2H NMR研究嵌段共聚物溶致液晶相的结构演化与水分子动力学行为  

2H NMR studies of the structural evolution and water dynamics in lyotropic liquid crystals containing block copolymers

作　　者：谭玉英[1] 陈铁红[1] 孙平川[1] 

机构地区：[1]南开大学化学学院与物理学院,功能高分子材料教育部重点实验室,天津300071

出　　处：《中国科学（B辑）》2009年第9期965-970,共6页Science in China(Series B)

基　　金：国家自然科学基金(批准号:20825416;20774054)资助

摘　　要：采用2H NMR实验结合谱图线型的理论模拟方法研究了两亲性嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯/氘代水/对二甲苯三元体系形成的不同液晶相的结构演化和水分子动力学行为.结果表明,对不同组分浓度的样品,2H谱线型发生明显的变化,对应体系从各向同性相、六角相和层状相间的系列结构转变.通过NMR弛豫模型获得了液晶相结构演化中序参数和分子运动相关时间的变化规律,理论模拟获得的自旋-晶格弛豫时间T1、自旋-自旋弛豫时T2等水分子动力学参数与实验测量结果吻合.结果表明:层状相四极劈裂及序参数随嵌段共聚物或二甲苯含量的增加呈现一个极大值,水分子的T1随着嵌段共聚物浓度增加而明显减小,而T2在六角相到层状相的转变中发生了明显的变化.研究表明,通过理论模拟2H NMR实验获得的谱图线型是研究液晶相结构演化和动力学的有力工具.2H NMR experiments in combination with theoretical analysis of the line shape were employed to investigate the dynamics behavior of water and structural evolution in a ternary isothermal system consisting of poly （eth- ylene oxide-b-propylene oxide-b-ethylene oxide） amphiphilic tri-block copolymer, deuterated water （D20） and p-xylene, where D20 and p-xylene are selective solvents for the different blocks of the copolymer. This system can self-assemble to form thermodynamically stable lyotropic liquid crystals with rich ordered phases, depending on co- polymer concentration. Remarkable changes of the 2H NMR line shape and the quadrupole splitting for samples with different copolymer concentration were observed, which is associated with the structural evolution of the system among lamellae, hexagonally packed cylinders and isotropic phases. Based on NMR relaxation model proposed by Westlund et al., we fitted the experimental 2H NMR spectrum and therefore, obtained the order parameters and motional correlation times. The spin-lattice and spin-spin relaxation times calculated from the model are consistent with those from experimental observations. The line shape of quadrupole splitting in 2H NMR power spectra displays a dip at the magic angle for hexagonal phase, which directly indicates that the dominant dynamic process in this phase is in the extreme narrowing region. A maximum value of quadrupole splitting and the order parameter were found with increasing the content of the copolymer or p-xylene for lamellar phase. The T1 of deuterated water deceases obviously with increasing the content of the copolymer, while T2 changes sharply during the transition from hexago- nal to lamellar phases. The present work demonstrates that the simulation of the 2H line shape based on NMR relaxation model is a powerful tool in the study of the structural evolution and dynamics in lyotropic liquid crystalline.

关 键 词：氘核磁共振 嵌段共聚物 溶致液晶 动力学 

分 类 号：O753.2[理学—晶体学]