The morphology of partially crystalline/ordered poly(butylene naphthalate) (PBN) forming on cooling the melt has been analyzed by polarized-light optical microscopy (POM) and microfocus-beam X-ray diffraction (XRD). Crystallization at rather low supercooling of the melt, at temperatures higher than about 200 Â°C, leads to slow and irregular spherulitic growth of Î²â²-crystals, with spherulites not showing a distinct Maltese cross in POM. At temperatures between approximately 200 and 160 Â°C, the melt partially converts directly to Î±-crystals, and the obtained spherulitic superstructure reveals an increasing nuclei density with decreasing crystallization temperature. At even lower temperature, a liquid crystalline (LC) phase develops. This mesophase may subsequently convert to Î±-crystals according to Ostwald's rule of stages. The transition of the LC-phase into Î±-crystals is suppressed at temperatures lower than about 120 Â°C or on cooling faster than about 200â500 K/s. X-ray analysis of PBN liquid crystals formed at well-defined cooling conditions in a fast scanning chip calorimeter revealed smectic periodicity while there is simultaneously observed a distinct Schlieren texture in POM.
|Titolo:||Smectic liquid crystal Schlieren texture in rapidly cooled poly(butylene naphthalate)|
|Data di pubblicazione:||2018|
|Appare nelle tipologie:||01.01 - Articolo su rivista|