Fernandez-Garcia M, Cheda JAR, Westrum EF, Fernandez-Martin F
Departamento de Quimica Fisica I, Universidad Complutense, Madrid, Spain
J Colloid Interface Sci. 1997 Jan 15;185(2):371-81. doi: 10.1006/jcis.1996.4610.
The phase, association, and aggregation behavior of the binary system [TlO2C(CH2)5CH3 + HO2C(CH2)5CH3] have been investigated through temperature and enthalpy vs composition diagrams by determination of the thermal behavior of the pure components and 30 mixtures over an interval of nearly 300 K, and by differential scanning calorimetry and polarized microscopy. Total miscibility was observed in liquid and liquid crystalline phases but essentially total immiscibility among crystalline phases. The phase behavior exhibits: (1) Formation of two intermediate compounds which dissociate in the solid state at low temperature; (2) A eutectic reaction at salt molar fraction x = 0.08 about 3 K below the acid melting point; (3) Unimolecular salt:acid association by very strong hydrogen bonding, which undergoes a crystal/crystal transition prior to incongruent melting at 295.5 K, occurring by a highly energetic peritectic reaction in which the compound evolves more than the sum of the total transition enthalpies of both components; (4) Lyotropic mesophase formation at 390.0 K over the x >/= 0.66 composition range by aggregation of a solid and a liquid phase to yield, on heating, a continuous series of liquid crystalline solutions with mixed-lamellar structure and interlamellar spacings around 20 A as determined by powder X-ray diffractometry, their texture being focal conic, consistent with the neat thermotropic mesophase of the pure salt. A tridimensional phase diagram is presented. All these main reactions have been fully characterized by their nature, stoichiometry, and relevant thermodynamic data.
通过绘制温度、焓与组成关系图，对二元体系[TlO₂C(CH₂)₅CH₃ + HO₂C(CH₂)₅CH₃]的相行为、缔合行为和聚集行为进行了研究。具体方法是测定纯组分以及30种混合物在近300 K温度区间内的热行为，并采用差示扫描量热法和偏光显微镜进行观察。结果表明，该二元体系在液相和液晶相中完全互溶，但在晶相中基本完全不互溶。其相行为表现为：(1)形成两种中间化合物，它们在低温下固态分解；(2)在盐摩尔分数x = 0.08处，约比酸熔点低3 K发生共晶反应；(3)通过非常强的氢键形成单分子盐:酸缔合物，该缔合物在295.5 K发生不一致熔融之前经历晶体/晶体转变，转变过程由一个高能包晶反应引发，在此反应中化合物释放的能量超过两种组分总转变焓之和；(4)在x≥0.66的组成范围内，于390.0 K通过固相和液相聚集形成溶致中间相，加热时产生一系列具有混合层状结构且层间间距约为20 Å的连续液晶溶液，粉末X射线衍射测定结果表明其织构为焦锥状，与纯盐的纯热致中间相一致。文中给出了三维相图。所有这些主要反应的性质、化学计量关系及相关热力学数据均已得到充分表征。
