Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session W19: Focus Session: Synchrotron X-ray and Neutron Techniques in Soft Matter and Biological |
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Sponsoring Units: DPOLY DBP Chair: Zhang Jiang, Argonne National Laboratory Room: B118-B119 |
Thursday, March 18, 2010 11:15AM - 11:51AM |
W19.00001: Characterizing 3-D Assembly of Block Copolymer Films using Rotational Small Angle Neutron Scattering Invited Speaker: Directed Self-Assembly (DSA) using graphoepitaxy, chemically patterned templates, and directed fields has been shown to be an effective route to achieving long range order over short time scales in block copolymer films designed for use as sacrificial resists. However, key questions remain regarding the materials-processing relationship that drives assembly in thin films. Understanding these relationships will become increasingly more important in emerging applications such as in photovoltaics and nanostructured membranes where the polymers are functional components. Utilizing a methodology to sample the entire 3-dimensional fourier space of a thin film coating, termed Rotational Small Angle Neutron Scattering (R-SANS), our group has discovered a complex process window that drives orientation and order in thin film block copolymer assembly. Data from R-SANS is complemented by specular neutron reflectivity (NR) and real time measurements using grazing incidence small angle x-ray scattering (GI-SAXS). In this talk, I will highlight some of our recent results that elucidate the effects of solvent content, evaporation rate, and thermal history on the average orientation and orientation distribution in block copolymer films. Of particular interest is the previously unreported effect of thermal gradients. Using static thermal gradients, we show that the kinetics of assembly are dramatically faster. Specifically, grain sizes on the order of 10s of microns are achievable in minutes for a system that would require $>$10 h to achieve the same results in a thermally uniform environment. The scaling of kinetics as a function of the static thermal gradient is also discussed and models of the physical processes involved presented. The complex evolution of morphological orientation is then further biased through the application of dynamic gradients in a technique we label as cold zone annealing, a technique suitable for manufacturing methods such as roll-to-roll processing. [Preview Abstract] |
Thursday, March 18, 2010 11:51AM - 12:03PM |
W19.00002: Development of Resonant Soft X-ray Scattering for Polymer Systems at Advanced Light Source Cheng Wang, Alexander Hexemer, James Nasiatka, Elaine Chan, Howard Padmore It is envisioned that many polymer applications will rely on the heterogeneous morphologies of polymer blends or block copolymers to yield specific functional properties, such as organic light-emitting diodes and photovoltaics. Over the past few years, it has been strongly demonstrated that scattering at soft x-ray energies near the carbon K-edge yields chemically specific and enhanced contrast, thereby enabling structural studies of heterogeneous polymer films with thicknesses of only tens of nanometers. Resonant soft x-ray scattering (RSoXS) will provide the capability for a high-resolution chemical probe with interfacial sensitivity. We will discuss here the development of a dedicated RSoXS setup at the ALS Beamline 11.0.1, which is an elliptically polarized undulator beamline that covers the energy range of 200-1300 eV. It can accommodate a large variety of thin film samples and scattering geometries, including transmission, specular and off-specular reflection, as well as grazing incidence geometries, that will enable users to study both laterally- and depth-resolved structures. The generality, strength, and ease of RSoXS will have significant and immediate impacts in many areas of polymer science and technology. This will be achieved through systematic, collaborative studies of materials with potentially high impact applications. [Preview Abstract] |
Thursday, March 18, 2010 12:03PM - 12:15PM |
W19.00003: X-ray reflectivity and diffuse studies of lipid bilayer stacks on solid substrates Gang Chen, M. Mukhopadhyay, Y. Ma, Sunil K. Sinha, C. DeCaro, J. Berry, Laurence B. Lurio, Z. Jiang, A. Brozell, D. Bricarello, Atul N. Parikh Recently, major efforts have been made to study model lipid membranes supported on a solid substrate. A typical bilayer is characterized by its static structure and dynamic thermal fluctuations which are described by three physical quantities, the bending modulus, the surface tension, and the external potential due to a nearby surface or neighboring bilayers. The solid substrate affects both the static and dynamic behaviors of the bilayer deposited on its top. We have carried out a systematic study of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) bilayer stacks up to five bilayers prepared with Langmuir-Blodgett (LB) and Langmuir-Schaeffer (LS) methods. A complete picture of the static bilayer structure, both in-plane and out of plane, and the dynamic fluctuations as a function of temperature and the number of stacks, i.e., the distance from the substrate, is obtained with x-ray reflectivity, Grazing Incidence Small Angle X-ray Scattering (GISAXS), and rocking scans. (Work supported by NSF, DMR0706369) [Preview Abstract] |
Thursday, March 18, 2010 12:15PM - 12:27PM |
W19.00004: Reduced Viscosity of Free Surface in Entangled Polymer Melt Films Tad Koga, C. Li, M. Endoh, J. Koo, M. Rafailovich, S. Narayanan, D. Lee, L. Lurio, S. Sinha The dynamics of polymer chains near the surface of a melt and within thin films remains a subject of inquiry along with the nature of the glass transition in these systems. By embedding ``dilute'' gold nanoparticles in single polystyrene thin films as ``markers'', we could probe the local viscosity of the free surface at temperatures far above the glass transition temperature ($T_{g})$. The technique used was X-ray photon correlation spectroscopy with resonance-enhanced X-ray scattering. The results clearly showed the viscosity was about 30 {\%} lower than the rest of the film. We found that this reduction is strongly associated with chain entanglements at the free surface rather than the reduction in $T_{g}$. [Preview Abstract] |
Thursday, March 18, 2010 12:27PM - 12:39PM |
W19.00005: Surface Freezing Controlled Meniscus Relaxation in Side Chain Comb Polymers Shishir Prasad, Zhang Jiang, Michael Sprung, Sunil Sinha, Ali Dhinojwala The formation of a frozen monolayer on the surface of poly(n-alkyl acrylate) melt results into a dramatic slowing down of the relaxation of liquid meniscus. There are no abrupt changes in bulk viscosity or surface tension at these temperatures. X-ray photon correlation spectroscopy measurements suggest that the surface ordered monolayer considerably slows down the surface capillary fluctuations and is responsible for the slower meniscus relaxation. This work demonstrates that the formation of a nanometer thin surface frozen layer has a dramatic influence on the macroscopic flow of the liquid contact line and provides important guidelines to determine the coating process parameters for these commercially important polymers. [Preview Abstract] |
Thursday, March 18, 2010 12:39PM - 12:51PM |
W19.00006: X-ray Photon Correlation Spectroscopy Measurements of Dynamics within Concentrated Eye-Lens Protein Suspensions Janae DeBartolo, V. N. C. Karunaratne, Justin Berry, Laurence Lurio, George Thurston, Alec Sandy, Suresh Narayanan, John Weizeorick X-ray photon correlation spectroscopy (XPCS) has been applied in recent years to the study of dynamics within a wide range of soft materials. Its application to protein diffusion has been hindered by the weak scattering and the susceptibility of proteins to damage. We report the first application of XPCS to study the dynamics of concentrated suspensions of alpha and gamma crystallin proteins extracted from bovine eye-lens. The limitations of low flux and x-ray damage were overcome through a combination of a fast, high efficiency CCD, a kinoform lens and by limiting exposures to short intervals. Dynamics were measured both for alpha crystallin suspended in a concentrated matrix of gamma crystallin and concentrated alpha crystallin suspensions, showing time constants of a few tens of milliseconds at length scales corresponding to the protein diameter. [Preview Abstract] |
Thursday, March 18, 2010 12:51PM - 1:03PM |
W19.00007: GISAXS Study of Lateral Instability in Nanoimprinted Polymer Gratings Yeling Dai, Oleg Shpyrko, Kyle Alvine, Joseph Strzalka, Alec Sandy, Hyun Wook Ro, Christopher Soles We experimentally investigate thermal decay instability that occurs in nanoimprinted lithography (NIL) polymer nanostructures. Thermal stability of soft polymer imprinted nanoscale patterns is a major challenge for NIL applications. Due to Laplace pressure, polymer patterns develop instability that reduces surface energy during annealing. Time-Resolved Grazing Incident Small Angle X-ray Scattering (GISAXS) allows us to precisely measure in-situ development of such thermal instability process with nanoscale resolution and timescale down to 10 ms. In addition to the conventional exponential pattern height decay, we also observe a lateral instability of the polymer lines during heating above glass transition temperature. This lateral instability is marked by an out-of-phase lateral ``zigzag'' undulation of the polymer lines and a local coalescence of the lines as they approach one another. We will show how this behavior can be studied with time-resolved GISAXS by characterizing instability parameters such as undulation wavelength, correlation lengths, pattern height etc. [Preview Abstract] |
Thursday, March 18, 2010 1:03PM - 1:15PM |
W19.00008: Electrostatic 2D assembly of bionanoparticles on a cationic lipid monolayer. Sumit Kewalramani, Suntao Wang, Masafumi Fukuto, Lin Yang, Zhongwei Niu, Giang Nguyen, Qian Wang We present a grazing-incidence small-angle X-ray scattering (GISAXS) study on 2D assembly of cowpea mosaic virus (CPMV) under a mixed cationic-zwitterionic (DMTAP$^{+}$-DMPC) lipid monolayer at the air-water interface. The inter-particle and particle-lipid electrostatic interactions were varied by controlling the subphase pH and the membrane charge density. GISAXS data show that 2D crystals of CPMV are formed above a threshold membrane charge density and only in a narrow pH range just above CPMV's isoelectric point, where the charge on CPMV is expected to be weakly negative. The particle density for the 2D crystals is similar to that for the densest lattice plane in the 3D crystals of CPMV. The results show that the 2D crystallization is achieved in the part of the phase space where the electrostatic interactions are expected to maximize the adsorption of CPMV onto the lipid membrane. This electrostatics-based strategy for controlling interfacial nanoscale assembly should be generally applicable to other nanoparticles. [Preview Abstract] |
Thursday, March 18, 2010 1:15PM - 1:27PM |
W19.00009: Biomimetic growth of calcium oxalate crystals: synchrotron X-ray studies Ahmet Uysal, Benjamin Stripe, Pulak Dutta Oriented crystals of calcium oxalate monohydrate (COM) form one of the major constituents of kidney stones in humans, and these crystals are also found in many plants. It is widely accepted that an organic matrix of lipids and proteins is involved in the crystallization of COM, though their role is not well-understood [1]. Langmuir monolayers of lipids on supersaturated aqueous solutions can be used to mimic the lipid-crystal interface during mineralization. We have studied nucleation and growth of COM crystals under heneicosanoic acid monolayers at the air-water interface. We used synchrotron x-rays in the grazing incidence geometry to determine the structure of the organic monolayer and the orientation of COM crystals \textit{in-situ }during crystallization. We see that the (-101) faces of COM crystals are parallel to the organic matrix. There is a commensurate relationship between the heneicosanoic acid monolayer and the (-101) crystal face that may be responsible from the oriented growth. Evolution of the monolayer structure with time will be described. [1]S. R. Khan, Calcium Oxalate in Biological Systems, CRC Press, Boca Raton, 1995 [Preview Abstract] |
Thursday, March 18, 2010 1:27PM - 2:03PM |
W19.00010: Neutron and X-ray Scattering From Single Supported Lipid Bilayers: Reflectometry, Grazing Incidence In-Plane Diffraction and Off-Specular Scattering Invited Speaker: Biological membranes mediate transport and communication between the cell and its surroundings. They defend the cell against invasive agents, and most present day drugs interact with membrane components. Complexity of the cell membranes renders many of their characteristics impenetrable to fundamental physical studies. As a result, a significant emphasis has been placed on developing model lipid membranes that facilitate the physical and chemical characterization of particular membrane features. X-ray (XR) and neutron reflectivity (NR) and grazing incidence X-ray diffraction (GIXD) techniques can be utilized to measure the structure of single, supported lipid bilayers in bulk water. GIXD studies demonstrated that bilayers formed by vesicle fusion have more disorder in the inner leaflet compared to structures prepared using the Langmuir-Blodgett/Schaeffer (LB/S) technique. In both cases, only a modest water cushion was detected between the bilayer and substrate. Diffraction from in-plane ordered domains was observed from bilayers prepared by either technique. In the case of 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) bilayers, the ordered domains were coupled across both leaflets, scattering as one entity. Contrastingly, the ordered domains were uncoupled in 1,2-Dipalmitoyl-sn-Glycero-3-Phosphoethanolamine (DPPE) bilayers. NR can be effectively used to study polymer-supported single lipid bilayers in bulk water. Using NR and fluorescence microscopy, we demonstrated that a hydrated, surface-tethered polymer network capable of five-fold change in thickness over a 25-37 C temperature range can be a novel support for single DPPC bilayers in a liquid environment. Moderate temperature change swells the polymer, lifting the membrane from the substrate, creating a nearly aqueous cushion. Additionally, as the polymer swells, it promotes both in- and out-of-plane undulations in the supported membrane. Off-specular neutron scattering was used to deduce the in-plane correlation length of the membrane distortions. [Preview Abstract] |
Thursday, March 18, 2010 2:03PM - 2:15PM |
W19.00011: \textit{In-situ} synchrotron small angle and wide angle X-ray scattering (SAXS/WAXS) study of polyethylene and polyethylene/clay nanocomposites during multiaxial deformation Bilge Gurun, David Bucknall, Yonathan Thio A unique \textit{in-situ} multiaxial deformation device (IMDD) has been designed and built specifically for simultaneous synchrotron SAXS and WAXS measurements. High-density poly(ethylene) (HDPE) /clay sheets were prepared using melt mixing and film extrusion techniques. SAXS and WAXS patterns of HDPE and HDPE/clay nanocomposites were measured in real time during \textit{in-situ} multiaxial deformation at room temperature and at 55\r{ }C. The morphological evolution of polyethylene was affected by the existence of clay platelets as well as the temperature. Martensitic transformation of orthorhombic HDPE crystal planes into monoclinic crystal was observed under strain, which was delayed and hindered in the presence of clay nanoplatelets. The thickness of the interlamellar amorphous domain, as measured in SAXS, increased with increasing strain. The increase was slightly higher for nanocomposites compared to the pure polymer. [Preview Abstract] |
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