Download or read book Manipulating Phase Behavior in Block Copolymers Using Polydispersity written by and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of polydispersity, or broad molecular weight distributions, on the phase behavior of block copolymer melts and thin films are systematically explored. Linear AB diblock, ABA triblock, and BAB triblock copolymers are synthesized with continuous polydispersity in the B block (Mw/Mn 8́ơ 1.70́32.0) and relatively monodisperse A blocks (Mw/Mn 8́ơ 1.10́31.3) to understand how the self0́3assembly of polydisperse block copolymers can be altered with chain architecture and block connectivity. Broad dispersity in the M block of poly(styrene0́3b0́3methyl methacrylate) (SM) diblock copolymer melts induces domain dilation and morphological transitions to higher M block volume compositions with respect to predictions for monodisperse SM diblock copolymers. A comparison between poly(styrene0́3b0́31,40́3butadiene0́3b0́3styrene) triblock copolymers (SBS) with mid0́3block (B) polydispersity and poly(methyl methacrylate0́3b0́3styrene0́3b0́3methyl methacrylate) triblock copolymers (MSM) with outer0́3block (M) polydispersity reveals that the location of the polydisperse block and how it is connected to the other blocks is critical. Center block polydispersity in SBS, where one block is constrained at two block junctions, leads to a lamellar phase window shift to higher volume fractions of B, increases in domain periodicity, and the stabilization of a new, disordered bicontinuous morphology. The domain periodicity in the MSM triblocks with outer M block polydispersity is at least twice that predicted for monodisperse MSM triblock copolymers. However, in contrast to the SBS triblocks, the polydisperse MSM triblocks exhibit a lamellar phase window shift to lower M block compositions. The behavior of the SBS and MSM triblock copolymers is clarified in the context of the chain architectures present in the melts resulting from the block polydispersity. Preliminary studies of the thin film behavior of the SM diblock and MSM triblock copolymers revealed that despite the polydispersity of the M block, perpendicular microdomain orientation can be achieved. The MSM triblock copolymer thin films exhibit film thickness0́3dependent morphological behavior arising from a confluence of M outer0́3block polydispersity and the presence of a random brush0́3modified substrate. In summation, this dissertation demonstrates that polydispersity can be used to manipulate the phase behavior of block copolymer melts and thin films and may facilitate access to new materials with potentially useful properties.
Download or read book Effects of Stiffness and Polydispersity on the Phase Behaviour of Block Copolymers written by Pieter Menno Jager and published by . This book was released on 2006 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tuning Melt phase Morphology in Block Copolymers Using Block Dispersity written by and published by . This book was released on 2014 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt: Block copolymers non-linearly combine the properties of two different homopolymers into a single material, by virtue of the connectivity between the two distinct homopolymer segments. Their microphase separation at the nanoscale leads to the formation of interesting and useful microstructures, such as spheres and cylinders ordered on regular lattices with high degrees of long-range order. The advent of newer controlled radical and tandem polymerization techniques enables the enchainment of an ever increasing number of functional monomers with new properties, yet these techniques typically result in copolymers with broader molecular weight dispersities. A thorough understanding of the morphological consequences of increased molecular weight dispersity in one or more segments in a block copolymer will enable the development of new materials incorporating unusual monomers with new chemical functionalities and properties. Herein, we describe the synthesis and characterization of a library of poly(lactide-b-1,4-butadiene-b-lactide) (LBL) triblock copolymer samples with broad dispersity center segments, and we compare their melt-phase self-assembly behavior to previously reported polydisperse SBS triblock copolymers. Based on these comparisons, we rationalize the dramatically different behaviors of the two systems in terms of specific chain packing arrangements that depend upon the degree of chemical incompatibility of the copolymer system. In an attempt to mimic the most important molecular heterogeneities of continuously polydisperse copolymers as identified by our studies, we designed bidisperse blends of triblock copolymers and studied their morphological and uniaxial mechanical properties. As with continuously polydisperse copolymers, these blends also adopted bicontinuous morphologies with substantial mechanical toughness. In the latter part of this thesis, we investigate the influence of macromolecular dispersity on the macrophase separation behavior of mixtures of poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) co-dissolved in water. The location of the concentration-dependent phase boundary, which separates the phase separated and phase mixed regions, is shown to depend on both the average molecular weight and dispersity of the polymeric components. Colloidal and copolymer surfactant additives are further shown to improve ATPS emulsion stability at higher temperatures and to mitigate emulsion coarsening.
Download or read book Phase Behavior of Block Copolymer Solutions written by Joona Bang and published by . This book was released on 2004 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Block Copolymers written by Kenneth J. Hanley and published by . This book was released on 2001 with total page 916 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Block Copolymers written by Ashish Kumar Khandpur and published by . This book was released on 1995 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Phase Behavior of Block Copolymers in Selective Solvents written by Yongsheng Liu and published by . This book was released on 2008 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The goal of this research is to study the phase behavior and kinetics of order-order (OOT) and order-disorder (ODT) phase transitions in block copolymers in selective solvents. We focus on examining temperature and pressure dependence of the phase diagram and the kinetics of phase transitions using small angle x-ray scattering (SAXS). The kinetics of ODT and OOT was studied for two block copolymer solutions by time-resolved SAXS using temperature ramp and fast quench methods: (i) Poly(styrene- b -isoprene) (PS-PI) diblock copolymer in tetradecane, selective solvent for PI, which displayed face-centered-cubic (FCC) structure at low temperature, body-centered-cubic (BCC) at intermediate temperature, and was disordered at high temperature. Following a quench from 110 C to 50 C, a long-lived meta-stable BCC phase was detected prior to the formation of FCC. The data agrees very well with Cahn's model for nucleation and growth. (ii) Poly(styrene- b -ethylene- co -butylene- b -styrene) triblock copolymer in dibutyl phthaphate, selective solvent for PS, which displayed hexagonally packed cylinders (HEX) at low temperature and lamellar (LAM) phase at high temperatures. This is unusual because in most block copolymer melts LAM occurs at lower temperature than HEX. A geometric model was developed to understand the mechanism of the transition from LAM to HEX. The calculated scattering intensity agrees very well with the experimental data. A pressure network system for SAXS capable of operating in the range of 1-4000 bars with pressure jump capability was built to study the pressure dependence of phase behavior. The system was used to investigate PS-PI diblock copolymer in diethyl phthaphate. The BCC to disorder transition temperature increased with pressure at 20 C/kbar, and the lattice constant increased with pressure. Brownian Molecular Dynamics simulations were carried out to study the phase behavior of multiblock copolymers in a selective solvent. Disordered, BCC, HEX, and LAM phases were obtained depending on the concentration and number of blocks. This research provides detailed information of the kinetics of structural changes in block copolymers in selective solvents. The results provide a good understanding of the mechanism of order-disorder and order-order transitions, and are directly related to industrial applications of block copolymers.
Download or read book Phase Behavior Structure and Properties of Model Block Polymers written by and published by . This book was released on 1993 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: This project brought together three distinct experimental methods in an integrated investigation of the phase behavior, structure and properties of block copolymers in the vicinity of the order-disorder transition. Anionic polymerization of polydiene diblock copolymers followed by catalytic hydrogenation was used to produce three classes of model saturated hydrocarbon materials. Dynamic mechanical spectroscopy and large amplitude dynamic shearing were employed to probe and manipulate, respectively, the melt state microstructure. Small angle neutron scattering (SANS) experiments provided detailed information regarding the structure of the materials. A significant achievement during this work was the development of a dynamic shearing device that could be operated in situ with a SANS instrument. Together with the spectrum of materials produced, this combined scattering-rheology technique has led to a qualitative improvement in our understanding of block copolymer phase behavior, and uncovered a rich polymorphism that is accompanied by dramatic variations in physical properties. Two new parameters have been shown to play a crucial role in determining block copolymer phase behavior. The degree of polymerization, controls the extent of composition fluctuations which strongly affects the types of phases encountered near the order-disorder transition. Conformational asymmetry, which is controlled by the block volume and radius of gyration, leads to different phases on either side of the phase diagram. These effects have not been accounted for theoretically.
Download or read book Theory for the Effect of Polydispersity on the Phase Behaviour of Diblock Copolymers written by David M. Cooke and published by . This book was released on 2002 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book On the Phase Behavior of Polydisperse Copolymers written by Christiaan Kok and published by . This book was released on 2001 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Block Copolymer Blend Phase Behavior written by Paul Martin Lipic and published by . This book was released on 1998 with total page 454 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Phase Behavior and Kinetics of Cylinder to Sphere Transition in Block Copolymers in Selective Solvents written by Minghai Li and published by . This book was released on 2008 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The main goal of this dissertation is to study the phase behavior and kinetics of cylinder to sphere phase transition in block copolymers in selective solvents using time- resolved small angle x-ray scattering (SAXS), rheology, Atomic Force Microscopy (AFM), modeling and simulation. Block copolymers consist of two or more chemically distinct polymer blocks connected by a covalent bond. The incompatibility of the constituent blocks leads to phase separation on length scales of 10-1000 nm instead of bulk phase separation. The addition of a selective solvent which preferentially solubilizes one of the components further enriches the phase behavior and provides easier control over the morphology of micellar domains. Although many studies have been made on the phase diagrams of block copolymer solutions the kinetics of phase transitions between two different crystalline symmetries are less understood. The experiments were conducted on a triblock copolymer of poly(styrene- b -ethylene- co -butylene- b -styrene) (SEBS), in mineral oil, a solvent selective to middle EB block. AFM measurements clearly showed the cylindrical micelles arranged hexagonally (HEX) at 110°C. Synchrotron based time-resolved SAXS measurements showed that the transition from HEX to spherical micelles arranged on body-centered cubic (BCC) lattice occurs via a nucleation and growth mechanism for shallow temperature jumps and via spinodal decomposition for deep temperature jumps. We developed a geometrical model of coupled anisotropic fluctuations to calculate the scattering and found very good agreement with the SAXS data. Brownian Molecular Dynamics simulations were carried out to provide microscopic insights on the HEX to cubic transition. HEX, face-centered cubic (FCC), lamellar, and hexagonally perforated lamellar ordered phases were obtained depending on the concentration, temperature and solvent selectivity. Kinetics of HEX to FCC was examined by quenching the temperature or rapidly changing the well-depth of the Lennard-Jones potential used in the simulation. The observations from snapshots, density profiles and calculated scattering intensity all agree well with the nucleation and growth mechanism. This work provides a detailed understanding of the mechanism and kinetics of phase transition of cylinders to spheres in block copolymer solution system. The results have relevance to block copolymer processing and other applications.
Download or read book Phase Behavior of Block Copolymers in Compressed CO2 and as Single Domain layer Nanolithographic Etch Resists for Sub 10 Nm Pattern Transfer written by Curran Matthew Chandler and published by . This book was released on 2011 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diblock copolymers have many interesting properties, which first and foremost include their ability to self-assemble into various ordered, regularly spaced domains with nanometer-scale feature sizes. The work in this dissertation can be logically divided into two parts - the first and the majority of this work describes the phase behavior of certain block copolymer systems, and the second discusses real applications possible with block copolymer templates. Many compressible fluids have solvent-like properties dependent on fluid pressure and can be used as processing aids similar to liquid solvents. Here, compressed CO2 was shown to swell several thin homopolymer films, including polystyrene and polyisoprene, as measured by high pressure ellipsometry at elevated temperatures and pressures. The ellipsometric technique was modified to produce accurate data at these conditions through a custom pressure vessel design. The order-disorder transition (ODT) temperatures of several poly(styrene-b-isoprene) diblock copolymers were also investigated by static birefringence when dilated with compressed CO2. Sorption of CO2 in each copolymer resulted in significant depressions of the ODT temperature as a function of fluid pressure, and the data above was used to estimate the quantitative amount of solvent in each of the diblock copolymers. These depressions were not shown to follow dilution approximation, and showed interesting, exaggerated scaling of the ODT at near-bulk polymer concentrations. The phase behavior of block copolymer surfactants was studied when blended with polymer or small molecule additives capable of selective hydrogen bonds. This work used small angle X-ray scattering (SAXS) to identify several low molecular weight systems with strong phase separation and ordered domains as small as 2-3 nanometers upon blending. One blend of a commercially-available surfactant with a small molecule additive was further developed and showed promise as a thin-film pattern transfer template. In this scenario, block copolymer thin films on domain thick with self-assembled feature sizes of only 6-7 nm were used as plasma etch resists. Here the block copolymer's pattern was successfully transferred into the underlying SiO2 substrate using CF4-based reactive ion etching. The result was a parallel, cylindrical nanostructure etched into SiO2.
Download or read book Block Copolymers written by Francisco Balta Calleja and published by CRC Press. This book was released on 2000-06-09 with total page 600 pages. Available in PDF, EPUB and Kindle. Book excerpt: A summary of block copolymer chemical structures and synthesis. It discusses physical methods of characterization such as computer simulation, microhardness, dielectric spectroscopy, thermal mechanical relaxation, ultrasonic characterization, transmission electron microscopy, X-ray scattering, and NMR, among others. It also outlines rheological and
Download or read book Diblock Copolymer Phase Behavior Near the Order disorder Transition written by Mark Frederic Schulz and published by . This book was released on 1995 with total page 476 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Phase Behavior of Model ABC Triblock Copolymers written by Joon Chatterjee and published by . This book was released on 2007 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Effects of Interactions on the Phase Behavior and Morphology of a Block Copolymer Blended with Various Polymers written by John Patrick Baetzold and published by . This book was released on 1993 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt:
