Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session R25: Adhesion and Viscoelasticity in Polymer Thin Films |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Karen Winey, University of Pennsylvania Room: Baltimore Convention Center 322 |
Wednesday, March 15, 2006 2:30PM - 2:42PM |
R25.00001: QCM Studies of Polymer Gel Spreading in Liquid Environments Frank Nunalee, Bruce Lee, Phillip Messersmith, Kenneth Shull Adhesion of polymer gels to substrates is a complicated phenomenon, particularly if the system is submerged in a liquid. Establishment of mechanical contact hinges upon the details of the gel's surface structure. In many cases, the polymeric component of the gel is shielded by a segregated solvent layer. These issues have important implications for those interested in soft, adhesive materials for biological applications. In this investigation, we utilize the surface sensitivity of the quartz crystal microbalance (QCM) to study the spreading behavior of polymeric liquids and gels on a rigid surface while submerged in a liquid medium. While the QCM has been used extensively to study adsorption by exploiting its sensitivity to material properties in the direction normal to the crystal's electrodes, few studies have utilized the QCM's ability to sense changes in loading in the plane of the electrodes. We propose equations to describe the predicted response of the QCM to a generalized viscoelastic material spreading at the QCM surface at the expense of the surrounding liquid medium. Several experimental examples are given in order to support the validity of the proposed equations, including situations where the spreading material is a Newtonian liquid, a polymer solution, or a polymer gel. [Preview Abstract] |
Wednesday, March 15, 2006 2:42PM - 2:54PM |
R25.00002: Frictional properties of hydrophobic nanopatches in different solvents. Matteo Castronovo, Robert Hudej, Denis Scaini, Martina Dell'Angela, Loredana Casalis, Giacinto Scoles Controlling friction at the micro- and nano-scale is of crucial importance, especially in applications as micromachines. In order to develop new ways of controlling friction, it is extremely important to understand how friction depends on the atomic structure of the interface. Using nanografting, an AFM-assisted lithographic technique, we correlated frictional properties of alkanethiols with hydrophobic termination (CH3) and of alkenethiols with hydrophilic termination (OH) on the same surface in water and in 2-butanol, using the same tip. In 2-butanol friction on C11OH is higher than on the C18 patch since OH groups on the SiO2 AFM tip surface interact more strongly with OH groups on C11OH than with CH3 groups on C18. In water, due to the strong interactions between the OH groups, the solvent molecules form an ordered layer on OH terminated SAM, which can be penetrated by the AFM tip only at relatively high applied forces.. [Preview Abstract] |
Wednesday, March 15, 2006 2:54PM - 3:06PM |
R25.00003: Viscoelastic behavior of PDMS thin films with POSS nanofillers Wen Yin, Jianjun Deng, John R. Hottle, Hyong-Jun Kim , Alan R. Esker Blends of amphiphilic poly(dimethylsiloxane) (PDMS) and a model polyhedral oligomeric silsesquioxane (POSS) nanofiller, trisilanolisobutyl-POSS, have been studied via the Wilhelm plate technique and surface light scattering (SLS). The surface pressure -- surface concentration isotherms indicate that as the weight percentage of POSS increases in the blend systems, the collapse pressure of PDMS. SLS results reveal that increasing film's POSS content increases the dilational modulus of the PDMS thin films. This system is ideal for studying how nanofillers affect the viscoelastic behavior of polymer thin films at an attractive surface. [Preview Abstract] |
Wednesday, March 15, 2006 3:06PM - 3:18PM |
R25.00004: Modified Side-Chain Liquid Crystalline Polymer Thin Films as Low Adhesion Surfaces Haris Retsos, Daewon Lee, Costantino Creton, Kookheon Char The adhesive properties of side-chain liquid crystalline block copolymer thin films against soft acrylic pressure-sensitive-adhesive layers have been investigated with the probe method. Since the structure of the thin films varies from crystalline to liquid crystalline or to fully isotropic state as a function of temperature, we investigated the effect of annealing temperature of the interface on the adhesive properties. All the layers displayed very low adhesion at room temperature but above the crystalline to LC transition temperature, this low adhesion property disappears, presumably due to the reorganization of interfacial structure. To avoid this reconstruction, the 14C alkyl side-chains were modified by the incorporation of SO$_{2}$ groups that experience the dipole-dipole interactions and provide remarkable temperature stability to the crystalline phases. We further investigated the influence of the position and the kind of polar group in the side-chains on the structural and adhesion properties of those block-copolymers. [Preview Abstract] |
Wednesday, March 15, 2006 3:18PM - 3:30PM |
R25.00005: Polydispersity Effects on Polymer-Polymer Welding. Anna Barnette, Richard Wool, Ian McAninch During polymer-polymer welding, it is generally accepted that molecular weight distribution $\phi $(M) and its polydispersity (PD) affects the weld strength and required welding times. However, current welding models do not adequately address the role of PD coupled with interdiffusion Reptation dynamics, entanglement connectivity and relations between the fractal interface structure and strength, which would allow the optimal selection of the molecular weight distribution $\phi $(M). A computer simulation was developed to predict the microscopic effects of PD on welding and the results are compared with experiments on model blends of monodisperse polystyrenes (PS). The validity of the model was tested using Double Cantilever Beam PS samples that were first wetted below, and then welded for various times t, above the glass transition temperature. Wedge cleavage fracture testing determined that the weld strength G$_{1c}$ reached the maximum strength G* at an interfacial penetration contour length of 240 kDa corresponding to M* = 8 M$_{c}$. The simulations and experiments for monodisperse interfaces yielded G$_{1c}$(t) = G*[t/$\tau $]$^{1/2 }$where the welding time behaved as $\tau \quad \sim $ M, and $\tau $ was less than the Reptation time T$_{r }\sim $ M$^{3}$. For polydisperse samples, the time exponent of $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ decreased empirically with increasing PDI and the welding times were related to various moments of $\phi $(M) and increased with increasing PDI until a PDI of approximately 12 was reached. The welding times for strength development are much shorter than the welding times for maximum fatigue resistance. [Preview Abstract] |
Wednesday, March 15, 2006 3:30PM - 3:42PM |
R25.00006: Lubrication by glycoprotein brushes. Bruno Zappone, Marina Ruths, George W. Greene, Jacob Israelachvili Grafted polyelectrolyte brushes show excellent lubricating properties under water and have been proposed as a model to study boundary lubrication in biological system. Lubricin, a glycoprotein of the synovial fluid, is considered the major boundary lubricant of articular joints. Using the Surface Force Apparatus, we have measured normal and friction forces between model surfaces (negatively charged mica, positively charged poly-lysine and aminothiol, hydrophobic alkanethiol) bearing adsorbed layers of lubricin. Lubricin layers acts like a versatile anti-adhesive, adsorbing on all the surfaces considered and creating a repulsion similar to the force between end-grafted polymer brushes. Analogies with polymer brushes also appear from bridging experiment, where proteins molecules are end-adsorbed on two opposing surfaces at the same time. Lubricin `brushes' show good lubricating ability at low applied pressures (P$<$0.5MPa), especially on negatively charged surfaces like mica. At higher load, the adsorbed layers wears and fails lubricating the surfaces, while still protecting the underlying substrate from wearing. Lubricin might thus be a first example of biological polyelectrolytes providing `brush-like' lubrication and wear-protection. [Preview Abstract] |
Wednesday, March 15, 2006 3:42PM - 3:54PM |
R25.00007: Understanding Polymer Adhesion: Calculations of Adsorption of Organic Molecules onto Si and SiO$_2$ Surfaces Karen Johnston, Risto Nieminen The adhesion of polymer films onto metal and oxide materials is important for many industrial and technological applications. It is therefore essential to understand the underlying structure and bonding of the polymer and the surface. The aim of this research is to seek methods to improve polymer adhesion by using a multiscale approach. The first step involves the use of density functional calculations to understand the atomic-scale structure and bonding of polymers on surfaces. I will present first-principles results for the adsorption of benzene and related molecules on Si and SiO$_2$ surfaces. I will then discuss how this information will be incorporated into larger scale methods, such as Kinetic Monte Carlo or coarse-graining techniques. This research is supported by a grant from the Finnish Technology Development Agency (TEKES). [Preview Abstract] |
Wednesday, March 15, 2006 3:54PM - 4:06PM |
R25.00008: Differential pressure experiment to probe adhesive interactions in thin films Anny Flory, David Brass, Kenneth Shull In our laboratory we have developed a highly sensitive experiment which allows the measurement of very weak adhesive interactions between interfaces joined together by specific bonds. In the experiment, we place a membrane across a glass tube and use a syringe pump to apply a pressure difference across the membrane. The membrane is then inflated into contact with a glass substrate or the quartz disk of a quartz crystal resonator that is functionalized as desired and is immersed in an aqueous environment. A Langmuir layer is placed at the interface between air and water providing the modification of the surface chemistry of the membrane. The asymmetric Laplace equation is used to derive the energy release rate (G) from the experimental results. The advantage of this method is that specific and weak adhesive interactions as the ones encountered in biological systems can be accessed but also that the approach can be extended to measurement of very strong adhesive interactions such as those in synthetic gels. In this discussion, the validity of the method will be presented through results obtained on adhesive interactions between various model systems. [Preview Abstract] |
Wednesday, March 15, 2006 4:06PM - 4:18PM |
R25.00009: Capillary wave dynamics on viscoelastic polymer thin-films: Monolayers and bilayers Mark Henle, Alex Levine We investigate the capillary wave dynamics of supported polymeric thin-films both at the free surface and at the buried polymer/polymer interface in a bilayer system. Recent XPCS experiments (J. Lal, \textit{private communication}) on such systems suggest that the decay rate of the coupled capillary waves at the free surface and at the buried interface are remarkably independent of the in-plane wavevector. In order to understand this phenomenon, we present the results of continuum hydrodynamic calculations of the capillary wave dynamics on supported monolayers and bilayers of both Newtonian and viscoelastic fluids. We find that the experimentally observed wavevector dependence of the capillary-wave decay rate can be accounted for by treating one or both of the polymers as a viscoelastic fluid with a single stress-relaxation time. We also investigate the effect of a finite slip length at either the polymer/polymer interface or the polymer/substrate interface. [Preview Abstract] |
Wednesday, March 15, 2006 4:18PM - 4:30PM |
R25.00010: Molecular recoiling forces in ultra-thin films of long entangled polymer chains Arnold Chang-Mou Yang, Tony Ming-Hsun Yang, Sen-Yen Hou, Yu-Lun Chang Molecular recoiling force stemmed from non-equilibrium chain conformation was found to play a very important role in the dewetting stability of polymer thin films. Correct measurements and inclusion of this molecular force into thermodynamic consideration are crucial for analyzing dewetting phenomena and nanoscale polymer chain physics. This force was measured using a simple method based on contour relaxation at the incipient dewetting holes. The recoiling stress was found to increase dramatically with molecular weight and decreasing film thickness. The corresponding forces were calculated to be in the range from 9.0 to 28.2 mN/m, too large to be neglected when compared to the dispersive forces ($\sim $10 mN/m) commonly operative in thin polymer films. This work is supported by Air Force (AFOSR-04-4074) and National Science Council of Taiwan. [Preview Abstract] |
Wednesday, March 15, 2006 4:30PM - 4:42PM |
R25.00011: The Effect of Nanobubbles on Microcantilever Bending Sangmin Jeon, Ramya Desikan, Fang Tian, Thomas Thundat Nanomechanical cantilevers are very small and extremely sensitive force and mass sensors. Here, we report on the impact of the vertical component of surface energy on microcantilevers when nanobubbles form on their surfaces. Young's equation, which is commonly used to determine the contact angle of liquid drops on a solid surface, ignores the vertical component of the surface energy. Despite this force being extremely small and its effect on the solid can be ignored, it plays a significant role for flexible surfaces such as microcantilevers. A gold-coated silicon microcantilever and a dodecanethiol coated silicon microcantilever were used to detect real-time formation of nanobubbles on their surfaces when exposed to air-rich water. As air nanobubbles form on the surfaces of the cantilever, the cantilever undergoes bending and we relate this to the vertical component of surface energy in Young's equation. This implies that the vertical component of the surface tension should be considered for flexible solid surfaces, and the formation of nanobubbles should be avoided when cantilevers are used as sensors to avoid artifacts. [Preview Abstract] |
Wednesday, March 15, 2006 4:42PM - 4:54PM |
R25.00012: Measuring local viscoelastic properties of complex materials with atomic force microscopy Paula Wood-Adams, Wensheng Xu Tapping mode atomic force microscopy is a technique to measure the topography and properties of surfaces involving a micro-cantilever with a tip at one end that is excited into an oscillation near its resonance frequency. The cantilever-tip assembly is positioned vertically such that the tip touches the surface at the bottom of its down-stroke and then scanned over the surface. The oscillation of the cantilever is affected by the topography of the surface, the local surface properties and the feed back controller which maintains the amplitude of the oscillation at a fixed set point value. The vertical movements needed to maintain constant oscillation amplitude are used to draw the topography image and the phase lag of the oscillation relative to the excitation force is used to draw the phase image. The phase lag is sensitive to local mechanical properties under certain experimental conditions and we have found that by using silicon as an internal standard reference surface we can unambiguously relate the phase lag to local viscolastic properties of a polymeric material. We have built a model describing this relation, validated the model with experimental data and finally inverted it such that it can be used to determine local properties. This allows us to measure high frequency local viscoelastic properties on length scales as small as several nanometers. This technique works well for relatively compliant polymer surfaces with a shear modulus less than about 1 GPa. Funding Provided by the Taiho Kogyo Tribology Research Foundation. [Preview Abstract] |
Wednesday, March 15, 2006 4:54PM - 5:06PM |
R25.00013: The kinetics of the reaction of telechelics at a soft interface by neutron reflectivity J. Kevin Rice, Helen Ji, Mark Dadmun, Jimmy Mays The aim of this study is to gain a fundamental understanding of the kinetics of the in- situ formation of blocky copolymer molecules at a soft, immiscible polymer interface by the reaction of telechelic polymers across that interface. The resultant interfacial morphology that is formed from this reaction is also studied. Specular neutron reflectivity measurements were made after various annealing times on bilayer PS/PMMA samples, each of which contains dPS telechelics in one layer and monochelic PMMA in the other. Three reactive chain-end pairs were studied: epoxy-amine, epoxy- carboxylic acid, and amine-anhydride. After sufficient annealing of each system, an interfacial layer forms between the PS and PMMA that contains triblock copolymer formed by the reaction of the telechelics and the reactive PMMA chains. The thickness of this interfacial modifier layer, as well as the roughness between the matrix layers, increases with annealing time. Several molecular weights of the telechelics were studied and results relating the time evolution of the blocky copolymer volume fraction at the interface to interfacial excess, as well as interfacial coverage and reaction rate constants will be discussed. [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