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首页> 外文期刊>Molecular physics >Theoretical investigation of the phase behaviour of model ternary mixtures containing n-alkanes, perfluoro-n-alkanes, and perfluoroalkylalkane diblock surfactants
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Theoretical investigation of the phase behaviour of model ternary mixtures containing n-alkanes, perfluoro-n-alkanes, and perfluoroalkylalkane diblock surfactants

机译：含正构烷烃，全氟正构烷烃和全氟烷基烷烃二嵌段表面活性剂的模型三元混合物相行为的理论研究

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We have used the hetero-SAFT-VR approach developed by McCabe and collaborators [Mol. Phys. 104, 571 (2006)] to investigate the phase equilibria of a number of binary and ternary mixtures of n-alkanes, perfluoro-n-alkanes, and perfluoroalkylalkane diblock surfactants. We focused our work on the understanding of the microscopic conditions that control the phase behaviour of these mixtures, with a particular emphasis of the effect on the liquid-liquid separation and the stabilisation of n-alkane + perfluoro-n-alkane mixtures when a diblock surfactant is added. We used very simple molecular models for n-alkanes, and perfluoro-n-alkanes that describe the molecules as chains with tangentially bonded segments with molecular parameters taken from the literature. In the particular case of semifluorinated alkanes or SFA surfactants, we used an hetero-segmented diblock chain model where the parameters for the alkyl and perfluoroalkyl segments taken from the corresponding linear alkanes and perfluoroalkanes, as shown in our previous work [J. Phys. Chem. B 111, 2856 (2007)]. Our goal was to identify the main effects on the phase behaviour when different perfluoroalkylalkane surfactants are added to mixtures of n-alkanes and perfluoro-n-alkanes. We selected the n-heptane + perfluoromethane binary mixture, and studied the changes on the phase behaviour when a symmetric (same number of alkyl and perfluoroalkyl chemical groups) or an asymmetric (different number of alkyl and perfluoroalkyl chemical groups) diblock surfactants is added to the binary mixture. We have obtained the phase diagrams of a wide range of binary and ternary mixtures at different thermodynamic conditions. We have found a variety of interesting behaviours as we modify the alkyl or/and the perfluoroalkyl chain-length of the diblock surfactants: the usual changes in the vapour-liquid phase separation, changes in the type of phase diagrams (typically from type I to type V phase behaviour according to the Scott and Konynenburg classification), azeotropy, and Bancroft points. We noted that the main effect of adding a symmetric or an asymmetric surfactant to the n-heptane + perfluoromethane mixture is to stabilise the system, i.e. to decrease the two-phase (liquid-liquid) immiscibility region of the ternary diagram as the surfactant concentration is increased. This effect becomes larger as the chain length of the surfactant is increased, which is consistent with a higher number of alkyl-alkyl and perfluoroalkyl-perfluoroalkyl favourable interactions in the mixture.
机译：我们使用了由McCabe及其合作者[Mol。物理104，571（2006）]研究了正构烷烃，全氟正构烷烃和全氟烷基烷烃二嵌段表面活性剂的二元和三元混合物的相平衡。我们将工作重点放在了控制这些混合物的相行为的微观条件的理解上，特别强调了在二嵌段反应时对液-液分离和正构烷烃+全氟正构烷烃混合物的稳定性的影响。加入表面活性剂。我们使用非常简单的正构烷烃和全氟正构烷烃分子模型，将分子描述为具有切向键合链段的链，其分子参数取自文献。在半氟化烷烃或SFA表面活性剂的特殊情况下，我们使用杂段二嵌段链模型，其中烷基和全氟烷基链段的参数取自相应的直链烷烃和全氟烷烃，如我们先前的工作所示。物理化学B 111，2856（2007）]。我们的目标是确定将不同的全氟烷基烷烃表面活性剂添加到正构烷烃和全氟正构烷烃的混合物中时对相行为的主要影响。我们选择了正庚烷+全氟甲烷二元混合物，并研究了向其中添加对称（相同数量的烷基和全氟烷基化学基团）或不对称（不同数量的烷基和全氟烷基化学基团）二嵌段表面活性剂时相行为的变化。二元混合物。我们获得了在不同热力学条件下各种二元和三元混合物的相图。当我们修改二嵌段表面活性剂的烷基或/和全氟烷基链长时，我们发现了多种有趣的行为：蒸气-液相分离的通常变化，相图类型的变化（通常从I型变为根据Scott和Konynenburg分类确定的V型行为），共沸点和Bancroft点。我们注意到向正庚烷+全氟甲烷混合物中添加对称或不对称表面活性剂的主要作用是稳定系统，即减小三元图的两相（液-液）不混溶区域，因为表面活性剂浓度增加。随着表面活性剂链长的增加，该作用变得更大，这与混合物中更高数量的烷基-烷基和全氟烷基-全氟烷基的有利相互作用相一致。

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