화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.108, No.35, 13163-13176, 2004
Structure-property correlations in model compounds of oligomer liquid crystals
Structure-property correlations of the following model compounds for oligomer liquid crystals (LCs) have been investigated: monomers, C6H5O(CH2)(x)CH3 (x = 4 and 5); dimers, C6H5O(CH2)(x)OC6H5 (x = 3, 4, 5, and 6); and tetramers, C6H5O(CH2)(x)OC6H4O(CH2)(x)OC6H4O(CH2)(x)OC6H5 (x = 5 and 6). Deuterium NMR quadrupolar splittings observed from the deuterated model compounds dissolved in a nematic solvent, 4'-methoxybenzylidene-4-n-butylaniline (MBBA) or p-azoxyanisole (PAA), were analyzed by the rotational isomeric state scheme with the maximum entropy method to yield the orientational order parameters, bond conformations, and molecular dimensions. For the dimers in particular, the solute shapes were estimated from phase diagrams of the dimer/MBBA systems, the crystal structures were determined by X-ray diffraction, and the melting points and enthalpies of fusion were evaluated from DSC measurements. From the dimers, the so-called odd-even effect was clearly observed in not only the orientational order and molecular shape in the nematic solution but also the crystal structure and thermal properties; that is, the dimers of x = 4 and 6 have larger order parameters, more anisotropic shapes, better-arranged crystal structures, higher melting points, and larger enthalpies of fusion than those of x = 3 and 5. In the nematic solution, the model compounds preserve the inherent conformational preferences of the ether chain and enhance the shape anisotropy by increasing the trans fractions. As the orientational correlation is expected to persist only within a short range, conformations of the tetramers may represent those of polymer LCs with the same ethereal spacers. The chainlike molecules adjust their spatial configuration to the LC environment, and consequently, physical properties of the LC system are affected.