Formation Mechanism of the Spiral-Like Structure of a Hydrogen Bond Network Confined in a Fluorinated Nanochannel: A Molecular Dynamics Simulation

Abstract

The structure of the hydrogen bond network inside of the proton conductive channel is of significant importance to proton transfer confined in a nanochannel. In order to investigate the independent effects of fluorination and confinement dimension on the hydrogen bond network, a one-dimensional carbon nanotube decorated with fluorine was built to mimic the environment of the proton conductive channel in the perfluorosulfonic membrane (Phys. Chem. Chem. Phys. 2016, 18(35), 24198−24209). It was found that a fluorinated nanochannel helps to form a spiral-like sequential hydrogen bond network with few branched hydrogen bonds in the central region, which is believed to promote unidirectional proton transfer along the channel axis without random movement. To explore the mechanism of the formation of the spiral-like hydrogen bond structure, molecular dynamics simulation was conducted to analyze the hydrogen bonding properties of water and a hydrated proton confined in the fluorinated CNT with chirality of (10,10). The hydrogen bond criteria were initially evaluated for the water−water and hydronium−water hydrogen bonds. It was found that the confined hydrated protons help maintain the connectivity of the hydrogen bond network along the axis of the fluorinated nanochannel at different temperatures. The hydronium ion prefers to form hydrogen bonds with two neighboring water molecules, resulting in a continuous hydrogen bond network. The non-hydrogen-bonded hydrogen atom of the hydronium ion has strong attraction with the fluorinated channel surface, stabilizing the hydrogen bond structure and making space in the central region of the nanochannel. The connectivity of the hydrogen bond network and the interaction between hydronium and the channel surface produce the spiral-like structure of the hydrogen bond network along the axis of the fluorinated nanochannel with few branched hydrogen bonds.

Effect of Hydrogen-Bonding Interaction on the Arrangement and Dynamics of Water Confined in a Polyamide Membrane: A Molecular Dynamics Simulation

“…The above-mentioned H-bond statistics only characterize the mean H-bonding ability of water in the bulk and confined phases. It is known that the H-bonding states have a great effect on the dynamic behaviors of water. ,, Thus, it is still necessary to describe the local structure of water with different H-bonding states, which are defined according to the H-bond constituents. The H-bonding state of one water molecule is characterized by a quantity f n ( n = 0–6), which denotes that the water molecule forms n W–W H-bonds.…”

Dynamically disordered hydrogen bonds in the hureaulite-type phosphatic oxyhydroxide Mn5[(PO4)2(PO3(OH))2](HOH)4

“…The dynamic disorder of protons over such sites and routes represents an interesting object for both experimental and theoretical studies of complex proton behaviors. 3,[16][17][18][19][20][21][22][23] Furthermore, according to Baranov,8 hureaulite shows a high theoretical intrinsic charge carrier concentration of N p = 2.629 × 10 22 protons per cm 3 , exceeding the boundary value N p, limit = 10 18 protons cm −3 between high and low proton mobility. 24 This motivated us to resolve a consistent picture of charge transport via protons over the DDHBs in this complex system by diffraction and spectroscopy tools in combination with density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations performed with the CP2K code, as described below.…”

Universal Intrinsic Dynamics and Freezing of Water in Small Nanotubes

“…72 Moreover, the number of the HBs may decrease, depending on the charge and interaction parameters of the atoms that form the nanostructures. 73,74 In addition, there seems to be a relationship between the dipole orientation and the HB network, 75 where the typical dipole orientation is measured with respect to the axial direction, z, which in CNTs is about ϕ = 30°. 76,77 Nonetheless, ϕ can be altered, depending on the nanotube and the partial charges of its constituent atoms.…”

“…The HBs can form and break faster, depending on the environment, or they can be broken upon deformation of the nanotubes’ walls . Moreover, the number of the HBs may decrease, depending on the charge and interaction parameters of the atoms that form the nanostructures. , In addition, there seems to be a relationship between the dipole orientation and the HB network, where the typical dipole orientation is measured with respect to the axial direction, z , which in CNTs is about ϕ = 30°. , Nonetheless, ϕ can be altered, depending on the nanotube and the partial charges of its constituent atoms. Mei et al reported that not only is the dipole angle ϕ of water confined in graphite layers different from 30° when the partial charges of the carbon atoms are [artificially] altered, but that water can form fewer HBs compared to the case in which the charges in the graphite walls are not altered.…”