Charge-signal multiplication mediated by urea wires inside Y-shaped carbon nanotubes

Unexpected spontaneous dynamic oxygen migration on carbon nanotubes

Combining density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, we show that oxygen functional groups exhibit unexpected spontaneous dynamic behaviors on the interior surface of single-walled carbon nanotubes (SWCNTs). The hydroxyl and epoxy migrations are achieved by the C-O bond breaking/reforming reactions or the proton transfer reaction between the neighboring epoxy and hydroxyl groups. It is demonstrated that the spontaneous dynamic characteristic is attributed to the sharply reduced energy barrier less than or comparable to thermal fluctuations. We also observe a stable intermediate state with a dangling C-O bond, which permits the successive migration of the oxygen functional groups. However, on the exterior surface of SWCNTs, it is difficult for the oxygen groups to migrate spontaneously because there are relatively high energy barriers, and the dangling C-O bond prefers to transform into the more stable epoxy configuration. The spontaneous oxygen migration is further confirmed by the oxygen migration process using DFT calculations and AIMD simulations at room temperature. Our work provides a new understanding of the behavior of oxygen functional groups at interfaces and gives a potential route to design new carbon-based dynamic materials.

Model of osmosis in a single-file pore

Single-file transport of water and other small molecules through narrow pores in osmosis has drawn considerable attention in recent years due to its extensive application in biology and industry. In this work, we propose a discrete model to describe nonideal osmosis through single-file pores. Every site is assumed to be occupied by a molecule according to experiments and simulations. Hence, a dense chain can always be found, and collective hopping is the only movement method enabling the molecular chain to move. The roles of solute in osmosis are clarified in this model. Those molecules reflected at the pore entrance produce osmotic pressure, and those inside the pore contribute to the flow resistance of the molecular chain. The solute molecules that can enter the pore but cannot penetrate it may significantly reduce the osmotic flux, although they are all rejected by the pore. This conclusion can help to clarify the emerging debate about whether the reflection coefficient of the fully rejected solute can be less than 1. The design of highly efficient membrane pores may also benefit from this study.

A controllable water signal transistor

We performed molecular dynamics simulations to study the regulating ability of water chains confined in a Y-shaped nanochannel. It was shown that a signal at the molecular level could be controlled by two other charge-induced signals when the water chains were confined in a Y-shaped nanochannel, demonstrating promising applications as water signal transistors in nanosignal systems. The mechanism of a water signal transistor is similar to a signal logic device. This remarkable ability to control the water signal is attributed to the strong dipole-ordering of the water chains in the nanochannel. The controllable water signal process of the Y-shaped nanochannel provides opportunities for future application in the design of molecular-scale signal devices.

From dimers to collective dipoles: Structure and dynamics of methanol/ethanol partition by narrow carbon nanotubes

Alcohol partitioning by narrow single-walled carbon nanotubes (SWCNTs) holds the promise for the development of novel nanodevices for diverse applications. Consequently, in this work, the partition of small alcohols by narrow tubes was kinetically and structurally quantified via molecular dynamics simulations. Alcohol partitioning is a fast process in the order of 10 ns for diluted solutions but the axial-diffusivity within SWCNT is greatly diminished being two to three orders of magnitude lower with respect to bulk conditions. Structurally, alcohols form a single-file conformation under confinement and more interestingly, they exhibit a pore-width dependent transition from dipole dimers to a single collective dipole, for both methanol and ethanol. Energetic analyses demonstrate that this transition is the result of a detailed balance between dispersion and electrostatics interactions, with the latter being more pronounced for collective dipoles. This transition fully modifies the reorientational dynamics of the loaded particles, generating stable collective dipoles that could find usage in signal-amplification devices. Overall, the results herein have shown distinct physico-chemical features of confined alcohols and are a further step towards the understanding and development of novel nanofluidics within SWCNTs.