Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q44: Focus Session: Dynamics of Polymers-Phenomena due to Confinement |
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Sponsoring Units: DPOLY Chair: Rob Riggleman, University of California, Santa Barbara Room: A309 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q44.00001: The effect of pattern dimensions on the thermal decay of polymer patterns created by nanoimprint lithography Kenneth Kearns, H.W. Ro, Heather J. Patrick, Thomas A. Germer, Christopher Soles Spectroscopic ellipsometry, combined with rigorous coupled wave modeling, is used to characterize the thermal decay of polymeric patterns prepared by nanoimprint lithography. When the residual layer is on the order of 10 nm, the pattern decay kinetics of patterns with a 420 nm periodicity near their glass transition temperatures are nearly an order of magnitude slower than patterns sitting on a thick residual layer. Pattern decay is not observed when the periodicity increased to 800 nm for the 10 nm residual layers. Polystyrene, poly(methyl methacrylate), and poly(4-t-butyl styrene) all show this behavior suggesting that changes in entanglement density are not important. The difference in the radius of curvature for the two different pattern periodicities is the likely origin for the pattern decay. The sensitivity of the technique to thin residual layers and nanoscale patterns is enhanced with an optical cavity of SiO$_{2}$ between the polymer and Si substrate. The SiO$_{2}$ layer enhances the changes in the ellipsometric parameters alpha and beta, which are related to psi and delta. The model dependent scatterometry data is corroborated by atomic force microscopy. [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q44.00002: Capillary levelling as a probe of rheology in polymer thin films Joshua D. McGraw, Nick M. Jago, Kari Dalnoki-Veress While measuring the rheology of bulk polymer systems is routine, when the size of a system becomes comparable to the molecular size, flow properties are poorly understood and hard to measure. Here, we present the results of experiments that are easily performed and can probe the rheological properties of polymer films that are mere tens of nanometres in thickness. We prepare glassy bilayer polymer films with height profiles well approximated by a step function. Upon annealing above the glass transition, broadening of the height profiles due to gradients in the Laplace pressure is observed. By validating the technique as a probe of the rheology with a range of molecular weights, we will show that this robust technique can be used to investigate the effects of confinement and interfaces on the rheology of ultrathin polymer films. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q44.00003: Direct evidence of heterogeneous dynamics within ultrathin polystyrene melt films Tad Koga, Naisheng Jiang, Peter Gin, Maya Endoh, Suresh Narayanan, Larry Lurio, Sunil Sinha We report heterogeneous dynamics associated with cooperative motions of polymer chains within single polystyrene (PS) films at temperatures far above its glass transition temperature. The technique used was a marker x-ray photon correlation spectroscopy technique using ``dilute'' gold nanoparticles embedded in PS films in conjunction with resonance-enhanced x-rays scattering which intensifies the probing electrical field in the regions of interest within the films. We found that as the thickness decreased below around 60 nm, the diffusive motions of the markers were significantly suppressed both at the free surface and the center of the film relative to those for the thicker films ($>$100 nm thickness). It is attributed to the long-range effects on the polymer dynamics induced by an immobile layer at the substrate interface. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q44.00004: Anisotropic Dependence of Capillary Dynamics of Confined Polymer Liquid Films Yeling Dai, Oleg Shpyrko, Kyle Alvine, Suresh Narayanan, Alec Sandy We experimentally investigate the effect of highly anisotropic confinement on the capillary dynamics of polymer liquid films. Polystyrene films confined laterally within line-space silicon grating patterns of varying channel width represent a highly anisotropic liquid. The capillary fluctuation modes of such system can be expected to persist along the direction of the channels, while fluctuations perpendicular to the channels are likely to be suppressed. We utilized X-ray Photon Correlation Spectroscopy (XPCS) to access this capillary wave dynamics. In addition to the channel-width dependence of the capillary relaxation times, we also observe the anisotropic dependence of the capillary wave fluctuations on the confined polymer surface. I will discuss how XPCS can access the directional dependence of capillary dynamics and comment on the role played by interfacial pinning in suppressing capillary fluctuations. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q44.00005: Surface Dynamics of Macrocyclic Polystyrene Films Shih-fan Wang, Mark D. Foster, Zhang Jiang, Suresh Narayanan Thermally stimulated fluctuations of the surface of a melt of macrocyclic polymers have been studied for the first time. The surface fluctuations of macrocyclic polystyrene (cPS) of 2k, 7k, 17k, and 37k molecular weight (M) were probed using x-ray photon correlation spectroscopy (XPCS), a recently-developed technique that has already been applied to study surfaces of linear PS melts. The surface fluctuations for the cPS films are slower than those of linear chain analogs for all M. However, the glass transition temperatures (Tg) of the cyclic chains are higher than those of the linear analogs, with the discrepancy decreasing with increasing M. A continuum hydrodynamic theory of thermally stimulated capillary waves with a nonslip boundary condition is adequate to rationalize the behavior of the cPS films. When results from cPS of different M are plotted as a function of T/Tg the data nearly collapse to a single curve, indicating that Tg is a key parameter for the surface dynamics of macrocyclics in the temperature range studied. Acknowledgements: NSF CBET 0730692 [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q44.00006: Surface dynamics of micellar diblock copolymer films Sanghoon Song, Wonsuk Cha, Hyunjung Kim, Zhang Jiang, Suresh Narayanan We studied the structure and surface dynamics of poly(styrene)-b-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer films with micellar PDMS surrounded by PS shells. By `in-situ' high resolution synchrotron x-ray reflectivity and diffuse scattering, we obtained exact thickness, electron density and surface tension. A segregation layer near the top surface was appeared with increasing temperature Surface dynamics were measured as a function of film thickness and temperature by x-ray photon correlation spectroscopy. The best fit to relaxation time constants as a function of in-plane wavevectors were analyzed with a theory based on capillary waves with hydrodynamics with bilayer model Finally the viscosities for the top segregated layer as well as for the bottom layer are obtained at given temperatures [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q44.00007: Polymer Transport Near Rough Surfaces Moses Bloom, Jonathan Whitmer, Erik Luijten The rheology of dilute polymer solutions under confinement is important in biology, medicine, microfluidic device design, synthetic polymer processing, and even geologic porous media. However, the solution's specific interactions with the confining surface are poorly understood. This situation is exacerbated for composite nanoparticles, such as polymer/metallic hybrids. Using multi-particle collision dynamics, we find a rich array of transport regimes depending on small-scale surface roughness and the specific surface/solute interactions. These factors couple to hydrodynamic conditions, including flow strength and confinement geometry in unexpected ways. Our findings may be relevant to transport phenomena in certain rough-walled capillaries, such as the distribution of various nanoconjugates in vivo. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q44.00008: Molecular dynamics simulation study of slip flows over surfaces with periodic and random anisotropic textures Nikolai Priezjev The influence of surface patterns on slip flow of a Lennard- Jones fluid is investigated using molecular dynamics simulations. We consider a situation when the typical pattern size is smaller than the channel width. First, anisotropic slip lengths are reported at low shear rates for flows over periodic stripes of different wettability when the shear flow direction is misaligned with respect to the stripe orientation. The results of MD simulations are compared with continuum predictions. Second, in case of random chemical patterning, the slip length depends sensitively on the total area of wetting texture. Finally, we found that at sufficiently high shear rates the slip length is anisotropic even for atomically flat crystalline surfaces; and, in particular, the slip length is enhanced when the shear flow is oriented along the crystallographic axis of the wall lattice. The simulation results indicate that the onset of the nonlinear regime between the slip length and shear rate is determined by the diffusion of fluid monomers within the first layer. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q44.00009: Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystyrene Films Zhaohui Yang, Yoshihisa Fujii, F.K. Lee, C.H. Lam, Dongdong Peng, Ophelia Tsui Most polymers solidify into a glassy amorphous state, accompanied by a rapid increase in the viscosity when cooled below the glass transition temperature (Tg). There has been an ongoing debate on whether the Tg changes with decreasing polymer film thickness and the origin of the changes. We measured the viscosity of unentangled, short-chain polystyrene (2.4kg/mol) films on silicon at different temperatures and found that the transition temperature for the viscosity decreases with decreasing films thickness, in agreement with the changes in the Tg of the films observed by thermal expansion measurements. By applying the hydrodynamics equations to the films, we are able to explain the data fully by assuming that a highly mobile layer is present within the top 2.3 nm thick region of the films and follows an Arrhenius dynamics while the remaining of the films is bulk-like. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:39PM |
Q44.00010: Fingering Instability of Debonding Soft Elastic Adhesives Invited Speaker: We study the crack-front fingering instability of an elastic adhesive tape that is peeled off a solid substrate. Our analysis is based on an energy approach using fracture mechanics and scaling laws and provides simple physical explanations for (i) the fact that the wavelength depends only on the thickness of the adhesive film and (ii) the threshold of the instability, and (iii) additionally estimates the characteristic size of the fingers. The scaling laws for these three observables are in agreement with existing experimental data. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q44.00011: Effect of molecular weight on surface mobility of polystyrene films Dongdong Peng, Zhaohui Yang, Ophelia Tsui There have been mounting experimental results showing that a two-layer model is appropriate for describing the dynamics of polymer films. The model postulates that a surface mobile layer exists at the free surface and can modify the dynamics of the entire film. In a recent study, we measured the viscosity of unentangled, short-chain polystyrene (Mw=2.4kg/mol) films supported by silicon at different temperatures including the bulk Tg, and found that the data could be fully explained by assuming a surface mobile layer with a constant thickness exists and sits atop a bulk-like layer. In this talk, I will report the result we obtained by measuring the viscosity of polystyrene films with a wide range of molecular weights from 6.4 to 2316 kg/mol supported by silicon. Our result shows that the same two-layer model is applicable in describing the data if the mobility of the surface layer assumes a molecular weight dependence that differs from either the Rouse or Reptation model. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q44.00012: Scaling of confined and interacting comb polymers Catherine Yeh, Philip Pincus We study the scaling of polymer chains grafted to a line, i.e. a 1-D brush or comb polymer, on a repulsive plane in good solvent using classical molecular dynamics. The grafting density is large enough to cause chain stretching. The confined comb geometry is motivated by intermediate filaments where the unstructured monomer c-termini form annular rings that can be modeled as a confined comb bent into a ring. We find that the scaling of brush size as a function of the number of monomers per chain is the same for a comb with and without confinement by a repulsive plane. We also consider the transition of a line of parallel interacting combs to the planar brush geometry as they are compressed from isolated combs; we present results for the dependence of brush height on the distance between combs. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q44.00013: Geometry and molecular architecture effects in nanobubble inflation measurements Shanhong Xu, Sylvie Castagnet, Gregory McKenna Confinement effects on the mechanical properties of ultrathin polymer films were investigated by a bubble inflation technique developed in our lab. Prior studies of ultrathin films of poly(vinyl acetate) (PVAc) and linear polystyrene (PS) were performed on circular bubbles of different diameters. Here the creep behaviors of ultrathin films of linear PS were investigated on rectangular bubbles. The modulus of the thin film rectangular bubbles was analyzed by approximation methods. The inflation of rectangular bubbles was simulated by finite element analysis (FEA). The mechanical properties of the thin films with the same thickness for circular and rectangular bubbles are compared and we find that the rubbery plateau compliance is geometry independent. We also investigated the creep behaviors of ultrathin films of 3-arm star PS on circular bubbles. We find the rubbery plateau compliance is molecular architecture independent. [Preview Abstract] |
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