A Langmuir film of poly(ethylene oxide) (PEO) has been prepared at the air−water interface using water as the spreading solvent. Unlike the conventional PEO film (prepared using chloroform as the solvent), which exhibits the highest surface pressure of 10 mN/m, the present film attains a surface pressure of 17.5 mN/m at high apparent polymer loading (35 mg/m 2 ).The π−A isotherm of a film prepared at low PEO loading was observed to be similar in nature to the conventional isotherm of PEO, and the surface pressure attained for the film is 10.5 mN/m at a loading of 1 mg/m 2 . The key step in the preparation of the film is to use a higher initial loading of polymer and multiple compression− expansion cycles to induce aggregation and compaction of PEO molecules in the film. The prepared Langmuir films were characterized in term of surface pressure−surface area isotherms, the hysteresis exhibited by these isotherms, and the static dilatational modulus. Article pubs.acs.org/IECR
One of the most important techniques to improve the functional properties of organized molecular films is to introduce nanometer-size solid particles into them. The Langmuir balance has proved to be useful for controlling and modifying these films by organizing molecules into highly ordered structures. Our aim is to study the efficacy of this technique to improve the compactness of biocompatible polymer films by incorporating nanosilica particles. The experimental technique consists of first adsorbing the polymer on silica particles in an aqueous medium, followed by preparation of a monolayer at the air–water interface in a Langmuir balance. The film is organized by repeated expansion and compression. The surface pressure-surface area characteristics are recorded during each cycle. The pressure of the film increases with decrease in the mean molecular area, but reaches a plateau, probably due to instability of the film. With repeated cycling, the plateau pressure increases indicating that the film has become more stable and rigid. The cycling is continued till plateau pressure does not change with further cycling. The amount of the polymer loaded on the subphase and the ratio of PEO to silica in the film, on the plateau pressure has been studied. A substantial increase in the stability and rigidity of the film is achieved by this technique.
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