Effect of solute size and shape on orientational order in liquid crystal systems
Effect of solute size and shape on orientational order in liquid crystal systems
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溶质尺寸和形状对液晶体系取向顺序的影响
DOI：
10.1039/f29767201673
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发表时间：
1976
期刊：
影响因子：
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通讯作者：
D. Patterson
中科院分区：
文献类型：
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作者：
B. Kronberg;D. Gilson;D. Patterson
宽线核磁共振已用于获得含有不同尺寸和形状的溶质的向列对甲氧基亚苄基-对正丁基苯胺 (MBBA) 的有序参数 S 作为温度的函数。这些分子包括：(i) 各向异性分子，能够将其方向与 MBBA 分子相关，即正己烷、正十六烷和反式十氢化萘，以及 (ii) 形状更加各向同性的异构体，显然无法进行方向相关，即 2,2-二甲基丁烷、2,2,4,4,6,8,8-七甲基壬烷和顺式十氢化萘。当各向异性溶质的摩尔分数 x2 相同时，S 也会相应降低，而各向同性溶质的降低则随着溶质尺寸的增加而增加。相图中单相向列区的参数 S > 0.36，沿加热时首次出现各向同性相的 (T, x2)N 线和冷却时出现向列相的 (T, x2)I 线均等于 0.36，即通过两相区 S= 0.36。对于所有系统，S 是 T/TN 比率的单函数。已获得 21 个 MBBA + 溶质系统的相图。溶质包括各向异性、取向相关的正构烷烃，n= 6、8、12、16、20、24 和反式十氢化萘以及各种各向同性、非相关的溶质：Cn 的高度支化烷烃异构体，n= 6、8、12 和 16；环烷烃；顺式十氢化萘； SnX4，其中X=甲基、丁基、辛基和月桂基； Pb(丁基)4 和二甲基硅氧烷低聚物。所有正烷烃溶质均获得相同的 (T, x2) 相图，它们对向列相各向同性转变的影响与其分子尺寸无关。这意味着分子横截面积是这些各向异性溶质的相关因素。相反，对于各向同性溶质，对 (T, x2)N 和 (T, x2)I 线的溶质尺寸有很强的依赖性。 TN 和 TI 相对于溶质摩尔分数的斜率值被校正为无限溶质稀释。结果与晶格模型、维里展开等理论的预测进行了比较。它们还用于给出向列型和各向同性 MBBA 中溶质活度系数的差异（γN∞2/γI∞2– 1）。对于正构烷烃溶质，该量与大小无关，但对于支链烷烃和其他各向同性溶质，该量迅速增加。
Wide-line n.m.r. has been used to obtain the order parameter, S, as a function of temperature, for nematic p-methoxybenzylidine-p-n-butylaniline (MBBA) containing solutes of differing size and shape. These consisted of : (i) anisotropic molecules, capable of correlating their orientations with MBBA molecules, viz n-hexane, n-hexadecane and trans-decalin, and (ii) isomers of more isotropic shape, apparently incapable of orientational correlation, viz 2,2-dimethylbutane, 2,2,4,4,6,8,8-heptamethylnonane, and cis-decalin. With the same mole fraction, x2, of anisotropic solute, there is the same lowering of S while the lowering with the isotropic solutes increases with solute size. The parameter S is > 0.36 in the one-phase nematic region in the phase diagram and is equal to 0.36 along both the (T, x2)N line where the isotropic phase first appears on heating and the (T, x2)I line where the nematic phase appears on cooling, i.e., S= 0.36 through the two-phase region. For all systems, S is a single function of the ratio T/TN. Phase diagrams have been obtained for 21 MBBA + solute systems. Solutes include the anisotropic, orientation-correlating normal alkanes, n= 6, 8, 12, 16, 20, 24 and trans-decalin and a variety of more isotropic, non-correlating solutes : the highly branched alkane isomers of Cn, n= 6, 8, 12 and 16; cycloalkanes; cis-decalin; SnX4, where X = methyl, butyl, octyl and lauryl; Pb(butyl)4 and dimethylsiloxane oligomers. Identical (T, x2) phase diagrams are obtained for all n-alkane solutes, their effect on the nematic-isotropic transition being independent of their molecular dimensions. This implies that the molecular cross-sectional area is the relevant factor for these anisotropic solutes. For the isotropic solutes, in contrast, there is a strong dependence on solute size of the (T, x2)N and (T, x2)I lines. Values of the slopes of TN and TI against solute mole fraction are corrected to infinite solute dilution. The results are compared with predictions of lattice model, virial expansion and other theories. They are also used to give the difference of solute activity coefficients in the nematic and isotropic MBBA(γN∞2/γI∞2– 1). This quantity is independent of size for the normal alkane solutes but increases rapidly for the branched alkanes and other isotropic solutes.