Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session D30: Fluid Structure and Properties |
Hide Abstracts |
Sponsoring Units: DFD Chair: David Vaknin, Affiliation: Ames Laboratory, Iowa State University Room: Colorado Convention Center 304 |
Monday, March 5, 2007 2:30PM - 2:42PM |
D30.00001: Crystallization-induced fluid flow in polymer melts undergoing solidification Zhigang Wang, Donghua Xu, Jack F. Douglas The formation of `plastic' polymer materials often occurs under confinement where high pressure imprinting or casting in a mold are involved. To gain insight into this highly non-equilibrium process, we examine the nature of fluid flow that occurs in the non-crystallized regions of melts during spherulitic crystallization by following the movement of tracer particles in isotactic polypropylene films using optical microscopy. We observe a relatively rapid (average particle velocity 13 $\mu $m/min at 138 $^{o }$C, compared to a spherulite growth rate of 0.86 $\mu $m/min) particle movement in the melt until the spherulites become geometrically percolated. We interpret this transient flow to arise from the buildup of local stresses under confinement. Crystallization-induced fluid flow is expected to significantly influence crystal morphology, defect formation and ultimate properties of materials forming by injection molding, pressure imprinting and other processing involving both polymeric and non-polymeric materials where crystallization occurs under confinement. [Preview Abstract] |
Monday, March 5, 2007 2:42PM - 2:54PM |
D30.00002: The reversible freezing and melting of colloidal crystal and glass Hua Guo, Gerard Wegdam, Peter Schall, T. Narayanan, Michael Sztucki We present the observation of gas-liquid and gas-solid phase transitions in a close density matched system of charge stabilized polystyrene spheres suspended in the quasi binary 3-methylpyridine /H$_{2}$O/D$_{2}$O mixture. The reversible phase transitions are induced by using the temperature as control parameter. The temperature control parameter can be varied actively and accurately and applied to the same system to study the phase behaviors. The ``aggregation'' observed by Beysens is in reality a phase transition of the colloidal system. Density matching enables us to observe stable gas-liquid and gas-solid equilibriums. Thus the phases formed could be characterized by the measurement of the structure factor with Small Angle X-ray Scattering (SAXS): dense liquid, glass and face centered cubic ( fcc) crystal. [Preview Abstract] |
Monday, March 5, 2007 2:54PM - 3:06PM |
D30.00003: The riddle of nanoconfined liquids -solid or liquid? Peter Hoffmann, George Matei, Mircea Pantea, Shiva Patil, Ashis Mukhopadhyay Using a specially designed Atomic Force Microscope (AFM), we recently found that the mechanical behavior of simple liquids can be surprisingly rich when liquids are confined to only a few molecular layers. Under nanoscale confinement, OMCTS, a model silicone oil, remains liquid at thermal equilibrium while exhibiting molecular layering. However, at the application of a very small squeeze rate of the order of 1 molecular layer/second, elastic (`solidlike') behavior can be induced. On the other hand a different silicone oil, TEHOS, which has a more open molecular structure, behaves `solidlike' even at very slow squeeze rate and there is an indication, using fluorescence correlation spectroscopy, that it may spontaneously `solidify' close to a flat solid surface. Shear measurements show that when the liquid is allowed to order between the AFM tip and the substrate, the shear stiffness is enhanced, supporting the notion that these liquids can indeed `solidify' under certain circumstances. [Preview Abstract] |
Monday, March 5, 2007 3:06PM - 3:18PM |
D30.00004: Phonons in a One-Dimensional Microfluidic Crystal at Very Low Re Tsevi Beatus, Tsvi Tlusty, Roy Bar-Ziv The development of a general theory for the behavior of a crystal driven far from equilibrium has proved difficult. Microfluidic crystals of water-in-oil droplets provide a convenient means to explore and develop models for non-equilibrium dynamics. Owing to the fact that these systems operate at low Reynolds number (Re), in which viscous dissipation dominates inertial effects, vibrations are expected to be over-damped. Against such expectations, we report the emergence of collective normal vibrational modes (equivalent to acoustic `phonons') in a 1D microfluidic crystal of droplets at Re$\sim $10-4. These phonons propagate at ultra-low sound velocity of $\sim $100$\mu $m/s and frequencies of a few Hz, exhibit unusual dispersion relations markedly different to those of harmonic crystals, and give rise to a variety of crystal instabilities that could have implications for the design of commercial microfluidic systems. First-principles theory shows that these phonons the symmetry-breaking flow field that induces long-range inter-droplet interactions, similar in nature to those observed in other systems including dusty plasma crystals, vortices in superconductors and active membranes.\newline Nature Physics 2, 743-748 (2006). [Preview Abstract] |
Monday, March 5, 2007 3:18PM - 3:30PM |
D30.00005: Synchrotron x-ray ultrafast x-ray imaging on dynamic multiphase flow studies Yujie Wang, Kamel Fezzaa, Jin Wang, Kyoung-Su Im To overcome the long-exposure time of x-ray imaging for liquid systems. In the past year, we have developed the first ultrafast white-beam synchrotron x-ray phase-contrast imaging technique in the world. With its unprecedented temporal (0.5 $\mu $s) and spatial resolutions (1 $\mu $m), this new technique has already shown great promises in the study of complex fluid mechanical systems. It can probe complex surface morphology and transient dynamics of these interfaces of fluid mechanical systems without the nuisance of multiple scattering. This technique is a big step forward in comparison to millisecond-temporal and micrometer-spatial imaging resolutions normally achieved at various synchrotron sources. With the development of this new technique, we can already carry out research in fluid mechanical systems in competition with world-leading research groups. Our study of the primary breakup process of a coaxial air-assisted liquid jet revealed that the dynamics is dominated by a ``liquid membrane breakup'' process instead of a simple ``ligament mediated breakup'' process owing to our far superior temporal and spatial resolutions. This observation will naturally lead to a cascade idea for the unified treatment of liquid jets, droplets, and liquid membranes breakup mechanism. [Preview Abstract] |
Monday, March 5, 2007 3:30PM - 3:42PM |
D30.00006: Circular polarization memory effect in low-coherence enhanced backscattering of light Young L. Kim, Prabhakar Pradhan, Min H. Kim, Vadim Backman We experimentally study the propagation of circularly polarized light in the subdiffusion regime by exploiting enhanced backscattering [(EBS), also known as coherent backscattering] of light under low spatial coherence illumination. We demonstrate for the first time, to the best of our knowledge, that a circular polarization memory effect exists in EBS over a large range of scatterers' sizes in this regime. We show that low-coherence EBS signals from the helicity preserving and orthogonal helicity channels cross over as the mean free path length of light in media varies, and that the cross point indicates the transition from multiple to double scattering in EBS. [Preview Abstract] |
Monday, March 5, 2007 3:42PM - 3:54PM |
D30.00007: Penetration depth of low-coherence enhanced backscattering photons in the sub-diffusion regime Hariharan Subramanian, Prabhakar Pradhan, Young Kim, Vadim Backman The mechanisms of photon propagation in random media in the diffusive multiple scattering regime have been previously studied using diffusion approximations. However, similar understanding in the low-order (sub-diffusion) scattering regime is not complete due to difficulties in tracking photons that undergo very few scatterings events in the medium. Recent developments in low-coherence enhanced backscattering (LEBS) overcome these difficulties and enable us to probe photons that travel very short distances and undergo only a few scattering events. We derive the analytical expression of the probability of penetration depth and most probable penetration depth of photons due to LEBS, and also performed Monte Carlo numerical simulations to support our analytical results. Our results demonstrate that, the most probable penetration depth $z_p $of photons that undergo low-order scattering events have only weak dependence on scattering mean free path $l_s $and anisotropy factor $g$ of the medium, and strong dependence on the spatial coherence length of illumination,$L_{sc} $. For very small $L_{sc} $ ($<< \quad l_s )$, we show that the penetration depth is proportional to $1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3$ power of the coherence volume, i.e. ${\kern 1pt}z_p \propto \;\,\left( {\,l_s \,\pi \,L_{sc}^2 } \right)^{1/3}$. Important implications of our results and its application in biological media are also discussed. [Preview Abstract] |
Monday, March 5, 2007 3:54PM - 4:06PM |
D30.00008: Dynamics of Single Polymer Chain in Colloidal Suspensions in Narrow Channels Amir Amini, Marc Robert The self-diffusion coefficient of a linear polymer in a narrow cylindrical channel is calculated. The Polymer is treated as a Gaussian chain in the external potential established by neighboring colloids considered as hard obstacles. The approach is based on the Kirkwood equation, in which the hydrodynamic interactions are taken into account approximately. Monomer-monomer correlation function is obtained via a self-consistent mean-field method. [Preview Abstract] |
Monday, March 5, 2007 4:06PM - 4:18PM |
D30.00009: In Situ Surface Enhanced Infrared Absorption Spectroscopy for the Analysis of the Adsorption and Desorption Process of Au nanoparticles on the SiO2/Si Surface D. Enders, T. Nagao, T. Nakayama The adsorption and desorption of Au nanoparticles (AuNP) in colloidal D2O suspension on the APTES treated SiO2/Si surface was investigated by in situ ATR-IR spectroscopy. With increasing surface density of AuNP the absorption of the vibrational modes of D2O and of the citrate molecules covering the AuNP increases due to surface enhanced infrared absorption (SEIRA). We show that the adsorption kinetics can be investigated by monitoring in situ the molecular vibrational modes of D2O and the citrate molecules, and furthermore we clarify that the adsorption process can be described very well by a diffusion-limited first-order Langmuir-kinetics model. When exposing a saturated AuNP submonolayer to 2-aminoethanethiol (AET)/D2O solution, the AuNP are removed from the surface and the IR absorption of the D2O vibrational modes become weaker again. Taking into account the time dependencies of the CH and the OD peaks, we propose a microscopic model, where the AET molecules quickly adsorb on the AuNP by replacing most of the precovering citrate molecules exposed to the AET solution. As this takes place, the AuNP are finally removed from the surface. [Preview Abstract] |
Monday, March 5, 2007 4:18PM - 4:30PM |
D30.00010: Opening the Pandora's box to understand flow behavior of polymeric fluids. Sham Ravindranath, Pouyan Boukany, Yangyang Wang, Shi-Qing Wang Structure-property relationship has been explored for decades in the context of flow behavior of entangled polymeric liquids. For a long time, it has been assumed that the structure of an entangled polymer, i.e., the entanglement network would experience smooth changes during flow. Using an effective particle-tracking velocimetric (PTV) method recently developed in our lab [1], we found that the nonlinear flow dynamics are associated with an elastic breakdown of the fluid structure. This cohesive failure does not necessarily occur homogeneously in a macroscopic-scale experiment, making it ambiguous to interpret traditional rheological measurements. The presentation complies a whole set of PTV observations to elucidate the physical origin of nonlinear flow phenomena in complex fluids such as polymers. [1] \textit{Phys. Rev. Lett. }\textbf{96}, 016001 (2006); \textit{ibid}. \textbf{96}, 196001; \textit{ibid.} \textbf{97}, 187801. [Preview Abstract] |
Monday, March 5, 2007 4:30PM - 4:42PM |
D30.00011: Critical stresses and cracking in thin films of colloidal dispersions Weining Man, William Russel Colloidal dispersions are often coated on a substrate to leave a uniform thin film after solvent evaporating. However, during drying, a negative capillary pressure develops as the air-water interface is pulled down into the interstices between particles, putting the drying film in tension. The film responds by collapsing normal to the surface but is constrained from shrinking laterally unless cracks open. In this study, we use a high-pressure ultra-filtration device to measure directly the pressure responsible for cracking in uniform films of latex or silica dispersions containing particles of varying radii, avoiding a drying process with edge effects that generate lateral flows and propagating fronts. The results confirm that cracking is controlled by the recovery of elastic energy with the critical pressure increasing with the modulus of the particle, decreasing with film thickness, and independent of particle size. The Griffith's criterion for equilibrium crack propagation along with the nonlinear stress-strain relation provides a necessary, but not sufficient, condition for cracking. When pressure increases beyond the critical value, additional cracks open in qualitative agreement with our elastic energy recovery model. We also find that films with randomly close packed particles crack at a higher pressure than predicted, while those with hexagonally ordered domains particles crack at the critical pressure. These observations suggest an important role for defects that nucleate cracks. [Preview Abstract] |
Monday, March 5, 2007 4:42PM - 4:54PM |
D30.00012: A Novel Approach to Extracting the Pair Distribution Function of Bulk Liquids and Liquid Surfaces David Vaknin, Wei Bu, Alex Travesset The liquid structure factor $S(Q;\alpha)$ of water was measured by synchrotron X-rays in a reflection mode using a liquid surface diffractometer up to $Q \approx 6$ {\AA}$^{-1}$ at various angles of incident beam $\alpha$. The measurements were conducted at incident beam angles above and below the critical angle for total reflection. We calculated the geometrical and penetration depth corrections to $S(Q;\alpha)$s above the critical angle that collapse them into a single bulk $S(Q)$ within experimental error. A new approach to determining the pair distribution function (PDF) from X-ray measured $S(Q)$ was used to analyze the data. The approach involves the calculation of $S(Q)$ from a model PDF, constructed by a linear combination of Error functions, and refined by non-linear least square fit procedure to the measured $S(Q)$. The advantages of this procedure is that no absolute scaling of the intensity is necessary and the PDF is determined with uncertainties. The methodology is currently implemented to determine the PDF at water and other liquid surfaces. [Preview Abstract] |
Monday, March 5, 2007 4:54PM - 5:06PM |
D30.00013: Femtosecond movies of water at sub-nanometer lengthscales Robert H. Coridan, Ghee Hwee Lai, Nathan S. Schmidt, Michael Krisch, Peter Abbamonte, Gerard C. L. Wong The nanometer-scale structure and picosecond-scale dynamics of water are relevant to a wide range of problems in physics, such as the hydrophobic interaction and ion hydration. The behavior of water at these scales has been subject of theoretical and MD studies for decades, and water dynamics has been recently accessed using femtosecond `pump-probe' optical experiments. We will show that it is possible to image dynamical sub-angstrom density fluctuations in water by extracting the density propagator from the dynamical structure factor measured via high-resolution inelastic x-ray scattering spectra at 3$^{rd}$ generation synchrotron sources. [Preview Abstract] |
Monday, March 5, 2007 5:06PM - 5:18PM |
D30.00014: Fluctuation dynamics of water-hydrophobic interface Sung Chul Bae, Adele Poynor, Steve Granick Previous x-ray reflectivity measurements of the interface between water and hydrophobic surfaces with contact angle $>$100\r{ } indicate the existence of depletion layer. However, x-ray measurements provide little information of the fluctuation dynamics. In this presentation, surface plasmon resonance imaging technique with $<$ 1ms temporal resolution and $<$ 1$\mu $m lateral resolution has been built to investigate interface between water and methyl-terminated gold surface. This technique enables to examine the fluctuation dynamics of the depletion layer with temporal and spatial correlation analysis. The characteristic time and length scales of this fluctuation are explored. [Preview Abstract] |
Monday, March 5, 2007 5:18PM - 5:30PM |
D30.00015: Anisotropic polarizability of single wall carbon nanotubes measured via the electro-optical effect Jeffrey A. Fagan, Barry J. Bauer, Erik K. Hobbie The electro-optical response of 400 nm long single wall carbon nanotubes (SWNTs) suspended in water with single stranded DNA was measured in response to high frequency electric fields. Specifically, the dichroism of the SWNTs at their chirality dependent optical transitions was recorded, allowing for calculation of the induced alignment of the SWNTs by the applied field. The anisotropic polarizability of an individual SWNT chirality can be clearly assigned from this data. Strong alignment with nematic order parameters above 0.5 was achieved at high field strengths. We find anisotropic polarizabilities a factor of five larger than that previously measured for gold colloidal rods and an order of magnitude larger than that previously measured for tobacco mosaic virus (TMV). The characterization of the anisotropic polarizability is a large step towards exploiting this property for the directed manipulation of specific nanotubes. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700