Crystal Orientation Changes in Two-Dimensionally Confined Nanocylinders in a Poly(ethylene oxide)-b-polystyrene/Polystyrene Blend

Abstract

A lamella-forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer has been blended with a low molecular weight polystyrene (PS) homopolymer to form a miscible polymer blend. The PEO volume fraction is 0.32, and the order-disorder transition temperature (T ODT) of this blend is 175 °C. Therefore, the PEO blocks form nanocylinders surrounded by a PS matrix below the TODT. Since the glass transition temperature of the PS is 64 °C and the PEO crystal melting occurs at ∼50 °C, the PEO-block crystallization takes place in a two-dimensionally confined glassy environment. The cylinder diameter is determined to be 13.7 nm, based on small-angle X-ray scattering (SAXS) and transmission electron microscopy results. Using simultaneous two-dimensional SAXS and wide-angle X-ray scattering techniques, the crystal orientation (the c-axes of the PEO crystals) within the nanocylinders is found to change simply depending upon the crystallization temperature (T c). At very low Tc (<-30 °C), PEO crystals are randomly oriented within the confined cylinders. Starting at Tc ) -30 °C, the crystal orientation changes to be inclined with respect to the cylinder axis, a ˆ. The tilt angle from a ˆcontinuously increases with increasing Tc, and finally it becomes 90°when Tc g 2 °C. Crystallographic analysis indicates that the crystal c-axis orientation at each Tc corresponds to a uniform crystal orientation.

Features, Questions and Future Challenges in Layered Silicates Clay Nanocomposites with Semicrystalline Polymer Matrices

“…Indeed, in small spaces we talk about confined crystallisation, as observed elsewhere too for organic fibres, [57,58] drawn matrices [59][60][61] or in block copolymers. [62][63][64] Unfortunately, no information is provided concerning intercalated PA-6 molecules in clay galleries as the authors focused on a fully exfoliated system.…”

Orientation Control and Crystallization in a Soft Confined Phase Separated Block Copolymer

“…In particular, crystallization in confinement has received great interest both experimentally [1][2][3][4][5][6][7][8][9][10][11] and through simulation 12 in recent years. One reason for exploring confinement effects is that confined systems are becoming increasingly widespread, as devices and materials are constrained due to miniaturization.…”

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.…”