We have studied the kinematics and rheological properties of undiluted polymers by modeling the fluids as a collection of interacting Kramers freely jointed bead-rod chains with anisotropic friction using Brownian dynamics simulations. The anisotropic friction depends on the instantaneous configuration of the system. The resulting stochastic differential equations have multiplicative noise. The correlation of the "Langevin" Brownian forces appearing in these equations turns out to be anisotropic as well. The excluded volume effect, often ignored in kinetic theory, plays an important role in the behavior of short polymer chains. The chain kinematics may be distorted in its absence. In this work, we also discuss the effects of two types of excluded volume (EV) forces (hard-sphere and soft-repulsive forces) on rheological properties of concentrated polymer solutions.

In this work, molecular dynamics simulation has been applied to investigate the influence of external electric field on the evaporation of the aqueous nano-film. The evaporation of the aqueous nano-film with 2240 water molecules and 50 NaCl on a gold (100) surface is analyzed at the electric fields with various intensities (0, 0.05, 0.1, 0.2 and 0.3 V nm -1 ) and directions. The predictions show that the evaporation of aqueous film is remarkably enhanced when the electric field Ex=0.2 or 0.3 V nm -1 is parallel to the aqueous film surface. It is also noted that free ions in the aqueous film are accelerated under the action of the higher Ex and water molecules in the hydration shell move together with the ions due to the hydration effect. As a result, the interaction between water molecules decreases, which is responsible for increasing the evaporation of the aqueous film under the action of the higher Ex. While applying the electric field Ey=  0.3 V nm -1 perpendicular to the aqueous film, ions cannot be in accelerated motion due to the existence of a solid-liquid interface and a liquid-gas surface in y-direction. Therefore, the evaporation enhancement is much lower than that of the aqueous film under the action of the Ex.

Water-based lubricants provide lubrication of rubbing surfaces in many technical, biological, and physiological applications. The structure of hydrated ion layers adsorbed on solid surfaces that determine the lubricating properties of aqueous lubricants is thought to be invariable in hydration lubrication. However, we prove that the ion surface coverage dictates the roughness of the hydration layer and its lubricating properties, especially under subnanometer confinement. We characterize different hydration layer structures on surfaces lubricated by aqueous trivalent electrolytes. Two superlubrication regimes are observed with friction coefficients of 10 −4 and 10 −3 , depending on the structure and thickness of the hydration layer. Each regime exhibits a distinct energy dissipation pathway and a different dependence to the hydration layer structure. Our analysis supports the idea of an intimate relationship between the dynamic structure of a boundary lubricant film and its tribological properties and offers a framework to study such relationship at the molecular level.

The transport of fluid and ions across nanotubes or nanochannels has attracted great attention due to the ultrahigh energy power density and slip length, with applications in water purification, desalination, energy conversion and even ion-based neuromorphic computing. Investigation on individual nanotube or nanochannel is essential in revealing the fundamental mechanism as well as demonstrating the property unambiguously. Surprisingly, while carbon nanotube is the pioneering and one of the most attractive systems for nanofluidics, study on its response and performance under osmotic forcing is lacking. Here, we measure the osmotic energy conversion for individual double-walled carbon nanotube with an inner radius of 2.3 nm. By fabricating a nanofluidic device using photolithography, we find a giant power density (up to 22.5 kW/m2) for the transport of KCl, NaCl, and LiCl solutions across the tube. Further experiments show that such an extraordinary performance originates from the ultrahigh slip lengths (up to a few micrometers). Our results suggest that carbon nanotube is a good candidate for not only ultrafast transport, but also osmotic power harvesting under salinity gradients.

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