Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H44: Surfaces, Interfaces, and Polymer Thin Films I |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: S. Michael Kilbey II, Oak Ridge National Laboratory/University of Tennessee Room: A309 |
Tuesday, March 22, 2011 8:00AM - 8:36AM |
H44.00001: Polymer Physics Prize Break |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H44.00002: Diffusion and Filtration Properties of Self-assembled Close-packed Nanocrystal Membranes Jinbo He, Xiao-Min Lin, Lela Vukovic, Henry Chan, Petr Kral, Heinrich Jaeger Small dyes are known to be able to penetrate through randomly packed nanoparticle monolayers, but a detailed understanding of the mechanisms for transport through the interstices between nanoparticles is still lacking. We report on systematic measurements of molecular transport across monolayers of close- packed, 5 nm diameter gold nanocrystals ligated with dodecanethiol. For water we find a filtration coefficient two orders of magnitude larger than for polymer-based nanofiltration membranes, while the self-diffusion coefficient is more than 100x smaller than in films of pure hydrocarbons. As we confirm by molecular dynamics simulations, larger molecules (tested molecular weight range: 200 - 43000) are unable to diffuse through the ligands. Instead, they most likely move through nm-sized regions of reduced ligand density, which are formed by slight variations in the local packing configuration and orientation of neighboring nanocrystals. In this intermediate size range we also find a pronounced dependence of the rejection rate on the molecules' charge. Molecules with cross-section above 2 nm are totally rejected. [Preview Abstract] |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H44.00003: Diffusion of Small Penetrants in Polybutadienes Ahmed E. Ismail, Flint Pierce, Gary S. Grest The diffusion coefficient $D$ in the dilute limit for three different penetrants--- oxygen, water, and methanol---in three different conformations of polybutadiene (all cis-1,4, all trans-1,4, and a random copolymer containing 50\% trans-1,4, 40\% cis- 1,4, and 10\% vinyl-1,2 repeat units) has been computed using molecular dynamics simulations for temperatures in the range $T=300$--$400$\,K. Simulations runs of 25 and 50 ns made for each of the 45 combinations of penetrant, conformation, and temperature studied. Over this temperature range the density of the all-cis-1,4 conformation is higher than that of the all-trans-1,4 and random copolymer conformations, which are approximately equal. For all three conformations, $D$ for oxygen and water are comparable and larger than that of methanol. However, for a given penetrant, strong differences were observed in the rate of increase of $D$ for the three conformations. We find that the activation barriers for the three penetrants are generally between 20 and 30 kJ/mol, in agreement with experimental results. The magnitude of the activation energy is directly proportional to the size, rather than the mass, of the penetrant molecule. (Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.) [Preview Abstract] |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H44.00004: Control dispersion of water in thin films of semi-fluorinated polymer/POSS nanocomposites Dilru Ratnaweera, Dvora Perahia, Manish Dubey, Jaroslaw Majewski The permeation and distribution of solvents in polymer nanocomposites is governed by the way the nanoparticles (NP) associate within the matrix polymer. We have previously shown that in thin films interfacial effects affect the distribution of the NP. The current work focuses on the response of a semi-fluorinated random copolymer, Biphenyl Perfluorocyclobutane, and Polyhedral Oligomeric Silsesquioxane (POSS) NP modified with fluorinated or protonated side chains, to presence of D$_{2}$O. POSS was introduced either as a free NP or tethered to a polymer chain. We found that the presence of POSS reduces the overall uptake of D$_{2}$O. It also changes the distribution of water in the film as well. In the pristine polymer film the water mainly accumulated at the substrate/polymer interface. In the nanocomposite, the water distribution is correlated with the NP distribution, where NP at the air interface minimize water penetration. [Preview Abstract] |
Tuesday, March 22, 2011 9:12AM - 9:24AM |
H44.00005: Water Desorption from Ferroelectric and Dipole-Oriented Polymers Carolina Ilie, Lillie Ghobrial, Gregory Maslak, Mark Stewart, Michael Evans, Luis G. Rosa, Peter A. Dowben Herein we compare the water absorption/ adsorption on three different polymer films: the ferroelectric co-polymer poly(vinylidene fluoride with trifluoroethylene) P(VDF-TrFE), the strongly dipole oriented polymer poly(methyl vinylidene cyanide) (PMVC) [1] and the dipole oriented poly(methyl methacrylate) PMMA. We investigate the dipole-dipole interaction of the water molecule and the ferroelectric/ dipole oriented polymer films and we propose that the dipole interactions may affect the surface chemistry at these polymer surfaces. Surface dipoles can affect the binding site of water species adsorbed at the surface and sterically hinder or enhance desorption of adsorbed and absorbed water.\\[4pt] [1] Dowben, P.A., Rosa, Luis G., Ilie, C.C., \textit{Zeitschrift f\"{u}r Physikalische Chemie} 222 (2008) 755-778. [Preview Abstract] |
Tuesday, March 22, 2011 9:24AM - 9:36AM |
H44.00006: Role of Diffusion in Scaling of Polymer Chain Aggregates Found in Vapor Deposition Polymerization Sairam Tangirala, David Landau Linear polymer chain aggregates grown by 1+1D Monte Carlo simulations of vapor deposition polymerization (VDP) were studied. The behavior of chain length distribution $n_{s}(t)$ as a function of chain length (s) and deposition time (t) was examined for relevant model parameters. The scaling of $n_{s}(t)$ was found to be sensitive to the ratio $G = D/F$ of deposition rate (F) and free monomer diffusion (D). A systematic approach is presented to isolate the dependence of $n_{s}(t)$ on $t$, $s$, and $G$. We found power law dependence of $n_{s}(t)$ on $t$ with exponent $\omega=1.01 \pm 0.02$ that was invariant with changes in $G$. For small $s$ and deposition time of $t$ = $1 \times10^3$, $5 \times 10^3$, and $10 \times10^3$, $n_{s}(t)$ showed a power-law decrease with $s$ and exponent $\tau=-0.58 \pm 0.02$. We observed a strong influence of $G$ on the rescaled $n_{s}(t)$ data that prevented the manifestation of unique scaling function for varying $G$. The dependence of scaling function of $n_{s}(t)$ on $G$ was found to be a characteristic of VDP and elucidates the sensitivity of polymer chain aggregates to $G$. [Preview Abstract] |
Tuesday, March 22, 2011 9:36AM - 9:48AM |
H44.00007: ABSTRACT WITHDRAWN |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H44.00008: Structure and dynamics of dense polymer chains in 2D Hendrik Meyer, Joachim P Wittmer, Albert Johner, Jorg Baschnagel Self-avoiding polymers in two-dimensional melts are known to adopt compact and segregated configurations. Compactness does obviously not imply Gaussian chain statistics nor does segregation of chains impose disk-like shapes minimizing the average perimeter length of the chains. Using scaling arguments and molecular dynamics simulations with chain length up to 2048 we show that the chain perimeters are highly irregular and characterized by a fractal line dimension 5/4. This result may be verified experimentally from the power-law scaling of the intrachain form factor in the intermediate wavevector regime in agreement with a generalized Porod law for a compact object of fractal border [1]. The dynamics of dense polymer chains exhibits two interesting features: the incompressibility induces long range correlations in the displacement auto-correlations and a relaxation channel due to friction at the fractal contours of compact sub-segments leads to relaxation faster than a Rouse model would predict [2].\\[4pt] [1] H. Meyer et al Phys. Rev. E 79 050802(R) (2009); J. Chem. Phys. (2010)\\[0pt] [2] J. Wittmer et al. Phys. Rev. Lett 105 (2010) 037802. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H44.00009: Dynamic surface tension effects from molecular dynamics simulations Alex Lukyanov Effects of dynamic surface tension have been studied in a model system using molecular dynamics simulations. The model system has been made of an artificially expanding liquid droplet, with the rate of change of the external surface area being comparable with the gas-liquid interface formation characteristic time, obtained from the estimates of macroscopic theories. The size of the liquid droplet has been chosen to have about 5.000-7,000 identical molecules, each having between 10-20 beads, to obtain well developed and separated the bulk and surface phases. The methodology of surface tension evaluation has been verified against the Laplace Law in a stationary state of the liquid drop. The results of the MD simulations will be discussed in comparison with the estimations obtained from macroscopic experiments on dynamic wetting using a sharp interface formation theory for different chain length of molecules and strength of intermolecular interactions. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H44.00010: Hierarchical roughness of sticky and non-sticky superhydrophobic surfaces Muhammad Akram Raza, Stefan Kooij, Arend van Silfhout, Harold Zandvliet, Bene Poelsema The importance of superhydrophobic substrates (contact angle $>$150\r{ } with sliding angle $<$10\r{ }) in modern technology is undeniable. We present a simple colloidal route to manufacture superstructured arrays with single- and multi-length-scaled roughness to obtain sticky and non-sticky superhydrophobic surfaces. The largest length scale is provided by (multi-)layers of silica spheres (1$\mu $m, 500nm and 150nm diameter). Decoration with gold nanoparticles (14nm, 26nm and 47nm) gives rise to a second length scale. To lower the surface energy, gold nanoparticles are functionalized with dodecanethiol and the silica spheres by perfluorooctyltriethoxysilane. The morphology was examined by helium ion microscopy (HIM), while wettability measurements were performed by using the sessile drop method. We conclude that wettability can be controlled by changing the surface chemistry and/or length scales of the structures. To achieve truly non-sticky superhydrophobic surfaces, hierarchical roughness plays a vital role. [Preview Abstract] |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H44.00011: Alkane Self Assembling Tomas Corrales, Pia Homm, Piero Ferrari, Maria Jose Retamal, Valeria del Campo, Ulrich G. Volkmann Self-assembling of organic molecules has awaken scientific and technological interest. In this work we study the self-assembling process of long chain hydrocarbons, mainly $n$-dotriacontane ($n$-C32H66). We dip-coated C32 monolayers onto silicon wafers covered by their native silicon oxide layer (Si(100)/SiO2). Our results show that withdrawing speed affects the coverage and morphology of the C32 films. For slow withdrawing speeds, alkanes formed islands with a dragon-fly shape, while for fast withdrawing alkanes assembled in stripes with widths in the order of microns. When we quantified coverage and morphology versus withdrawing speed, we found an inflection, which we associate with a transition between two film deposition kinetics. These transitions have been previously described by de Gennes [1]. For slow withdrawing, film deposition follows the Langmuir-Blodget process and above a threshold speed, solution on the solid enters a Landau-Levich regime. This work opens the possibility for growing microstructures with nanometric thickness using a very simple method. These organic microstructures could be used as templates or as grids for optical diffraction. \\[0pt] [1] P.G. de Gennes, Colloid {\&} Polymer Sci. 264, 463-465 (1986). [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H44.00012: A Thermodynamic Treatment of Polymer Thin Film Glasses Ronald White, Jane Lipson We have recently developed a mean field equation of state (EOS) approach to model the thermodynamic properties of polymer thin films. The model is analytic and transparent yielding characteristic film properties as a ``whole sample'' average. We focus on the properties of freestanding thin films and, parameterizing only with bulk data, demonstrate how the EOS leads to predictions of film properties as a function of film thickness under varied thermodynamic conditions. We share some thoughts on how to use this model for the prediction of the thickness-dependent depression of the thin film glass transition temperature. [Preview Abstract] |
Tuesday, March 22, 2011 10:48AM - 11:00AM |
H44.00013: Non-equilibrium behavior of spin-cast films Katherine Thomas The behavior of polystyrene films cast from various solvents using an electric field to weakly perturb the free surface of the polymer melt was examined. The effective viscosity and residual stresses of the as-spun films strongly depend on the casting solvent. As-cast films had a substantially reduced viscosity compared to annealed films, with the greatest reduction in films cast from solutions near $\theta$-temperature. The reduced viscosity is explained in terms of non-equilibrium effects from the film formation process; rapid quenching during spin-coating results in a lower entanglement density of chains compared to an equilibrium melt. The difference in films spun from the various solvents is explained by changes in chain conformations in the initial solutions and the vitrification point. The wavelength of the instabilities in as-cast films was higher than expected, indicating a weak stabilizing pressure. This is attributed to frozen-in normal stresses resulting from an asymmetric deformation of the chains due to evaporation of residual solvent after vitrification. The results show the non-equilibrium nature of as-cast polymer films and that processing conditions strongly influence their behavior. [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