Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A28: Polymer Surfaces I |
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Sponsoring Units: DPOLY Chair: Chang Yeol Ryu, Rensselaer Polytechnic Room: LACC 506 |
Monday, March 21, 2005 8:00AM - 8:12AM |
A28.00001: Surface Diffusion of Single Polymer Chain Using Molecular Dynamics Simulation Tapan Desai, Pawel Keblinski, Sanat Kumar, Steve Granick Results of recent experiments on polymer chains adsorbed from dilute solution at solid-liquid interface show the power scaling law dependence of the chain diffusivity, D, as a function of the degree of polymerization, N, D $\sim $ N $^{-1.5}$. By contrast, for DNA molecules bound to fluid cationic lipid bilayers D $\sim $ N $^{-1}$. We use molecular dynamics simulations to gain an understanding of these scaling behaviors. Our model systems contain chains comprised of N monomers connected by springs, embedded into athermal solvent confined between two solids plates. We will discuss the nature of dynamic adsorption transition and effects of hydrodynamics forces on chain diffusion and scaling exponent. [Preview Abstract] |
Monday, March 21, 2005 8:12AM - 8:24AM |
A28.00002: Single-Molecule Studies of Polymer Translational Diffusion at Surfaces Liang Hong, Steve Granick Single-polymer diffusion at solid and organic solvent interfaces has been investigated with polydimethylsiloxane (PDMS) using both fluorescence correlation spectroscopy (FCS) and single-molecule imaging (SMI). In contrast to previous related work from this laboratory, here we cover a broad range of concentrations, from the melt state to polymers adsorbed from dilute solution. As the surface coverage increases above the dilute regime, the translational diffusion coefficient as well as the polymer conformations vary with a complex interdependence. Initially diffusion speeds up with increasing surface coverage; this is followed by an obvious jamming process at higher surface coverage. Studies in progress involve not only the dependence on polymer molecular weight and its concentration in the liquid phase, but especially on film thickness when the polymers are confined into molecularly-thin films inside a modified surface forces apparatus. [Preview Abstract] |
Monday, March 21, 2005 8:24AM - 8:36AM |
A28.00003: Wetting of Heterogeneous Surfaces by Polymer Nanodroplets David R. Heine, Gary S. Grest, Edmund B. Webb III The development of microfluidics, micro-contact printing, and other micron scale processes has led to renewed interest in surface wetting at sub-micron length scales. Molecular dynamics simulation is used to study the dynamics of polymer nanodroplets wetting heterogeneous surfaces, specifically cylindrical polymer droplets on surfaces composed of strips oriented perpendicular to the droplets that have either strong or weak interactions with the polymers. Each polymer droplet contains $\sim$200,000 to 350,000 monomers described using the bead-spring model with either 10 or 100 monomers per chain. The droplets are initially placed in contact with a patterned surface at a contact angle near 90$^{\circ}$. As the droplets wet the surface, the spreading dynamics over different regions of the surface is monitored through measurement of the contact angle, contact radius, and velocity profiles. The spreading dynamics are strongly dependent on the wavelength of the strips relative to the polymer chain length. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 8:48AM |
A28.00004: Non-Spherical Droplets of Diblock Copolymer: Equilibrium Shape and Spreading Kinetics Andrew B. Croll, Michael V. Massa, Kari Dalnoki-Veress, Mark W. Matsen Conventional liquid droplets minimize surface energies by acquiring the shape of a spherical cap. In the case of symmetric diblock copolymers microphase separation yields the additional energy constraint of a lamellar microstructure. We present a study of droplets of symmetric polystyrene-b-poly (methyl methacrylate) (PS-b-PMMA), which consist of stacked lamellar disks. Ordered PS-b-PMMA droplets are found to have a non-spherical shape that can be nearly conical under certain conditions. Most significantly, this droplet shape becomes spherical upon passing through the order disorder transition. The near conical equilibrium droplet shape can be understood from a simple model with a repulsive interaction between the lamellar edges in adjacent disks. Furthermore, droplet spreading is found to deviate from Tanner's law in a predictable way. [Preview Abstract] |
Monday, March 21, 2005 8:48AM - 9:00AM |
A28.00005: Origin of surface ordered phase in poly(n-alkyl acrylates) above the bulk melting temperature (Tm) Shishir Prasad, Laurie Hanne, Ali Dhinojwala We present the first surface tension ($\gamma )$ measurements as a function of temperature above T$_{m}$ for poly(n-alkyl acrylates) to explain the presence of surface ordered phase. The surface tension increases with increase in temperature indicating that the surface molecules have lower entropy than in the bulk. There is an abrupt change in slope of $\gamma $ \textit{vs} T at T$_{s2}$ ($>$T$_{m})$ indicating a first order surface transition. The temperature range of the ordered phase is much larger than that observed for small molecule alkanes and alcohols. We determine that this is primarily due to partial crystallinity within the side chains. The consequences of these results have important implications in similar systems containing chemically attached hydrophobic side chains such as surfactants, dendrimers and biomolecules. [Preview Abstract] |
Monday, March 21, 2005 9:00AM - 9:12AM |
A28.00006: Functional gradients with controlled steepness on self-assembled aminosilane monolayers Ying Zou, Steve Story, Shane Harton, Harald Ade A high throughput, and cost-effective way to fabricate functional gradients of controlled steepness (up to $\sim $10$\mu $m for full gradient) on organic self assembled monolayer (SAM) films has been achieved. The exposure of a aminopropyltriethoxylsilane(APTES) film prepared on a SiOx substrate to ultraviolet (UV) light, with and without the creation of ozone, is controlled by a movable shutter that shadows the sample from the UV source. The shutter to the substrate spacing sets a lower limit to the steepness of the gradient, whereby both the diffusion field of ozone and the divergence of incident UV light are responsible. Through the attachement of 0.26 $\mu $m sized polystyrene (PS, carboxyl-group ended) microspheres (MSs) onto the exposed APTES films via chemical reaction in an activated MS suspension, the fabricated gradient can be visualized directly with a visible light microscope operated in Normarsky interference mode. The short MS density-saturation time observed suggests that covalent bonding is established between the MSs and the APTES film through the reaction of carboxyl- with amine- groups [1]. The use of a linar, variable shutter speed in conjuction with the saturation time allows for the variation and control of the gradients steepness. Reference: [1] S. Herrwerth et al Langmuir 19(2003) 1880-1887 [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:24AM |
A28.00007: Measurement of Adhesion Energy and Young’s Modulus in Thin Polymer Films Using a Novel Axi-symmetric Peel Test Geometry Adam N. Raegen, Kari Dalnoki-Veress We present a method of probing adhesion between solids, particularly in systems involving polymers. This method uses the axi-symmetric deformation of a thin spincast polymer membrane brought into contact with a film supported on a substrate to measure the work of adhesion between the pair. In this geometry, the contact area and constitutive relation (force versus displacement curve), are measured. This enables the determination of Young's modulus, surface energy, and the pretension of the free-standing film, which are in good agreement with accepted values. [Preview Abstract] |
Monday, March 21, 2005 9:24AM - 9:36AM |
A28.00008: Changes in the Molecular Orbitals during Photochemical Patterning of Polymers K. M. Pellerin, F. J. Himpsel, E. W. Edwards, P. F. Nealey Patterning of surfaces by EUV irradiation into hydrophilic and -phobic stripes has recently been demonstrated as promising technique for directed self-assembly [1]. In order to better understand this process we have detected the changes in the molecular orbitals at the surface using near edge X-ray absorption fine structure (NEXAFS) sepctroscopy. In particular, the effect of extreme ultra-violet (EUV) radiation on PS-r-MMA is studied. Irradiation causes spectral weight to be transferred from C 1s to pi* transitions of C=C bonds and similar transitions at C=O bonds, which indicates insertion of oxygen into pi-bonded carbon sites. The effect is quantified by dose-dependent studies. [1] Kim, et al. Nature 424, 411 - 414 (2003) [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A28.00009: Water adsorption and desorption from crystalline P(VDF-TrFE) copolymers Jie Xiao, Luis Rosa, Peter Jacobson, Peter Dowben Water adsorption and absorption on crystalline poly(vinylidene fluoride -- trifluoroethylene), was examined by thermal desorption spectroscopy. Two distinctly different water adsorption sites are identified: one adsorbed species that resembles ice and another species that interacts more strongly with the polymer thin film. The existence of the latter species is consistent with X-ray diffraction studies of water absorbed into the bulk of copolymers of poly(vinylidene fluoride -- trifluoroethylene) crystalline thin films. There are strong steric effects observed in the angle-resolved thermal desorption that may be a result of the large polymer thin film surface dipoles. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A28.00010: Polymer size and affinity effects on nanopore adsorption with a wide range of pore sizes Chansu Kim, Chang Yeol Ryu We study polymer nanopore adsorption in solution using nanoporous silica and investigate how these processes differ from those on flat surfaces. In particular, we studied the adsorption of monodisperse polystyrenes onto nanoporous silica with an average pore size ranging from 8 to 100 nm at various solvent quality conditions. We found that the polymer nanopore adsorption phenomena were greatly affected by time, temperature, concentration and solvent quality. In general, the surface excess of polystyrene adsorption exhibits a maximum when the radius of gyration is similar to that of the small pores. However, in large pores, the polystyrene shows the maximum adsorption when the radius of gyration was approximately half the diameter of the pores. This result reveals that the polymer entanglement due to steric crowding at the nanopore entrance on the outer surface has a critical role for controlling diffusion and the subsequent adsorption into the pore. [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A28.00011: Solvent-Assisted Formation of Nanostrand Networks of Supramolecular Diblock Copolymer-Surfactant Complexes at the Air-Water Interface C. Geraldine Bazuin, Qing Lu A block copolymer of majority styrene and minority vinylpyridine (PS-b-P4VP; PS 40K, P4VP 5.6K) mixed with a stoichiometric amount (relative to the VP block) of hydrogen-bonding 3-n-pentadecylphenol (PDP) was investigated at the air-water interface and as transferred films imaged by AFM. By respecting the conventional waiting period to allow solvent evaporation following spreading of the polymer solution on the Langmuir bath and before barrier compression, circular aggregates of variable sizes were obtained at moderate surface pressures. When, instead, the barriers were compressed to the same surface pressures as soon as possible after spreading, a dense and infinite network of nanostrands was obtained. This phenomenon may be attributed to the solvent maintaining the necessary flexibility for the polymer chains to undergo reorganization in response to the change in surface pressure. [Preview Abstract] |
Monday, March 21, 2005 10:12AM - 10:24AM |
A28.00012: Contact Mechanics Studies with the Quartz Crystal Microbalance F. Nelson Nunalee, Kenneth R. Shull The mechanism of adhesion between two surfaces that are immersed in a liquid medium is a problem of critical scientific and industrial importance. Practical applications range from targeted drug delivery systems to coatings that are designed to resist fouling by marine organisms. However, quantitative measurement of adhesion in liquids is often complicated by difficulties in determining the true nature of the contact between the two surfaces. In some cases a lack of optical contrast makes it difficult to visualize the contact area, whereas in other cases the optically determined contact may not represent a region of true mechanical contact. We have utilized the quartz crystal microbalance (QCM) in contact mechanics experiments because its response is coupled to the surface rheological properties of the materials that are pressed against it. We have shown that when a hemispherical polymer gel is brought into contact with the electrode surface of the QCM, changes in both the resonant frequency and the dissipation are proportional to the gel/QCM contact area. The actual proportionality constants are determined by the high frequency rheological response of the gel. As a result we have been able to calibrate the QCM for use as a highly sensitive contact sensor for fundamental studies of adhesion of polymer gels. [Preview Abstract] |
Monday, March 21, 2005 10:24AM - 10:36AM |
A28.00013: Quantitative measurement of adhesion of ink on plastic films with a Nano Indenter and a Scanning Probe Microscope Weidian Shen, Bin Jiang Plastic film packaging is widely used these days, especially in the convenience food industry due to its flexibility, boilability, and microwavability. Almost every package is printed with ink. The adhesion of ink on plastic films merits increasing attention to ensure quality packaging. However, inks and plastic films are polymeric materials with complicated molecular structures. The thickness of the jelly-like ink is only 500nm or less, and the thickness of the soft and flexible film is no more than 50$\mu $m, which make the quantitative measurement of their adhesion very challenging. Up to now, no scientific quantitative measurement method for the adhesion of ink on plastic films has been documented. We have tried a technique, in which a Nano-Indenter and a Scanning Probe Microscope were used to evaluate the adhesion strength of ink deposited on plastic films, quantitatively, as well as examine the configurations of adhesion failure. It was helpful in better understanding the adhesion mechanism, thus giving direction as to how to improve the adhesion. [Preview Abstract] |
Monday, March 21, 2005 10:36AM - 10:48AM |
A28.00014: Puzzles in Surface Force Apparatus (SFA) Experiments Janet Wong, Yingxi Zhu, Steve Granick Since Frantz and Salmeron (1998) found that the surface energy of recleaved mica is 50{\%} higher than that cleaved using conventional cleaving method detailed in Israelachvili et al. (2004), there is concern in the SFA community on how the mica surface preparation influences observations. In addition, mica's surface condition might be responsible for the divergence between experiments and computer simulation in this area. Our group has been working on mica cleaved based on the ``Salmeron method.'' While some differences in results were obtained from mica prepared by different methods, the underlying cause for such discrepancy is not well understood. In addition, it is not clear if mica preparation affects all SFA results performed in different experimental conditions equally. This presentation will give a comparison on results obtained using mica with different cleaving methods. Experimental parameter(s) that renders mica surface condition an important consideration will be discussed. [Preview Abstract] |
Monday, March 21, 2005 10:48AM - 11:00AM |
A28.00015: Confocal Raman-AFM, A New Tool for Materials Research Ute Schmidt, Klaus Weishaupt, Wolfram Ibach, Matthias Kress, Olaf Hollricher Characterization of heterogeneous systems, e.g. polymers, on the nanometer scale continues to grow in importance and to impact key applications in the field of materials science, nanotechnology and catalysis. The development of advanced polymeric materials for such applications requires detailed information about the physical and chemical properties of these materials on the nanometer scale. However, some details about the phase-separation process in polymers are difficult to study with conventional characterization techniques due to the inability of these methods to chemically differentiate materials with good spatial resolution, without damage, staining or preferential solvent washing. The CR-AFM is a breakthrough in microscopy. It combines three measuring techniques in one instrument: a high resolution confocal optical microscope, an extremely sensitive Raman spectroscopy system, and an Atomic Force Microscope. Using this instrument, the high spatial and topographical resolution obtained with an AFM can be directly linked to the chemical information gained by Confocal Raman spectroscopy. To demonstrate the capabilities of this unique combination of measuring techniques, polymer blend films, spin coated on glass substrates, have been characterized. AFM measurements reveal the structural and mechanical properties of the films, whereas Raman spectral images show the chemical composition of the blends. [Preview Abstract] |
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