Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B9: Nanofluidics |
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Sponsoring Units: DFD Chair: Daniel Ou-Yang, Lehigh University Room: D220 |
Monday, March 21, 2011 11:15AM - 11:27AM |
B9.00001: Message in a bottle: the statistical behavior of nanoparticles in optical confinement H. Daniel Ou-Yang, Joseph Junio, Liangcheng Zhou In an aqueous medium, container surfaces can significantly alter the behavior of suspended nanoparticles. We propose a method to investigate nanoparticle behavior in a boundary-free environment by transiently trapping them with a focused laser beam. While optical confined, as in an optical bottle, these particles are affected by both particle-light and particle-particle interactions. Time-averaged fluorescence imaging produces results in 3D mapping of the nanoparticle concentration in the bottle. We report how we analyze the messages in the bottle, i.e. the statistical behavior of these particles, by using the 3D distributions obtained under both controlled optical and interparticle forces. [Preview Abstract] |
Monday, March 21, 2011 11:27AM - 11:39AM |
B9.00002: Low-frequency dielectric response of a single particle in aqueous suspensions Jingyu Wang, H. Daniel Ou-Yang $\alpha -$relaxation, the counterion diffusion in the electric double layer, has been used to described the anomalous low frequency dielectric dispersion of aqueous suspensions of colloidal particles. A microscopic theory describing this relaxation process proposed by Schwarz, however, has not been investigated systematically. We propose to use a single particle dielectrophoresis (DEP) force spectroscopy to study the relaxation mechanism as a function of particles size, temperature and solvent viscosity. Specifically, we measure the dependence of the DEP crossover frequency force and compare results with predictions by Schwarz. [Preview Abstract] |
Monday, March 21, 2011 11:39AM - 11:51AM |
B9.00003: Investigation of MEMS force sensors for nano-scale water measurements Soyoung Kwon, Wonho Jhe, Corey Stambaugh Nanoscale water formed by capillary condensation has typically been studied by means of an atomic force microscope (AFM). While this approach can provide details about the dynamic visco-elastic properties, it is limited in the type of information that can be measured. Here we propose replacing the fixed sample surface generally used in AFM systems with movable micro-mechanical force sensors (MEMS) fabricated specifically for tapping mode or shear mode. By incorporating a MEMS device we can directly measure the adhesion force, pull-in distance and capillary force of nano confined water while the AFM collects information pertaining to the dynamic visco-elastic properties. In this talk, we will characterize the force measurement in the system and discuss the behavior of the device in the presence of nano-scale water. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:03PM |
B9.00004: Investigation of the Static and Dynamic Mechanical Properties of Nano-scale Water Corey Stambaugh, Soyoung Kwon, Wonho Jhe The behavior of liquids on the nano-scale has become an area of interest as new fabrication techniques have allowed for increasingly smaller structures to be made. While much work has been done on the interactions forces at liquid and solid interfaces, questions still remain regarding the behavior of nano-scale liquids. By incorporating a micro-electromechanical force sensor (MEMS) into the quartz tuning fork based atomic force microscope (QTF-AFM) probe setup we are able to both manipulate and measure nano-scale water, which in turn provides information beyond the standard AFM approach. Here we look at both the static and dynamic mechanical properties of water formed between the tip of a (QTF-AFM) probe and the polysilicon surface of a MEMS device. [Preview Abstract] |
Monday, March 21, 2011 12:03PM - 12:15PM |
B9.00005: Thermophoretic stretching of DNA in polymer nanochannels Jonas Pedersen, Lasse Thamdrup, Henrik Flyvbjerg, Anders Kristensen We demonstrate that thermophoretic forces generated by light-induced local heating can enhance the extension of genomic-length DNA confined in a polymer nanochannel. By temperature control on the micron-scale, bacteriophage T4 DNA is locally stretched to 80{\%} of its contour length, although the cross-section of the nanochannel is as large as 250x250nm$^2$. A coarse-grained model of the forces at play captures the DNA-molecule's response to thermophoretic forces with accuracy and precision, and allows for fitting the density profile of the stretched DNA with only a single fit-parameter. The forces involved are relatively strong, because they add up along the molecule. They are measured by using the molecule as an entropic spring balance. Pending a calculation of these forces, this experiment might discriminate between the competing theories for thermophoretic forces. [Preview Abstract] |
Monday, March 21, 2011 12:15PM - 12:27PM |
B9.00006: Poisson or not Poisson: Probability distribution of colloidal nanoparticles in an optical trap Yi Hu, Xuanhong Cheng, H. Daniel Ou-Yang In a colloidal suspension of nanoparticles, the presence of an optical trap can exponentially enhance the probability of finding the particles in the vicinity of the trap. Intriguing questions arise regarding whether the probably distribution of particle number in the trap follows Poisson approximation, and if so, what is the upper limit of the trapping energy at which Poisson is followed. To answer these questions, we conduct experiments to determine directly the variance and the mean particle number in the trap at different trapping energies and compare with the predictions of the probability theory. [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 12:39PM |
B9.00007: Charging Dynamics of Sub-nanometer Pores Ying Liu, Guang Feng, Jingsong Huang, Bobby Sumpter, Vincent Meunier, Rui Qiao Electrodes featuring sub-nanometer pores can potentially improve the energy density of supercapacitors significantly. However, ions entering such narrow pores often need to pay an energy penalty because part of their salvation shell must be removed. This can potentially limit the charging kinetics of such nanopores. In this work, we investigate the charging dynamics of sub-nanometer pores connected with an electrolyte bath. We quantify the energy barrier for ions to enter 0.82-nm wide slit pores and determine the time constant for charging of the pores using Molecular Dynamics simulations. Strong concentration polarization is found during the charging process and the charging kinetics is much slower than that predicted using the classical equivalent circuit model. The results are rationalized using a modified Poisson-Nernst-Planck model. [Preview Abstract] |
Monday, March 21, 2011 12:39PM - 12:51PM |
B9.00008: Statics and Dynamics of Stretched Single DNA Molecules Tug-of-War at Micro-Nanofluidic Interfaces JiaWei Yeh, Alessandro Taloni, Yeng-Long Chen, Chia-Fu Chou Understanding single molecule dynamics at micro-nanoscale interfaces has implications to polymer transport in biological processes, device design for single molecule analysis and biotechnological applications. We report our study on single DNA molecules straddling across a nanoslit, bridging two micro-nanofluidic interfaces, for both its tug-of-war behavior and confinement-induced entropic recoiling at varying length and height (h: 30$\sim $100 nm) of a nanoslit. From a modified worm-like chain model in the tug-of-war scenario and the scaling analysis in the entropic recoiling process, we demonstrate the entropic recoiling force is essentially constant, given the degree of confinement, irrespective of the DNA length inside the nanoslit and the slit length. The scaling exponents for the entropic force will also be discussed. [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B9.00009: Long time dynamics of single linear and circular ds-DNA confined in sub-100nm nanoslits Po-Keng Lin, Jen-Fang Chang, I. Stachiv, Chia-Fu Chou, Y.- L. Chen We investigate the role of topological constraints on DNA dynamics in very strong confinement to study the dynamics of nuclear chromosome and DNA viral packaging. Experiments and simulations were carried out to investigate the equilibrium shape and dynamics of the single linear and circular $\lambda $-DNA confined in a silicon/glass nanoslit. We measured the chain extension $r$, shape asphericity $A$, extensional (\textit{$\tau $}$_{\vert \vert}$) and rotational relaxation time\textit{ $\tau $}$_{r}$, and examined the dependence on chain topology as functions of the slit height $h $(20 $\sim $ 780 nm) and the solvent ionic strength $I$ (0.8 $\sim $250 mM). We observed that the shape asphericity increases as $h$ and$ I$ decrease as the chain shape becomes anisotropic. Moreover, in sub-Kuhn length confinement, the DNA relaxation time increases with decreasing $h$ in a smooth and broad transition. [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:15PM |
B9.00010: Heat-Driven Release of a Drug Molecule From Carbon Nanotubes Vitaly Chaban, Oleg Prezhdo Hydrophobicity and ability to absorb light that penetrates through living tissues make carbon nanotubes (CNTs) promising intracellular drug delivery agents. Following insertion of a drug molecule into a CNT, the latter is delivered into a tissue, is heated by near infrared radiation, and releases the drug. In order to assess the feasibility of this scheme, we investigate the rates of energy transfer between CNT, water and the drug molecule, and study the temperature and concentration dependence of the diffusion coefficient of the drug molecule inside CNTs. We use ciprofloxacin (CIP) as a sample drug: direct penetration of CIP through cell membranes is problematic due to its high polarity. The simulations show that a heated CNT rapidly deposits its energy to CIP and water. All estimated timescales for the vibrational energy exchange between CNT, CIP and water are less than 10 ps at 298 K. As the system temperature grows from 278 K to 363 K, the diffusion coefficient of the confined CIP increases 5-7 times, depending on CIP concentration. The diffusion coefficient slightly drops with increasing CIP concentration. This effect is more pronounced at higher temperatures. The simulations support the idea that optical heating of CNTs can assist in releasing encapsulated drugs. [Preview Abstract] |
Monday, March 21, 2011 1:15PM - 1:27PM |
B9.00011: Characterization of Nanostructured Silicon Membranes for Control of Molecular Transport Bernadeta Srijanto, Scott Retterer, Jason Fowlkes , Mitchel Doktycz Fabrication of nanoporous membranes for selective transport of molecular species requires precise engineering at the nanoscale. The membrane permeability can be tuned by controlling the physical structure and the surface chemistry of the pores. We use a combination of electron-beam and optical lithography, along with cryogenic deep reactive ion etching, to fabricate silicon membranes that are physically robust and have uniform pore sizes. Pore sizes are further reduced using plasma enhanced chemical vapor deposition and atomic layer deposition of silicon dioxide onto the membrane surfaces. Integrating nanoporous membranes within a microfluidic network provides a platform for tailoring molecular exchange between microchannels, independent of hydrodynamic effects. In enzymatic reactions, for example, tuning the pores size will allow smaller enzymatic substrates to traverse the membrane at controlled rates while larger enzymes remain spatially separated. Our results from membrane cross-sectioning using focused ion beam milling show that pore sizes can be controlled at dimensions below 10nm. Functional characterization was performed by quantitative fluorescence microscopy to observe the selective transport of molecular species of different sizes. [Preview Abstract] |
Monday, March 21, 2011 1:27PM - 1:39PM |
B9.00012: Thermal resistance of thin water films during phase-change Nitin Shukla, Nenad Miljkovic, Ryan Enright, Evelyn N. Wang The thermal resistance of a thin water film during phase-change processes is of interest for fundamental studies and of importance for various engineering systems. In particular, as the thickness of the water film approaches the nanoscale, the thermal resistance across the liquid-vapor interface can contribute significantly to the overall heat transport. In this work, we experimentally investigate the thermal resistance of thin water films during phase change on metallic substrates using transient thermoreflectance (TTR) spectroscopy. This technique offers a novel method to examine heat transport in evaporating liquid films less than a 100 nm in thickness. The understanding gained from this work will aid in the design of high performance phase-change based micro/nanoscale devices. [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 1:51PM |
B9.00013: Effect of hydrogen bond cooperativity on the behavior of water Kevin Stokely Four scenarios have been proposed for the low--temperature phase behavior of liquid water, each predicting different thermodynamics. The physical mechanism which leads to each is debated. Moreover, it is still unclear which of the scenarios best describes water, as there is no definitive experimental test. Here we address both open issues within the framework of a microscopic cell model by performing a study combining mean field calculations and Monte Carlo simulations. We show that a common physical mechanism underlies each of the four scenarios, and that two key physical quantities determine which of the four scenarios describes water: (i) the strength of the directional component of the hydrogen bond and (ii) the strength of the cooperative component of the hydrogen bond. The four scenarios may be mapped in the space of these two quantities. We argue that our conclusions are model-independent. Using estimates from experimental data for H bond properties the model predicts that the low-temperature phase diagram of water exhibits a liquid--liquid critical point at positive pressure. [Preview Abstract] |
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