Abolhasani Mohammad Mahdi, Naebe Minoo, Guo Qipeng
Chemical Engineering Department, University of Kashan, Kashan, Iran.
Phys Chem Chem Phys. 2014 Jun 14;16(22):10679-87. doi: 10.1039/c4cp00031e.
This paper proposes a new mechanism for ferroelectric polymorph formation of poly(vinylidene fluoride) (PVDF) nanocomposites. Utilizing time-resolved Fourier transform infrared spectroscopy (FTIR), the real-time investigation of the conformational changes of the PVDF chain segment during crystallization of neat PVDF and the corresponding nanocomposite was performed. Whilst PVDF-clay nanocomposites exhibited mainly the β crystal phase coexisting with the γ phase at low Tc (Tc < 155 °C), the coexistence of γ and β crystalline phases was found at a high Tc temperature range (Tc > 155 °C). Experimental results were compared with predictions of the Lauritzen and Hoffman (LH) model and discrepancies were observed between model predictions and experiments. We then recalled the Brochard-de Gennes (BD) model and proposed that different crystalline polymorph formation should be inferred as a transition in the reeling-in rate dependence of the friction coefficient on nanocomposites rather than as a change in the relative rates of secondary nucleation and substrate completion. Combining LH and BD models we proposed a new mechanism to answer the contradictory questions associated with nanocomposite polymorphism. The coexistence of different polymorphs in nanocomposites was proposed to be associated with the coexistence of fast and slow moving chains, which were recognized as the free and adsorbed chains by nanofillers.
本文提出了一种聚偏二氟乙烯（PVDF）纳米复合材料铁电多晶型形成的新机制。利用时间分辨傅里叶变换红外光谱（FTIR），对纯PVDF及其相应纳米复合材料结晶过程中PVDF链段构象变化进行了实时研究。在低温（Tc < 155 °C）下，PVDF-粘土纳米复合材料主要呈现β晶相与γ相共存，而在高温（Tc > 155 °C）温度范围内发现γ相和β晶相共存。将实验结果与劳里茨森和霍夫曼（LH）模型的预测进行了比较，发现模型预测与实验之间存在差异。然后我们回顾了布罗沙尔-德热纳（BD）模型，并提出不同结晶多晶型的形成应推断为纳米复合材料上摩擦系数的卷入速率依赖性的转变，而不是二次成核和基底完成相对速率的变化。结合LH和BD模型，我们提出了一种新机制来回答与纳米复合材料多晶型相关的矛盾问题。纳米复合材料中不同多晶型的共存被认为与快速和慢速移动链的共存有关，快速和慢速移动链分别被纳米填料识别为自由链和吸附链。
