Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A20: Focus Session: Microfluidics and Nanofluidics I - The Physics of Confined Fluids |
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Sponsoring Units: DPOLY DFD GSNP Chair: German Drazer, Rutgers University Room: 405 |
Monday, March 3, 2014 8:00AM - 8:12AM |
A20.00001: Processing Cyclic Peptide-polymer Conjugates in Block Copolymer Thin Films for Sub-nm Porous Membranes Chen Zhang, Ting Xu Porous thin films containing subnanometer channels oriented normal to the surface exhibit unique transport and separation properties and can serve as selective membranes for separation. Inspired by natural protein channels, we have developed an approach using cyclic peptide nanotubes (CPNs) embedded in polymeric matrix to mimic the transport of natural channels. The co-assembly of polymer-covered CPNs in a block copolymer (BCP) thin film requires the synchronization of two self-assembly processes, namely the microphase separation of BCP and the nanotube growth of CP-polymer conjugates. We systematically investigated the co-assembly of isolated CP-poly(ethylene glycol) (CP-PEG) conjugates and polystyrene-b-poly (methyl methacrylate) (PS-b-PMMA) in thin films as a function of CP-PEG loading (f$_{CP-PEG}$) and solvent-polymer interactions. We find that there is a strong dependence of the co-assembly process on f$_{CP-PEG}$ due to thermodynamic limit of incorporating one CPN in one PMMA microdomain, as well as the kinetic pathway in which favorable PEG-solvent interaction helps to disperse CPNs and thus lowers the activation energy barrier of the system. This study presents critical insights in guided assemblies of functional building blocks within nanoscopic frameworks. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A20.00002: Tunable water desalination across Graphene Oxide Frameworks Adrien Nicolai, Vincent Meunier ``Water, water, everywhere, nor any drop to drink.'' wrote Samuel Taylor Coleridge in 1798. Today's scientific advances in water desalination promise to change the second part of the sentence into ``and every drop to drink,'' by transforming sea water into fresh water and quench the thirst of 1.2B people facing shortages of water. To achieve this, the design of nanoporous materials with high water permeability and coupled with high salt rejection capacity is crucial. Graphene Oxide Frameworks (GOF) materials are a class of porous materials consisting of layers of graphene oxide sheets interconnected by linear boronic acid linkers. Water desalination across GOF is studied using classical Molecular Dynamics simulations. We used quantum mechanically obtained boron-related force field parameters to study the diffusion of water molecules inside bulk GOF. Properties, such as the self-diffusion coefficient of water molecules increases linearly with linker concentration $n$. Further, the desalination performance of GOF membranes reveals that the water permeability of GOF is several orders of magnitude higher than conventional membranes and an high water permeability can be coupled with a 100{\%} efficiency of salt rejection by choosing the appropriate concentration $n$ and thickness $h$. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A20.00003: Quantized Water Transport: Ideal Desalination through Graphyne-4 Membrane Chongqin Zhu, Hui Li, Xiao Cheng Zeng, E.G. Wang, Sheng Meng The shortage of clean and fresh water is one of most pervasive problems afflicting human being's life in the world. Desalination is one viable solution to produce clean water, since 98{\%} of the available water in the form of salty water. Using molecular dynamics simulations, we demonstrate that graphyne sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. In addition, Graphyne sheets also are mechanically robust with high tolerance to deformation. Especially, $\gamma $-graphyne-4 has the best performance with 100{\%} slat rejection and an unprecedented water permeability of $\sim$ 13L/cm2/day/MPa. 3 orders of magnitude higher than prevailing commercial membranes based on reverse osmosis, and $\sim$ 10 times higher than the state-of-the-art nanoporous graphene. Strikingly, water permeability across graphyne exhibits unexpected nonlinear dependence on the pore area. This counter-intuitive behavior is attributed to the quantized nature of water flow at the nanoscale, which has wide implications in controlling nanoscale water transport and designing highly effective membrane. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A20.00004: Electro-Induced Dewetting and Concomitant Ionic Current Avalanche in Nanopores Xikai Jiang, Jingsong Huang, Bobby Sumpter, Rui Qiao Electrically driven ionic transport of room-temperature ionic liquids (RTILs) through nanopores is studied by molecular dynamics simulations. It is observed that a gradual dewetting transition occurs in nanopores originally wetted by RTILs if the applied voltage is increased, and meanwhile the ionic current through the system increases sharply. These phenomena originate from the solvent-free nature of RTILs in which the ions' mobility increases sharply when their concentration decreases and are contrary to the transport of conventional electrolytes through nanopores. The results also show that the amplification of ionic current is possible by manipulating the properties of the nanopore and RTILs and is especially pronounced in charged nanopores. The results highlight the unique physics of nonequilibrium transport of RTILs in confined geometries and point to potential experimental approaches for manipulating ionic transport in nanopores, which can benefit diverse techniques including nanofluidic circuitry and nanopore analytics. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A20.00005: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 9:00AM - 9:12AM |
A20.00006: Green-Kubo relation and hydrodynamic tails of friction at solid/liquid interfaces Kai Huang, Izabela Szlufarska Understanding boundary conditions at the liquid/solid (L/S) interface has been a subject of many scientific investigations. It also has important implications for design of materials for such applications as micro-/nanofluidics. Design of functionalized surfaces and interfaces with optimized friction and slip properties is hindered by existing challenges in measuring these properties either in experiments or in simulations. Here, we have developed a Green-Kubo (GK) relation that enables accurate calculations of friction at L/S interfaces directly from equilibrium molecular dynamics (EMD) simulations and that provides a pathway to bypass the time scale limitations of typical non-equilibrium molecular dynamics (NEMD) simulations. The theory has been validated for a number of different of interfaces and it is demonstrated that the L/S slip is an intrinsic property of an interface. Because of the high numerical efficiency of our method, it opens up new opportunities for computational design of functionalized surfaces for L/S applications. Details of the friction correlation function also permit a full analysis of the time-dependent and frequency-dependent friction in a dynamic system. At the hydrodynamic time scale, the memory kernel of the friction coefficient exhibits an algebraic decay, which leads to a -3/2 power long time tail in the velocity autocorrelation function of fluid particles near a wall. This behavior differs from the predictions of previous theoretical and simulation results, which employed no-slip boundary conditions. Our findings provide new insights into understanding the dynamics of interfacial colloids and nano-particle flow in liquids. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A20.00007: The interplay between apparent viscosity, wettability, and slip in nanoconfined water Elisa Riedo, Deborah Ortiz, Hsiang-Chih Chiu, Suenne Kim Understanding and manipulating fluids at the nanoscale is a matter of growing scientific and technological interest. Here we show that the viscous shear forces in nanoconfined water can be orders of magnitudes larger than in bulk water if the confining surfaces are hydrophilic, whereas they greatly decrease when the surfaces are increasingly hydrophobic. This decrease of viscous forces is quantitatively explained with a simple model that includes the slip velocity at the water surface interface. The same effect is observed in the energy dissipated by a tip vibrating in water perpendicularly to a surface. Comparison of the experimental data with the model shows that interfacial viscous forces and compressive dissipation in nanoconfined water can decrease up to two orders of magnitude due to slippage. These results offer a new understanding of interfacial fluids, which can be used to control flow at the nanoscale. NATURE COMMUNICATIONS (2013) \textbar DOI: 10.1038/ncomms3482 [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A20.00008: Unsteady electrokinetic microfluidics with hydrodynamic slippage effect Myung-Suk Chun, Yoona Yang The nature of low Reynolds number flows and confined spaces inherent in microscale or extended nanoscale channels imply the significant influence of solid wall boundaries. We investigate the unsteady pulsatile electrokinetic flows by extending our previous simulations concerning electrokinetic microfluidics. The body force originated from between the nonlinear Poisson--Boltzmann field and the flow-induced electric field is employed in Navier--Stokes equation, and Nernst--Planck equation in connection with the net current conservation is further coupled. Our explicit model allows one to quantify the effects of time delay, oscillating frequency, and conductance of the Stern layer, considering the fluid slippage at hydrophobic surfaces and the electric double layer interaction. This presentation reports new results regarding the implication of pressure pulsations toward realizing mechanical to electrical energy transfer with high conversion efficiency. A combined role of the fluid slippage and conductance of channel wall is examined to obtain possible enhancements of streamwise velocity and streaming potential, with taking advantage of pulsating pressure field. Note that our framework can serve as a useful basis for micro/nanofluidics design. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A20.00009: Effects of ionic strength on nonlinear electrophoretic mobility of fd virus in solid-state nanopore Wang Miao, Liping Liu, Anna Lu, Hongwen Wu, Prerna Sharma, Zvonimir Dogic, Xinsheng Ling We report an experimental study of electrophoretic mobility of rod-like \textit{fd} virus in solid-state nanopores. It is found that the velocity $v$ is a nonlinear function of the electric filed E, and can be described by $v = \mu ^{\mathrm{(1)}}$E $+ \mu^{(3)}$E$^{3}$. In addition to the linear Smoluchowski term, there is a second term with cubic dependence on E which has been described as a Stotz-Wien effect caused by the polarization of the Debye counter ion cloud. Here we report a study of this nonlinear electrophoresis effect under different salt concentrations. We found that at low ionic strength, the cubic mobility term becomes less pronounced. The origin of this observation will be discussed. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A20.00010: Water confinement in three different substances Sahar Mirshamsi, Hai-Ping Cheng Confined water in nano-pores of different materials appears in geological, physical, industrial and biological systems. Confined water demonstrates significantly different behavior than bulk water, which has motivated researchers to study the effects of confinement on structural and dynamical properties of water. We study the confinement of water in silica, carbon nanotubes, and gold nano-pores and compare the effect of these different materials on the properties of water. Compared to bulk water viscosity, we find that the viscosity of water increases in silica nano-pores but decreases when confined in carbon nanotubes. Increasing water density inside the silica nano-pores further increases water viscosity. Finally, we discuss how the diffusion coefficient of water and its density profile changes due to confinement. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A20.00011: On the Strong Localization and Rapid Time Scales of Superheating and Vapor Nucleation in Nanopores Edlyn Levine, Gaku Nagashima, David Hoogerheide, Michael Burns, Jene Golovchenko Extreme localized superheating and homogeneous vapor nucleation have recently been demonstrated in thin, solid state nanopores. Electrolytic solution present within the pore is superheated to well above its boiling point by ohmic heating from ionic current driven through the pore. Continued heating of the metastable liquid can eventually lead to explosive nucleation of a vapor bubble in the pore. Here we report on the consistency of theoretical predictions with experimental results concerning the thermal, spatial and temporal scales involved. Calculations demonstrate that extreme spatial localization of the temperature distribution is achieved in the nanopore heating experiments. Our results indicate that the liquid at the center of the pore can be rapidly superheated to several hundred degrees kelvin above the boiling point within tens of microseconds. The temperature within the pore is shown to increase by about 100K from the edge to the center of a 60nm radius pore. This degree of localization strongly indicates that vapor nucleation is homogeneous due to the high temperature dependence of the kinetic nucleation rate. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A20.00012: Observation of Superheating and Single Bubble Nucleation in Thin, Solid State Nanopores Gaku Nagashima, Edlyn Levine, David Hoogerheide, Michael Burns, Jene Golovchenko We demonstrate localized and extreme superheating, and homogeneous single bubble nucleation in a nanopore in a thin silicon nitride membrane immersed in an electrolyte solution. The high temperatures are achieved by Joule heating from a highly focused ionic current induced to flow through the pore by a modest voltage bias applied across the membrane. The superheating of the electrolyte is observed by monitoring a change in electrical conductance of the system which increases with temperature. The high temperatures can lead to transient explosive vapor bubble nucleation in the pore. The nucleation event is detected both electronically and optically. The bubble nucleation event is highly deterministic and reproducible. Optical transmission experiments indicate that the bubble nucleation is homogeneous, occurring near the pore center. These phenomena have been observed in pores down to 60 nm in radius. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A20.00013: Escape of water molecular from Carbon Nanotubes Jiaxi Li, Wenfeng Li, Jianwei Zhang Understanding and controlling the transport of water molecules through nanopores have attracted great interest due to potential applications for designing novel nanofluidic devices, machines and sensors. In this work, we theoretically investigate the effects of an external nonuniform electric field on the escape of water molecules through single-walled carbon nanotubes (SWNTs) by using of molecular dynamics (MD) simulations. When polar water molecules are placed in the gradient electric field, the electric force is experienced that can drive the water molecules. Molecular dynamics simulations show that the escape probability of water obeys the Boltzmann distribution. Our results show that energy barrier delta E is independent of temperature which indicates that it is a single-barrier system. From the MD results statistics, the key parameters could be determined such that the relationship between energy barrier delta E and diameter of SWNTs and nozzle distance of the charge r would be revealed that could deepen our current theoretical understanding on transport of water molecular inside SWNTs with the nonuniform electric field. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A20.00014: Multiscale transport concept for nanoporous materials incorporating microstructure and interface properties at nanoconfinement Arturas Ziemys, Miljan Milosevic, Milos Kojic Transport theories based on the continuum hypothesis may not be appropriate, especially in case of diffusion, due to surface effects at nanoscale. Our computational and experimental findings, supported by studies elsewhere, revealed the necessity to account for interface and confinement effects. Thermodynamic aspects were established that might be responsible for reduced diffusivity at interface; more specifically -- due to entropy-enthalpy compensation and cage-breaking processes. The thickness of liquid with altered diffusivity at solid-liquid interface depends on material and diffusing molecule nature and properties. We have developed a concept and computational model to bridge those molecular effects within nanoconfinement with transport at macro scale for systems where interface dominates over other properties (e.g. nanochannels, nanopores, polymers). The concept was validated against molecular transport through nanochannels and polymers. Novel parameters are introduced that determine diffusion regime and kinetics within the nanoscale confined fluids. New diffusion transport characteristics are established when nanochannel confining dimension approaches sizes of diffusing molecules, determining bounds of the non-Fickian transport regimes. The developed multiscale method could be used to study material transport and optimize nanoporous materials for biomedical and industrial applications. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A20.00015: Continuum-based multiscale approach to predict the structure and theromdynamic properties of confined fluids S.Y. Mashayak, N.R. Aluru We present a continuum-based theory to predict the structure and thermodynamic properties of fluids confined in multiple length-scales, ranging from few Angstroms to micron length channels. In this work, we introduce a free energy functional for classical DFT (cDFT) based on the empirical potential-based quasi-continuum theory (EQT). EQT is a simple and fast approach to predict the inhomogeneous density and potential profiles of confined fluids, and the results from EQT compare well with MD simulations. Using the density and potential profiles from EQT, we construct a grand potential functional for cDFT. EQT-cDFT based grand potential can be used to predict various thermodynamic properties of confined fluids. Here, we demonstrate applicability of the EQT-cDFT approach by simulating water confined inside slit-like channels of graphene at various thermodynamic states and channel widths. Using EQT-cDFT approach, we calculate the structure and thermodynamic properties of confined water, such as density profiles, adsorption, PMF profiles, surface tension, local pressure profiles, and solvation forces. It is found that the EQT-cDFT results compare well with the reference water MD simulation results. [Preview Abstract] |
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