The Study Of The PLA Ultrathin Films Using The Grazing Angle Reflectance Infrared Spectroscopy

In this paper, we used the grazing angle IR reflection absorption spectroscopy (IRRAS)、the grazing incidence X-ray diffraction (GIXRD) and the Differential scanning calorimetry (DSC) as the effective means to analysis the crystallization behavior Lamellae orientation and phase transition of the PLLA ultrathin films which have different thicknesses and the factors that affect those behaviors of the PLLA ultrathin films. Meanwhile, we studied the difference of the crystallization behavior and phase transition between the PLLA/PDLA stereocomplex bulk and the ultrathin film.By modulating the concentration of the PLLA/CHCL3 solution, we acquired the PLLA ultrathin films with different thicknesses and collected the IRRAS and GIXRD datas. First, by analyzing the structures of the PLLA ultrathin film, we found that the α and the a form were coexisted during the cool crystallizantion. Second, through studying the orientation of the 10/7 helix chain of the PLLA ultrathin film during the cooling and melting crystallization, it shows that the orientations of the 10/7 helix chain during those two processes are quite different (the Lamellae takes the edge-on orientatioan during the cool crystallization, while it takes the flat-on orientation during the melt crystallization). Meanwhile, after carefully analysis, we found that the lamellae orientation of the PLLA ultrathin film can be modulated by the factors such as crystallization temperature and film thickness.We used the variable temperature grazing angle reflectance infrared technology to study the phase transition behavior of the PLLA ultrathin films with different thicknesses, we found that The glass transition temperature (Tg) appears a gradually increasing trend with the decrease of the film thickness. We believe that the reason caused this phenomenon is that the movement of the molecular chain which located in the interlayer of the polymer/substrates is strongly inhibited, as a result, The glass transition temperature (Tg) appears a gradually increasing trend.The difference of the crystallization behavior and phase transition between the PLLA/PDLA stereocomplex bulk and the ultrathin film was also investigated. We found that the α、α and Pc form were coexisted during the cooling and melting crystallization in the PLLA/PDLA stereocomplex bulk, in contrast, there was only the βc form in the PLLA/PDLA stereocomplex ultrathin film. During the cooling crystallization, the Lamellae in the PLLA/PDLA stereocomplex ultrathin film takes the edge-on orientation, while it takes the flat-on orientation during the melt crystallization.