College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, No. 16 Xuelin Rd., Hangzhou 310036, China.
J Phys Chem B. 2012 Feb 2;116(4):1256-64. doi: 10.1021/jp209116u. Epub 2012 Jan 18.
The crystal orientation behavior and shape-memory performance of miscible poly(vinylidene fluoride) (PVDF)/acrylic copolymer blends in various ratios have been investigated. With the incorporation of amorphous acrylic copolymer into the gallery of PVDF lamellae, the molecular connection (tie molecule concentration) between the neighboring PVDF crystals decreases gradually. For the blends with more than 80 wt % PVDF, most of the PVDF α-crystals are transformed into β-crystals upon deformation, and the molecular chains of the β-crystals are aligned along the stretching direction because tie molecules transfer the loading effectively. For the blends with less than 30 wt % PVDF, almost all of the PVDF crystals are isolated from each other with very few tie molecules. Mechanical deformation induces the perpendicular crystal molecular chain arrangement with no crystal form transitions. For the blends with 40 wt % to 70 wt % PVDF, the c-axis-oriented β-phase and the tilt-oriented α-phase coexist in the uniaxially stretched blends. The shape-memory properties of the blends were also evaluated over the same blend composition range. The maximum shape-memory recovery properties were observed for the blend sample containing 50 wt % PVDF, in which a small amount of tie molecules connect the PVDF crystallites to form a deformable elastic network. This network contributes to the good shape-memory properties of the blend. For the blends with very few tie molecules or high tie molecule concentrations, the deformation induces the slipping of the amorphous molecules or the large fibrillar crystal structure, respectively; thus, these samples exhibit relatively low shape-memory performance.
已经研究了在各种比例下可混溶性聚偏二氟乙烯（PVDF）/丙烯酸共聚物共混物的晶体取向行为和形状记忆性能。随着无定形丙烯酸共聚物掺入到 PVDF 层片的夹层中，相邻 PVDF 晶体之间的分子连接（tie molecule concentration）逐渐降低。对于共混物中含有超过 80wt%的 PVDF，大多数 PVDF α-晶体在变形时转化为β-晶体，并且β-晶体的分子链沿着拉伸方向排列，因为 tie molecules 有效地传递负载。对于共混物中含有小于 30wt%的 PVDF，几乎所有的 PVDF 晶体彼此隔离，tie molecules 很少。机械变形诱导垂直于晶体分子链排列，没有晶体形态转变。对于共混物中含有 40wt%到 70wt%的 PVDF，在单向拉伸共混物中存在 c 轴取向的β相和倾斜取向的α相。还评估了共混物在相同的共混组成范围内的形状记忆性能。在含有 50wt%PVDF 的共混物样品中观察到最大的形状记忆恢复性能，其中少量的 tie molecules 将 PVDF 结晶连接起来形成可变形的弹性网络。这个网络有助于共混物的良好形状记忆性能。对于含有很少 tie molecules 或高 tie molecule 浓度的共混物，变形会分别诱导无定形分子的滑动或大纤维状晶体结构，因此这些样品表现出相对较低的形状记忆性能。
