Phase behavior of an amphiphilic fluid.
Phase behavior of an amphiphilic fluid.
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两亲流体的相行为
DOI：
10.1103/physreve.89.012310
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
Sabine H. L. Klapp
中科院分区：
文献类型：
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作者：
Martin Schoen;Stefano Giura;Sabine H. L. Klapp
我们调用平均场密度泛函理论（DFT）来研究由硬球核加上叠加的不等轴Lennard-Jones微扰组成的两亲流体的相行为。相互作用的取向依赖性包括一个贡献类似于一对“自旋”之间的相互作用潜力的经典，三维海森堡流体和另一个让人想起（电或磁）点偶极子之间的相互作用。在固定的方向上，这两种贡献在性质上都是短程的，衰减为（一对两亲分子的质心之间的分离）。基于两个平均场近似的对相关函数，不同的复杂程度，我们推导出表达式的各向同性和极性相位之间的相位边界，我们解决数值的牛顿-拉夫逊方法。对于海森堡“自旋”之间足够强的耦合，两种平均场近似都产生了三种拓扑上不同的通用类型的相图，这些相图与早期的工作一致[参见，例如，塔瓦雷斯，Phys.Rev.E52，1915（1995）1063-651X10.1103/PhysRevE.52.1915]。而偶极贡献单独是无法稳定极性相，由于其短程性质，但它仍然是重要的相图的细节，如气体各向同性液体临界点，三重和三临界点的位置。通过适当地调整偶极耦合常数，实际上可以在拓扑不同的相图之间切换。还采用Monte Carlo模拟的等温等压系综的DFT相图的一般拓扑结构得到确认。
We invoke mean-field density functional theory (DFT) to investigate the phase behavior of an amphiphilic fluid composed of a hard-sphere core plus a superimposed anisometric Lennard-Jones perturbation. The orientation dependence of the interactions consists of a contribution analogous to the interaction potential between a pair of “spins” in the classical, three-dimensional Heisenberg fluid and another one reminiscent of the interaction between (electric or magnetic) point dipoles. At fixed orientation both contributions are short-range in nature decaying as(being the separation between the centers of mass of a pair of amphiphiles). Based upon two mean-field-like approximations for the pair correlation function that differ in the degree of sophistication we derive expressions for the phase boundaries between various isotropic and polar phases that we solve numerically by the Newton-Raphson method. For sufficiently strong coupling between the Heisenberg “spins” both mean-field approximations generate three topologically different and generic types of phase diagrams that are observed in agreement with earlier work [see, for example, Tavares , Phys. Rev. E 52, 1915 (1995)1063-651X10.1103/PhysRevE.52.1915]. Whereas the dipolar contribution alone is incapable of stabilizing polar phases on account of its short-range nature it is nevertheless important for details of the phase diagram such as location of the gas-isotropic liquid critical point, triple, and tricritical points. By tuning the dipolar coupling constant suitably one may, in fact, switch between topologically different phase diagrams. Employing also Monte Carlo simulations in the isothermal-isobaric ensemble the general topology of the DFT phase diagrams is confirmed.