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    Enantiomeric Polylactides at the Air-Water Interface: p-A Isotherms and PM-IRRAS Studies of Enantiomers and Their Blend

    Year: 2003

    Journal: Langmuir 2003, 19, 333-340, 20111221

    Authors: Joy M. Klass, R. Bruce Lennox, and G. Ronald Brown Helene Bourque and Michel Pezolet

    Organizations: 1 Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, Quebec H3A 2K6, Canada 2 Centre de recherche en sciences et ingenierie des macromolecules, Departement de chimie, Universite Laval, Cite Universitaire, Quebec G1K 7P4, Canada

    The surface pressure-area (π-A) isotherms of enantiomeric polylactides and their equimolar blend reveal differences in the appearance of features and compression rate effects. Surface potential data indicate that the poly(L-lactide) monolayer interacts differently than the 50:50 poly(L-lactide)/poly(D-lactide) blend film with the water subphase. In the case of the 50:50 blend at 25 °C, compression-expansion experiments confirm that the change in the monolayer is irreversible within the time frame of the experiment. In the poly(L-lactide) case, hysteresis is also observed, but the film readily reverts to its original state. Infrared spectra of the polymer monolayers at the air-water interface were obtained using the polarizationmodulation infrared reflection-absorption spectroscopy (PM-IRRAS) technique. PM-IRRAS spectra of a compressed poly(L-lactide) monolayer are consistent with the polylactide helices lying in the plane of the air-water interface. No absorbances are observed in the PM-IRRAS spectra of poly(L-lactide) prior to the plateau in the π-A isotherms, suggesting that the helix formation is linked to the increase in surface density which accompanies film compression. The PM-IRRAS spectra establish that the conformation of the poly(L-lactide) helices with respect to the air-water interface is different than the conformation of the D/L blend helices.