title: Real-time imaging of crystallization in polylactide enantiomeric monolayers at the air-water interface.
abstract: A newly developed planar array infrared reflection-absorption spectrograph (PA-IRRAS) offers significant advantages over conventional approaches including fast acquisition speed, excellent compensation for water vapor, and an excellent capacity for large infrared accessories, e.g., a water trough. In this study, the origin of stereocomplexation in a polylactide enantiomeric monolayer at the air-water interface was investigated using PA-IRRAS. PA-IRRAS was used as a probe to follow the real-time conformational changes associated with intermolecular interactions of polymer chains during the compression of the monolayers. It was found that a mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) (D/L) formed a stereocomplex when the two-dimensional monolayer developed at the air-water interface before film compression, indicating that there is no direct correlation between film compression and stereocomplexation. PA-IRRAS spectra of the stereocomplex exhibited distinct band shifts in crystalline sensitive components, e.g., the vas(C-O-C, h) mode, as well as amorphous-dependent components, e.g., the vs(C-O-C) mode, when compared with the spectra of PLLA alone. On the other hand, time-resolved PA-IRRAS spectra, which were obtained as the films were being compressed, revealed that both monolayers of PLLA and mixed PLLA/PDLA stereocomplex were crystallized into a 10(3)-helix and a 3(1)-helix, respectively, with a distinct band shift in crystalline sensitive components only. Fourier self-deconvolution of the spectra demonstrated that the band shift in crystalline sensitive components is correlated with the intermolecular interaction of polymer chains.
authors.affiliation: Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Young Shin
authors.initials: YS
authors.lastname: Kim
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Snively
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Liu
authors.forename: John F
authors.initials: JF
authors.lastname: Rabolt
authors.forename: D Bruce
authors.initials: DB
authors.lastname: Chase
mesh_terms: D003460:Crystallization; D005740:Gases / Q000737:chemistry*; D011091:Polyesters / Q000737:chemistry*; D011312:Pressure; D012997:Solvents; D013057:Spectrum Analysis; D013237:Stereoisomerism; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D005740:Gases; D011091:Polyesters; D012997:Solvents; D014867:Water; C033616:poly(lactide)