Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A30: Block Copolymers I |
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Sponsoring Units: DPOLY Chair: Eric Cochran, UCSB Room: LACC 505 |
Monday, March 21, 2005 8:00AM - 8:12AM |
A30.00001: Long-Lived Metastable bcc Phase during Ordering of Micelles Joona Bang, Timothy P. Lodge We report a metastable bcc phase that intervenes between a disordered micellar suspension and an fcc crystal in a block copolymer solution. A symmetric poly(styrene-$b$-isoprene) diblock copolymer in the isoprene-selective solvent squalane at a volume fraction of 0.20 was investigated using small angle x-ray scattering and rheology. Upon heating, the metastable bcc phase nucleates first, and then transforms over the course of hours to the stable fcc phase. At still higher temperatures the fcc phase transforms to an equilibrium bcc phase. The metastability of the bcc phase was confirmed by oscillatory shear and annealing using small angle x-ray scattering. These results constitute an interesting experimental manifestation of Ostwald's step rule, and also support recent theory and simulation results whereby bcc nucleates more readily from a melt of spheres. [Preview Abstract] |
Monday, March 21, 2005 8:12AM - 8:24AM |
A30.00002: Kinetics of BCC-FCC Transition in SI Diblock Copolymer Micelles in a Selective Solvent Rama Bansil, Yongsheng Liu, Huifen Nie, Milos Steinhart, Joona Bang, Timothy P. Lodge Synchrotron based time-resolved small angle x-ray scattering (SAXS), was used to study the kinetics of ordering transition (OOT) in a 0.15(w/v) solution of a polystyrene-polyisoprene diblock (SI 15-15, Mw = 30K) copolymer in $n$-tetradecane, a selective solvent for the Isoprene block. This solution of spherical micelles is known to exhibit both FCC and BCC phases. From a temperature ramp experiment the OOT was identified at about 77C C and an ODT above 100 C. Several temperature jump experiments were performed over the temperature range of 50-110C. A disordered micellar solution at 110 C rapidly quenched to 50 C shows that a BCC phase appears very quickly following the temperature drop, which slowly transforms to the FCC phase at constant temperature. Two- dimensional SAXS patterns reveal the presence of grains. When the sample is melted for a short time the grains reappear producing almost the same scattering pattern as before the melting transition. Detailed analysis of the time evolution of the intensities of the Bragg peaks to follow the kinetics of the growth of the FCC phase will be presented. [Preview Abstract] |
Monday, March 21, 2005 8:24AM - 8:36AM |
A30.00003: Evolution of disordered micelles to hexagonally packed cylinders in a diblock copolymer studied by X-ray Photon Correlation Spectroscopy Amish Patel, Simon Mochrie, Suresh Narayanan, Alec Sandy, Nitash Balsara A poly(styrene-\textit{block}-isoprene) diblock copolymer melt was quenched from the disordered state to a temperature where the hexagonally packed cylinder (HEX) phase is stable. During the quench, disordered micelles (DM), which are obtained during the early stages of the phase transition gradually transform into the HEX phase. The dynamics of the evolving system on molecular length scales, was measured by X-ray Photon Correlation Spectroscopy (XPCS). The relaxation of concentration gradients at a given time during the disorder-to-order transition is slowest at the wave vector corresponding to the small angle X-ray scattering peak. The conversion of micelles to cylinders results in an increase in relaxation time. Complementary dynamical data was obtained by conducting time-resolved rheological measurements on the same sample. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 8:48AM |
A30.00004: Twinning and Growth Kinetics of Lamellar Grains Thomas Chastek, Timothy Lodge The kinetics and grain growth behavior during a thermally induced transition from disorder to lamellae have been determined by polarized optical microscopy (POM). Measurements were made on a poly(styrene-b-isoprene) copolymer, f$_{PS}$ = 0.50, in solution with dioctyl phthalate (DOP), at a 70\% polymer volume fraction. Upon cooling from above the order-disorder transition temperature, four distinct types of grain were observed: ellipsoidal single grains, twinned ellipsoidal grains, 2-fold twinned grains, and spherulites. These grain types cover a range of lamellae orientation. For example, the surface of a 2- fold twinned grain is composed of lamellar edges, whereas the spherulite surface is composed of lamellar planes. The specific grain types that arise give insight into the thermodynamic and kinetic forces governing lamellae ordering. Furthermore, growth front velocities of individual grains were measured after rapid quenches from above T$_{ODT}$. These results were quantitatively compared to the predictions of Goveas and Milner, with good agreement observed. The results will be compared to analogous studies on cylinders and gyroid. [Preview Abstract] |
Monday, March 21, 2005 8:48AM - 9:00AM |
A30.00005: On elasticity of block-copolymer mesophases with glassy domains Kirill Katsov, Glenn Fredrickson The standard Self-Consistent Field Theory of equilibrium self-assembly in copolymer melts is modified to describe effects of glassiness. The glassy domains are modeled by incorporating a variety of structural constraints on chain degrees of freedom. Effects of inter-domain bridging, compressibility, chain pullout and micro-domain deformation on linear and non-linear elasticity are presented. In particular, we study lamellae-forming multi-block copolymers with interleaving glassy and semi-crystalline domains. We predict coexistence between essentially undeformed and highly expanded (micro-cavitating) domains upon sample deformation. Our results are compared to recent experiments on poly(cyclohexylethylene) and poly(ethylene) multi-block copolymer systems. [Preview Abstract] |
Monday, March 21, 2005 9:00AM - 9:12AM |
A30.00006: The Fddd Network Phase in Triblock and Diblock Copolymer Melts Christopher Tyler, David Morse The phase behavior of ABC triblock and AB diblock copolymer melts has been investigated by self-consistent field theory (SCFT), while allowing for (among other candidates) the orthorhombic Fddd ($O^{70}$) network phase identified in recent experiments with poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblocks. Predicted phase diagrams for triblocks with interaction parameters similar to those of ISO contain an $O^{70}$ phase bordered by gyroid, lamellar, and alternating gyroid phases, in agreement with experiment. The $O^{70}$ network is also found to be stable in diblock melts within a narrow region that overlaps the weak segregation end of the gyroid region found in previous calculations. A previous hint of the existence of an unidentified phase in this part of the diblock phase diagram was given in the work of A.-C. Shi and coworkers, who found the gyroid phase to be locally unstable with respect to composition fluctuations in the region of parameter space in which we find the $O^{70}$ network to be preferred over the gyroid. [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:24AM |
A30.00007: Order-disorder transition in 2-D sphere forming diblock copolymers Leopoldo R. G\'{o}mez, Daniel A. Vega, Enrique M. Vall\'{e}s The order disorder transition corresponding to the two dimensional hexagonal patterns formed by sphere forming diblock copolymers is studied through the Cahn-Hilliard model by taking into account a long range term in the free energy functional. The growth kinetic of the equilibrium patterns at deep quenches is dominated by spinodal decomposition. At shallow quenches the phase separation is a two-steps process, initiated by a long lived intermediate state with a well defined characteristic length, but ill defined symmetry. The mean-life of this state increases with a power law with the reduced temperature as the order disorder transition is approached. At long times the system evolutes towards equilibrium by nucleation and growth. [Preview Abstract] |
Monday, March 21, 2005 9:24AM - 9:36AM |
A30.00008: Determination of Order-Disorder Transition of Polystyrene-block-poly(n-pentyl methacrylate) Copolymer by Temperature-dependent FTIR Spectroscopy Jin Kon Kim, Hye J. Kim, Young M. Jung, Seung B. Kim, Du Yeol Ryu, Kristopher Lavery, Thomas P. Russell The lower disorder-to-order transition (LDOT) and the upper order-to-disorder transition (UODT) temperatures of polystyrene-block-poly(n-pentyl methacrylate) (PS-PnPMA) were measured by temperature-dependent Fourier transform infrared (FTIR) spectra with principal component analysis (PCA) and two-dimensional (2D) correlation spectroscopy. These two transitions are determined from sudden changes of the intensity (A) at specific wavelength as a function of temperature. We found that when the first derivative of A with respective to temperature (dA/dT) is plotted against temperature, the maximum in dA/dT at all wavelengths was observed at these two transitions. [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A30.00009: Phase Behavior of Poly(styrene-b-isoprene) Diblock Copolymers Loaded with $\gamma$-Fe$_{2}$O$_{3}$ Nanoparticles Moon Jeong Park, Jongnam Park, Taeghwan Hyeon, Kookheon Char We investigate the effect of hard additives, i.e., magnetic nanoparticles, on the phase behavior of polystyrene-block- polyisoprene (PS-b-PI) diblock copolymers by varing the size of nanoparticles (6 nm and 14 nm). For the design of multicomponent materials with spatially defined order of different components, two PS-b-PI diblock copolymers showing lamellar (SI1) and cylindrical (SI2) morphologies are used as structure-directing matrices for the nanoparticle arrangement. Fine maghemite ($\gamma$-Fe$_{2}$O$_{3}$) particles with surfaces modified by oleic acid have been synthesized and two different solvents, hexane and toluene, were used to prepare film specimens by static casting. The interactions between mesophase-forming copolymers and nanoscopic particles can lead to highly organized hybrid materials. Notably, the morphology of such composites strongly depends on the preparation conditions as well as the characteristics of templating copolymers. The $\gamma$-Fe$_{2}$O$_ {3}$ were selectively incorporated into the PI domains under hexane condition, while they were preferentially aggregated when toluene is used. Particularly, under toluene condition, we observed the well-defined body centered cubic structure for SI2 as well as the undulating lamellar morphology for SI1. The structural information obtained from X-ray scattering is in good agreement with the transmission electron microscopy images. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A30.00010: Nanocellular formation of supercritical CO$_2$ in block copolymer thin films Hideaki Yokoyama, Lei Li, Taichi Nemoto, Kenji Sugiyama The production of large-area structured surfaces with a featured size of nanometer scale still remains a challenge by conventional photolithography. In particular, block copolymer thin films have been considered as the ideal lithography templates. Here we present our novel supercritical carbon dioxide (scCO$_2$) process to fabricate thin films with a single layer of empty cells of a diameter of ca. 30 nm in block copolymer thin films. By absorbing CO$_2$ in CO$_2$-philic block domains of a block copolymer followed by depressurization, empty cells are introduced in CO$_2$-philic domains. This process was successful even in a block copolymer thin films with a thickness less than 100 nm. The typical nanocellular structures introduced by our novel scCO$_2$ process (10MPa) have an average spacing of 34 nm and a density of 9 $\times$ 10$^{10}$ cm$^{-2}$. The size and the spacing of such nanocells can be adjusted by changing saturation pressure of scCO$_2$. The obtained structures are significantly different from those expected from the volume ratio of domains swollen by CO$_2$. Spherical cells in block copolymer thin films are found even when the porosity is more than 30\%. [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A30.00011: Phase Transitions and Spatial Organization in Nanoparticle-Block Copolymer Mixtures Jaeup Kim, Ben O'Shaughnessy Introducing nanoparticles into nanostructured block copolymer phases can dramatically influence the polymer host. Computer simulations [Balazs et al., PRL, 89, 155503 (2002)] suggest inclusions can actually trigger transitions from one polymer phase to another. Simultaneously, the nanoparticles can be organized into complex superstructures, giving composite materials with novel mechanical, electrical and optical properties. Potential applications include catalysts, selective membranes and optical filters. We have developed a first principles theory predicting polymer phases and nanoparticle distributions. We find modification by nanoinclusions of the free energy of stretched polymer domains in lamellar, cylindrical or spherical geometries triggers structural changes and determines particle distributions. Our framework builds on Semenov's description of AB copolymers in the strongly stretched limit by incorporating nanoinclusions. Energy favors segregation into particle-rich regions, while entropy favors particle mixing into the energetically preferred block, say A. When entropy wins (small particles), an A-core cylindrical-to-lamellar phase transition is induced. Interestingly, large particles by contrast microphase separate into copolymer domains (analogous to Semenov's conclusions for homopolymer-copolymer mixtures) triggering reverse phase transitions (e.g. lamellar to A-core cylindrical). We present our results as a complete phase diagram. [Preview Abstract] |
Monday, March 21, 2005 10:12AM - 10:24AM |
A30.00012: Elastic Properties of Ordered Block Copolymer / Nanoparticle Composites Russell Thompson, Kim Rasmussen, Turab Lookman A hybrid self-consistent field/density functional theory has been used to predict the elastic moduli of a diblock copolymer melt with added spherical nanoparticles with an affinity for one block. It was found that the addition of nanoparticles lowers the tensile modulus of the composite material, while the shear modulus was unaffected. Explanations for the physical origins of these results will be given. [Preview Abstract] |
Monday, March 21, 2005 10:24AM - 10:36AM |
A30.00013: On the influence of temperature and volume fraction on liquid crystalline block copolymer nanoscale architectures Kishore Tenneti, Christopher Li, Yingfeng Tu, Xinhua Wan, Qu-Feng Zhou, Carlos Avila-Orta, Benjamin Hsiao Liquid crystalline block copolymers (LCBCs) form complex hierarchical structures. We report the phase structures of a series of poly(styrene-\textit{block}-(2,5-bis-(4-methoxyphenyl)oxycarbonyl)styrene) (PS-b-PMPCS) rod-coil diblock copolymers based on the results obtained from thermal analysis, x-ray analysis and transmission electron microscopy. The PS-b-PMPCS system formed lamellar structures of alternating PS and PMPCS domains. Each PMPCS domain contained a bilayered rod-like structure whose axis is parallel to the lamellar normal. In low MW BCs, a S$_{Ad}$-like interdigitated metastable phase was observed which changed into a bilayered structure upon heating. As the PS content increased, the LC layer was gradually punctuated by PS and a perforated layer structure was observed. The ``degree of perforation'' depends on the LC volume fraction. [Preview Abstract] |
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A30.00014: The Effect of Segregation Strength on Network Formation in ABC Triblocks Thomas Epps, Joon Chatterjee, Frank Bates The effects of segregation strength on network phases were investigated in linear poly(isoprene-$b$-styrene-$b$-ethylene oxide) triblocks with various molecular weights. Morphological behavior at higher molecular weights indicated that network long-range order decreased as the polymer molecular weight increased. The signature Q$^{230}$ and O$^{70}$ X-ray scattering patterns were retained in the lowest molecular weight specimens, while the highest molecular weight data were ambiguous, displaying broad peaks at approximately q* and 2q*. TEM results on these materials showed network-like structures with reduced long-range order. It is unclear whether the highest molecular weight structures represent poorly ordered versions of equilibrium networks or kinetically trapped metastable states. Interestingly, this effect was specific to triply-periodic structures, as lamellar samples of comparable molecular weights displayed excellent long-range order. The reduced organization of the networks likely arises from a decrease in coordinated chain motion as a result of the different diffusion mechanisms available to lamellar versus triply-periodic microstructures. [Preview Abstract] |
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A30.00015: Stability of Core-Shell-Cylinder Structure of Poly(styrene-b-1,3-cyclohexadiene) Diblock Copolymers Ashoutosh Panday, Samuel Gido, Kunlun Hong, Jimmy Mays A new free energy model for rod-coil block copolymer systems is proposed in which the distortion splay energy of continuum elasticity theory is incorporated into the rod domain energies. The model is applied to explain the stability of a core-shell-cylinder morphology which was observed by Gido and coworkers for diblock copolymers of polystyrene (PS) and poly-(1,3-cyclohexadiene) (PCHD). Based on its Kuhn length, the PCHD block can be treated as a rod. The model suggests that the core-shell-cylinder structure is energetically favorable for this system compared to a solid cylinder structure. [Preview Abstract] |
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A30.00016: LDOT Diblock Copolymers: Specific Interactions, Compressibility, and Fluctuations Junhan Cho, Duyeol Ryu, Jin Kon Kim We perform the recently developed compressible Hartree analyses on the phase behavior of LDOT-type diblock copolymers based on polystyrene and homologous poly(n-alkyl methacrylates).~ Specific interactions between dissimilar monomers, compressibility difference between block components, and concentration fluctuations are all considered to illuminate the complicated phase behavior of those homologous copolymers.~ Microphase transition temperatures and their pressure dependence are compared with the corresponding theoretical values for the copolymers.~ We provide suggestions for the design of a better nanostructured material using those copolymers. [Preview Abstract] |
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