Showing papers on "Nanofluidics published in 2013"

Giant osmotic energy conversion measured in a single transmembrane boron nitride nanotube

Abstract: New models of fluid transport are expected to emerge from the confinement of liquids at the nanoscale1, 2, with potential applications in ultrafiltration, desalination and energy conversion3. Nevertheless, advancing our fundamental understanding of fluid transport on the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores. A major challenge for nanofluidics thus lies in building distinct and well-controlled nanochannels, amenable to the systematic exploration of their properties. Here we describe the fabrication and use of a hierarchical nanofluidic device made of a boron nitride nanotube that pierces an ultrathin membrane and connects two fluid reservoirs. Such a transmembrane geometry allows the detailed study of fluidic transport through a single nanotube under diverse forces, including electric fields, pressure drops and chemical gradients. Using this device, we discover very large, osmotically induced electric currents generated by salinity gradients, exceeding by two orders of magnitude their pressure-driven counterpart. We show that this result originates in the anomalously high surface charge carried by the nanotube's internal surface in water at large pH, which we independently quantify in conductance measurements. The nano-assembly route using nanostructures as building blocks opens the way to studying fluid, ionic and molecule transport on the nanoscale, and may lead to biomimetic functionalities. Our results furthermore suggest that boron nitride nanotubes could be used as membranes for osmotic power harvesting under salinity gradients.

Lattice Boltzmann Method for Simulation of Shale Gas Transport in Kerogen

Abstract: Fluid mechanics of natural gas in organic-rich shale involves nanoscale phenomena that could lead to potential non-Darcy effects during gas production. In general, these are low-Reynoldsnumber and noncontinuum effects and, more importantly, porewall-dominated multiscale effects. In this study, we introduce a new lattice Boltzmann method (LBM) to investigate these effects numerically in simple pore geometries. The standard method was developed in the 1980s to overcome the weaknesses of lattice gas cellular automata and has emerged recently as a powerful tool to solve fluid dynamics problems, in particular in the areas of microand nanofluidics. The new approach takes into account molecularlevel interactions by use of adsorptive/cohesive forces among the fluid particles and defining a Langmuir-slip boundary condition at the organic pore walls. The model allows us to partition mass transport by the walls into two components: slippage of free gas molecules and hopping (or surface transport) of the adsorbed gas molecules. By use of the standard 2D D2Q9 lattice, lowReynolds-number gas dynamics is simulated in a 100-nm model organic capillary and later in a bundle of smaller-sized organic nanotubes. The results point to the existence of a critical Knudsennumber value for the onset of laminar gas flow under typical shale-gas-reservoir pressure conditions. Beyond this number, the predicted velocity profile shows that the mechanisms of slippage and surface transport could lead to molecular streaming by the pore walls, which enhances the gas transport in the organic nanopores. The work is important for development of new-generation shale-gas-reservoir flow simulators, and it can be used in the laboratory for organic-rich-shale characterization.

Transport Rectification in Nanopores with Outer Membranes Modified with Surface Charges and Polyelectrolytes

Abstract: This work reports a comprehensive theoretical study of the transport-rectification properties of cylindrical nanopores with neutral inner walls and chemically modified outer membrane. The chemical species on the two outer sides of the membrane have charges of opposite sign and can be either surface-confined species (i.e., surface charges) or polyelectrolyte brushes. The advantage of this design over other types of rectifying nanopores is that it requires controlling the composition of the outer walls of the pore (which are easy to access) rather than the inner walls, thus simplifying the fabrication process. Ion-current rectification in nanopores with charged outer walls is ascribed to applied-potential-induced changes in the ionic concentration within the pore. The rectification efficiency is studied as a function of pore length, radius, surface charge and bulk electrolyte concentration. An analytical model is derived for the case of surface-confined charges that predicts the current–potential curves in ...

Nanoscale Liquid Interfaces : Wetting, Patterning and Force Microscopy at the Molecular Scale

Abstract: Interfaces and Nanowetting Liquid structuration at solid-liquid interface: S. Jarvis Wetting, roughness and hydrodynamic slip: O. Vinogradova Wetting phenomena at nanometer scale: S. Dietrich, M. Rauscher M. Napiorkowski Droplets morphology at nanometer scale: A. Checco Nanomeniscus mechanical properties: JP Aime, R. Boisgard T. Ondarcuhu Liquid films in total wetting and liquid crystals: AM Cazabat Stability of thin liquid films: G. Reiter Surface nanobubbles: D. Lohse Wetting in/of nanotubes and channels: D. Mattia Nanofluidics: N. Tas Applications in Nanopatterning Manipulation of liquid nanodrops: T. Ondarcuhu, E. Dujardin Capillary assembly of nanoparticles: L. Malaquin Unconventional wet lithography: F. Biscarini Meniscus alignment of DNA and carbon nanotubes: C. Khripin, M. Zheng, A. Jagota Nanostructuration through nanomeniscus electrochemistry: R. Garcia. AFM in liquids, molecular resolution on complex biosystems Theory: AFM dynamic in liquid Cantilever oscillating properties in liquid. J.E. Sader Cantilever oscillating properties at proximity of a surface Hydrodynamic interaction R. Boisgard, JP Aime High harmonic imaging: R. Garcia Imaging physical properties of complex systems: A. Raman Experiences: High resolution, proteins structures and membranes AFM Molecular resolution on native membrane: S. Scheuring AFM Molecular resolution on self assembled and biological system: T. Fukuma High Speed AFM: T. Ando Evanescent waves: particulates absorbates: D. Johannsmann

Insights into the "free state" enzyme reaction kinetics in nanoconfinement.

Abstract: The investigation of enzyme reaction kinetics in nanoconfined spaces mimicking the conditions in living systems is of great significance. Here, a nanofluidics chip integrated with an electrochemical detector has been designed for studying “free state” enzyme reaction kinetics in nanoconfinement. The nanofluidics chip is fabricated using the UV-ablation technique developed in our group. The enzyme and substrate solutions are simultaneously supplied from two single streams into a nanochannel through a Y-shaped junction. The laminar flow forms in the front of the nanochannel, then the two liquids fully mix at their downstream where a homogeneous enzyme reaction occurs. The “free state” enzyme reaction kinetics in nanoconfinement can thus be investigated in this laminar flow based nanofluidics device. For demonstration, glucose oxidase (GOx) is chosen as the model enzyme, which catalyzes the oxidation of beta-D-glucose. The reaction product hydrogen peroxide (H2O2) can be electrochemically detected by a microelectrode aligning to the end of nanochannel. The steady-state electrochemical current responding to various glucose concentrations is used to evaluate the activity of the “free state” GOx under nanoconfinement conditions. The effect of liquid flow rate, enzyme concentration, and nanoconfinement on reaction kinetics has been studied in detail. Results show that the “free state” GOx activity increases significantly compared to the immobilized enzyme and bath system, and the GOx reaction rate in the nanochannel is two-fold faster than that in bulk solution, demonstrating the importance of “free state” and spatial confinement for the enzyme reaction kinetics. The present approach provides an effective method for exploiting the “free state” enzyme activity in nanospatial confinement.

A DLVO model for catalyst motion in metal-assisted chemical etching based upon controlled out-of-plane rotational etching and force-displacement measurements

Abstract: Metal-assisted Chemical Etching of silicon has recently emerged as a powerful technique to fabricate 1D, 2D, and 3D nanostructures in silicon with high feature fidelity. This work demonstrates that out-of-plane rotational catalysts utilizing polymer pinning structures can be designed with excellent control over rotation angle. A plastic deformation model was developed establishing that the catalyst is driven into the silicon substrate with a minimum pressure differential across the catalyst thickness of 0.4–0.6 MPa. Force–displacement curves were gathered between an Au tip and Si or SiO2 substrates under acidic conditions to show that Derjaguin and Landau, Verwey and Overbeek (DLVO) based forces are capable of providing restorative forces on the order of 0.2–0.3 nN with a calculated 11–18 MPa pressure differential across the catalyst. This work illustrates that out-of-plane rotational structures can be designed with controllable rotation and also suggests a new model for the driving force for catalyst motion based on DLVO theory. This process enables the facile fabrication of vertically aligned thin-film metallic structures and scalloped nanostructures in silicon for applications in 3D micro/nano-electromechanical systems, photonic devices, nanofluidics, etc.

Nanofluidics for Giant Power Harvesting

Abstract: Nanochannels for power generation: The confinement of fluid motion in a single boron nitride nanotube can provide an efficient means of power harvesting owing to the osmotically driven streaming current under a salt concentration difference (see picture) Devices based on this principle may open a new avenue in the exploration for new sources of renewable energy

Multiwalled Carbon Nanotube/Water Nanofluid or Helical Coiling Technique, Which of Them Is More Effective?

Abstract: A set of experiments were performed to investigate the effect of two different techniques of heat transfer enhancement: nanofluidics and helical coiling. The convection heat transfer behavior of multiwalled carbon nanotube (MWCNT)/water nanofluids through helical coiled tubes with different geometries was reported. Solutions of 0.1, 0.3, and 0.5% particle weight concentration of MWCNT in distilled water were prepared using a two-step method, and the effects of a wide range of different parameters such as Reynolds and Helical numbers, geometrical parameters of the coils, and nanofluid weight fractions were studied. It was observed that by increasing the Reynolds number or weight concentration of nanofluid, the Nusselt number increases considerably. The maximum thermal performance factor at 4.24 was achieved in this study. Also, the helical coiling technique showed better performance than nanofluidics in these experiments. In addition, the empirical correlations were developed for Nusselt number and pressur...

Numerical simulation of proton distribution with electric double layer in extended nanospaces.

Abstract: Understanding the properties of liquid confined in extended nanospaces (10–1000 nm) is crucial for nanofluidics. Because of the confinement and surface effects, water may have specific structures and reveals unique physicochemical properties. Recently, our group has developed a super resolution laser-induced fluorescence (LIF) technique to visualize proton distribution with the electrical double layer (EDL) in a fused-silica extended nanochannel (Kazoe, Y.; Mawatari, K.; Sugii, Y.; Kitamori, T. Anal. Chem.2011, 83, 8152). In this study, based on the coupling of the Poisson–Boltzmann theory and site-dissociation model, the effect of specific water properties in an extended nanochannel on formation of EDL was investigated by comparison of numerical results with our previous experimental results. The numerical results of the proton distribution with a lower dielectric constant of approximately 17 were shown to be in good agreement with our experimental results, which confirms our previous observation showing...

Quantitative probing of surface charges at dielectric–electrolyte interfaces

Abstract: The intrinsic charging status at the dielectric–electrolyte interface (DEI) plays a critical role for electrofluidic gating in microfluidics and nanofluidics, which offers opportunities for integration of wet ionics with dry electronics. A convenient approach to quantitatively probe the surface charges at the DEI for material pre-selection purpose has been lacking so far. We report here a low-cost, off-chip extended gate field effect transistor configuration for direct electrostatic probing the charging status at the DEI. Capacitive coupling between the surface charges and the floating extended gate is utilized for signal transducing. The relationship between the surface charge density and the experimentally accessible quantities is given by device modeling. The multiplexing ability makes measuring a local instead of a globally averaged surface charge possible.

Conduction of water molecules through graphene bilayer

Abstract: Water conduction across a two-dimensional (2D) graphene bilayer was investigated through molecular dynamic simulations. Different from one-dimensional (1D) nanofluidics in carbon nanotubes (CNTs) where CNT chirality has only a secondary effect, when the bilayer structure is changed from the turbostratic state to the commensurate state, the water infiltration pressure decreases considerably, as energy valleys are formed. Compared with the 1D nanofludics in a CNT, the infiltration pressure of 2D nanofluidics in a graphene bilayer tends to be much lower, primarily because of the additional degree of freedom of water molecular motion.

Phase diagrams of confined solutions of dimyristoylphosphatidylcholine (DMPC) lipid and cholesterol in nanotubes

Abstract: We have studied equilibrium morphologies of dimyristoylphosphatidylcholine lipid solution and cholesterol solution confined to nanotubes using dissipative particle dynamics (DPD) simulations. Phase diagrams regarding monomer concentration c versus radius of nanotube r for both solutions are attained. Three types of the inner surface of nanotubes, namely hydrophobic, hydrophilic, and hydroneutral are considered in the DPD simulations. A number of phases and molecular assemblies for the confined solutions are revealed, among others, such as the spiral wetting and bilayer helix. Several phases and assemblies have not been reported in the literature, and some are non-existence in bulk solutions. The ability to control the morphologies and self-assemblies within nanoscale confinement can be exploited for patterning interior surface of nanochannels for application in nanofluidics and nanomedical devices.

Friction between solids and adsorbed fluids is spatially distributed at the nanoscale.

Abstract: The widespread developments in the use of nanomaterials in catalysis, adsorption, and nanofluidics present significant new challenges in achieving optimal adsorbed fluid flow characteristics. Here we demonstrate, using molecular dynamics simulations of nanoconfined fluids, that at nanoscales, fluid-solid friction is not restricted to a sharp interface as is commonly assumed; instead it is distributed over the whole adsorbed fluid phase, and is strongest in an interfacial region that is not negligible in comparison to the system size. Our simulations yield position-dependent dynamical fluid-solid friction coefficients, and lead to a modification of conventional hydrodynamics, incorporating distributed momentum loss in the fluid due to fluid-solid interaction. The results demonstrate that the usual concepts of slip length or interfacial friction coefficient are meaningful only for uniform fluids, and lose their significance for adsorbates in nanospaces, which are intrinsically inhomogeneous. We show that static friction coefficients, based on equilibrium density distributions, follow the same spatial dependence as the dynamical coefficients. These results open up possibilities for tailoring nanomaterials and surfaces to engineer low friction pathways for adsorbed fluid flow by tuning the potential energy landscape.

Fast Ion Transport and Phase Separation in a Mechanically Driven Flow of Electrolytes through Tortuous Sub‐Nanometer Nanochannels

Abstract: Both nanostructured materials and nanotubes hold tremendous promises for separation and purification applications, such as water desalination. By using molecular dynamics, herein, we compare the transport of aqueous electrolyte solutions through a Y-zeolite, which features interconnected, tortuous sub-nanometer nanopores, and a model silica nanotube, which has the same composition but is straight and has much lower surface complexity. In the Y-zeolite, ion transport is faster than the transport of water molecules, thus leading to a phenomenon of phase separation in which a gradient of salt concentration is generated along the flow direction. However, similar transport characteristics and phase separation are not found in the model silica nanotube. Detailed analysis suggests that, in nanochannels with complicated geometries, such as those of the Y-zeolite, the structural and flow characteristics of confined nanofluids are highly coupled, thus influencing the transport of ions and solvents and causing the phenomenon of phase separation.

Fluid Dynamics and Electrical Detection of λDNA in Electrode-Embedded Nanochannels*

Abstract: In the present study, we address theoretical approaches for the experimental results to investigate the flow dynamics of λDNA through a nanochannel in which two nanoelectrodes are integrated. In order to elucidate the relationship between the longitudinal ionic current and the electrophoresis of λDNA in the specific micro/nanofluidics, we develop a theoretical model for the macroscopic fluid dynamics in a Lagrangian framework. The measured current change associated with a single molecule translocation through the channel is explained by the principle of the Coulter counter that allowed to predict the conformation of λDNA. We also analyze the local velocity of λDNA passing through a nanoscaled confined channel. A result from the model is in considerable agreement with the experimental observations for the electrophoretic flow of λDNA. The basic knowledge obtained here may be useful in developing electrical methods for controlling the electrophoretic velocity of single-molecule DNA for realizing the nanopore sequencer.

Nanofluidic delivery of molecules: integrated plasmonic sensing with nanoholes

Abstract: This article presents the detailed analysis of nanofluidics as a mechanism for the delivery of residual vapour/gas molecules in the air to nanoscale apertures in a porous metal or composite membrane with surface plasmons producing field hotspots near the apertures. Finite element analysis is used to calculate and to optimise the flow rate of air through apertures of different diameters with partial slip boundary conditions. Comparison of the calculated nanofluidic delivery rates with those due to diffusion of the tested residual molecules in the air is also conducted. Typical structural and material parameters at which either of these delivery mechanisms appears dominant are determined. Ways for further optimisation and enhancement of the operational capabilities of the described structures as nano-optical sensors and measurement techniques are also identified and discussed.

Non-Equilibrium Topographies: Surface Tension Driven Flows Reveal Polymer Properties at the Nanoscale

Abstract: In this thesis, experiments designed to elucidate properties of polymer molecules in confinement are described. Here, confinement means that some dimension of the space in which the polymers are placed in is comparable to the size of the molecules themselves. This smallest dimension is typically a few to ten times the molecular size, which for the polymer molecules described here is normally in the range of tens to hundreds of nanometres. In most cases, the experiments were designed around the concept that nature tends to minimize the surface area of a liquid. The most important results are those concerned with the levelling of a stepped film’s height profile. Films are prepared such that their height profiles are well described by a Heaviside step function and to a good approximation, they are invariant in one dimension. The temporal dependence of the levelling gives rheological information about the molecules making up the stepped films. For the range of heights that is much larger that the typical size of molecules making up the film, we use classical hydrodynamics to model the flows in these stepped films. Having measured the temporal and geometric dependence of the energy dissipation in time, we find that the hydrodynamic models are in excellent agreement. Apart from the liquid state evolution of stepped films this thesis also contains material concerned with non-equilibrium properties of thin polymer films. A common method of preparing films is spin coating. This violent process can leave polymer chains in non-equilibrium configurations. We have made measurements addressing the questions: what are the conformations of as-cast, spin coated polymer chains? Furthermore, if we anneal as-cast films, how long does it take for the polymer chains to relax to an equilibrium? We found that polymer chains are strongly stretched by the spin coating process, and that it takes about one bulk polymer relaxation time to lose memory of the preparation procedures for our films prepared on mica. In related experiments, we confined molecules to films thinner than a typical length scale for the polymers, then made bilayers out of such films. This creates what we refer to as an entropic interface, across which polymer chains suffer a reduction in entropy due to their inability to explore some conformations. We find that this entropic interface heals on a time scale that is much faster than one bulk polymer relaxation time.

Laser induced damage in porous glass - a pathway to 3D fabrication of micro-/nanofluidics

Abstract: We report on controllable production of nanostructures embedded in a porous glass by femtosecond laser direct writing. We show that a hollow nano-void with a lateral size of ~40 nm and an axial size of ~1500 nm can be achieved by manipulating the peak intensity and polarization of the writing laser beam. The single nano-voids can be smoothly connected into a continuous nanochannel by water-assisted femtosecond laser direct writing. With this technique, integrated micro-nanofluidic systems have been achieved by simultaneously writing micro- and nanofluidic channels arranged into various 3D configurations in glass substrates. The fabricated micro- and nanofluidic systems have been applied to demonstrate DNA analysis, e. g., stretching of DNA molecules. Our technique offers new opportunities to develop novel 3D micro-nanofluidic systems for a variety of lab-on-a-chip applications.

Fabrication of functional micro- and nanofluidics embedded in glass using femtosecond laser microprocessing

Abstract: We resolve long-standing difficulties in fabrication of large-scale 3D microfluidics and demonstrate fabrication of nanochannels of a width of ~40 nm (~1/20 of writing beam wavelength) in glass with femtosecond laser pulses.

A low-cost, high-efficiency and high-output-power nanofluidic energy harvester

Abstract: Nanofluidics is attracting great attention lately as a novel energy harvesting strategy. This study presents nanoparticle crystal, which equivalently forms a network of nanochannels, as the functional nanofluidics structure for energy harvesting from concentration gradient by reverse electrodialysis. Ion concentration gradient was applied across a 40×40 μm2 micropore containing self-assembled nanoparticle crystal with particle diameter of 100/210/500 nm to harvest energy from the Gibbs free energy. The maximum single-pore output power was 1.17 + 0.09 nW (power density 2.82±0.22 W m-2), and the maximum efficiency was 42.3 2±1.84% in this work. The present work might be an alternative and promising approach for developing self-powered micro/nanofluidic systems.

Al 2 O 3 /W hetero-structured nanopore membranes: From native to tunable nanofluidic diodes

Abstract: We present here Al2O3/W hetero-structured nanopore membranes which function as native and electrical field tunable nanofluidic diodes. A typical membrane is 100×100 μm2 in size with pore density of ~20/μm2. The nanopores are 26 nm in diameter and 400 nm in length. Owing to the opposite surface charge states of Al2O3 (positive) and W (negative with native oxide), the membrane exhibits clear rectification of ion current in electrolyte solutions. After thermal heating at 350°C for 2 hrs, approximately 10 nm WOx grows on the surface of W, forming a conformal and dense dielectric layer. The W layer allows the application of an electrical field to further modulate the ionic transport through the nanopores with low gate potentials and ultra low gate leakage current. We have demonstrated the control of rectifying factor from 2 to 11. Our experimental findings have a valuable potential for controllable high throughput molecular separation and chemical processors.

Scalable nanoparticle synthesis in liquids using laser induced plasmas at phase boundaries

Abstract: Summary form only given. Nanofluids are a new class of fluids engineered by dispersing nanoparticles of size less than 100 nm in base fluids. Nanofluids have been found to possess highly enhanced physical, chemical, thermal and transport properties compared to the base fluids, which demonstrates the great potential for combustion, liquid propellant, microelectronics, optical and thermal emission devices, energy storage, heat exchanger-cooling systems, hydrogen generation, nuclear safety, and in underwater and military applications. In this experimental investigation the feasibility results of producing scalable enhanced nanoparticles in liquids laser induced plasmas at liquid-metal (Al) phase boundaries using our laser plasma facility will be presented. The formation and dynamics of laser plasmas and shock waves at liquid-metal phase boundary was affected by the conditions of strong liquid confinement. The plasma and shock spatio-temporal dynamics and velocities varied for different laser transfer matrix and experimental conditions. The plasma electron density of the laser induced plasma at liquid-Al phase boundaries was measured using a two-wavelength laser interferometry. In order to better understand the relationship and synthesis of effective nanofluids the preliminary results of correlating the plasma characteristics with the nanoparticles size and size distribution will be presented.

Temperature-induced nanochannel array synthesis in microchannels

Abstract: An novel on-chip synthesis technique for nanochannel arrays inside microfluidic channels is reported. The microfluidic channels are constructed with etched silicon trenches and a polydimethylsiloxane (PDMS) slab. These silicon microchannels provide a confined environment for highly oriented nanostructure synthesis. Triblock copolymer (SBA-15) is self-assembled inside the microchannel array as template for silica precursor polymerization under an induced temperature gradient. The temperature gradient is maintained by thermoelectric pads and used to control the direction and rate of organic solvent evaporation. This evaporation-induced self-assembly (EISA) process is confined within the microfluidic channels and guided into formation of highly ordered nanochannels with long range alignment. The fabrication and synthesis process is developed and the resultant nanomaterial is characterized. A fluorescent molecule dye, fluorescein, is used to demonstrate the potentials of the integrated device in nanofluidics applications.