Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X43: Focus Session: Assembly, Structure, & Instabilities in Polymer Films, Network Films, & Interfaces II |
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Sponsoring Units: DPOLY Chair: Ryan Toomey, University of Southern Florida Room: A306/307 |
Thursday, March 24, 2011 2:30PM - 3:06PM |
X43.00001: Hydrogels with Spatially and Temporally Controlled Properties to Control Cellular Interactions Invited Speaker: Stem cells (e.g., mesenchymal stem cells, MSCs) respond to many cues from their microenvironment, which may include chemical signals, mechanics, and topography. Importantly, these cues may be incorporated into scaffolding to control stem cell differentiation and optimize their ability to produce tissues in regenerative medicine. Despite the significant amount of work in this area, the materials have been primarily static and uniform. To this end, we have developed a sequential crosslinking process that relies on our ability to crosslinked functional biopolymers (e.g., methacrylated hyaluronic acid, HA) in two steps, namely a Michael-type addition reaction to partially consume reactive groups and then a light-initiated free-radical polymerization to further crosslink the material. With light exposure during the second step comes control over the material in space (via masks and lasers) and time (via intermittent light exposure). We are applying this technique for numerous applications. For example, when the HA hydrogels are crosslinked with MMP degradable peptides with thiol termini during the first step, a material that can be degraded by cells is obtained. However, cell-mediated degradation is obstructed with the introduction of kinetic chains during the second step, leading to spatially controlled cell degradability. Due to the influence of cellular spreading on MSC differentiation, we have controlled cell fates by controlling their spread ability, for instance towards osteoblasts in spread areas and adipocytes when cell remained rounded. We are also using the process of stiffening with time to investigate mechanically induced differentiation, particularly in materials with evolving mechanics. Overall, these advanced HA hydrogels provide us the opportunity to investigate diverse and controlled material properties on MSC interactions. [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X43.00002: Hydrogel Stamping of Polyelectrolyte Multilayers for Directed Cell Growth Nicole Zacharia, Chungyeon Cho The authors have recently introduced the use of hydrogel stamp materials to pattern polyelectrolyte multilayer (PEM) films. It has been demonstrated that using a stamp equilibrated in either low or high pH can cause local swelling in these films, leading to patterns. It has also been shown that stamps soaked in high ionic strength salt solutions are able to locally etch PEM films. This hydrogel stamping technique gives both lateral control of surface properties and depth control over the film's properties. This technique is a promising way to pattern chemical reactions within PEM, phase transformation, and physical properties such as film thickness, Young's modulus, and swelling. By using hydrogels for the stamp material, stamping becomes a process of continuously delivering aqueous reagent of interest to a film, instead of merely a single layer of material, as is the case when using hydrophobic stamp materials such as PDMS. While chemical modification of only the surface may be desirable in some cases, the hydrogel stamping technique is more versatile. By creating local variations in swelling, we are able to pattern mechanical stiffness, and in turn cell adhesion. We demonstrate the creation of gradients in mechanical stiffness which we are able to use to direct cell growth and adhesion on these films. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X43.00003: Patterned Poly-N-isopropylacrylamide Surfaces for Culture and Harvest of Muscle Fibers Samuel DuPont, Kranthi Kumar Elineni, Nathan Gallant, Ryan Toomey Swelling of surface confined poly-N-isopropylacrylamide (pNIPAAm) structures leads to non-uniform patterns that can be switched by a thermal cue. Based on the geometry of the surface confined patterns, various forms of structural instabilities arise such as bulk buckling, differential lateral swelling and edge buckling. Instabilities that arise from the swelling of patterned pNIPAAm surfaces present a unique platform for tissue engineering applications. Recent work has demonstrated the attachment, survivability, and alignment of fibroblasts grown atop rectangular pNIPAAm surface extrusions. Detachment of contiguous and aligned fibroblasts grown on these surfaces was observed when the geometry of the structure was such that a bulk buckling instability formed upon thermally induced gel swelling. Current work is aimed at utilizing this switchable platform to culture aligned myoblasts, which upon differentiation, form multicellular myotubes, an important structure in skeletal muscle. Myotubes for tissue engineering can then be harvested by non-enzymatic detachment facilitated by thermally induced non-uniform gel swelling. [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X43.00004: Controlled Release from Model Blended Polyelectrolyte Multilayer Films Bulent Akgun, Yeongseon Jang, Sushil Satija, Kookheon Char We propose a new concept of controlled release platforms based on the model blended multilayer films composed of positively charged weak polyelectrolyte (linear poly(ethylenimine),LPEI) layer and blended layer with negatively charged strong (poly(sodium-4-styrene sulfonic acid),PSS) and weak (poly(methacrylic acid),PMAA) polyelectrolytes. The blended multilayer films ((LPEI/PSS:PMAA)$_{n})$ with well-defined internal structure are prepared by spin-assisted LbL deposition method, and their release behavior is systematically characterized with combined techniques of neutron reflectivity, ellipsometry, AFM, QCM and FT-IR. Since PSS provides the robust skeleton within the multilayer films independently on pH variation, the burst erosion of multilayer films is dramatically suppressed, and the release kinetics of PMAA can be precisely controlled by simply changing PSS contents within the multilayer films. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X43.00005: Surface wrinkling driven by swelling and its applications Hyun Suk Kim, Alfred Crosby The nature of reversible surface wrinkling offers great promise for designing responsive or adaptive materials. We experimentally explore the reversibility and geometry of surface wrinkles driven by swelling an elstically-supported stiff plate by solvent vapor and liquid. We use crosslinked polydimethylsiloxane (PDMS) substrates with surfaces modified by ultraviolet-ozone (UVO) processing, creating materials with rigid, surface films that swell differentially in comparison to the underlying substrates. We observe the dependence of the wrinkle wavelength on the UVO time and thickness of elastomers. Furthermore, we identify a critical length scale for the swelling region below which wrinkle formation is suppressed. Taking advantage of the reversibility and geometric relations, we demonstrate advanced applications such as smart windows with swichable optical transparency and responsive channels in microfluidics. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X43.00006: Nanoporous Conductive Films Derived from Polymeric Bicontinuous Microemulsions Brad Jones, Kai-Yuan Cheng, Russell Holmes, Timothy Lodge Ternary blends of two homopolymers and a diblock copolymer can self-assemble into interpenetrating, 3D-continuous networks with a characteristic length scale of 100 nm. These polymeric bicontinuous microemulsions (B$\mu $E) can be designed to serve as templates for the synthesis of nanoporous materials with 3D-continuous pore networks. We have investigated the behavior of B$\mu $E-forming blends of polyolefins as precursors to nanoporous polyethylene (PE) films. The effect of interfaces in these films can drastically disrupt the B$\mu $E structure, leading to a macro-phase separated morphology. Proper consideration of several factors, including substrate surface energy, film thickness, and annealing time, is necessary to retain a B$\mu $E structure in such films. Finally, we use the B$\mu $E-like, nanoporous PE films as templates in the synthesis of nanoporous films of the conducting polymer poly(3,4-ethylenedioxythiophene), having potential application in organic electronic devices. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X43.00007: Particle Behavior at Anisotropically Curved Liquid Interfaces Kathleen McEnnis, Chuan Zeng, Benny Davidovitch, Anthony Dinsmore, Thomas Russell A particle bound to an anisotropically curved liquid interface, such as a cylinder or catenoid, cannot maintain a constant contact angle without deforming the interface. Theory suggests that the particles will experience a force that depends on the interfacial shape and migrate to minimize the total interfacial energy. To test these predictions, particles were deposited on top of liquid semi-cylinders of ionic liquid or melted polystyrene confined on chemically patterned surfaces. Particles were also deposited on liquid catenoid structures created by placing a melted polymer film under an electric field. The location of the particles on these structures was observed by optical, confocal, and scanning electron microscopy. The implications for the directed assembly of particles and stability of Pickering emulsions are also discussed. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X43.00008: Hierarchically Ordered Block Copolymer Micelles Formed by Controlled Evaporative Self-Assembly Wei Han, Myunghwan Byun, Zhiqun Lin Highly ordered gradient stripes of PS-b-P4VP block copolymer were obtained by combining the microscopic controlled evaporative self-assembly (CESA) of confined microfluid of PS-b-P4VP toluene solution in a ``cylinder-on-Si'' geometry with spontaneous self-assembly of micellar hexagonal arrays of PS-b-P4VP at the nanometer scale. The order of packed micelles within microstripes could be significantly improved by subsequent THF vapor annealing. The surface reconstruction of micelles led to the formation of nanoporous arrays when immersed in a selective solvent of the pore component. Gold nanoparticles were then selectively deposited into the core of micelles, and eventually forming the hexagonal arrays of gold nanoparticles after removal of polymer templates by oxygen plasma. The formation of gold particle arrays was verified by XPS measurement. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X43.00009: Viscoelastic properties of ultrathin polymer films using the liquid dewetting technique Jinhua Wang, Gregory McKenna There is considerable interest in studying the behavior of polymers at the nanoscale. Here we describe experiments using the Bidiguel and Fretigny's liquid dewetting technique in which no great glass transition temperature (Tg) reduction or rubbery plateau compliance change for polystyrene (PS) films was observed [1]. These results are contrary to observations by others of Tg reductions on free standing polystyrene films and of large rubbery stiffening observed in our lab using a bubble inflation method [2,3]. Preliminary results of PS film dewetting are consistent with the Bidiguel and Fretigny's results. Also, annealing time and confinement effects on the creep behavior of polystyrene thin film were examined. Then, the range of investigated materials is being expanded to polycarbonate (PC) and poly(methyl methacrylate) PMMA with the ultimate goal to determine the reasons for the differences between the bubble inflation method and liquid dewetting technique of polymer film charicterization. References: [1] H. Bodiguel and C. Fretigny, ``Viscoelastic dewetting of a polymer film on a liquid substrate,'' \textit{Eur.Phys. J. E}., 19, 185-193 (2006). [2] K. Dalnoki-Veress, J. A. Forrest, P. G. de Gennes and J. R. Dutcher, \textit{J. Phys. IV.}, 10, 221-226 (2000). [3] O' Connell P. A. and McKenna G. B., ``Rheological Measurements of the Thermoviscoelastic Response of Ultrathin Polymer Films'',\textit{ Science}, 307, 1760-1763 (2005). [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X43.00010: Elastic Moduli of Nanoparticle-Polymer Composite Thin Films via Buckling on Elastomeric Substrates Hongyi Yuan, Alamgir Karim Polymeric thin films find applications in diverse areas such as coatings, barriers and packaging. The dispersion of nanoparticles into the films was proven to be an effective method to generate tunable properties, particularly mechanical strength. However, there are very few methods for mechanical characterization of the composite thin films with high accuracy. In this study, nanometric polystyrene and polyvinyl alcohol films with uniformly dispersed cobalt and Cloisite nanoparticles at varying concentrations were synthesized via flow-coating and then transferred to crosslinked polydimethylsiloxane (PDMS) flexible substrates. The technique of Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) was employed to determine the elastic moduli of the films, which were calculated from the buckling patterns generated by applying compressive stresses. Results on moduli of films as a function of the concentrations of nanoparticles and the thicknesses of the composite films will be presented. *Corresponding author: alamgir@uakron.edu [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X43.00011: Effect of Chain Architecture on the Physical Aging of Thin Polymer Filims Bradley Frieberg, Emmanouil Glynos, Peter Green Physical aging, glassy structural relaxations, is an important phenomenon that has an important influence on a range of physical properties, such as optical, mechanical and electrical, of polymeric materials properties. When a polymeric material is cooled below its glass transition temperature (Tg) it resides in a non-equilibrium state, and over time it attempts to return to equilibrium via a structural relaxation process. We have previously demonstrated that chain architecture can influence the Tg in supported thin films. Specifically, star-shaped molecules possessing sufficiently high functionality (f) and low molecular weight of the arm (Mw), exhibit significant differences in vitrification trends from their linear analogs. In this presentation we show that when f is sufficiently high, or Mw is sufficiently low, the physical aging rate is suppressed compared to linear chains. Moreover, the aging rates of thin, supported films of star shaped molecules are strongly thickness dependent. [Preview Abstract] |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X43.00012: Perturbing the Tg of Polymers by 50-100 K in Nanoconfined Freely Standing Films and by the Presence of Neighboring Layers of Other Polymers John Torkelson, Soyoung Kim We demonstrate via the temperature dependence of fluorescence intensity intrinsic to the polymer of interest or from dye labels that the glass transition temperature (Tg) of a polymer can be altered by 50-100 K by nanoconfinement in freely standing films and in multilayer systems in which the neighboring layers are different polymers. In the former case, Tg always decreases from bulk Tg; in the latter case, Tg decreases or increases depending on the Tg of the neighboring polymer layer and factors that may be related to fragility. We employ fluorescence to characterize the gradient in Tg from the perturbing interfaces. These studies reveal that the theory by de Gennes for the Tg reduction in freely standing films cannot be correct and that the perturbation to Tg by a neighboring layer of another polymer can extend as much as 100 nm into the layer of interest. [Preview Abstract] |
Thursday, March 24, 2011 5:18PM - 5:30PM |
X43.00013: ABSTRACT WITHDRAWN |
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