Monolayers of Poly( l ‐lactic acid) on the Water Surface Spread From Solid Tablets and Their Langmuir–Blodgett Films

Using a recently proposed Langmuir monolayer spreading method from solid tablets without the use of organic solvents, we successfully prepared the first Langmuir monolayer of poly( l ‐lactic acid) (PLLA) using this method. When a solid PLLA tablet was placed in ultrapure water, the surface pressure was detected after 5 h. After 22 h of standing while monitoring the surface pressure–time isotherm, the surface pressure gradually increased to 10 mN m −1 . When two‐dimensional compression was applied to this system and the surface pressure‐area isotherms were measured, the two‐dimensional phase‐transition behavior from the expanded phase to the condensed phase in the low‐surface‐pressure region, which has frequently been observed in previous reports using conventional solution‐spreading method, disappeared. Consequently, only the behavior of the highly condensed monolayer was confirmed. The surface morphology at 10 mN m −1 , at which a spontaneous Langmuir monolayer was formed immediately before compression, consisted of aggregated fibrous monolayer on the nanometer scale, appearing to possess unique characteristics. By comparing this method with monolayer formation from a spreading solution, we found that the results suggest the existence of a unique morphological formation mechanism in this monolayer formation process, which does not involve the evaporation of the spreading solvent.