Liu Gang, Fang Dong, Dan Yongjie, Luo Huan, Luo Cong, Niu Yanhua, Li Guangxian
College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Chengdu 610065, China.
Phys Chem Chem Phys. 2022 Jul 6;24(26):16388-16396. doi: 10.1039/d2cp02223k.
Imidazolium ionic liquids (ILs) with various alkyl chain lengths on the cations ([Cmim], = 2, 4 and 8) and different combined anions ([TFSI] and [PF]) were blended with poly(methyl methacrylate) (PMMA), and the effects of the IL structure on the chain dynamics of PMMA were experimentally investigated by rheology and DSC measurements combined with a simulation method. The results indicate that the interaction between PMMA and ILs becomes stronger as the alkyl chain length on the imidazolium ring increases or the anion changes from [PF] to [TFSI]. As a result, a higher critical entanglement concentration and a larger entanglement molecular weight of PMMA were found in [Cmim][TFSI] due to the stiffer conformation. Molecular dynamics (MD) simulations further demonstrated stronger interactions between PMMA and ILs with longer cationic alkyl chain lengths or [TFSI] anions, which showed smaller Flory-Huggins interaction parameters and larger radii of gyration, . However, the larger size of alkyl chains or [TFSI] anions produced a larger free volume in the system as evidenced by positron annihilation lifetime spectroscopy (PALS), which competed with the molecular interaction and dominated the segmental motion. Therefore, a lower and accelerated segmental relaxation were observed. Compared to alkyl chain length, the effect of anions on the interactions between ILs and PMMA is more prominent.
将阳离子上具有不同烷基链长度（[Cmim]，m = 2、4和8）以及不同组合阴离子（[TFSI]和[PF]）的咪唑鎓离子液体（ILs）与聚甲基丙烯酸甲酯（PMMA）共混，并通过流变学和DSC测量结合模拟方法，实验研究了IL结构对PMMA链动力学的影响。结果表明，随着咪唑环上烷基链长度的增加或阴离子从[PF]变为[TFSI]，PMMA与ILs之间的相互作用增强。因此，由于构象更刚性，在[Cmim][TFSI]中发现了更高的临界缠结浓度和更大的PMMA缠结分子量。分子动力学（MD）模拟进一步证明，PMMA与具有更长阳离子烷基链长度或[TFSI]阴离子的ILs之间的相互作用更强，这表现为更小的弗洛里-哈金斯相互作用参数和更大的回转半径。然而，正电子湮没寿命谱（PALS）表明，更大尺寸的烷基链或[TFSI]阴离子在体系中产生了更大的自由体积，这与分子间相互作用相互竞争并主导了链段运动。因此，观察到更低的玻璃化转变温度和加速的链段弛豫。与烷基链长度相比，阴离子对ILs与PMMA之间相互作用的影响更为显著。
