Nonclassical Spherical Packing Phases Self-Assembled from AB-Type Block Copolymers (original) (raw)
Related papers
Origins of low-symmetry phases in asymmetric diblock copolymer melts
Proceedings of the National Academy of Sciences of the United States of America, 2018
Cooling disordered compositionally asymmetric diblock copolymers leads to the formation of nearly spherical particles, each containing hundreds of molecules, which crystallize upon cooling below the order-disorder transition temperature (). Self-consistent field theory (SCFT) reveals that dispersity in the block degrees of polymerization stabilizes various Frank-Kasper phases, including the C14 and C15 Laves phases, which have been accessed experimentally in low-molar-mass poly(isoprene)--poly(lactide) (PI-PLA) diblock copolymers using thermal processing strategies. Heating and cooling a specimen containing 15% PLA above and below the from the body-centered cubic (BCC) or C14 states regenerates the same crystalline order established at lower temperatures. This memory effect is also demonstrated with a specimen containing 20% PLA, which recrystallizes to either C15 or hexagonally ordered cylinders (HEX) upon heating and cooling. The process-path-dependent formation of crystalline ord...
Binary Blends of Diblock Copolymers: An Efficient Route to Complex Spherical Packing Phases
Macromolecular Theory and Simulations
The phase behaviour of binary blends composed of A 1 B 1 and A 2 B 2 diblock copolymers is systematically studied using the polymeric selfconsistent field theory, focusing on the formation and relative stability of various spherical packing phases. The results are summarized in a set of phase diagrams covering a large phase space of the system. Besides the commonly observed body-centered-cubic (BCC) phase, complex spherical packing phases including the Frank-Kasper A15 and σ and the Laves C14 and C15 phases could be stabilized by the addition of longer A 2 B 2-copolymers to asymmetric A 1 B 1-copolymers. Stabilizing the complex spherical packing phases requires that the added A 2 B 2-copolymers have a longer A-block and an overall chain length at least comparable to the host copolymer chains. A detailed analysis of the block distributions reveals the existence of inter-and intradomain segregation of different copolymers, which depends sensitively on the copolymer length ratio and composition. The predicted phase behaviours of the A 1 B 1 /A 2 B 2 diblock copolymer blends are in good agreement with available experimental and theoretical results. The study demonstrated that binary blends of diblock copolymers provide an efficient route to regulate the emergence and stability of complex spherical packing phases.
Crystallization in block copolymer melts: Small soft structures that template larger hard structures
The Journal of Chemical Physics, 2001
The crystallization of shear oriented oxyethylene/oxybutylene ͑E/B͒ diblock copolymers has been studied by simultaneous small and wide angle x-ray scattering. Crystallization of ordered melts can be accompanied by a change in length scale and retention of the melt orientation. Lamellar melts crystallize with an increase in length scale with multiply folded E blocks and the B blocks slightly stretched from their melt conformation. Crystallization from oriented gyroid melts leads to an increase in length scale with preferred melt directions being selected. The retention of layer planes on crystallization from an ordered melt is caused by the local stretching of chains and the locally one-dimensional structure, despite the relative strength of the structural process. We demonstrate that an interfacial preordering effect can cause crystallographic register to jump length scales in a soft matter system showing epitaxial crystallization.
A Strategy to Explore Stable and Metastable Ordered Phases of Block Copolymers
The Journal of Physical Chemistry B, 2013
Block copolymers with their rich phase behavior and ordering transitions have become a paradigm for the study of structured soft materials. A major challenge in the study of the phase behavior of block copolymers is to obtain different stable and metastable phases of the system. A strategy to discover complex ordered phases of block copolymers within the self-consistent field theory framework is developed by a combination of fast algorithms and novel initialization procedures. This strategy allows the generation of a large number of candidate structures, which can then be used to construct phase diagrams. Application of the strategy is illustrated using ABC star triblock copolymers as an example. A large number of candidate structures, including many three-dimensionally ordered phases, of the system are obtained and categorized. A phase diagram is constructed for symmetrically interacting ABC star triblock copolymers.
Phases and Phase Transitions of Block Copolymers
Progress of Theoretical Physics Supplement
Spontaneous formation of ordered structures from amphiphilic molecules has attracted tremendous attentions in the last decades. Among the many different amphiphilic systems, block copolymers with their rich phase behaviour and ordering transitions have become a paradigm for the study of structural self-assembly. In this mini-review I will give a brief account on our studies on phases, phase diagrams, and kinetic pathways of order-to-order phase transitions of block copolymers.
Dual modes of self-assembly in superstrongly segregated bicomponent triblock copolymer melts
Physical review. E, Statistical, nonlinear, and soft matter physics, 2015
While ABC triblock copolymers are known to form a plethora of dual-mode (i.e., order-on-order) nanostructures, bicomponent ABA triblock copolymers normally self-assemble into single morphologies at thermodynamic incompatibility levels up to the strong-segregation regime. In this study, we employ on-lattice Monte Carlo simulations to examine the phase behavior of molecularly asymmetric A(1)BA(2) copolymers possessing chemically identical endblocks differing significantly in length. In the limit of superstrong segregation, interstitial micelles composed of the minority A(2) endblock are observed to arrange into two-dimensional hexagonal arrays along the midplane of B-rich lamellae in compositionally symmetric (50:50 A:B) copolymers. Simulations performed here establish the coupled molecular-asymmetry and incompatibility conditions under which such micelles form, as well as the temperature dependence of their aggregation number. Beyond an optimal length of the A(2) endblock, the propen...
Polymer, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Self-Assembly of Block Copolymers: Theoretical Models and Mathematical Challenges
Block copolymers are macromolecules composed of two or more chemically distinct polymer chains linked together by covalent bonds. The thermodynamical incompatiblility between the different sub-chains drives the system to phase separate. However the covalent bonds between the different sub-chains prevent phase separation at a macroscopic length scale. As a result of these two competing trends, block copolymers undergo phase separation at a nanometer length scale, leading to an amazingly rich array of nanostructures. These structures present tremendous potentials for technological application because they allow for the synthesis of materials with tailored mechanical, electrical and chemical properties (see [2, 8, 11]).
Crystallization in Block Copolymers with More than One Crystallizable Block
Progress in Understanding of Polymer Crystallization
Recent results on the crystallization of block copolymers with more than one crystallizable block are reviewed. The effect that each block has on the nucleation, crystallization kinetics and location of thermal transitions of the other blocks has been considered in detail. Depending on the thermodynamic repulsion between the blocks, the initial melt morphology in weakly segregated double crystalline diblock copolymers can be sequentially transformed by the crystallization of the different blocks. The crystallization kinetics of each block can be dramatically affected by the presence of the other, and by the crystallization temperature; the magnitude of the effect is a function of thermodynamic repulsion. Also the morphology has been investigated and peculiar double crystalline spherulites with intercalated semi-crystalline lamellae of each component have been observed in weakly segregated diblock copolymers. In the case of ABC triblock copolymers with more than one crystallizable block, many interesting effects have been found; among them, self-nucleation, sequential or coincident crystallization, and fractionated crystallization can be mentioned. Additionally, the effect of the topological constrains due to the number of free ends has been studied. Factors like chemical structure, molecular weight, molecular architecture and number of crystallizable blocks provide a very large number of possibilities to tailor the morphology and properties of these interesting novel materials.
The Journal of Chemical Physics, 2012
The thermodynamics and kinetics of the self-assembly of cylinder-forming diblock copolymers directed by the lateral confinement of hexagons have been studied by the combination of self-consistent field theory (SCFT) calculation and time-dependent Ginzburg-Landau (TDGL) theory simulation. The SCFT calculations are used to determine the stability of candidate 2D and 3D equilibrium phases formed in small-size hexagons. Our phase diagram predicts the existence of stable phase regions with respect to the hexagonal size, which is centered around the optimal size with an extent of about a period, for the phases of perfect hexagonal cylinders. Our TDGL simulations reveal that the ordering event, in which the structure evolves toward the perfect state, occurs stochastically according to the Poisson distribution, and the ordering time grows roughly with a power-law relation of the hexagonal size. This prediction is helpful to estimate the annealing time for larger systems with the knowledge of the annealing time of a small system in experiments.