Hamid Ilyar, Jalali Hossein, Peeters Francois M, Neek-Amal Mehdi
Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.
Department of Physics, University of Zanjan, 45195-313 Zanjan, Iran.
J Chem Phys. 2021 Mar 21;154(11):114503. doi: 10.1063/5.0038359.
Dielectric properties of nano-confined water are important in several areas of science, i.e., it is relevant in the dielectric double layer that exists in practically all heterogeneous fluid-based systems. Molecular dynamics simulations are used to predict the in-plane dielectric properties of confined water in planar channels of width ranging from sub-nanometer to bulk. Because of suppressed rotational degrees of freedom near the confining walls, the dipole of the water molecules tends to be aligned parallel to the walls, which results in a strongly enhanced in-plane dielectric constant (ε) reaching values of about 120 for channels with height 8 Å < h < 10 Å. With the increase in the width of the channel, we predict that ε decreases nonlinearly and reaches the bulk value for h > 70 Å. A stratified continuum model is proposed that reproduces the h > 10 Å dependence of ε. For sub-nanometer height channels, abnormal behavior of ε is found with two orders of magnitude reduction of ε around h ∼ 7.5 Å, which is attributed to the formation of a particular ice phase that exhibits long-time (∼μs) stable ferroelectricity. This is of particular importance for the understanding of the influence of confined water on the functioning of biological systems.
纳米受限水的介电性质在多个科学领域都很重要，例如，它与几乎所有基于非均相流体的系统中存在的双电层相关。分子动力学模拟用于预测宽度从亚纳米到本体的平面通道中受限水的面内介电性质。由于在限制壁附近旋转自由度受到抑制，水分子的偶极子倾向于与壁平行排列，这导致面内介电常数（ε）大幅增强，对于高度为8 Å < h < 10 Å的通道，其值可达约120。随着通道宽度增加，我们预测ε会非线性降低，并且当h > 70 Å时达到本体值。提出了一个分层连续介质模型，该模型再现了ε对h > 10 Å的依赖性。对于亚纳米高度的通道，发现ε存在异常行为，在h ∼ 7.5 Å附近ε降低了两个数量级，这归因于形成了一种表现出长时间（∼微秒）稳定铁电性的特殊冰相。这对于理解受限水对生物系统功能的影响尤为重要。
