Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session B25: Focus Session: Adhesion, Swelling, and Elastic Properties of Thin Polymer Films |
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Sponsoring Units: DPOLY Chair: Theresa Hermel-Davidock, Dow Chemical Room: Colorado Convention Center 203 |
Monday, March 5, 2007 11:15AM - 11:51AM |
B25.00001: Interaction and Viscoelastic Deformation of Polymeric Surfaces Measured with the Atomic Force Microscope Invited Speaker: Methods are described for the measurement and analysis of deformable surfaces with the atomic force microscope (AFM). It is shown how to obtain the zero of separation and how to calibrate the photo-diode for quantitative force measurement [1]. The properties of viscoelastic materials (relaxation times, Youngs moduli) may be extracted by modeling particular sorts of force measurements [2]. Results are shown for a biopolymer agar [3], and for a polyelectrolyte polydimethylsiloxane [4], both of which are viscoelastic, and for polystyrene, which is elastic [5]. The potential for using the AFM as a nanorheometer is discussed. \newline \newline [1] P. Attard, ``Friction, Adhesion, and Deformation: Dynamic Measurements with the Atomic Force Microscope'', J. Adhesion Sci. Technol. 16, 753--791 (2002). \newline [2] P. Attard, ``Interaction and Deformation of Viscoelastic Particles. Non-adhesive Particles'', Phys. Rev. E 63, 061604 (2001) \newline [3] J. W. G. Tyrrell and P. Attard, ``A Viscoelastic Study Using and Atomic Force Microscope Modified to Operate as a Nanorheometer'', Langmuir 19, 5254--5260 (2003) \newline [4] G. S. Gillies, C. A. Prestidge, and P. Attard, ``An AFM Study of the Deformation and Nano-rheology of Cross-Linked PDMS Droplets'', Langmuir 18, 1674--1679 (2002) \newline [5] M. W. Rutland, J. W. G. Tyrrell, and P. Attard, ``Analysis of Atomic Force Microscopy Data for Deformable Materials'', J. Adhesion Sci. Technol. 18, 1199--1216 (2004) [Preview Abstract] |
Monday, March 5, 2007 11:51AM - 12:03PM |
B25.00002: Surface wrinkling of grafted polymer brushes and its effect on interfacial adhesion Christopher M. Stafford, Heqing Huang, Jun Young Chung Grafted polymer brushes present a simple and convenient route to generate a rich and diverse parametric space that expresses the chemical complexity found at materials surfaces and interfaces. For example, adhesion at the interface can be tuned by controlling the chemistry, length, and density of the grafted polymer brush. If constructed on a soft elastomer, these polymer brushes can undergo wrinkling at the interface, creating a powerful combination of surface chemistry and topography, both of which play a critical role in interfacial adhesion. Here, we present strategies to control the adhesion strength through changes in brush length and composition, solvent quality, and modulus of the elastomer. A phenomenological model for the development and growth of the wrinkled surface is developed to explain the observed results. [Preview Abstract] |
Monday, March 5, 2007 12:03PM - 12:15PM |
B25.00003: Experiments of compaction of an elastic sheet closely-packed in a rigid container Deboeuf Stephanie, Boue Laurent, Adda-Bedia Mokhtar, Boudaoud Arezki When crumbling a sheet of paper, it is known that deformation essentially appears in localized and lineic singularities, the so-called developable cones and ridges. But how relate the emergence of such patterns to the global shape of the sheet and to the compression force needed to compact it? We try to answer to such a question in the case of a model experiment of compaction. When a circular sheet is pulled through a rigid hole, first it exhibits a conical shape -developable cone-, then it develops folded patterns to achieve close-packed configurations. Our experimental set-up allows simultaneously for the observation and statistical characterization of folded configurations and for the measure of mechanical forces. Different patterns of folds are observed and systematically characterized as a function of the packing fraction of the sheet within the hole. [Preview Abstract] |
Monday, March 5, 2007 12:15PM - 12:27PM |
B25.00004: Dependence of the in-plane modulus of thin free-standing polymer films Adam N. Raegen, Kari Dalnoki-Veress We employ an axi-symetric deformation and modulus test to measure the in-plane elastic modulus of free-standing polymer films. This method measures the deformation of a thin spincast film when a flat circular punch is brought into contact with the sample. The use of a small, flat punch minimises uncertainties in the experiment, while the use of spincast films provides a very smooth surface. We will present a study of the dependence of the elastic modulus on the film thickness and the annealing history of the samples. [Preview Abstract] |
Monday, March 5, 2007 12:27PM - 12:39PM |
B25.00005: Measuring Correlation Functions and Elastic Constants of 2D Layers of Block Copolymers by Single Crystal Diffraction Gila Stein, Edward Kramer, Xuefa Li, Jin Wang Monolayers of spherical-domain block copolymer, exhibiting hexagonal symmetry with a periodicity of 29nm, are laterally confined in hexagonal wells 12$\mu$m wide and 26nm deep that span the entire area of a 2-inch diameter silicon wafer. At 210 $^{\circ}$C, films that are 41nm thick (monolayer plus brush) form oriented single crystals in each well, where the close- packed rows of the lattice are aligned parallel to the edges. The structure is characterized with grazing-incidence small- angle x-ray diffraction, and results are interpreted within the KTNHY framework for a 2D crystal. Translational order decays algebraically with a correlation function of the form g$_t$(r) $\sim$r$^{-0.25}$, and from the magnitude of the decay exponent, the 2D shear modulus of the crystal $\mu=1.7\times10^ {-4}$N/m can be extracted. Orientational order is long-range, with a full width at half maximum of 1.1$^{\circ}$. Decreasing the film thickness by 1nm produces hexatic ordering with a translational correlation length on the order of 0.5$\mu$m, and diminished orientational order with a full width at half maximum of 2.4$^{\circ}$. These results agree qualitatively with high resolution scanning force microscopy images of the lattice. [Preview Abstract] |
Monday, March 5, 2007 12:39PM - 12:51PM |
B25.00006: Polymer-Solid Interface Connectivity and Adhesion: Design of a Pressure Sensitive Adhesive Shana P. Bunker, Richard P. Wool Adhesion at polymer-solid interfaces was explored for a new bio-based PSA in terms of sticker groups $\phi _{X }$ on the polymer, receptor groups $\phi _{Y}$ on the solid and the strength of the X-Y acid-base interaction, $\chi $. The polymer-solid interface models of Gong, Lee and Wool were extended with new percolation models of entanglements and interface strength to determine the optimal sticker group concentration $\phi $*$_{X}$. For the general case where $\phi _{Y}$ and $\chi $ are constant, it is predicted that when $\phi _{X}<\phi $*$_{X}$, the peel strength behaves as G$_{1c}\sim \phi _{X}$/$\phi $*$_{X}$ and the locus of failure is adhesive between the polymer and the solid. However, when $\phi _{X}>\phi $*$_{X}$, failure occurs cohesively in a polymer-polymer interface adjacent to the solid and the strength decreases as G$_{1c}\sim \phi $*$_{X}$/$\phi _{X}$. The switch from adhesive to cohesive failure can be understood in terms of the changes in the chain conformations of the adhered chains and their decreasing interpenetration X with the bulk chains, via X$\sim $1/r, where r = $\chi \phi _{X}\phi _{Y}$. The optimal value of $\phi _{X}$ which maximizes the adhesion and determines the mode of failure is given by $\phi $*$_{X}\approx $0.07/C$_{\propto }$, and for typical values of the characteristic ratio C$_{\propto }$ in the range 7-10, $\phi $*$_{X}\approx $1{\%} mole fraction, corresponding to about 2 sticker groups per critical entanglement length M$_{c}$. Supported by USDA [Preview Abstract] |
Monday, March 5, 2007 12:51PM - 1:03PM |
B25.00007: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 1:03PM - 1:15PM |
B25.00008: Welding Immiscible Polymer with Supercritical Fluid Xiaochu Wang, Isaac Sanchez Polymer adhesion between two immiscible polymers is usually poor because there is little interpenetration of one polymer into the other at the interface. Thus, increasing the width of the interfacial zone can enhance adhesion and mechanical properties. In principle, this can be accomplished by exposing the solid polymer materials to high pressure CO2. The CO2 acts as a common solvent and promotes interpenetration. It also increases the mobility at the interface which helps to promote the ?welding? of the two polymers. A combination of the gradient theory of inhomogeneous systems and the Sanchez-Lacombe Equation of State was used to investigate this phenomenon. We calculate the interfacial density profile, interfacial thickness and interfacial tension between the two polymers with and without CO2. We find that the interfacial tension is decreased and the interfacial thickness is increased with high pressure CO2, which means that the presence of CO2 does help polymer welding. [Preview Abstract] |
Monday, March 5, 2007 1:15PM - 1:27PM |
B25.00009: Off-Specular Neutron and X-ray Reflectometry for the Structural Characterization of Buried Interfaces Kristopher Lavery, Vivek Prabhu, Eric Lin, Wen-li Wu, Kwang-Woo Choi, Sushil Satija, Matthew Wormington For applications in semiconductor processing and nanotechnology, the lateral structure of interfaces can significantly affect the performance of a given device. For example, roughness on the edges of developed photoresist patterns can reduce the performance of the final devices. Off-specular reflectometry is a non-destructive scattering technique sensitive to lateral compositional variations at surfaces and interfaces. It is particularly well-suited as a means of measuring the form and amplitude of surface roughness, as well as separating contributions from physical roughness and gradients in material density. In this work, model rough surfaces were prepared on float glass substrates and the roughness and lateral correlation lengths were cross-correlated using neutron and x-ray off-specular reflectometry measurements. These techniques were extended to observe the lateral correlation length of the reaction-diffusion front in a model photoresist using a polymer-polymer bilayer designed to mimic an ideal lithographic line edge. These experiments highlight the advantages of the technique for the investigation of buried interfaces while illustrating how x-ray and neutron techniques work complementarily to measure interfacial roughness. [Preview Abstract] |
Monday, March 5, 2007 1:27PM - 1:39PM |
B25.00010: Confinement Effects on the Swelling Behavior of Thin Polymer Films Aleta Hagman, Kenneth R. Shull, Jin Wang, Martin Tolkiehn, Xuefa Li, Suresh Narayanan Marker motion can be used to measure polymer dynamics in polymer/metal nanocomposite thin films. In our current experiments, thermally evaporated gold particles (few nanometers in diameter) act as a marker layer between two polymer layers with different mobilities. To create the differing mobilities we are using a low molecular weight poly(2-vinyl pyridine) (PVP) on one side of the marker layer and a high molecular weight PVP on the other. The low molecular weight PVP will swell into the higher molecular weight polymer, when heated above the polymer glass transition temperature, creating a flux of the marker atoms in the opposite direction. We have used X-ray standing waves (XSWs), generated by total external reflection above a mirror surface, as a probe to monitor the time evolution of the gold nanoparticle distribution in the nanocomposite ultrathin films. Swelling kinetics are obtained from the measured time-dependence of the nanoparticle distribution. We will also discuss the effects the free surface and the mirror surface have on the amount of swelling observed. [Preview Abstract] |
Monday, March 5, 2007 1:39PM - 1:51PM |
B25.00011: Equilibrium and Kinetic Water Uptake in Ultrathin Chitosan Films Chris Murray, John Dutcher We present the results of ellipsometry and surface plasmon resonance experiments of equilibrium and kinetic water uptake in ultrathin films of chitosan that have been prepared by spincoating from dilute solution. Exposure of the films to increasing relative humidity results in increases in thickness and mass due to the absorption of water from the surrounding atmosphere. The equilibrium water content measured at different RH values can be interpreted in terms of either the average size of water clusters forming within the polymer matrix, or multilayers of water adsorbed onto specific sites within the matrix. Measurement of the time-dependence of water uptake allows the calculation of the diffusion coefficient of water in the films. We observed dramatic reductions in the water uptake of chitosan films that have been heated to temperatures 150 $^{o}$C $< \quad T \quad <$ 200 $^{o}$C: the equilibrium water content is reduced by more than a factor of four and the diffusion coefficient of water in the films decreases by more than a factor of two. We suggest that this irreversible reduction in the equilibrium water content and the diffusion coefficient for water in the films is caused by the formation of new inter- and intra-molecular bonds within the polymer matrix, and we present one possible mechanism that is consistent with all of our observations. [Preview Abstract] |
Monday, March 5, 2007 1:51PM - 2:03PM |
B25.00012: Grafting of Telechelic Polymers onto Functionalized Substrate in Polymeric Matrices Rujul Mehta, Zhenyu Huang, Haining Ji, Jimmy Mays, Mark D. Dadmun We have investigated the grafting of polymer chains on an inorganic surface by reaction of the functional end-groups on the polymer chains. Specifically, polystyrene (PS) terminated at one or both ends with carboxylic acid groups is grafted onto silica modified with epoxy groups by spin coating a thin film of a blend of reactive and non-reactive PS onto the silica wafer and promoting the grafting reaction. This generates a model system to study the impact of the volume fraction of reactive polymer and the chain length of both reactive and matrix polymers on the resultant grafted brush. The interfacial excess isotherms are correlated to a theoretical model proposed by Shull, which describes the end adsorption of polymers at polymer/substrate interfaces in brushes based on scaling arguments and self-consistent field theory. Comparison is made between the characteristics of brushes formed from PS chains that are reactive at one or both ends. [Preview Abstract] |
Monday, March 5, 2007 2:03PM - 2:15PM |
B25.00013: Kinetics of Grafting and Loop Formation of Telechelic Polymers on Solid Substrate Mark Dadmun, Zhenyu Huang, Haining Ji, Jimmy Mays A simple system was used to examine loop formation at polymer/substrate interfaces. Telechelic polystyrene terminated with carboxylic acid end groups was grafted from the melt onto a silicon wafer modified with epoxy-terminated silane layers. This study focuses on understanding how molecular weight, annealing temperature, and surface functionality affect the grafted amount and grafting kinetics. It was found that the practical limit of the grafted amount scales as $R_{g}$ leading to a -0.5 power law for the surface density as a function of molecular weight. The kinetic results suggest that the grafting process is most likely reaction controlled. By labeling the free carboxylic acid groups on singly bound chains with a fluorescence probe, the time dependence of the amount of the singly bound chains was monitored using fluorimetry. The obtained results provide a method to control the loop formation at interfaces and understand their structure and properties. [Preview Abstract] |
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