Surface and bulk structure of poly-(lactic acid) films studied by vibrational sum frequency generation spectroscopy

The surface and bulk structure of various poly-(lactic acid) (PLA) films were examined by vibrational sum frequency generation (VSFG). In contrast to linear infrared spectroscopy, the VSFG spectra show significantly different characteristics in the CH stretching region. For crystalline PLLA we observed strong surface and bulk signals, which were caused by both the order and the symmetry of the space group. Amorphous PLLA and racemically composed PDLLA were found to consist of a relatively disordered bulk. Contrary to the bulk, all surfaces studied generated VSFG signal caused by the broken symmetry at the polymer/air interface. (c) 2007 Elsevier B.V. All rights reserved.