Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P44: Focus Session: Assembly, Structure, & Instabilities in Polymer Films, Network Films, & Interfaces I |
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Sponsoring Units: DPOLY Chair: Zhiqun Lin, Iowa State University Room: A309 |
Wednesday, March 23, 2011 8:00AM - 8:36AM |
P44.00001: An interplay between self-organization and interfacial modification of diblock copolymers in bi-layered thin film laminates Invited Speaker: We study the interfacial partitioning of poly(styrene-b-methyl methacrylate) (SM) diblock copolymers at interfaces between thin planar films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) homopolymers. SM copolymers with constant PS and varying PMMA block lengths are incorporated into the top PS layer and the resulting dewetting kinetics of the top PS film decrease by reducing the length of the PMMA block and increasing the molecular weight of the host PS homopolymer. Similar behavior is observed when the SM copolymers are added to the bottom PMMA homopolymer. Systems incorporating SM copolymers possessing short PS blocks and long PMMA blocks exhibit dewetting rates that are higher than those of the copolymer-free PS/PMMA bilayer. This behavior is attributed to the segregation of SM aggregates at the PS/PMMA interface, which migrate to and roughen the interface and destabilize the film. The dewetting kinetics of systems with mixtures of asymmetric copolymers (stabilizing and destabilizing) added in the PS homopolymer lie between those of the individual copolymers pure copolymers. Using block copolymer mixtures rather than single copolymers to tune stabilizing/compatibilizing efficacy provides an unexplored route to achieving property control in thin polymer films. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P44.00002: Formation of Nanoparticle Stripe Patterns via Flexible-Blade Flow Coating Dong Yun Lee, Hyun Suk Kim, Cassandra Parkos, Cheol Hee Lee, Todd Emrick, Alfred Crosby We present the controlled formation of nanostripe patterns of nanoparticles on underlying substrates by flexible-blade flow coating. This technique exploits the combination of convective flow of confined nanoparticle solutions and programmed translation of a substrate to fabricate nanoparticle-polymer line assemblies with width below 300 nm, thickness of a single nanoparticle, and lengths exceeding 10 cm. We demonstrate how the incorporation of a flexible blade into this technique allows capillary forces to self-regulate the uniformity of convective flow processes across large lateral lengths. Furthermore, we exploit solvent mixture dynamics to enhance intra-assembly particle packing and dimensional range. This facile technique opens up a new paradigm for integration of nanoscale patterns over large areas for various applications. [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P44.00003: Hierarchically Organized Structures Engineered from Controlled Evaporative Self-Assembly Zhiqun Lin, Myunghwan Byun, Wei Han, Ned Bowden By constraining an asymmetric comb block copolymer (CBCP) toluene solution to evaporate in a wedge-on-Si geometry composed of a wedge lens situated on a Si substrate, gradient concentric stripe-like surface patterns of CBCP at the microscopic scale were yielded as a direct consequence of \textit{controlled} evaporative self-assembly of CBCP. The formation of either straight stripes or jagged stripes was dictated by the height of the wedge. Upon subsequent solvent vapor annealing, hierarchically organized structures of CBCP were produced, resulting from the interplay of solvent vapor-assisted, unfavorable interfacial interaction-driven destabilization of CBCP from the Si substrate at the microscopic scale and the solvent vapor-promoted reconstruction of CBCP nanodomains within the stripes at the nanometer scale. This facile approach of combining \textit{controlled} evaporative self-assembly with subsequent solvent vapor annealing offers a new platform to rationally design and engineer self-assembling building blocks into functional materials and devices in a simple, cost-effective manner. [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P44.00004: Wrinkling instabilities in compressed networks of polymer supported single-wall carbon nanotubes John Harris, Swathi Iyer, Ji Yeon Huh, Jeffrey A. Fagan, Jun Young Chun, Steven D. Hudson, Jan Obrzut, Christopher M. Stafford, Erik K. Hobbie Strain-induced structural and electronic changes in polymer supported membranes of purified single-wall carbon nanotubes (SWCNTs) are evaluated through the wrinkling instabilities that develop under both uniaxial and isotropic compression. Nanotubes that have been purified by length or electronic type using density-gradient ultracentrifugation are assembled as surfactant-free thin membranes on prestrained polydimethylsiloxane (PDMS) substrates, and the strain response is measured using a broad range of techniques. The small-strain behavior is inferred from kinetic changes in the wrinkling topography of the SWCNT membranes during the slow drying of pre-swelled polymer supports. The measurements suggest a remarkable degree of strain softening that strongly couples to the anisotropic sheet resistance of the films, which we in turn relate to the microscale anisotropy that develops through excluded volume interactions. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P44.00005: Confinement-Induced Molecular Stresses and Wetting Instability in Ultrathin Polymer Films Y. Chein, P.W. Lee, A.C.-M. Yang Chain packing and molecular behavior of polymers confined below unperturbed coil sizes are still poorly understood. To explore the physical state and condensation process, molecular recoiling stresses in polystyrene films (4-100 nm) were measured through wetting instability at above T$_{g}$(100 C). The films demonstrated strikingly different instability mechanisms in regimes divided by entanglement molecular weight (M$_{e})$. Moreover, the recoiling stress decreased with chain length above M$_{e}$, consistent with the condensation process dominated by solvent evaporation, but plunged below M$_{e}$, apparently due to diminishing deformations. A small fraction of MEH-PPV added in films manifested photoluminescence (PL) following the same trend as recoiling stress confirming stress-enhanced PL characteristic of conjugated polymers. As aging temperature lowered but still above T$_{g}$, film stability increased but recoiling stress underwent significant changes, in contrast to that below T$_{g}$ where no changes was observed. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P44.00006: Nucleation and growth of creases on swelled polymer gel surfaces Jinhwan Yoon, Jungwook Kim, Ryan Hayward We have studied the processes by which surface creases form, evolve, and disappear using thin temperature-responsive poly(N-isopropylacrylamide) copolymer hydrogels. For shallow quenches beyond the critical level of compression, creases nucleate and growth, and thus the observed onset and morphology are typically dominated by heterogeneous defects. Measurements of crease growth velocities at different quench depths are used to precisely determine the compression at which the surface first becomes unstable, and this critical strain is found to be slightly elevated as film thickness is reduced. This behavior is captured by a simple model for the energy change upon forming a fold, with a nucleation barrier to fold formation provided by the gel/water surface-energy. While hysteresis between onset and disappearance is often observed in experiments, this reflects predominantly the degree of ``undercooling'' necessary to yield nucleation and growth of creases. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P44.00007: Effect of polymer architecture on the interfacial properties of thin films Emmanouil Glynos, Bradley Frieberg, Peter Green Many physical properties of polymers, such as phase transitions, mechanical properties, dynamics, crystallization and the glass transition, Tg, are influenced by film thickness constraints, and associated with the interactions between the constituent macromolecules and external interfaces. We show that star-shaped molecules, possessing sufficiently high functionality, exhibit significant differences in their average Tg-vs-thickness (H) behavior, both in the magnitude and the thickness dependent trends, from their linear analogs. In this talk, we will discuss the effect of polymer architecture on the interfacial properties of supported thin films, and more specifically how chain segments near the free and the solid interfaces influence the average Tg of the film. These effects are discussed in terms of the role of macromolecular architecture and entropic effects on the structure and dynamics of the polymer chains close to the interfaces, and their influence on the average properties of thin supported films. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P44.00008: Interfacial Effects on Pentablock Ionomer Thin Films Thusitha Etampawala, Dilru Ratnaweera, Naresh Osti, Umesh Shrestha, Dvora Perahia, Jaroslaw Majewski The interfacial behavior of multi block copolymer thin films results from a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interactions of the individual blocks with the interfaces. Here in we report a study of thin films of ABCBA penta block copolymers, anionically synthesized, comprising of centered randomly sulfonated polystyrene block to which rubbery poly-ethylenebutalene is connected, terminated by blocks of poly-t-butylstyrene, kindly provided by Kraton. AFM and neutron reflectometry studies have shown that the surface structure of pristine films depends on film thickness and ranges from trapped micelles to thin layered films. Annealing above Tg for the styrene block results in rearrangements into relatively featureless air interface. Neutron reflectivity studies have shown that annealed films forms layers whose plane are parallel to the solid substrate with the bulky block at the air interface and the ionic block at the solid interface. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P44.00009: Directed Morphology of Nanofilled Polymer Films on Flexible Substrates Diya Bandyopadhyay, Arzu Hayirlioglu, Manish Kulkarni, Alamgir Karim We demonstrate viable meso-patterning techniques that have relevance to electronics and organic photovoltaic applications via tunable control of polymer thin film instabilities. To this end, we examine the influence of fullerene (C$_{60}$) nanoparticles on multicomponent polymer thin films on patterned and flexible polydimethylsiloxane substrates and compare these results to morphologies on hard silica xerogel substrates of variable roughness and surface energy. Controlled incorporation of nanoparticles (NPs) can be used to tune polymer thin film instabilities and morphology. At NP concentrations below a threshold value, we observe directed dewetting of blend thin films consisting of uniformly aligned dewet domains that mimic the periodicity of the confining media, consistent with our previous experiments where it was observed that C$_{60}$ NPs preferentially segregate to a PS/PB blend interface up to a certain saturation concentration. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P44.00010: Fiber Formation From the Melting of Free-standing Polystyrene, Ultra-thin Films: A Technique for the Investigation of Thin Film Dynamics, Rheological Properties and Confinement Effects Jeremy M. Rathfon, Robert W. Cohn, Alfred J. Crosby, Jonathan P. Rothstein, Gregory N. Tew The processes of fiber formation from the melting of ultra-thin films are explored in high detail and produce a new technique for the investigation of rheological properties, confinement effects, and the dynamics of thin films and polymer chains. Ultra-thin films of polystyrene are suspended atop micro-arrays of pillars. Films are then annealed above the $T_{g}$ and studied via optical microscopy. Hole nucleation is quantified with a free energy barrier based on a simple capillary model. Holes then grow exponentially in a shear thinning, high shear strain regime. These holes impinge upon each other to form suspended fibers which thin according to a model for elasto-capillary thinning of fluid filaments. Monitoring fiber thinning allows for the acquisition of rheological properties as well as the apparent extensional viscosity. The breakup of the fiber network indicates the effects of confinement on chain entanglements in ultra-thin films. A transition below a critical film thickness, comparable to the dimensions of a polymer chain, shows reduced interchain entanglements and a remarkably faster breakup of fibers. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P44.00011: Self-Repair of Polymer Films Through Monomer Filled Ni-Zn Microcapsules Marcia Patchan, Lance Baird, Yo-Rhin Rhim, Erin LaBarre, Adam Maisano, Ryan Deacon, Jason Benkoski A novel polymer additive composed of isocyanate resin-filled metal microcapsules has been successfully synthesized through a combination of emulsification, interfacial polymerization, and electroless Ni-Zn deposition. The resulting metallic microcapsules impart self-healing and galvanic protection capabilities to off-the-shelf primers. Once scratched, the microcapsules release their contents into the scratch, where they harden and restore the moisture barrier. If healing is incomplete, the Ni-Zn shell acts as a sacrificial anode to galvanically protect the underlying steel. ASTM adhesion, wear resistance, and moisture resistance tests evaluated the ability of microcapsule-filled primers to heal scratches, provide galvanic protection, and prevent corrosion. We found that self- healing was most effective for broad, shallow scratches (3 mm) and narrow scratches (75 $\mu$m). [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P44.00012: Structural Rearrangement of Semifluorinated Diblock copolymer Thin Films Exposed to Selective Solvents Umesh Shrestha, Dvora Perahia, Stephen Clarson A neutron reflectometry study reveals the response of a semifluorinated diblock co-polymer poly trifluoro propyl methyl siloxane -$b$- polystyrene co-polymer thin films of ca. 50-70nm, to selective solvents. This diblock forms surface induced layered structure at volume fractions of the F segment ranging from 0.03 to 0.50. When exposed to toluene, a selective solvent for PS, the film swelled instantaneously, while retaining its layered structure. The solvent however penetrates into both the PS and the semifluorinated layers. In contact with decane vapor, the solvent penetrates predominantly the top fluorinated layers. The rate of penetration increases with increasing volume fraction of the fluorinated segment. In contrast with toluene, the solvent remains at the top layer only for extended periods again retaining the layered structure. The incompatibility and specific affinity of different blocks drive structural rearrangements at the interface as a response to external stimuli, retaining the layers structure. [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P44.00013: Wetting induced instabilities in miscible polymer blends Nigel Clarke, Katherine Thomas, Ullrich Steiner, Rosa Poetes, Mihai Morariu The behaviour of miscible blends of polystyrene (PS)/poly(vinyl methyl ether)(PVME) of varying compositions has been investigated [1] at temperatures where PS and PVME are miscible. The PVME is seen to enrich the polymer-air surface, forming a layer with a width that is comparable to the correlation length. Further heating close to the demixing temperature results in the formation of a capillary instabilities at the polymer surface exhibiting a spinodal-like pattern with a characteristic wavelength that depends on the blend composition. Formation of these instabilities is seen for all blend compositions. We propose that these wetting induced instabilities result from coupled height and composition fluctuations in the PVME enriched surface layer, driving the build-up of long wavelength fluctuations. \\[4pt] [1] Thomas, K.R.; Clarke, N.; Poetes, R.; Morariu, M.; Steiner, U.; Soft Matter, 6, 3517, 2010 [Preview Abstract] |
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