Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H54: Tribology of Polymers and Soft Materials I: Time-Dependence and WearFocus
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Sponsoring Units: DPOLY GSOFT DFD GSNP Chair: Saad Khan, North Carolina State Univ Room: BCEC 254A |
Tuesday, March 5, 2019 2:30PM - 3:06PM |
H54.00001: Dillon Prize talk break
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Tuesday, March 5, 2019 3:06PM - 3:18PM |
H54.00002: Thermal-Induced Slippage of Soft Solid Films Xuanji Yu, Fei Chen, Chi-Hang Lam, Ophelia Tsui The dynamics of interfacial slippage of entangled polystyrene (PS) films on an adsorbed layer of polydimethylsiloxane (PDMS) on silicon was studied from the surface capillary dynamics of the films. By using PS with different molecular weights, we observed slippage of the films in the viscoelastic liquid and rubbery solid state respectively. Remarkably, all our data can be explained by the linear equation, J = -M▽P and a single friction coefficient, ξ, where J is the unit-width current, M is mobility and P is Laplace pressure. For viscous films, M is accountable by using conventional formulism. For rubbery films, M takes on different expressions depending on whether the displacements associated with the slip velocity, vs (~▽P/ξ), dominate or elastic deformations induced by ▽P dominate. For viscoelastic liquid films, M is the sum of the mobility of the films in the viscous and rubbery states. |
Tuesday, March 5, 2019 3:18PM - 3:30PM |
H54.00003: ABSTRACT WITHDRAWN
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Tuesday, March 5, 2019 3:30PM - 3:42PM |
H54.00004: Model Friction Studies of Chemical Mechanical Planarization using a Pin-on-Disk Tribometer Catheryn Jackson, David Mosley Chemical mechanical planarization (CMP) uses polyurethane polishing pads and highly engineered slurries to planarize, or polish, silicon wafers for semiconductor manufacturing. Friction is present as a critical aspect of this complex process, and is a function of pH, isoelectric point of the slurry particles, particle concentration, pad design, and other variables. Despite the connection of friction with CMP outcomes, detailed studies of friction and polishing are lacking due to the expense and difficulty of modifying commercial equipment to make precise tribology measurements. A pin-on-disk tribology attachment for the Anton-Paar MCR-502 rheometer can simulate a commercial polisher, to condition the pad in-situ and then polish the Si wafer. We measure both friction and the z-displacement, or change in gap, at realistic downpressures (1-5 psi) and sliding velocities (up to 1 m/s), which allows careful study of lubrication mechanisms, pad wear and slurry performance. The friction and z-displacement results for water at different pH’s are consistent with some mechanistic models used to represent surface and colloidal forces in these systems. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H54.00005: Eliminating the challenges associated with physically oscillating contact instruments Daniel Garcia, Thomas Angelini The material properties of soft matter systems are measured with rheometers and tensile testing instruments whenever there exist few limitations on sample volume and fixturing where samples can be prepared specifically to work with the hardware of a given instrument. By contrast, indentation methods are advantageous for measuring material properties when sample preparation and geometry are highly constrained, which is often the case with tissue samples, hydrogel coatings, or soft objects with defined shapes like contact lenses. However, many soft matter materials exhibit frequency-dependent moduli, which are challenging to account for using the simple models of Hertz and Winkler. In this talk I will review our recent work to developed a Fourier-analysis method that leverages the Kramers-Kronig relations to extract frequency dependent elastic and viscous moduli from Force-indentation curves, eliminating the challenges associated with physically oscillating contact instruments. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H54.00006: Rate and State Dependent Friction Law Showing Convex Velocity Dependence and Vanishing Static Friction Force Derived from Microscopic Point of View. Hiroshi Matsukawa Rate and state dependent friction law, which describe the behavior of the friction force in terms of the sliding velocity and the state varible, is well employed in the study of earthquake and so on. I derive new type of rate and state dependent friction law from microscopic point of view. It turns out that the static fricion force vanishes in generall. The kinetic friction force grows from zero with increasing sliding velocity. Under some condition the kinetic friction force shows maximun as a function of the sliding velocity in the stedy state. The physical mechanism of these behavior of the friction force is explained. The relation with the earthquake is also discussed. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H54.00007: Structure-Based Design of Anti-Fouling Polymer Nanocoating Maya Endoh, Daniel Salatto, Zhixing Huang, Mani K Sen, Yuma Morimitsu, Weiyi Li, Daisuke Kawaguchi, Keiji Tanaka, Yizhi Meng, David Thanassi, Tadanori Koga Fouling is the undesirable accumulation of a material on a wide variety of objects, such as medical devices, ship hulls, and membranes, and has now become a widespread global problem from land to ocean with both economic and environmental penalties. Here we report a radically new designed polymeric coating that is a few nanometers thick (“polymer nanocoating”) with an anti-fouling property. It is found that the anti-fouling property of this polymer nanocoating is generalizable to various homopolymer systems regardless of their hydrophilicity/hydrophobicity and their surface energy. This is attributed to the highly packed chain conformations via the self-organization process of the adsorbed polymer chains on the impenetrable solid surfaces. Furthermore, the preparation of the polymer nanocoating is a simple and versatile top-down approach based on good solvent rinsing. We hypothesized that the origin of the anti-fouling property is the highly packed conformation of polymer chains with a large number of segment/solid contacts within a two-dimensional space. This finding facilitates a simple and versatile structure-based design of an anti-fouling coating using common types of synthetic polymers. |
Tuesday, March 5, 2019 4:18PM - 4:54PM |
H54.00008: Mechanisms of Ultra-Low Wear Polymeric Solid Lubricants Invited Speaker: David Burris Polymeric solid lubricants can address the many limitations of more traditional lubrication systems including complexity, cost, maintenance requirements, vapor pressure, and sensitivity to environmental contamination, temperature, and composition. At present, commercially available materials have been designed based on the conventional wisdom that wear reductions require increased strength and toughness, and friction reductions require increased availability of soft/lamellar phases. Unfortunately, friction and wear reductions compete in this framework, which fundamentally limits overall tribological performance. The fundamental problem with the conventional wisdom is that it neglects to account for the transfer film, a layer of adhered debris that ultimately protects the solid lubricant from the counterface and vice versa. It is now understood that the friction and wear properties of these systems depend as much (and likely more) on the formation, properties, and stability of the transfer film as they do on the composition, structure, and properties of the solid lubricant itself. Unfortunately, the relevant transfer film properties have proven difficult to measure and the extent to which they contribute to friction and wear reduction remains unclear. In this talk, I will review some of the ultra-low wear polymeric solid lubricants we have developed and studied over the last decade, our efforts to understand the attributes of and specific roles played by the transfer film, and how we have applied these insights to a more useful materials design framework that prioritizes the properties and stability of the transfer film. |
Tuesday, March 5, 2019 4:54PM - 5:06PM |
H54.00009: Poroelastic sliding of thin grafted hydrogel layers Jessica delavoipière, Yvette Tran, Bertrand Herteufeu, Emilie Verneuil, Chung Yuen Hui, Antoine Chateauminois We investigate the sliding friction of thin (µm), water swollen, hydrogel layers grafted onto glass substrate with an emphasis on the contribution to friction of stress-induced poroelastic drainage of the hydrogel network. Friction experiments using poly(dimethylacrylamide) hydrogels films are carried out with the contact immersed in water. In addition to friction force measurements, an optical set-up allows imaging the contact. The velocity-dependence of friction force Ft and contact shape is found to be controlled by a Péclet number Pe corresponding to the ratio of advective (sliding) to diffusive components (fluid drainage). When Pe<1, the equilibrium circular contact achieved under normal indentation remains unchanged during sliding. Conversely, for Pe>1, a decrease in the contact area is observed together with the development of a contact asymmetry when velocity is increased. These findings are discussed in the light of a poroelastic model based on a thin film approximation. This model indicates that changes in contact geometry are due to the development of a pore pressure imbalance when Pe>1. An order of magnitude estimate of Ft and its dependence on normal load and velocity is provided under the assumption that most of frictional energy is dissipated by poroelastic flow. |
Tuesday, March 5, 2019 5:06PM - 5:18PM |
H54.00010: Time-dependent friction and polymer dynamics in hydrogel surface contacts Nicholas L Cuccia, Suraj Pothineni, Justin Burton Hydrogels are composed of a sparse, crosslinked polymer matrix infused with water. They can be found in a multitude of biological settings, from cell nuclei to cartiledge, and are used in many industrial applications. However, their material properties are not well-understood due to their heterogenous nature. Here we investigate the interfactial rheology of both polyacrylamide and agarose hydrogels using a custom, low-force pin-on-disc tribometer under a variety of environmental conditions. Under a constant normal load, these hydrogels exhibit a dynamic frictional transition characterized by a precipitous drop in the friction coefficient at a critical velocity. Within a range of speeds near this dynamic frictional transition, transient behavior can be observed. Upon increasing the speed, the coefficient of friction decreases exponentially, with a characteristic decay time of order 5-10 minutes. Surprisingly, a cessation of sliding results in a much more rapid recovery of the friction coefficient, suggesting that nonlinear processes control these timescales. We will show how this transition can be tuned by varying the liquid salt concentration, liquid viscosity, and sliding geometry. |
Tuesday, March 5, 2019 5:18PM - 5:30PM |
H54.00011: Granular charging at a distance Troy Shinbrot, Behrooz Ferdowsi, Sankaran Sundaresan, Nuno Araujo Contact charging of granular materials can play a dominant role in effects as varied as lightning in sandstorms, the formation of extraterrestrial planetesimals, and segregation of pharmaceutical powders. Yet the physics underlying this charging is exceptionally poorly understood. For example we have no clear theory for how insulating grains recruit enough charge carriers to deposit charge but not enough to discharge. In this talk, we note that charging and discharging kinetics may be distinct, and from this observation we develop a mathematical model. The model surprisingly predicts that charging can decrease as contact frequency increases. We confirm this prediction experimentally in a vibrated bed and propose future steps. |
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