In this work, isotherms for mixtures of methylene blue (MB(+)) and dim
yristoyl phosphatidic acid (DMPA) were studied. Cc-spreading technique
s were used to spread a mixed solution of MB(+) and DMPA in 3:1 CHCl3/
CH3OH at the air-water interface. This system exhibits markedly expand
ed isotherms at low pi values. By using the Langmuir-Blodgett (LB) tec
hnique, a 1:1 DMPA/MB(+) monolayer was transferred to an indium tin ox
ide electrode at pi = 25 mN m(-1). The presence of MB + in LB films wa
s detected by visible spectroscopy and electrochemical methods.