Structure of Macroscopic Monodomains and Its Soft Confinements of Chiral Smectic Phases on Crystallization in a Main-Chain Nonracemic Liquid Crystalline Polyester

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• 作者：Shi Jin ; Kwang-Un Jeong ; Yingfeng Tu ; Matthew J. Graham ; Jing Wang ; Frank W. Harris ; Stephen Z. D. Cheng
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：July 24, 2007
• 年：2007
• 卷：40
• 期：15
• 页码：5450 - 5459
• 全文大小：1174K
• 年卷期：v.40,no.15(July 24, 2007)
• ISSN：1520-5835

文摘

A main-chain nonracemic chiral liquid crystalline (LC) polyester was synthesized using an A-Btype condensation reaction of a chiral monomer, R-(-)4'-{-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-heptyloxy}-4-biphenylcarboxylic acid, and was abbreviated as PET(R*-7). Wide-angle X-ray diffraction (WAXD)experiments combined with differential scanning calorimetry measurements revealed multiple phase transitionsincluding a chiral twist grain boundary A (TGBA*) phase, a chiral smectic A (SmA*) phase, a chiral smectic C(SmC*) phase, and a highly ordered monoclinic crystalline (K_M) phase with decreasing temperature. Flat-elongatedand right-handed double-twisted helical single crystals were grown thermotropically in the smectic LC states.Both crystal types possessed the identical monoclinic unit cell: a = 1.04 nm, b = 0.46 nm, c = 5.59 nm, = = 90, and = 84.2 based on the WAXD and selected area electron diffraction results. Uniaxial elongationof centimeter-sized films (along the xz-plane in a three-dimensional, 3D, coordinate system) of submillimeterthickness (along the y-axis) resulted in macroscopic smectic monodomains. Analysis of the detailed 2D WAXDresults indicated that in the SmA* phase the molecules are parallel to the layer normal in the direction of elongation.However, in the SmC* phase, the 3D macroscopic monodomain was constructed with the layers which possessa 13 synclinically tilted layer normal with respect to the elongation direction (the z-axis). The molecules in the3D monodomains of SmC* phase were tilted ~8 synclinically with respect to the elongation direction withinthe "in-plane" of the film (within the xz-plane), translating to a ~21 tilt with respect to the layer normal. Duringthe crystallization of the K_M phase in the SmA* phase, the c-axis of the K_M crystal is along the elongationdirection (the z-axis), yet the d-spacing of the (00l) (l = even number) planes were slightly larger than the layerspacing of the SmA* phase. When the crystallization occurred in the 3D monodomain of the SmC* phase, on theother hand, the synclinically tilted LC layers and the tilted layer normal orientation with respect to the elongationdirection (the z-axis) were retained in the K_M crystal, although the d-spacing of the (00l) (l = even number)planes was larger than the layer spacing of the SmC* phase. The most striking observation was that in order toform the K_M crystals in the SmC* phase the molecules must undergo a remarkable reorientation (~21 tilting)to became a single-crystal-like monodomain while retaining the synclinically tilted layer structure.