### Session X20: Long Range Order in Polymer Structures and Morphologies

 Thursday, March 19, 2009 2:30PM - 3:06PM X20.00001: Long range ordering in block copolymer thin films Invited Speaker: Caroline Ross Thin films of microphase separated block copolymers, which can form patterns consisting of dense arrays of lines or dots, are attractive materials for self-assembled nanoscale lithography. The long range order of the block copolymer microdomains can be controlled by the use of chemical or topographical patterns. In this work, we discuss how Si-containing block copolymers, polystyrene-b-polyferrocenyldimethylsilane (PS-PFS) and polystyrene-b-polydimethylsiloxane (PS-PDMS), can be templated on substrates patterned with posts or steps. In the case of 40 nm period spherical morphology PS-PDMS, $<$20 nm diameter posts, which are coated with a grafted layer of PDMS homopolymer, define the locations of surrounding PDMS microdomains. The lattice spacing and orientation of the templated PDMS microdomain array can be predicted from the ratio between the post spacing and the equilibrium microdomain spacing. PFS spheres, formed from spherical-morphology PS-PFS, can be aligned within shallow trenches to form a close-packed array with row spacing determined by the trench width. We also show how 32 nm period cylindrical morphology PS-PDMS can be templated using topographical features. Templating using posts or linear substrate features gives arrays of straight parallel cylinders with controllable period and orientation, while templating in circular pits creates sharply curved, concentric toroidal structures. The overall morphology and period of the block copolymer microdomain arrays can be varied by solvent annealing in mixed solvent vapors, for example cylindrical-morphology PS-PDMS can form perforated lamellae by annealing in toluene plus heptane. These results will be discussed in the context of nanolithography, including examples of pattern transfer to form metal, oxide and polymer functional nanostructures. Bita et al, Science 321 939 (2008); Jung et al, Nano Letts. 7 2046 (2007); 8 2975 (2008). Thursday, March 19, 2009 3:06PM - 3:18PM X20.00002: Surface Morphology Diagram for Cylinder-Forming Block Copolymer Thin Films Alamgir Karim , Xiaohua Zhang , Jack Douglas , Ronald Jones We investigate the effect of annealing temperature (T) and film thickness (hf) on the surface morphology of flow coated films of a cylinder forming block copolymer, poly (styrene-block-methyl methacrylate) (PS-b-PMMA). A transition from a perpendicular to a parallel cylinder orientation with respect to the substrate is observed upon increasing hf when the substrate interaction is highly selective for one of the blocks (PMMA) and the polymer-air interface has a nearly neutral interaction with both blocks. Surface morphology transitions with increasing hf are observed in these model frustrated-interaction' films: (a) first, a transition occurs from cylinders oriented parallel to the substrate to a mixed or hybrid' state where the two orientations coexist (b) this hybrid morphology then transforms to cylinders oriented perpendicularly to the polymer-air interface for larger hf. The characteristic values of hf defining these surface morphological transitions depend on T and we construct a surface morphology diagram as a function of hf and T. The surface morphology diagram is found to depend on the method of film formation (flow coated versus spun cast films) so non-equilibrium effects evidently have a large effect on the surface pattern morphology. In particular, the residual solvent within the film (quantified by neutron reflectivity measurements) can have a large effect on the surface morphology diagram and the physics of glass-formation is also apparently important. Thursday, March 19, 2009 3:18PM - 3:30PM X20.00003: Practical Implementation of Order Parameter Calculation for Directed Assembly of Block Copolymer Thin Films Chi-Chun Liu , Gordon Craig , Paul Nealey , Ricardo Ruiz , Nicola Ferrier The assembled morphologies in thin films of block copolymers are gaining interest for potential applications in advanced lithography and template fabrication due to their low defect density, pattern rectification, and resolution enhancement. For such applications, the ability to quantify the extent of order achieved with different assembly methods and materials is crucial. Previous studies analyzed the translational order parameter ($\Psi$T) based on reciprocal lattice vectors obtained from Fourier Transforms, but discussed neither the accuracy of these vectors nor the effect of domain positioning on the calculation results. In both simulations and real systems we have shown the inaccuracy of these parameters can lead to huge difference in $\Psi$T. Here we present a computational procedure to delineate the importance of these parameters and analyze with a high level of accuracy the translational and orientational order parameters of the guiding pattern, the domains of a block copolymer directed to assemble on this pattern, as well as the underlying structure after lift-off. We observe that order can be preserved over a large area and can be retained in subsequent processing. Thursday, March 19, 2009 3:30PM - 3:42PM X20.00004: Controlling the self-assembly of block copolymer materials in thin-films Eungnak Han , Karl Stuen , Paul Nealey , Padma Gopalan We present a simple and efficient strategy towards surface modification for controlling the self-assembly of P(styrene-b-methylmethacrylate) diblock copolymer (BCP) in thin films. Photo-patternable, substrate-independent neutral surface was created to achieve vertical orientation of block copolymer (BCP) microdomains. A random copolymer of styrene (f= 0.58-0.63), methylmethacrylate (f= 0.41-0.46) and glycidyl methacrylate (f= 0.01-0.02) was synthesized. The copolymer uses photo-crosslinking reaction of epoxy groups by photoacid generator to formulate the neutral surface. Ultra-thin (2-6 nm) crosslinked film was created as a neutral interfacial layer between the block copolymer and the substrate. The composition of the copolymer was fine tuned to tailor the wetting behavior and hence the domain orientation (parallel or perpendicular to the substrate) in the top self-assembled block copolymer film. The effectiveness of the new neutral polymer on a range of substrates such as glass and gold coated silicon wafer and for both symmetric and asymmetric BCPs is demonstrated. Thursday, March 19, 2009 3:42PM - 3:54PM X20.00005: Shear Alignment and Realignment of Cylinder-Forming Block Copolymer Thin Films Andrew Marencic , Richard Register , Paul Chaikin The microdomains in cylinder-forming block copolymer thin films can be oriented by applying a sufficient shear stress to the film; the cylinders lie in-plane and align with the shear direction, as shown by atomic force microscopy (AFM) post-shear. To understand the alignment process, we applied a stress gradient to the film, and focused on the structure in the transition region from unaligned to aligned. To sample a statistically useful number of grains, we used the moir\'{e} patterns formed by interference of the AFM scanning grid with the microdomain lattice to determine the cylinder orientation. The results are compared with a simple melting-recrystallization model, in which grains misaligned with the shear direction are eliminated as the shear stress is increased. In addition, we have applied two shear gradients to the sample in different directions, to directly probe how ordered cylinders can be realigned by a subsequent shear. We again find qualitative agreement with the simple model, but the stress required is a factor of 1.7 larger than required for single shear. We also observed grain boundary generation within the area between alignment with the first shear direction and alignment with the second shear direction. Thursday, March 19, 2009 3:54PM - 4:06PM X20.00006: Structural transition with thickness in films of poly-(styrene-b-2vinylpyridine) (PS-b-P2VP) diblock copolymer/homopolymer blends Vindhya Mishra , Edward Kramer , Su-mi Hur , Glenn Fredrickson , Michael Sprung In multilayer thin films of spherical morphology block copolymers, the surface layers prefer hexagonal symmetry while the inner layers prefer BCC. Thin films with spherical morphology of PS-b-P2VP blends with short homopolymer polystyrene (hPS) chains have an HCP structure up to a thickness n* at which there is a transition to a face centered orthorhombic structure. Using grazing incidence small angle X-ray scattering and transmission electron microscopy we show that that n* increases from 5 to 9 with increase in hPS from 0 to 12 vol{\%}. For thicknesses just below n* the HCP and FCO structures coexist, but on long annealing HCP prevails. We hypothesize that the PS segregates to the interstices in the HCP structure reducing the stretching of the PS blocks and the free energy penalty of HCP versus BCC inner layers. Self consistent field theoretic simulations are being carried out to see if this idea is correct. Thursday, March 19, 2009 4:06PM - 4:18PM X20.00007: A Modular and Hierarchical Supramolecular Block Copolymer Self-assembling Strategy Towards Square Arrays Chuanbing Tang , Erin Lennon , Michael Dimitriou , Glenn Fredrickson , Edward Kramer , Craig Hawker We present a modular and hierarchical self-assembling strategy for the generation of novel nanoscale patterns suitable for block copolymer lithography. Supramolecular block copolymers consisting of poly(ethylene oxide)-b-poly(styrene-r-4-hydroxystyrene) and poly(styrene-r-4-vinylpyridine)-b-poly(methyl methacrylate) diblock copolymer blends with hydrogen-bonding interactions between the polystyrene majority segments were prepared by living free radical polymerization. By combining supramolecular assembly of H-bonding phenolic and pyridyl units with controlled phase separation of diblock copolymers, highly ordered square arrays were obtained. The compositions of H-bonding components were critical for generating both long range order and for controlling the spatial arrangement of ordered arrays. The utilization of these materials as lithographic masks was successful and allowed transfer of the polymeric template with high fidelity to silicon oxide substrates, leading to a highly ordered array of 20 nm cylindrical pores with a spacing of 50 nm. This modular blending approach to block copolymer resists demonstrates a new and powerful strategy for the fabrication of unique patterns for nanolithographic applications. Thursday, March 19, 2009 4:18PM - 4:30PM X20.00008: Macroscopic Addressable Arrays of Block Copolymer Microdomains Soojin Park , Dong Hyun Lee , Bokyung Kim , Sung Woo Hong , Ji Xu , Unyong Jeong , Ting Xu , Thomas P. Russell Generating addressable, macroscopic arrays of nanoscopic elements with perfect lateral order has the potential to revolutionize the microelectronic and storage industries. A novel approach is shown using faceted surfaces of commercially available sapphire wafers to guide the self-assembly of block copolymer (BCP) microdomains into arrays with single crystal textures over the entire wafer surface. Perfectly ordered arrays of BCP microdomains, with areal densities in excess of 10 Terabit/inch$^{2}$, have been produced. The sawtoothed substrate topography provides registered, directional guidance of the BCP self-assembly that is tolerant of surface defects, maintaining the lateral registry and ordering of the microdomains over the entire surface. The approach provides unprecedented areal densities, and opens simple, yet versatile routes to ultrahigh density, addressable systems. Thursday, March 19, 2009 4:30PM - 4:42PM X20.00009: Self-Extinguishing Crystallization: Copolymer Behavior under Flow Diana Smirnova , Meisam Hajimorad , Julia Kornfield It is known that short chain branches in copolymers act as crystal defects, resulting in materials with low crystallinity and poorly-defined morphology. We are interested in the behavior of copolymers under flow in the presence of species that readily form well-defined shish-kebab morphologies. Bimodal blends containing small concentrations of high molecular weight, high density polyethylene (HDPE, Mw = 526 kg/mol, Mw/Mn = 3) in an ethylene-co-hexene matrix (Mw = 50 kg/mol, Mw/Mn = 2, 5 mol {\%} hexene) were studied via rheo-optical and rheo-xray techniques. HDPE concentrations were selected above and below the overlap concentration of 0.6{\%}, but maintained below 1{\%} such that the rheology of the blends was not significantly altered from that of the copolymer matrix. DSC traces were collected to ensure that co-crystallization between the two blend components occurs. Crystallization after shear quickly leveled off revealing a self-extinguishing behavior. The time frame for this extinction is coupled with a loss of anisotropy in scattering patterns indicating random crystallization uncorrelated with existing oriented structures. Thursday, March 19, 2009 4:42PM - 4:54PM X20.00010: Quasicrystalline long-range order in an ABC star block copolymer Tomonari Dotera We report the formation of a dodecagonal quasicrystal (DDQC) in a lattice Monte Carlo simulation of a star-shaped three component polymeric alloy. We have observed a series of Archimedean and quasicrystalline phases $(4.8^2) \rightarrow (3^2.4.3.4) \rightarrow {\rm DDQC} \rightarrow (4.6.12)$ with increase of one component of ABC star polymers. This phase behavior can be regarded as a transition from square tiling to triangle tiling via square-triangle tiling. The simulation is associated with the recent striking experimental manifestation of quasicrystalline order: A mesoscopic tiling pattern with twelvefold symmetry in a three-component star polymer system composed of polyisoprene, polystyrene, and poly (2-vinylpyridine). Since, the same kind of quasicrystalline structures have been found for metal alloys, chalcogenides, and liquid crystals, the present result confirms the universal nature of quasicrystalline long-range order over several hierarchical length scales. \\[4pt] T. Dotera and T. Gemma, Philos. Mag. {\bf 86}, 1085 (2006).\\[0pt] T. Dotera, Phil. Mag. {\bf 88}, 2245 (2008). \\[0pt] K. Hayashida, et al., Phys. Rev. Lett. {\bf 98}, 195502 (2007). Thursday, March 19, 2009 4:54PM - 5:06PM X20.00011: Effect of chain extender on the phase behavior and morphology of high hard block content polyurethanes Alberto Saiani , Achilleas Tsiotas Thermoplastic Polyurethanes (TPU) are linear block copolymers typically constructed of statistically alternating soft (SS) and hard (HS) segments. Due to their numerous industrial applications these materials have received considerable attention. We have investigated the phase behavior and morphology of a set of high hard block content polyurethanes and varied the chain extender used. Using mainly calorimetry, scattering and microscopy techniques we were able to elucidate the origins of all the thermal events observed through differential scanning calorimetry. Correlating our thermodynamic work with our structural work we were able to propose a new morphological model of the structure and the phase behavior of high hard block content polyurethanes. We have shown that above 65{\%} hard segment content the melt-quenched samples present a two-phase morphology one pure hard segment phase co-existing with a mixed phase with the same hard segment content of 65{\%} for all samples. When annealed at high temperature the mixed phase undergoes phase separation resulting in the same phase-separated mesophase. Changing the chain extender has a significant impact of the phase behavior and morphology of these systems Thursday, March 19, 2009 5:06PM - 5:18PM X20.00012: Ligand-induced order in Spotted vesicles and Striped micelles David Christian , Wouter Ellenbroek , Andrea Liu , Dennis Discher Mixtures of amphiphiles are ubiquitous and assemble into various morphologies, including giant vesicles and cylinder micelles that raise the possibility of mesoscopic segregation within the assemblies -- perhaps even in response to binding of small ligands. Here, with anionic and neutral polymer amphiphiles mixed within vesicle and cylinder morphologies, divalent cations are shown to induce meso-scale domains and thus generate `\textit{responsive} \textit{Janus }structures'. Whereas past reports with lipid systems appear conflicted, calcium forms definitive crossbridges between the anionic polymer amphiphiles, rigidifying the charged membranes across a fluid-gel transition and also leading to lateral phase separation without disrupting the assemblies. A systematic phase diagram for these robust assemblies shows that long-lived domains occur in an unexpectedly narrow region near the polyanion's p$K$'s for protonation and cation association. The phase behavior appears well described by a relatively simple model in which -- among electrostatic and entropic contributions -- counterion entropy outcompetes attractive crossbridging to drive remixing of the highly charged polyacid at high pH, contrary to intuition. Thursday, March 19, 2009 5:18PM - 5:30PM X20.00013: Electrospinning of semicrystalline polymer fibers Ying Liu , Shuang Chen , Chunhua Li , Elaine DiMasi , Gad Marom , Miriam Rafailovich Electrospinning of polymeric fibers has been attracted increased interest in recent years. However, the research for ethylene-vinyl acetate (EVA) and linear polyethylene (PE) is still limited, due to their relatively poor solubility in conventional solvent systems at ambient temperature. In this study, EVA and PE fibers were electrospun with different fiber diameter when the electrospinning solution was kept at a temperature greater than that of the solidification temperature of the polymer solutions. The effects of the fiber physical dimension to its crystallization and mechanical properties were thus detected. The morphology of the fibers was measured by scanning electron microscope (SEM) and atomic force microscope (AFM). The shear modulation force microscopy technique (SMFM) was used to measure the melting point, $T_{m}$, which was found to increase with increased fiber diameter and crystallinity. AFM three-point bending test demonstrated that the Young's modulus of the fibers drastically increased as fiber diameter decreased.$_{ }$Grazing-incidence small angle x-ray scattering (GISAX) showed that, compared to the bulk material, the crystallinity of the electrospun fibers had been changed.