Burba Christopher M, Woods Lauren, Millar Sarah Y, Pallie Jonathan
Department of Natural Sciences, Northeastern State University, Tahlequah, OK.
Electrochim Acta. 2011 Dec 15;57(15):165-171. doi: 10.1016/j.electacta.2011.06.025.
Polymer chain orientation in tensile-stretched poly(ethylene oxide)-lithium trifluoromethanesulfonate polymer electrolytes are investigated with polarized infrared spectroscopy as a function of the degree of strain and salt composition (ether oxygen atom to lithium ion ratios of 20:1, 15:1, and 10:1). The 1359 and 1352 cm(-1) bands are used to probe the crystalline PEO and P(EO)(3)LiCF(3)SO(3) domains, respectively, allowing a direct comparison of chain orientation for the two phases. Two-dimensional correlation FT-IR spectroscopy indicates that the two crystalline domains align at the same rate as the polymer electrolytes are stretched. Quantitative measurements of polymer chain orientation obtained through dichroic infrared spectroscopy show that chain orientation predominantly occurs between strain values of 150% and 250%, regardless of salt composition investigated. There are few changes in chain orientation for either phase when the films are further elongated to a strain of 300%; however, the PEO domains are slightly more oriented at the high strain values. The spectroscopic data are consistent with stretching-induced melt-recrystallization of the unoriented crystalline domains in the solution-cast polymer films. Stretching the films pulls polymer chains from the crystalline domains, which subsequently recrystallize with the polymer helices parallel to the stretch direction. If lithium ion conduction in crystalline polymer electrolytes is viewed as consisting of two major components (facile intra-chain lithium ion conduction and slow helix-to-helix inter-grain hopping), then alignment of the polymer helices will affect the ion conduction pathways for these materials by reducing the number of inter-grain hops required to migrate through the polymer electrolyte.
采用偏振红外光谱法，研究了拉伸后的聚环氧乙烷-三氟甲烷磺酸锂聚合物电解质中聚合物链的取向与应变程度和盐组成（醚氧原子与锂离子的比例分别为20:1、15:1和10:1）之间的关系。分别使用1359 cm⁻¹和1352 cm⁻¹波段来探测结晶态的聚环氧乙烷和聚（环氧乙烷）₃LiCF₃SO₃区域，从而可以直接比较两相中链的取向。二维相关傅里叶变换红外光谱表明，随着聚合物电解质的拉伸，两个结晶区域以相同的速率排列。通过二向色红外光谱获得的聚合物链取向的定量测量结果表明，无论所研究的盐组成如何，链取向主要发生在150%至250%的应变值之间。当薄膜进一步拉伸至300%的应变时，两相的链取向几乎没有变化；然而，在高应变值下，聚环氧乙烷区域的取向略强。光谱数据与溶液浇铸聚合物薄膜中未取向结晶区域的拉伸诱导熔体再结晶一致。拉伸薄膜会将聚合物链从结晶区域中拉出，随后这些链会重新结晶，聚合物螺旋平行于拉伸方向。如果将结晶聚合物电解质中的锂离子传导视为由两个主要部分组成（链内锂离子的快速传导和螺旋间缓慢的晶粒间跳跃），那么聚合物螺旋的排列将通过减少穿过聚合物电解质迁移所需的晶粒间跳跃次数来影响这些材料的离子传导途径。
