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 (Tm), 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 α and β form was observed at 250 °C which could be attributed to the accelerated crystal growth of both crystalline phases by shear flow.

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