Shear-induced conformational fluctuations of polystyrene probed by 2D infrared microspectroscopy

In-situ shear-induced conformational fluctuations of isotactic and syndiotactic polystyrene (iPS and sPS) were studied by 2D infrared microspectroscopy measurements. For iPS at temperatures above the nominal melting temperature (T-m), it was found that the area of long helices induced by shear flow mainly corresponded to macro 'row-nucleated' or 'shish-like' precursors while only short helices in amorphous domain. The long helices became to disappear during the heating process which was consistent with the melting of micron-scale precursors. From an intra-molecular view, long helices in precursors could be related to shear-induced coil-helix transition. To our knowledge, this is the first in-situ FT-IR evidence for flow-induced macro-precursors. For sPS after applying a pulse shear flow, compared with the monophonic morphology in absence of flow, a dual crystalline morphology including alpha and beta form was observed at 250 degrees C which could be attributed to the accelerated crystal growth of both crystalline phases by shear flow. (c) 2012 Elsevier Ltd. All rights reserved.