Large Increase in the Heat Transfer through Monolayers Detected by Beam Deflection

We report the application of photothermal beam deflection for studying heat transfer across the liquid/ gas interface covered with surfactant monolayers. Laser-induced Marangoni convection was generated on the surface of an absorbing aqueous solution with and without a monolayer. The change in heat transfer to the air was monitored by the deflection of a probe beam propagating close to the solution surface. A large increase in the deflection as well as in the air temperature for monolayer-covered surfaces was observed. A film-balance study showed that the magnitude of deflection increases as a function of monolayer compression.