College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, No. 16 Xuelin Road, Xiasha High-tech Zone, Hangzhou 310036, China.
ACS Appl Mater Interfaces. 2012 Sep 26;4(9):4825-31. doi: 10.1021/am301161s. Epub 2012 Aug 27.
Polyvinylidene fluoride (PVDF)/acrylic copolymer (ACP) blends are a typical miscible crystalline/amorphous system over the whole composition range. Our previous investigation indicated that blend samples with controlled component ratios and crystallization conditions exhibit good shape memory properties (J. Phys. Chem. B 2012, 116, 1256-1264). In this work, we systematically investigated the cold crystallization temperature effects on the crystal morphologies and the shape memory properties for the 50/50 blend. It was found that the quenched blend is an amorphous material with a low glass transition temperature. Annealing at temperatures above T(g) of the blend induces crystallization of PVDF from the miscible amorphous PVDF/ACP phase, leading to an increased glass transition temperature of the blend. High annealing temperature results in large PVDF spherulites, while low annealing temperature produces tiny crystals in the blend. Furthermore, tiny crystals serve as the physical cross-link points and the amorphous regions among them act as the reversible phase for the blend materials during the mechanical deformations. Therefore, the PVDF/ACP blends with tiny crystals show not only high shape fixity but also excellent recovery ratios.
聚偏二氟乙烯（PVDF）/丙烯腈-丁二烯-苯乙烯共聚物（ACP）共混物在整个组成范围内是典型的可混溶性结晶/无定形体系。我们之前的研究表明，具有受控成分比和结晶条件的共混物样品表现出良好的形状记忆性能（J. Phys. Chem. B 2012, 116, 1256-1264）。在这项工作中，我们系统地研究了冷结晶温度对 50/50 共混物的晶体形态和形状记忆性能的影响。结果发现，淬火共混物是一种具有低玻璃化转变温度的无定形材料。在高于共混物玻璃化转变温度的温度下退火会导致 PVDF 从可混溶的无定形 PVDF/ACP 相中结晶，从而使共混物的玻璃化转变温度升高。高退火温度会导致 PVDF 球晶较大，而低退火温度会在共混物中产生微小的晶体。此外，微小的晶体充当物理交联点，而其中的无定形区域在机械变形过程中充当共混材料的可逆相。因此，具有微小晶体的 PVDF/ACP 共混物不仅具有高形状固定率，而且具有优异的恢复率。
