Sahu Pooja, Ali Sk M
Chemical Engineering Division, Bhabha Atomic Research Center, Mumbai 400085, India.
J Chem Phys. 2015 Nov 14;143(18):184503. doi: 10.1063/1.4935373.
Water in nanotube exhibits remarkably different properties from the bulk phase, which can be exploited in various nanoconfinement based technologies. The properties of water within nanotube can be further tuned by varying the nanotube electrostatics and functionalization of nanotube ends. Here, therefore, we investigate the effect of quantum partial charges and carbon nanotube (CNT) termination in terms of associated entropic forces. An attempt has been made to correlate the entropic forces with various dynamical and structural properties. The simulated structural features are consistent with general theoretical aspects, in which the interfacial water molecules at H terminated CNT are found to be distributed in a different way as compared to other CNTs. The rotational entropy components for different cases of CNTs are well corroborated by the decay time of hydrogen bond (HB) correlation functions. A part of this event has been explained in terms of orientation of water molecules in the chain, i.e., the change in direction of dipole moment of water molecules in the chain and it has been revealed that the HBs of CNT confined water molecules show long preserving correlation if their rotations inside CNT are restricted. Furthermore, the translational entropy components are rationally integrated with the differing degree of translational constraints, added by the CNTs. To the best of our information, perhaps this is the first study where the thermodynamic effects introduced by H-termination and induced dipole of CNT have been investigated. Additionally, we present a bridge relation between "translational diffusivity and configurational entropy" for water transport from bulk phase to inside CNTs.
纳米管中的水表现出与本体相显著不同的性质，这可在各种基于纳米限域的技术中加以利用。通过改变纳米管的静电作用和纳米管末端的功能化，可以进一步调节纳米管内水的性质。因此，我们在此研究量子部分电荷和碳纳米管（CNT）末端在相关熵力方面的影响。已尝试将熵力与各种动力学和结构性质相关联。模拟的结构特征与一般理论方面一致，其中发现与其他碳纳米管相比，氢终止的碳纳米管处的界面水分子以不同方式分布。不同情况下碳纳米管的旋转熵分量通过氢键（HB）相关函数的衰减时间得到了很好的证实。这一现象的一部分已根据链中水分子的取向来解释，即链中水分子偶极矩方向的变化，并且已经表明，如果碳纳米管内水分子的旋转受到限制，碳纳米管受限水分子的氢键会表现出长期保持的相关性。此外，平移熵分量与碳纳米管添加的不同程度的平移约束合理地整合在一起。据我们所知，这可能是首次研究氢终止和碳纳米管诱导偶极引入的热力学效应。此外，我们给出了从本体相到碳纳米管内部水传输的“平移扩散率与构型熵”之间的桥梁关系。
