Sarith P. Sathian

Bio: Sarith P. Sathian is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Graphene & Interfacial thermal resistance. The author has an hindex of 14, co-authored 56 publications receiving 624 citations. Previous affiliations of Sarith P. Sathian include National Institute of Technology Calicut.

Rayleigh instability at small length scales.

Abstract: The Rayleigh instability (also called the Plateau-Rayleigh instability) of a nanosized liquid propane thread is investigated using molecular dynamics (MD). The validity of classical predictions at small length scales is verified by comparing the temporal evolution of liquid thread simulated by MD against classical predictions. Previous works have shown that thermal fluctuations become dominant at small length scales. The role and influence of the stochastic nature of thermal fluctuations in determining the instability at small length scale is also investigated. Thermal fluctuations are seen to dominate and accelerate the breakup process only during the last stages of breakup. The simulations also reveal that the breakup profile of nanoscale threads undergo modification due to reorganization of molecules by the evaporation-condensation process.

Fast transport of water in carbon nanotubes : a review of current accomplishments and challenges

Abstract: The intriguing mass transport properties of carbon nanotubes (CNTs) have received widespread attention, especially the rapid transport of water through CNTs due to their atomically smooth wall interiors. Extensive research has been dedicated to the comprehension of various aspects of water flow in contact with CNTs, the most prominent ones being the studies on slip and flow rates. Experimental and computational studies have confirmed an enhanced water flow rate through this graphitic nanoconfinement. However, a quantitative agreement has not yet been attained. These disparities coupled with incomplete knowledge of the mechanisms of water transport at nanoscale regimes are hindering the possibilities to integrate CNTs in numerous nanofluidic applications. In the present review, we focus on the slip and flow rates of water through CNTs and the factors influencing them. We discuss the key sources of discrepancies in water flow rate and suggest directions for future study.

Prediction of Kapitza resistance at fluid-solid interfaces.

Abstract: Understanding the interfacial heat transfer and thermal resistance at an interface between two dissimilar materials is of great importance in the development of nanoscale systems. This paper introduces a new and reliable linear response method for calculating the interfacial thermal resistance or Kapitza resistance in fluid-solid interfaces with the use of equilibrium molecular dynamics (EMD) simulations. The theoretical predictions are validated against classical molecular dynamics (MD) simulations. MD simulations are carried out in a Lennard-Jones (L-J) system with fluid confined between two solid slabs. Different types of interfaces are tested by varying the fluid-solid interactions (wetting coefficient) at the interface. It is observed that the Kapitza length decreases monotonically with an increasing wetting coefficient as expected. The theory is further validated by simulating under different conditions such as channel width, density, and temperature. Our method allows us to directly determine the Kapitza length from EMD simulations by considering the temperature fluctuation and heat flux fluctuations at the interface. The predicted Kapitza length shows an excellent agreement with the results obtained from both EMD and non-equilibrium MD simulations.

Combining molecular dynamics simulation and transition state theory to evaluate solid-liquid interfacial friction in carbon nanotube membranes.

Abstract: A molecular dynamics (MD) methodology based on Eyring theory of reaction rates is proposed for investigating solid-liquid interfacial properties crucial to the development of many nanotechnology applications. The method involves the calculation of activation energy required for the flow process directly from the MD trajectory information. We have applied this methodology to study the behavior of water in hydrophobic confinement in carbon nanotubes (CNTs) and also between graphene sheets. In the case of confined water molecules in CNTs and between graphene sheets the degree of confinement and curvature effects were found to have more influence on the solid-liquid interfacial friction, with almost negligible friction below a certain characteristic dimension in both the cases. This behavior of confined and unconfined water molecules is explained on the basis of molecular interactions and subsequent changes in the activation energy. Analysis based on this method also revealed that a finite amount of friction does exist at the channel entry and exit region. This could limit the flow of liquid molecules through the nanochannels and hence needs to be taken into account in the design of nanofluidic devices.

Thermophoretically driven water droplets on graphene and boron nitride surfaces.

Abstract: We investigate thermally driven water droplet transport on graphene and hexagonal boron nitride (h-BN) surfaces using molecular dynamics simulations. The two surfaces considered here have different wettabilities with a significant difference in the mode of droplet transport. The water droplet travels along a straighter path on the h-BN sheet than on graphene. The h-BN surface produced a higher driving force on the droplet than the graphene surface. The water droplet is found to move faster on h-BN surface compared to graphene surface. The instantaneous contact angle was monitored as a measure of droplet deformation during thermal transport. The characteristics of the droplet motion on both surfaces is determined through the moment scaling spectrum. The water droplet on h-BN surface showed the attributes of the super-diffusive process, whereas it was sub-diffusive on the graphene surface.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Wettability effect on nanoconfined water flow

Abstract: Understanding and controlling the flow of water confined in nanopores has tremendous implications in theoretical studies and industrial applications. Here, we propose a simple model for the confined water flow based on the concept of effective slip, which is a linear sum of true slip, depending on a contact angle, and apparent slip, caused by a spatial variation of the confined water viscosity as a function of wettability as well as the nanopore dimension. Results from this model show that the flow capacity of confined water is 10 −1 ∼10 7 times that calculated by the no-slip Hagen–Poiseuille equation for nanopores with various contact angles and dimensions, in agreement with the majority of 53 different study cases from the literature. This work further sheds light on a controversy over an increase or decrease in flow capacity from molecular dynamics simulations and experiments.

Single-Layer Behavior and Its Breakdown in Twisted Graphene Layers

Abstract: We report high magnetic field scanning tunneling microscopy and Landau level spectroscopy of twisted graphene layers grown by chemical vapor deposition. For twist angles exceeding ~3° the low energy carriers exhibit Landau level spectra characteristic of massless Dirac fermions. Above 20° the layers effectively decouple and the electronic properties are indistinguishable from those in single-layer graphene, while for smaller angles we observe a slowdown of the carrier velocity which is strongly angle dependent. At the smallest angles the spectra are dominated by twist-induced van Hove singularities and the Dirac fermions eventually become localized. An unexpected electron-hole asymmetry is observed which is substantially larger than the asymmetry in either single or untwisted bilayer graphene.

Driven Polymer Translocation Through a Narrow Pore

Abstract: Motivated by experiments in which a polynucleotide is driven through a proteinaceous pore by an electric field, we study the diffusive motion of a polymer threaded through a narrow channel with which it may have strong interactions. We show that there is a range of polymer lengths in which the system is approximately translationally invariant, and we develop a coarse-grained description of this regime. From this description, general features of the distribution of times for the polymer to pass through the pore may be deduced. We also introduce a more microscopic model. This model provides a physically reasonable scenario in which, as in experiments, the polymer's speed depends sensitively on its chemical composition, and even on its orientation in the channel. Finally, we point out that the experimental distribution of times for the polymer to pass through the pore is much broader than expected from simple estimates, and speculate on why this might be.