Kartashynska Elena S, Vysotsky Yuri B, Belyaeva Elena A, Fainerman Valentin B, Vollhardt Dieter, Miller Reinhard
Donetsk National Technical University, 58 Artema Str., 83000 Donetsk, Ukraine.
Phys Chem Chem Phys. 2014 Dec 7;16(45):25129-42. doi: 10.1039/c4cp04081c.
In the framework of the quantum chemical semiempirical PM3 method the monolayers of the monoethoxylated normal alcohols CnH2n+1OCH2CH2OH with n = 6-16 (CnE1) at the air/water interface are described. The optimized structures of small clusters (dimers, trimers, tetramers, pentamers, hexamers and heptamers) comprising the hexagonal monolayer are obtained. For these aggregates thermodynamic parameters of formation and clusterization are calculated. The correlation dependencies of the clusterization enthalpy, entropy and Gibbs energy on the number of CHHC interactions and interactions between the functional groups realized in the cluster are obtained on the basis of calculated data. The calculated parameters of the hexagonal monolayer unit cell are: a = 4.02 Å; b = 7.94 Å, t = 4°, close to those for an aliphatic alcohol monolayer according to GIXD experiments: a = 5.0 Å; b = 7.5 Å, t = 0-9°. Spontaneous clusterization of monoethoxylated alcohols at the air/water interface under standard conditions is shown to be possible for molecules possessing more than 14 carbon atoms in the alkyl chain, in good agreement with the characteristics of the surface pressure-molecular area (π-A) isotherms. It is found that addition of the -O-CH2-CH2- unit to the hydrophilic part of aliphatic alcohols results in a shift of their spontaneous clusterization threshold to that of the compounds with hydrocarbon chains 3 methylene units longer. The temperature effect of CnE1 is assessed. It corresponds to the spontaneous clusterization temperature decrease of 10-20 K per two methylene units taken from the alkyl chain in agreement with experimental data. The comparison of clusterization Gibbs energy dependencies for small aggregates of CnE1 confirms the experimental fact that the crystalline monolayers are formed by preferential aggregation of trimers.
在量子化学半经验PM3方法的框架下，描述了具有n = 6 - 16（CnE1）的单乙氧基化正醇CnH2n + 1OCH2CH2OH在空气/水界面的单层结构。获得了由六边形单层组成的小簇（二聚体、三聚体、四聚体、五聚体、六聚体和七聚体）的优化结构。计算了这些聚集体的形成和聚集的热力学参数。基于计算数据，得到了聚集焓、熵和吉布斯自由能与簇中实现的CHHC相互作用数和官能团之间相互作用的相关依赖性。计算得到的六边形单层晶胞参数为：a = 4.02 Å；b = 7.94 Å，t = 4°，与根据掠入射X射线衍射（GIXD）实验得到的脂肪醇单层的参数接近：a = 5.0 Å；b = 7.5 Å，t = 0 - 9°。结果表明，在标准条件下，对于烷基链中碳原子数超过14的分子，单乙氧基化醇在空气/水界面可能会自发聚集，这与表面压力 - 分子面积（π - A）等温线的特征相符。研究发现，在脂肪醇的亲水部分添加 -O-CH2-CH2- 单元会导致它们的自发聚集阈值向具有长3个亚甲基单元的烃链化合物的阈值移动。评估了CnE1的温度效应。它对应于每从烷基链中取出两个亚甲基单元，自发聚集温度降低10 - 20 K，这与实验数据一致。对CnE1小聚集体的聚集吉布斯自由能依赖性的比较证实了实验事实，即晶体单层是由三聚体的优先聚集形成的。
