langmuir-Blodgett monolayers

A new method for measuring the water permeation resistances of monolayers has been developed to overcome the lack of sensitivity of the usual technique of Langmuir and Schaefer. In the new method, a monolayer is deposited onto a cylinder of agar gel by the Langmuir-Blodgett technique. The cylinder is then transferred to a vacuum chamber where the evaporation rate is measured under reduced pressure. This reduction in air pressure, together with other aspects of the design, reduces the total resistance of the transport pathway so that the effect of a monolayer on the evaporation rate is more marked and lower resistance can be measured. Results for the high resistance monolayer octadecanol are in reasonable accord with data obtained by the Langmuir-Schaefer method, conforming the validity of the new technique. Data for distearoylphosphatidyl choline, dipalmitoyl-phosphatidyl cholesterol and mixtures of dipalmitoylphosphatidyl choline and cholesterol are presented and discussed