The Langmuir technique is one of the most common methods for preparing twodimensional
molecular assemblies. In this method, a solution of an amphiphilic compound in a low-boiling solvent, usually immiscible with water, is spread on a water subphase. After the solvent has evaporated, the amphiphilic molecules form a monolayer in which their hydrophilic heads interact with the water subphase and the hydrophobic tails are directed away from it. Compression of the monolayer on the water subphase leads to a reduction of the area available per molecule (A), thus causing an increase in surface pressure (!). The resulting π–A isotherm (surface pressure as a function of the molecular area at constant temperature) provides information on the molecular packing within the monolayer, the orientation of the headgroups, the molecular area requirement, and possible interactions with molecules or ions dissolved in the aqueous subphase. The monolayer formed at the air-water interface can be transferred onto a solid support (Langmuir–Blodgett deposition). Due to the ease in assembling amphiphiles into a variety of thin films with defined composition, structure, and thickness, the Langmuir and Langmuir–Blodgett (LB) techniques have allowed the development of novel functional materials by many scientists.