Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F42: Wetting, Adhesion and Dynamics of Polymer Films and Interfaces |
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Sponsoring Units: DPOLY Chair: Ryan Hayward, Unversity of Massachusetts, Amherst Room: 214B |
Tuesday, March 3, 2015 8:00AM - 8:36AM |
F42.00001: BREAK |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F42.00002: Molecular Velcro constructed from polymer loop brushes showing enhanced adhesion force Tian Zhou, Biao Han, Lin Han, Christopher Li Molecular Velcro is commonly seen in biological systems as the formation of strong physical entanglement at molecular scale could induce strong adhesion, which is crucial to many biological processes. To mimic this structure, we designed, and fabricated polymer loop brushes using polymer single crystals with desired surface functionality and controlled chain folding. Compared with reported loop brushes fabricated using triblock copolymers, the present loop bushes have precise loop sizes, loop grafting density, and well controlled tethering locations on the solid surface. Atomic force microscopy-based force spectroscopy measurements using a polymer chain coated probe reveal that the adhesion force are significantly enhanced on the loop brush surface as compared with its single-strand counterpart. This study directly shows the effect of polymer brush conformation on their properties, and suggests a promising strategy for advanced polymer surface design. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:00AM |
F42.00003: Probing the adhesion of particles to responsive polymer coatings with hydrodynamic shear stresses Ryan Toomey, Gulnur Efe Lower critical solution temperature (LCST) polymers in confined geometries have found success in applications that benefit from reversible modulation of surface properties, including drug delivery, separations, tissue cultures, and chromatography. In this talk, we present the adhesion of polystyrene microspheres to cross-linked poly(N-isopropylacrylamide), or poly(NIPAAm) coatings, as studied with a spinning disk method. This method applies a linear range of hydrodynamic shear forces to physically adsorbed microspheres along the radius of a coated disk. Quantification of detachment is accomplished by optical microscopy to evaluate the minimum shear stress to remove adherent particles. Experiments were performed to assess the relationship between the surface chemistry of the microsphere, the thickness and cross-link density of the poly(NIPAAm) coating, the adsorption (or incubation) time, and the temperature on the detachment profiles of the microspheres. Results show that both the shear modulus and slow dynamic processes in the poly(NIPAAm) films strongly influence the detachment shear stresses. Moreover, whether an adsorbed microsphere can be released (through a modulation in the swelling of the poly(NIPAAm) coating by temperature) depends on both the surface chemistry of the microsphere and the extent of the adsorption time. Finally, the results show that the structure of the poly(NIPAAm) coating can significantly affect performance, which may explain several of the conflicting findings that have been reported in the literature. [Preview Abstract] |
Tuesday, March 3, 2015 9:00AM - 9:12AM |
F42.00004: Dynamic Polymer Brush at Polymer/Water Interface Hideaki Yokoyama, Kazuma Inoue, Kohzo Ito, Manabu Inutsuka, Keiji Tanaka, Norifumi Yamada A layer of polymer chains tethered by one end to a surface is called polymer brush and known to show various unique properties such as anti-fouling. The surface segregation phenomena of copolymers with surface-active blocks should be useful for preparing such a brush layer in spontaneous process. We report hydrophilic polymer brushes formed at the interface between water and polymer by the segregation of amphiphilic diblock copolymers blended in a crosslinked rubbery matrix and call it ``dynamic polymer brush.'' In this system, the hydrophilic block with high surface energy avoids air surface, but segregates to cover the interface between hydrophobic elastomer and water. The structures of the brush layers at D$_2$O/polymer interfaces were measured by neutron reflectivity. The dynamic polymer brush layer surprisingly reached 75\% of the contour length of the chain and 2.7 chains/nm$^{2}$. The brush density was surprisingly comparable to the polymer brush fabricated by the ``grafting-from'' method. We will discuss the dependence of the brush structure on molecular weight and block fraction of amphiphilic block copolymers. Such a surprisingly thick and dense polymer brush were induced by the large enthalpy gain of hydration of hydrophilic block. [Preview Abstract] |
Tuesday, March 3, 2015 9:12AM - 9:24AM |
F42.00005: Planar dipolar polymer brush: field theoretical investigations Jyoti Mahalik, Rajeev Kumar, Bobby Sumpter Physical properties of polymer brushes bearing monomers with permanent dipole moments and immersed in a polar solvent are investigated using self-consistent field theory (SCFT). It is found that mismatch between the permanent dipole moments of the monomer and the solvent plays a significant role in determining the height of the polymer brush. Sign as well as magnitude of the mismatch determines the extent of collapse of the polymer brush. The mismatch in the dipole moments also affects the force-distance relations and interpenetration of polymers in opposing planar brushes. In particular, an attractive force between the opposing dipolar brushes is predicted for stronger mismatch parameter. Furthermore, effects of added monovalent salt on the structure of dipolar brushes will also be presented. This investigation highlights the significance of dipolar interactions in affecting the physical properties of polymer brushes. [Preview Abstract] |
Tuesday, March 3, 2015 9:24AM - 9:36AM |
F42.00006: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 9:36AM - 9:48AM |
F42.00007: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 9:48AM - 10:00AM |
F42.00008: Universal Regimes in the Relaxation of Stepped Liquid Interfaces near Contact Lines Oliver Baeumchen, Thomas Salez, Michael Benzaquen, Elie Raphael, Marco Rivetti A liquid droplet on a perfectly smooth surface wets or dewets the substrate according to the difference between initial and equilibrium contact angles. Such a scenario, however, becomes much less intuitive whenever the initial shape of the interface is non-spherical. Indeed, the capillary-driven relaxation of the liquid surface may be in competition with the relaxation of the contact angle at the three-phase contact line. Here, we study the dynamics of stepped interfaces of thin polystyrene films on hydrophilic substrates. Annealing the polymeric film above its glass transition temperature induces flow which is precisely monitored using ex- and in-situ atomic force microscopy. Both pinned and receding contact line regimes are observed, corresponding to capillary levelling and dewetting of the liquid film. Rescaling with regard to the viscosity, surface tension and film thickness collapses the data on a master curve, providing a universal time for the transition between both regimes. In addition, we prove that the pinned interface exhibits self-similar height profiles which are captured by a thin film model in lubrication approximation. [Preview Abstract] |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F42.00009: Tracking particles in ionic liquid thin films with in-situ scanning electron microscopy Paul Kim, Alexander Ribbe, Thomas Russell, David Hoagland Ionic liquids (ILs) have unique solvent properties, including close to zero vapor pressure and high conductivity, which combine to make IL-solvated ``soft matter'' systems suitable and safe for scanning electron microscopy (SEM) and other high vacuum techniques. To illustrate the capability for SEM, the diffusional dynamics of polymer-coated silica nanoparticles in ultra-thin IL films were studied via direct visualization and multiple-particle tracking. Selecting appropriate viewing conditions to avoid charging and beam damage artifacts (neither trivial concerns), individual particles could be followed at one frame per second for over one minute. In films thick compared to particle diameter, random Brownian motion followed the Stokes-Einstein equation. Unexpected particle pairing, both dynamic and static, was observed in films thin compared to particle diameter, suggesting a complicated interplay of capillary forces and hydrodynamic interactions; the latter are extremely long ranged in 2D fluids. This study positively demonstrates a new method to visualize in situ the nanoscale dynamics of solvated systems. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F42.00010: How do evaporating thin films evolve? Unravelling phase-separation mechanisms during solvent-based fabrication of polymer blends Olga Wodo, Baskar Ganapathysubramanian Solvent-based fabrication is a flexible and affordable approach to manufacture organic thin films made from any combination of polymer, copolymers and/or small molecules. The properties of products made from such films can be tailored by the morphology of the films. Hence, it is of paramount importance to understand morphology evolution during fabrication. However, it is challenging to experimentally visualize morphology evolution during processing (processes involved are highly dynamic at low scale and typical components do not show high contrast). Consequently, details of morphology evolution during solvent-based thinning deposition are still under debate. Here, we identify four modes of phase formation and subsequent propagation within the thinning film during solvent-based fabrication. We unravel the origin of this behavior. Specifically, we focus on fundamental questions, when and where phases are formed, and how they evolve to form the final structure. We utilize a linear stability analysis to identify which mechanism of phase-separation is chosen for a given processing condition. Finally, we construct a mode diagram that maps processing conditions with individual modes. The idea introduced here enables choosing processing conditions to tailor film morphology characteristics and paves the ground for a deeper understanding of morphology control with the ultimate goal of precise, yet affordable, morphology manipulation for a large spectrum of applications. [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F42.00011: Polymeric surfaces exhibiting photocatalytic activity and controlled anisotropic wettability Spiros H. Anastasiadis, Melani A. Frysali, Lampros Papoutsakis, George Kenanakis, Emmanuel Stratakis, Maria Vamvakaki, Grigoris Mountrichas, Stergios Pispas In this work we focus on surfaces, which exhibit controlled, switchable wettability in response to one or more external stimuli as well as photocatalytic activity. For this we are inspired from nature to produce surfaces with a dual-scale hierarchical roughness and combine them with the appropriate inorganic and/or polymer coating. The combination of the hierarchical surface with a ZnO coating and a pH- or temperature-responsive polymer results in efficient photo-active properties as well as reversible superhydrophobic / superhydrophilic surfaces. Furthermore, we fabricate surfaces with unidirectional wettability variation. Overall, such complex surfaces require advanced design, combining hierarchically structured surfaces with suitable polymeric materials. Acknowledgment: This research was partially supported by the European Union (European Social Fund, ESF) and Greek national funds through the ``ARISTEIA II'' Action (SMART-SURF) of the Operational Programme ``Education and Lifelong Learning,'' NSRF 2007-2013, via the General Secretariat for Research \& Technology, Ministry of Education and Religious Affairs, Greece. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F42.00012: The Role of Contact Angle on the Depletion Layer when at the Interface Between Water and a Hydrophobic Surface Adele Poynor, Shannon Petersen, Brooke Ollander By definition hydrophobic substances hate water. Water placed on a hydrophobic surface will form a drop in order to minimize its contact area. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low-density depletion layer forms near the surface. We investigate the role of contact angle on depletion layer formation using the surface sensitive technique of Surface Plasmon Resonance. [Preview Abstract] |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F42.00013: Wetting Properties of Chemically Modified Surfaces: The role of hydrogen bonding Selemon Bekele, Mesfin Tsige Many industrial processing operations involve the spreading of a liquid on a solid material. Controlling the wetting of one material by another is of crucial importance in such applications as adhesion, coating and oil recovery. A strategy often employed to control the wettability of solid surfaces is a combination of surface patterning and chemical surface modification. In order to understand the effect of surface chemistry on the wetting process, we have carried out all-atom molecular dynamics (MD) simulations of a water droplet spreading on pure and oxidized polystyrene surfaces. Our previous results\footnote{\textit{Langmuir} \textbf{2013} 29, 13230-13238} show that the contact angle generally decreases with increasing oxygen concentration and there is a correlation between the spreading and hydrogen bonding. In this talk, we will present results on the structure and dynamics of the hydrogen bonds in the interfacial region between water and the polystyrene substrate. We will discuss our findings on hydrogen bond lifetimes, time correlations functions and number of hydrogen bonds per water molecule for the hydrogen bonds around the water/polystyrene interface which are found to play a role in the spreading process. [Preview Abstract] |
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