With high brilliance synchrotron radiation provides a great advantage on time resolved in situ measurements on structural development during polymer processing, which is expected to play an important role on targeting the scientific challenges in polymer industry.
Spherulite is the basic element in semicrystalline polymers, which directly influences the mechanical, optical and other properties of final products. However, an unambiguous molecular image and mechanism are still missing. Synchrotron radiation scanning X-ray micro-diffraction (SR-μSXRD) owns the spatial resolution of 1.5 μm which is suitable to detect the structure distribution in micro zone. Combining a hot stage with SR-μSXRD, the crystallinity distribution of a growing spherulite is obtained. Unexpectedly, the real boundary of the growing spherulite is revealed to be 40 μm outside of the boundary determined with optical microscope. These results break up the traditional view and provide a new physical image of growing spherulite.
With the information about the real boundary in hand, the filling process of spherulite is further studied in details. In the recent 10 years, information is collected to suggest that the existence of pre-ordering might during the transition between disordered melt and crystal, though more direct evidence is still required. With a combination of a mini hot stage and IR micro-spectroscopic imaging (μ-IRSI), conformational ordering inside spherulite is studied. The experimental results reveal that a boundary layer around the growth front of spherulite has large contents of conformational ordered segments (CORS), which implies pre-ordering (CORSp) occurs at the growing layer of spherulite. The thickness of the boundary layer depends on the competition between rates of pre-ordering and its transformation to crystal. Incorporating the data of SR-μSXRD and μ-IRSI, an illustration of the growth front with conformational ordered segments is shown in Fig. 2. [Macromolecules, 2010, 43, 9859–9864 ]
Fig . Schematic picture of the growth model of polymer spherulite
The infrared/X-ray diffraction micro-tensile devices were developed, and used in the in-situ studies on structure and properties of macromolecule materials, such as lyotropic supramolecular liquid crystals with anisotropic ionic conductivities, deformation-induced phase transitions of polyamide 12 at different temperatures, and flow-induced conformational ordering in the supercooled isotactic polypropylene (iPP). The relationship between mechanical properties and microstructure of macromolecule materials was depicted in the atomic scale, showing broad application prospects in life and energy materials. [Chemical Communications 48, 7560 (2009); Macromolecules 42, 1428 (2009); 42, 4343 (2009); 43, 602 (2010); 43, 2406 (2010)]
Fig . Engineering stress-strain curve and the selected WAXS patterns during uniaxial tensile deformation of PA 12 at room temperature (a), and change of d spacing of (b) (020) plane and (c) (001) plane by WAXS in conjunction with engineering stress-strain curve
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