Crystalline Structures, Melting, and Crystallization of Linear Polyethylene in Cylindrical Nanopores

Abstract

The crystalline structures associated with melting and crystallization behaviors of monodisperse linear polyethylene confined in cylindrical nanopores were investigated by X-ray diffraction and differential scanning calorimetry. The crystalline structures, melting, and crystallization behaviors of PE under the imposed cylindrical confinement were noticeably different from those of the bulk state. The isothermal crystallization experiments showed that the overall crystallization of polyethylene in cylindrical nanopores was dominated by the nucleation rather than the growth of crystallites. The c- and a-axes of orthorhombic PE crystals developed in nanoporous alumina were preferentially oriented perpendicular to the long axis of cylindrical nanopore while the b-axis was parallel to the pore axis. The melting temperature of polyethylene in the nanopores was substantially depressed, and it was analyzed with the Thomson−Gibbs equation. The crystallinity of linear polyethylene in cylindrical nanopores was less than 50%, whereas the bulk value was 71.6%.

Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: Catalytic aspects of in situ polymerization, crystalline features and mechanical properties

“…Most usually, a simplified version of that equation is employed [38][39][40] when dealing with lamellar crystals of finite size along the macromolecular chain but with very large sizes for the lateral dimension. In the present case, however, a more general equation is needed [41,42] Table 1.…”

Orientation of Syndiotactic Polystyrene Crystallized in Cylindrical Nanopores

“…[7][8][9][10][11][12] In general the crystals in the nanopores crystallized at low supercooling temperatures exhibit a perpendicular orientation because of the kinetic selection of crystal growth processes. [7][8][9] For poly(vinylidene difluoride) (PVDF), homogeneous nucleation was found to dominate in the separated nanostructures, while for the nanorods in connection with bulk, the crystal orientation in the nanorods is dominated by the bulk owing to the kinetic 'gate effect'. [8] In addition, polyethylene (PE) crystallization in nanopores was found to be controlled by the nucleation rather than the growth of the crystallites.…”

Molecular composition distribution of polycarbonate/polystyrene blends in cylindrical nanopores

“…1 Attention has been focused on structure formation processes such as chain dynamics, 2-5 crystallization [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and phase separation [20][21][22][23][24][25][26][27][28] under the influence of the two-dimensional confinement imposed by cylinder geometry and interfacial interactions with pore walls. Owing to the special shape of nanocylinders with high aspect ratios (length to diameter), the fabricated nanomaterials have unusual mechanical, chemical, optical and electronic properties, as well as specific surface properties.…”

“…1 For amorphous polystyrene (PS) confined in cylindrical alumina nanopores, an unexpected enhancement of flow and a reduction in intermolecular entanglement have been observed, leading to higher mobility of polymer in the confined geometry than that of unconfined chains. 2 In the case of semicrystalline polymers under nanocylindrical geometry, the polymers exhibit novel orientation, [5][6][7][8][9][10][11][12][13][14][15][16][17] polymorphism 18 and segmental dynamic behavior. 5,17 The crystals that form in nanorods at low supercooling show perpendicular orientation; that is, the c-axes of the polymer crystals that develop in cylindrical nanopores preferentially orient perpendicular to the long axis of the nanopore.…”

“…5,17 The crystals that form in nanorods at low supercooling show perpendicular orientation; that is, the c-axes of the polymer crystals that develop in cylindrical nanopores preferentially orient perpendicular to the long axis of the nanopore. [5][6][7][8][9][10][11][12][13][14][15][16][17] The crystallinities [8][9][10] and melting temperatures 10,17 of nanorods are reduced compared with those of bulk polymer, owing to the spatial confinement of the nanopores. Strong deviation from the normal relaxation behavior of poly(vinylidene fluoride) was observed inside nanopores.…”