ROUTINE ABSORBENCY SPECTROSCOPY AT THE AIR-WATER-INTERFACE

A Langmuir-Blodgett instrument has been assembled that is capable of providing side-by-side comparisons of two separate monolayers in a true double-beam absorption geometry with no moving parts. Absorbance spectra of two different films are monitored at the air/water interface, with the use of fiber optics in conjunction with a charge-coupled-device detector and a single-stage spectrograph. The utility of this instrument is demonstrated by simultaneous measurement of monomer, dimer, and aggregate components in a single-component carbocyanine dye monolayer and a mixed carbocyanine dye/phospholipid monolayer, as the isotherm of each of these films is generated. A linear relationship between number density and the carbocyanine monomer/dimer ratio is observed.