Higher Colleges of Technology, ETS, MZWC, Abu Dhabi, 58855, United Arab Emirates.
Department of Physics, Missouri University of Science and Technology, Rolla, MO 65409, USA.
Phys Chem Chem Phys. 2023 Feb 15;25(7):5808-5816. doi: 10.1039/d2cp05735b.
Molecular dynamics simulations (MD) are performed to study the interfacial structure/tension and wetting behavior of water/-alkane systems (water/C5 to water/C16 where C = CH(2 + 2)). In particular, we study complete-to-partial wetting transitions by changing the -alkane chain length () at a constant temperature, = 295 K. Simulations are carried out with a united-atom TraPPE model for -alkanes and the TIP4P-2005 model of water. Simulation results are in excellent agreement with the initial spreading coefficients and contact angles calculated using experimental values of the surface and interfacial tensions. In addition, it has been determined that water/(C5-C7) and water/(C8-C16), respectively, exhibit complete and partial initial wetting modes. Simulations show that the interfacial structures of water/(C5-C7) are different from water/(C8-C16) systems. In the latter, water preferentially orients near the interface to increase the number of hydrogen bonds and the charge and mass densities. Moreover, the orientation of -alkane molecules at water/(C8-C16) interfaces has a long-range persistence, resulting in layered structures that increase with . In addition, simulation results of the orientational order parameter show alignment behavior of the -alkane molecules with respect to the interfaces. Simulations predict that the central segments of -alkane are strongly packed in the interfaces while the end segments (methyl groups) form smaller peaks in the outer edge of the layer. This observation confirms the "horseshoe" or "C-shaped" structure of -alkane molecules in the water/-alkane interfaces. At constant temperature, the interface widths of both water and the -alkanes decrease with increasing -alkane molecular length. These results suggest that increasing the -alkane chain length affects the water/-alkane interfacial properties in a manner similar to that of cooling.
采用分子动力学模拟（MD）研究了水/-链烷烃体系（水/C5 至水/C16，其中 C = CH(2 + 2)）的界面结构/张力和润湿行为。特别是，我们通过改变-链烷烃的链长（）在恒定温度下（= 295 K）研究了完全到部分润湿转变。模拟采用统一原子 TraPPE 模型对-链烷烃和 TIP4P-2005 模型的水进行。模拟结果与使用表面张力和界面张力实验值计算得到的初始扩展系数和接触角非常吻合。此外，确定了水/(C5-C7)和水/(C8-C16)分别表现出完全和部分初始润湿模式。模拟表明，水/(C5-C7)的界面结构不同于水/(C8-C16)体系。在后一种体系中，水优先在界面附近取向以增加氢键数量以及电荷和质量密度。此外，-链烷烃分子在水/(C8-C16)界面上的取向具有长程持久性，导致层状结构随增加。此外，取向序参量的模拟结果显示了-链烷烃分子相对于界面的取向行为。模拟预测，-链烷烃的中心段在界面处紧密堆积，而末端段（甲基）在层的外边缘形成较小的峰。这一观察结果证实了-链烷烃分子在水/-链烷烃界面上的“马蹄铁”或“C 形”结构。在恒定温度下，水和-链烷烃的界面宽度都随-链烷烃分子长度的增加而减小。这些结果表明，增加-链烷烃链长以类似于冷却的方式影响水/-链烷烃界面性质。
