Abstract
Molecular self-assembly of nylon-12 rods in self-organized nanoporous alumina cylinders with two different diameters (65 and 300 nm) is studied with transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) in symmetrical reflection mode. In a rod with a 300 nm diameter, the tendency of the hydrogen-bonding direction of a γ-form crystal parallel to the long axis of the rod is not clear because of weak two-dimensional confinement. In a rod with a diameter of 65 nm, the tendency of the hydrogen-bonding direction of a γ-form crystal parallel to the long axis of the rod is more distinct because of strong two-dimensional confinement. For the first time, selected-area electron diffraction (SAED) is applied in a transmission electron microscope to a polymer nanorod in order to determine the hydrogen-bond sheet and lamellar orientations. Results of TEM-SAED and WAXD showed that the crystals within the rod possess the γ-form of nylon-12 and that the b axis (stem axis) of the γ-form crystals is perpendicular to the long axis of the rod. These results revealed that only lamellae with 〈h0l〉 directions are able to grow inside the nanopores and the growth of lamellae with 〈hkl〉 (k ≠ 0) directions is stopped owing to impingements against the cylinder walls. The dominant crystal growth direction of the 65 nm rod in stronger two-dimensional confinement is in between the [-201] and [001] directions due to the development of a hydrogen-bonded sheet restricted along the long axis of the rod.
Highlights
Polymer crystallization under soft or hard cylindrical confinements has been widely studied during the past decade
Polymer doi:10.1107/S2052252514020132 439 research papers melt of polyvinylidene fluoride (PVDF) (Steinhart et al, 2006), isotactic polypropylene (Duran et al, 2011), polyethylene (PE) (Shin et al, 2007), isotactic polystyrene (Wu et al, 2013), syndiotactic polystyrene (Wu et al, 2007), poly(3-hexylthiophene) (Chen et al, 2012), poly(vinylidene difluoride–trifluoroethylene) [P(VDF-TrFE)] (Shingne et al, 2013), polyethylene oxide (Guan et al, 2013; Suzuki et al, 2013), etc. were fabricated into rod-shaped samples with diameters ranging from 10 nm to 300 nm within the alumina oxide (AAO) templates
Combining the selected-area electron diffraction (SAED) and wide-angle X-ray diffraction (WAXD) results, we found that two-dimensional confinement of nylon-12 imposed by AAO significantly influences the hydrogen-bonding direction in the -form crystals inside the rod
Summary
Polymer crystallization under soft or hard cylindrical confinements has been widely studied during the past decade. Only crystallographic planes parallel to the AAO template surface (perpendicular to the long axis of the rod) could be observed in the diffraction pattern Both TEM–SAED and WAXD results show that the most common monoclinic (pseudohexagonal) -form crystals grow in the nylon-12 rod identified from SAED patterns in both the 300 nm and the 65 nm rod. In the 300 nm-diameter rod, the tendency of the hydrogen-bonding direction of the -form crystal parallel to the long axis of the rod is not clear because of weak two-dimensional confinement. In the 65 nm-diameter rod, the tendency of hydrogen-bonding direction of the form crystal parallel to the long axis of the rod is more distinct because of strong two-dimensional confinement. To understand the molecular arrangement of polymers at the nanoscale could give guidance on how to manipulate or control the molecular orientation so as to fabricate the advanced polymer nanorod with anisotropic performance
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