Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session C34: Thin Films of Block Copolymers and Hybrid Materials: Mechanics and Dynamics |
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Sponsoring Units: DPOLY Chair: Alamgir Karim, University of Akron Room: 342 |
Monday, March 18, 2013 2:30PM - 2:42PM |
C34.00001: Structural response of a pre-aligned cylindrical block copolymer to uniaxial extensional flow Erica McCready, Wesley Burghardt In situ small angle x-ray scattering (SAXS) is used to probe structural changes in a cylindrically ordered triblock copolymer melt during uniaxial extensional flow. The sample is a styrene-ethylene butylene-styrene triblock copolymer melt. Sheets of macroscopically oriented polymer were produced using a lubricated planar squeezing flow die, from which sample strips were cut. Uniaxial extensional flow was imposed in the melt state using an SER extensional flow fixture housed in a custom built convection oven that allows x-ray access, to facilitate SAXS measurements of microdomain re-orientation and deformation during stretching and subsequent relaxation. Individual sample strips were cut from the molded sheet to facilitate measurements in which the stretching was imposed either parallel or perpendicular to the pre-alignment axis. Offline measurements of transient extensional rheology were also conducted using the SER fixture in a conventional rotational rheometer, using similar samples in order to explore connections between, and impact of initial orientation state one, both structural and mechanical responses. [Preview Abstract] |
Monday, March 18, 2013 2:42PM - 2:54PM |
C34.00002: Imaging surface mechanical properties of complex polymer thin films using Intermodulation Atomic Force microscopy Daniel Forchheimer, Daniel Platz, David B. Haviland, Erik A. Thol\'en The atomic force microscope (AFM) has been the method of choice to measure surface topography of thin films on the sub-micron scale. In addition to topography, dynamic AFM, where the cantilever is oscillated at its resonance frequency, gives a qualitative image of material heterogeneity by recording the phase lag of the oscillation. As new materials become increasingly more complex, containing multiple components and phases, there is an increased need for more sensitive and also more quantitative characterization polymer surfaces at the nanometer scale. We have developed Intermodulation AFM in which the cantilever is excited at two frequencies close to resonance. By measuring the intermodulation products, or mixing products, of the drive frequencies more information regarding the tip-surface interaction is revealed, providing better material contrast and allowing quantitative reconstruction of the tip-surface force curve. We have applied this method to the study of thin films of polymer blends and block copolymers in which it was possible to quantify material stiffness of the different phases of the material and relate those to quantitative measurements of the pure polymer components. [Preview Abstract] |
Monday, March 18, 2013 2:54PM - 3:06PM |
C34.00003: Morphology and Surface Energy of a Si Containing Semifluorinated Di-block Copolymer Thin Films. Umesh Shrestha, Stephen Clarson, Dvora Perahia The structure and composition of an interface influence stability, adhesiveness and response to external stimuli of thin polymeric films. Incorporation of fluorine affects interfacial energy as well as thermal and chemical stability of the layers. The incompatibility between the fluorinated and non-fluorinated blocks induces segregation that leads to long range correlations where the tendency of the fluorine to migrate to interfaces impacts the surface tension of the films. Concurrently Si in a polymeric backbone enhances the flexibility of polymeric chains. Our previous studies of poly trifluoro propyl methyl siloxane-polystyrene thin films with SiF fraction 0.03-0.5 as a function of temperature have shown that the SiF block drives layering parallel to the surface of the diblock. Here in we report the structure and interfacial energies of SiF-PS in the plane of the films, as a function of the volume fraction of the SiF block obtained from Atomic Force microscopy and contact angle measurement studies. [Preview Abstract] |
Monday, March 18, 2013 3:06PM - 3:18PM |
C34.00004: Elastic Properties of Bilayer Membranes Self-Assembled from Diblock Copolymers Kyle Pastor, Jianfeng Li, An-Chang Shi The elastic properties of bilayer membranes are studied using self-consistent field theory (SCFT). The membranes are formed in a blend of AB diblock copolymers and C-homopolymers which act as the solvent. The free energy of a membrane is determined from the SCFT solutions. Fitting the membrane free energy to a continuum elastic model allows the determination of the bending and Gaussian modulus of the bilayers. More importantly, a comparison of the SCFT free energy and the Helfrich model can be used to determine the limit of the linear elastic model. A threshold curvature, at which the linear elasticity theory breaks down, is used to determine the validity region of the Helfrich model in the parameter space of the system. [Preview Abstract] |
Monday, March 18, 2013 3:18PM - 3:30PM |
C34.00005: Exploring the atom-resolution properties of peptoid nanosheets Ranjan Mannige, Ronald Zuckermann, Stephen Whitelam Peptoids are artificial positional isomers of peptides, where the sidechains are attached to the backbone nitrogen in stead of the alpha carbon. Recently, an amphiphilic peptoid was found to form bilayers (nano-sheets) that expand in area to the mesoscopic level but which display uniform thickness of only between 2 to 3 nanometers. While progress in the chemical synthesis of these sheets have witnessed leaps, an atomistic understanding of peptoid nanosheets is lacking. We report recent developments in the atomistic simulation of assembled peptoid nanosheet candidates which resulted in a configurational energy landscape where only specific arrangements of peptoids are energetically feasible. Additionally, we find that while the charged sidechains situated on the exterior of the bilayer describe the general arrangement of the sheet, the exact positions of each peptoid appears to be dominated primarily by the hydrophobic residues that interact in the interior of the bilayer. These results provide a novel picture of the atomistic features of peptoid nanosheets, which serves as a useful platform for the further and rational development of novel peptoid nanosheets. [Preview Abstract] |
Monday, March 18, 2013 3:30PM - 3:42PM |
C34.00006: 3D TEM Tomography of Bilayer Diblock Copolymer Thin Films Kevin Gotrik, Thomas Lam, Adam Hannon, J. Alexander Liddle, Caroline Ross Being able to control the orientation and direction of block copolymer microdomains is of interest for lithographic applications due to the ability to form sub-10 nm feature sizes. Bilayer diblock copolymer films (42 nm as-cast film thickness) of cylinder forming poly(styrene-b-dimethylsiloxane) (PS-PDMS, 45 kg/mol, Flory-Huggins interaction parameter($\chi )=$0.224 at room temperature) can be precisely controlled by templating arrays of PS functionalized post barriers (15 nm diameter) that are periodically spaced on the order of 30-60 nm. The resulting morphologies are 3D in nature due the ability of the posts to decouple the orientation and direction of the two different layers of cylinders. Self-consistent field theory predicts a range of possible bilayer structures that are similar in energetics and that would appear similar when viewed from the top down as is commonly done with SEM after selectively etching the PS with an oxygen plasma (50W CF$_{4})$. This destructive method of imaging therefore limits the ability to compare between different bilayer morphologies that may be forming. Here we show how 3D TEM tomography can be used as a non-destructive way to image the cylindrical microdomains to determine the block copolymer morphology before etching. [Preview Abstract] |
Monday, March 18, 2013 3:42PM - 3:54PM |
C34.00007: High Resolution Imaging of Polymers Using Stochastic Optical Reconstruction Microscopy (STORM) M.W. Gramlich, J. Bae, R. Hayward, J.L. Ross Recent super-resolution fluorescence imaging techniques represent attractive new methods for structural characterization of polymeric systems. STORM is a technique developed over the last decade to image structure and dynamics in biological systems. The high spatial resolution approaches that of other well-established techniques, such as atomic force microscopy (AFM) or scanning electron microscopy, but with all the advantages of a far-field optical technique. We have adapted STORM imaging techniques to polymeric materials, specifically using thin film blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) as a model system. We labeled PMMA with Alexa-647 fluorescent dye, and combined 10wt{\%} label to un-labeled PMMA, then prepared 50:50 by weight blends with PS. We find the lateral PMMA domain size increases with film thickness. Furthermore, we show that the structure and size of the domains is equivalent to results from AFM. Funding is acknowledged from NSF MRI grant{\#}DBI-0923318 to Ross and Wadsworth, ``Development of FPALM-STORM for Live Cell Single~Molecule Microscopy''; NSF MRSEC grant {\#}DMR-0820506 to UMass. We would like to acknowledge Rachel Letteri, Brent Hammer, Todd Emrick, Weiyin Gu, and Tom Russell for help with material preparation. [Preview Abstract] |
Monday, March 18, 2013 3:54PM - 4:06PM |
C34.00008: Nano-spectroscopic vibrational chemical imaging of block-copolymer phase behavior Benjamin Pollard, Markus B. Raschke Block copolymers phase-separate to form a wide range of different types of structures on mesoscopic length scales, controlled by relative chain lengths, solvent, and substrate interactions. However, the investigation of their complex phase behavior has remained difficult using traditional scanning-probe techniques due to a lack of the desired nanoscale chemical specificity. Here, we demonstrate the combination of scattering Scanning Near-field Optical Microscopy (\textit{s}-SNOM) with ultrahigh sensitive infrared vibrational spectroscopy to provide compositional mapping on the sub-domain level. Probing the carbonyl resonance in thin films of poly(methylmethacrylate)-b-polystyrene (PMMA:PS) diblock copolymers, we identify distinct local PMMA density distributions and surface terminations comparing micellar and lamellar structures. With this technique we demonstrate an infrared spectroscopic sensitivity as high as a few 100 monomers and 10 nm spatial resolution. We discuss the extension to related soft-matter systems, including self-assembled monolayers and biomaterials. [Preview Abstract] |
Monday, March 18, 2013 4:06PM - 4:18PM |
C34.00009: Tuning the lateral mobility of thin block copolymer films Harry Bermudez, Andreas Kourouklis Polymer mobility in confined environments is of both theoretical and practical interest. The controlled formation and characterization of systems where such effects can be studied remain active areas of investigation. In this work, we created ultrathin ($<$ 50 nm) supported films of amphiphilic polybutylene-poly(ethylene) oxide diblock copolymers, through Langmuir-Blodgett and Langmuir-Schaefer techniques. To adjust the lateral mobility of these ultrathin films, short polyisobutylene homopolymer was introduced during the film assembly process. Preliminary fluorescence recovery after photobleaching (FRAP) results show that the lateral mobility of the block copolymers is proportional to the logarithm of homopolymer concentration. The mobility can be varied by up to a factor of 8 with as little as 1 mol\% of homopolymer. The role of the added homopolymer on the block copolymer lateral mobility is likely to be related with several features such as chain entanglements, interfacial constraints, and interlayer friction. By varying the concentration and the molecular weight of the homopolymer introduced into the films, we attempt to explain the underlying physical mechanisms that are responsible for changes in lateral mobility. [Preview Abstract] |
Monday, March 18, 2013 4:18PM - 4:30PM |
C34.00010: Autophobic dewetting of symmetric diblock copolymer films on ordered lamellae Mark Ilton, Pawel Stasiak, Mark W. Matsen, Kari Dalnoki-Veress Autophobic dewetting is the process in which a material retracts from a substrate of the same material. This has been observed for homopolymer melts on brush layers as well as in diblock copolymer systems. In the case of diblock copolymer films, autophobic dewetting can arise above the bulk order-disorder transition temperature due to a gradient of segregation strength induced by the film interfaces. We have measured the contact angle of autophobically dewetting droplets of symmetric polystyrene-b-poly(2-vinyl pyridine) as a function of temperature and the number of ordered lamellae that form the substrate layer. The contact angle decreases monotonically with both temperature and the number ordered lamellae, which can be understood as a dependence on the degree of order at the substrate interface. We compare our experimental results to a self-consitent field theory calculation which includes the decaying order away from the interfaces. [Preview Abstract] |
Monday, March 18, 2013 4:30PM - 4:42PM |
C34.00011: Experimental diffusion measurements of entangled rod-coil block copolymers Muzhou Wang, Ksenia Timachova, Alfredo Alexander-Katz, Bradley Olsen A fundamental theory for the dynamics of rod-coil block copolymers is important for understanding diffusion, mechanics, and self-assembly kinetics in functional nanostructured materials for organic electronics and biomaterials. Recently our group has proposed a reptation theory for the diffusion of entangled rod-coil block copolymers, showing the slower dynamics of rod-coils is due to the mismatch between the curvature of the rod and coil blocks. Here we present experimental tracer diffusion measurements of model rod-coil diblock and coil-rod-coil triblock copolymers that support this theory. The model systems are composed of poly(ethylene oxide) coils and polyalanine $\alpha $-helical rods synthesized by bacterial expression and bioconjugation, and tracer diffusion in entangled solutions is measured by forced Rayleigh scattering. The experiments support both the activated reptation and arm retraction mechanism for the small and large rod regimes that were previously presented in our theory. Comparison of both simulation and experiments between diblock and triblock copolymers suggests that the diffusion mechanisms are independent of the different symmetry and molecular architecture of the molecules. [Preview Abstract] |
Monday, March 18, 2013 4:42PM - 4:54PM |
C34.00012: Dynamic Processes in Diblock Copolymer Micelles Megan Robertson, Avantika Singh Diblock copolymers, which form micelle structures in selective solvents, offer advantages of robustness and tunability of micelle characteristics as compared to small molecule surfactants. Diblock copolymer micelles in water have been a subject of great interest in drug delivery applications based on their high loading capacity and targeted drug delivery.~ The aim of this work is to understand the dynamic processes which underlie the self-assembly of diblock copolymer micelle systems which have a semi-crystalline core.~ Due to the large size of the molecules, the self-assembly of block copolymer micelles occurs on significantly longer time scales than small molecule analogues. The present work focuses on amphiphilic diblock copolymers containing blocks of poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic, semi-crystalline polymer), which spontaneously self-assemble into spherical micelles in water. A variety of experimental techniques are used to probe the kinetic processes relevant to micelle self-assembly, including time-resolved neutron scattering, dynamic light scattering, pulsed field gradient nuclear magnetic resonance, and fluorescence resonance energy transfer experiments. [Preview Abstract] |
Monday, March 18, 2013 4:54PM - 5:06PM |
C34.00013: Molecular exchange in block copolymer micelles: when corona chains overlap Jie Lu, Timothy Lodge, Frank Bates, SooHyung Choi The chain exchange kinetics of poly(styrene-b-ethylenepropylene) (PS-PEP) diblock copolymer micelles in squalane (C$_{30}$H$_{62}$) was investigated using time-resolved small angle neutron scattering (TR-SANS). The solvent is a mixture of h-squalane and d-squalane that contrast-matches a mixed 50/50 h/d PS micelle core. As isotope labeled chains exchange, the core contrast decreases, leading to a reduction in scattering intensity. This strategy therefore allows direct probing of the chain exchange rate. Separate copolymer micellar solutions containing either deuterium labeled (dPS) or normal (hPS) poly(styrene) core blocks were prepared and mixed at room temperature, below the core glass transition temperature. The samples were heated to several temperatures (around 100 $^{\circ}$C) and monitored by TR-SANS every 5 min. As polymer concentration was increased from 1\% to 15\% by volume, we observed a significant slowing down of chain exchange rate. Similar retarded kinetics was found when part of the solvent in the 1\% solution was replaced by homopolymer PEP (comparable size as corona block). Furthermore, if all the solvent is replaced with PEP, no exchange was detected for up to 3hr at 200 $^{\circ}$C. These results will be discussed in terms of a molecular model for chain exchange [Preview Abstract] |
Monday, March 18, 2013 5:06PM - 5:18PM |
C34.00014: Direct solvent induced microphase separation, ordering and nano-particles infusion of block copolymer thin films Arvind Modi, Ashutosh Sharma, Alamgir Karim Kinetics of block copolymer (BCP) microphase separation by thermal annealing is often a challenge to low-cost and faster fabrication of devices because of the slow ordering. Towards the objective of rapid processing and accessing desired nanostructures, we are developing methods that enable a high degree of mobility of BCP phases while maintaining phase separation conditions via control of effective interaction parameter between the blocks in BCP thin films. We study the self-assembly of PS-P2VP thin films in various solvent mixtures. While non-solvent prevents dissolution of film into the bulk solution, the good solvent penetrates the film and makes polymer chains mobile. As a result of controlled swelling and mobility of BCP blocks, solvent annealing of pre-cast BCP thin films in liquid mixture of good solvent and non-solvent is a promising method for rapid patterning of nanostructures. Interestingly, we demonstrate simultaneous BCP microphase separation and infusion of gold nano-particles into selective phase offering a wide range of application from plasmonics to nanoelectronics. [Preview Abstract] |
Monday, March 18, 2013 5:18PM - 5:30PM |
C34.00015: Synthesis of Well-Defined Miktoarm Star Copolymer composed of Poly(3-hexylthiophene) and Poly(methyl methacrylate) via combining anionic polymerization and click reaction Jicheol Park, Hong Chul Moon, Jin Kon Kim We synthesized well-defined miktoarm star copolymer composed of regioregular poly(3-hexylthiophene) and poly(methyl methacrylate) ((P3HT)$_2$-$b$-PMMA) by combining anionic polymerization and click reaction. First, we synthesized PMMA terminated with 1,3,5-tris(bromomethy)lbenzene (PMMA-(br)$_2$) by anionic polymerization. Then, the bromide end groups transformed to azide group (PMMA-(N$_3)_2)$. For the synthesis (P3HT)$_2$-$b$-PMMA, click reaction between ethynyl-capped P3HT and PMMA-(N$_3)_{\mathrm{2}}$ was performed. The optical property and thin film morphology of (P3HT)$_2$-$b$-PMMA were investigated by using UV-Vis spectra and atomic force microscopy, respectively. [Preview Abstract] |
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