Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H10: Physics of Polymer Surfaces and Interfaces IFocus
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Sponsoring Units: DPOLY GSOFT Chair: Julie Albert, Tulane University Room: 269 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H10.00001: EMPTY SLOT |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H10.00002: EMPTY SLOT |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H10.00003: EMPTY SLOT |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H10.00004: Repulsive interactions between two polyelectrolyte networks Aykut Erbas, Monica Olvera de la Cruz Surfaces formed by charged polymeric species are highly\textunderscore abundant in both synthetic and biological systems, for which maintaining\textunderscore an optimum contact distance and a pressure balance is paramount. We investigate interactions between surfaces of two same-charged and\textunderscore highly swollen polyelectrolyte gels, using extensive molecular dynamic\textunderscore simulations and minimal analytical methods. The external-pressure\textunderscore responses of the gels and the polymer-free ionic solvent layer separating\textunderscore two surfaces are considered. Simulations confirmed that the surfaces are\textunderscore held apart by osmotic pressure resulting from excess charges diffusing out\textunderscore of the network. Both the solvent layer and pressure dependence are well\textunderscore described by an analytical model based on the Poisson$-$Boltzmann solution for low and moderate electrostatic strengths. Our results can be of great importance for systems where charged gels or gel-like structures interact in various solvents, including systems encapsulated by gels and microgels in confinement. [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H10.00005: Dynamic Surface Tension and Adsorption Kinetics of Polyelectrolyte Solutions Nikhila Parsi, Leidy N. Jimenez, Vivek Sharma Adsorption of polyelectrolyte at fluid-fluid interfaces influences the stability and physical properties of emulsions, and foams used in cosmetics, food, petrochemical and pharmaceutical applications. In this study, we measure the dynamic surface tension of polyelectrolytes using pendant drop tensiometry as a function of polyelectrolyte concentration, molecular weight and added salt concentration. While polyelectrolytes can reduce the surface tension at liquid/air interface, the overall kinetics is quite slow in contract to small molecule surfactants, and appears to be strongly correlated with charge fraction and counterion type and concentration. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H10.00006: First Contact: Adhesion Hysteresis in Soft Interfaces Kyle Schulze, Alexander Bennett, Yongliang Ni, Thomas Angelini, Greg Sawyer Characterization and contact mechanics of soft materials continue to be of extreme importance to the world of medicine and health. Many studies in the recent past have thus been conducted on soft materials such as tissues and their proxies at the micro, meso, and macro scale to better understand the materials of life. Here we examine a soft tunable material that can be used as a proxy for soft biotribological interfaces that have adhesion considerations with PDMS. Specifically, we examine that by systematically changing the contact indentation experiment conditions the mechanical property predictions from traditional contact theories such as JKR can be readily manipulated. By in situ observation of real area of contact of PDMS indentation we examine rate, geometry, indentation, and modulus dependence on the contact hysteresis of the system. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H10.00007: Exploring the Origin of Hysteretic Memory Behavior in Polyelectrolyte Brushes Vivek Yadav, Megan Robertson, Jacinta Conrad Polyelectrolyte brushes attached to surfaces change their conformation when exposed to solutions of varying pH. As responsive materials, polyelectrolyte brushes are widely employed to control surface wettability, adhesion, friction, and biofouling. Many of these applications require reversible pH-switching of the surface properties, and therefore it is essential to understand brush response to variations in pH. Numerous brush properties, including contact angle and degree of swelling, exhibit hysteretic memory behavior: a response dependent on the direction of pH change. Despite widespread use of brushes, the role of polyelectrolyte brush length and dispersity in the observed hysteretic memory behavior is not well understood. Here, we synthesized poly(acrylic acid) (PAA) brushes with controlled brush length and dispersity using the grafting-from approach at a constant grafting density. We identified three trends in the response of the PAA brushes to changes in pH. First, the thickness of dry brushes decreased as the pH was decreased. Second, the water contact angle measured at low pH increased with dispersity. Finally, disperse brushes exhibited hysteretic memory behavior in the contact angle The origin of hysteretic memory is consistent with dispersity-driven pH-dependent conformational changes in these polyelectrolyte brushes. Together, these results indicate that increasing brush dispersity significantly alters the pH-response. To demonstrate the usefulness of controlling brush properties, we showed that the response of brushes to an abrupt change in solution pH was correlated to release of bacteria from the brush surface. [Preview Abstract] |
(Author Not Attending)
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H10.00008: Abstract Withdrawn
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Tuesday, March 14, 2017 4:06PM - 4:18PM |
H10.00009: Influence of Bulk PDMS Network Properties on Water Wettability Matthew Melillo, Edwin Walker, Zoe Klein, Kirill Efimenko, Jan Genzer Poly(dimethylsiloxane) (PDMS) is one of the most common elastomers, with applications ranging from sealants and marine antifouling coatings to absorbents for water treatment. Fundamental understanding of how liquids spread on the surface of and absorb into PDMS networks is of critical importance for the design and use of another application -- medical devices. We have systematically studied the effects of polymer molecular weight, loading of tetra-functional crosslinker, and end-group chemical functionality on the mechanical and surface properties of end-linked PDMS networks. Wettability was investigated through the sessile drop technique, wherein a DI water droplet was placed on the bulk network surface and droplet volume, shape, surface area, and contact angle were monitored as a function of time. Various silicone substrates ranging from incredibly soft and flexible materials (E' \textasciitilde 50 kPa) to highly rigid networks (E' \textasciitilde 5 MPa) were tested. The dynamic behavior of the droplet on the surfaces demonstrated equilibration times between the droplet and surface on the order of \textasciitilde 5 minutes. Similar trends were observed for the commercial PDMS material, Sylgard-184. Our results have provided new evidence for the strong influence that substrate modulus and molecular network structure have on the wettability of PDMS elastomers. These findings will aid in the design and implementation of efficient, accurate, and safe PDMS-based medical devices and microfluidic materials that involve aqueous media. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:54PM |
H10.00010: Designing Durable Icephobic Surfaces Invited Speaker: Anish Tuteja Ice accretion has a negative impact on critical infrastructure, as well as a range of commercial and residential activities. Icephobic surfaces are defined by an ice adhesion strength $\tau_{ice}$ \textless 100 kPa. However, the passive removal of ice requires much lower values of $\tau _{ice}$, such as on airplane wings or power lines ($\tau_{ice}$ \textless 20 kPa). Such low $\tau_{ice}$ values are scarcely reported, and robust coatings that maintain these low values have not been reported previously. Here we show that, irrespective of material chemistry, by tailoring the crosslink density of different elastomeric coatings, and by enabling interfacial slippage, it is possible to systematically design coatings with extremely low ice-adhesion ($\tau_{ice}$ \textless 0.2 kPa). These newfound mechanisms allow for the rational design of icephobic coatings with virtually any desired ice adhesion strength. By utilizing these mechanisms, we fabricate extremely durable coatings that maintain $\tau_{ice}$ \textless 10 kPa after severe mechanical abrasion, acid/base exposure, 100 icing/de-icing cycles, thermal cycling, accelerated corrosion, and exposure to Michigan wintery conditions over several months.\\ \\In collaboration with: Kevin Golovin, Department of Material Science and Engineering, University of Michigan. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H10.00011: Structural and dynamic heterogeneity of interfacial water on chemically modified polymer surfaces Selemon Bekele, Mesfin Tsige Using molecular dynamics (MD) simulations, we investigate the structural and dynamical properties of water molecules in a slab of water in contact with atactic polystyrene surfaces of varying polarity. We find that the dynamics of water molecules in the interfacial region slows down with increasing polarity of the polystyrene surface. In addition, the interfacial water molecules exhibit structural and dynamic heterogeneity with respect to diffusion, hydrogen bond distribution and relaxation of the hydrogen bond network. The results obtained enhance our understanding of water structure and dynamics at the polymer/water interface with important implications for such desired functional properties as lubrication, adhesion and friction. Interfacial properties of water at hydrophobic and hydrophilic SAM (Self Assembled Monolayers) surfaces will also be presented for comparison. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H10.00012: Multi-functional surfaces with controllable wettability and water adhesion Spiros H. Anastasiadis, Melani A. Frysali, George Kenanakis, Georgia Kaklamani, Lampros Papoutsakis The design of multifunctional surfaces based on biomimetic structures has gained the interest of the scientific community. Novel multifunctional surfaces have been developed, able to alter their wetting properties in response to temperature and pH as well as light illumination, by combining proper chemistry and surface micro/nano-structuring using ultrafast (femtosecond) laser irradiation. The combination of the hierarchical surface with a ZnO and/or a responsive polymer coating results in efficient photo-active properties as well as reversible superhydrophobic / superhydrophilic surfaces in response to external stimuli. These surfaces can be optimized to exhibit high or zero water adhesion and/or controllable directionality as well. Moreover, they can be seeded with human fibroblasts to examine the cellular response on both surface roughness and surface chemistry. Acknowledgements: This research has been co-financed by the General Secretariat for Research and Technology ("ARISTEIA II" Action, SMART-SURF) and the European Union (NFFA Europe -grant agreement No. 654360). [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H10.00013: Water adsorption on surface-modified cellulose nanocrystals Zonghui Wei, Robert Sinko, Sinan Keten, Erik Luijten Cellulose nanocrystals (CNCs) have attracted much attention as a filler phase for polymer nanocomposites due to their impressive mechanical properties, low cost, and environmental sustainability. Despite their promise for this application, there are still numerous obstacles that prevent optimal performance of CNC--polymer nanocomposites, such as poor filler dispersion and high levels of water absorption. One way to mitigate these negative effects is to modify CNC surfaces. Computational approaches can be utilized to obtain direct insight into the properties of modified CNC surfaces and probe the interactions of CNCs with other materials to facilitate the experimental design of nanocomposites. We use atomistic grand-canonical Monte Carlo simulations to study how surface modification of ion-exchanged sulfated cellulose nanocrystals (Na-CNCs) impacts water adsorption. We find that methyl(triphenyl)phosphonium-exchanged CNCs adsorb less water than Na-CNCs at the same relative humidity, supporting recent experimental dynamic vapor sorption measurements. By characterizing the distribution and configuration of water molecules near the modified CNC surfaces we determine how surface modifications disrupt CNC--water interactions. [Preview Abstract] |
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