Phase equilibria in model surfactants forming Langmuir monolayers.
Phase equilibria in model surfactants forming Langmuir monolayers.
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DOI：
10.1063/1.2802505
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发表时间：
2007-12
期刊：
影响因子：
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通讯作者：
E. Ramírez;A. Santana;A. Cruz;G. López
中科院分区：
文献类型：
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作者：
E. Ramírez;A. Santana;A. Cruz;G. López
朗缪尔单分子膜由于其独特的性质和尚不清楚的相平衡而引起了研究人员的关注。这些单层膜显示出有趣的相图，其中可以观察到单组分单层膜不寻常的液-液平衡。利用蒙特卡罗计算机模拟得到了虚拟吉布斯系综中朗缪尔单层膜的相图。通过建立cailleet - mathias相图，考虑了液-汽平衡和液-液相平衡。利用伊辛模型和直线近似确定了两种平衡态的临界性质。这些关键参数被计算为表面活性剂分子与水相之间相互作用强度的函数。结果，我们确定了液体膨胀态(LES)-蒸汽和液体冷凝态(LES)-蒸汽之间的共存，与文献中的实验和理论证据一致。我们得到了清晰的相分离，并且对所用溶剂的强度有很强的依赖性。也就是说，随着溶剂和表面活性剂头部之间相互作用的增加，临界性能也会增加。通过计算热力学量作为温度和溶剂强度的函数来表征平衡状态。
The study of Langmuir monolayers has generated the attention of researchers because of their unique properties and their not well understood phase equilibrium. These monolayers exhibit interesting phase diagrams where the unusual liquid-liquid equilibrium can be observed for a single component monolayer. Monte Carlo computer simulations in the virtual Gibbs ensemble were used to obtain the phase diagram of Langmuir monolayers. The liquid-vapor and liquid-liquid phase equilibria were considered by constructing the Cailletet-Mathias phase diagrams. By using the Ising model and the rectilinear approximations the identification of the critical properties for both equilibria was determined. These critical parameters were calculated as a function of the strength of the interaction between the surfactant molecules and the aqueous subphase. As a result, we have identified the coexistence between a liquid expanded state (LES)-vapor and the liquid condensed state-LES, in agreement with experimental and theoretical evidence in the literature. We obtained a clear separation of phases and a strong dependence on the strength of the solvent used. Namely, as the interaction between the solvent and the head of the surfactant increases, the critical properties also increase. Equilibrium states were characterized by computing thermodynamic quantities as a function of temperature and solvent strength.