A theoretical and simulation study of the self-assembly of a binary blend of diblock copolymers

Abstract

Pure diblock copolymer melts exhibit a narrow range of conditions at which bicontinuous and cocontinuous phases are stable; such conditions and the morphology of such phases can be tuned by the use of additives. In this work, we have studied a bidisperse system of diblock copolymers using theory and simulation. In particular, we elucidated how a short, lamellar-forming diblock copolymer modifies the phase behavior of a longer, cylinder-forming diblock copolymer. In a narrow range of intermediate compositions, self-consistent field theory predicts the formation of a gyroid phase although particle-based simulations show that three phases compete: the gyroid phase, a disordered cocontinuous phase, and the cylinder phase, all having free energies within error bars of each other. Former experimental studies of a similar system have yielded an unidentified, partially irregular bicontinuous phase, and our simulations suggest that at such conditions the formation of a partially transformed network phase is indeed plausible. Close examination of the spatial distribution of chains reveals that packing frustration (manifested by chain stretching and low density spots) occurs in the majority-block domains of the three competing phases simulated. In all cases, a double interface around the minority-block domains is also detected with the outer one formed by the short chains, and the inner one formed by the longer chains.

Phase diagrams of block copolymer melts by dissipative particle dynamics simulations

“…Whereas cylinders are almost as well studied as lamellas, the S microstructure in copolymers is rather common only in experimental systems, where it can be obtained either by orderdisorder transition (ODT) 56 or order-order transition (OOT). 57 Its identification by SCFT, 13 in Monte Carlo 19,20 and even DPD 25,41 simulations is usually difficult, if not impossible because of the long equilibration time. Figure 5 reports on the least ordered structures with illdefined peaks on the S(q) dependence.…”

“…In the field of block copolymers, this general tendency stimulated two lines of research. First of them implies developing hybrid techniques [10][11][12][13] that involve the concept of a self-consistent field into the calculation of interactions in the ensemble of particles. In that way, the evaluation of interchain interactions becomes a considerably less time-consuming procedure.…”

Topological Frustration as a New Parameter to Tune Morphology Revealed through Exploring the Continuum between A-B-C 3-Arm Star and Linear Triblock Polymers

“…Investigation of the phase morphology and evolution kinetics of the materials was performed using a mesoscale molecular dynamics method. Dissipative particle dynamics (DPD) is a simulation technique that typically maps multiple chain “mers” into highly coarse-grained “particles” to study the mesophase formation of block polymers with various molecular architectures. − Accordingly, DPD can model physical phenomena occurring at the larger time and spatial scales than typical molecular dynamics. DPD incorporates the Flory–Huggins χ parameter by adding a scaling factor a ij to a repulsive conservative potential; that is, a ij ≈ a ii + 3.27χ ij , when a ii = 25 for a particle number density (ρ) of 3.…”

Versatile Controls of Microdomain Morphologies and Temperature Dependencies in Lamellar Spacing by Blending Diblock Copolymers Bearing Antisymmetric Compositions

“…The binary blends of diblocks, AB/AB, have been intensively examined both experimentally and theoretically since the 1980s, 3−39 not only for the purpose of the morphology control 3,7,10−12,14,15,18,21,22,25,33 but also for many other aspects, such as elucidation of the cosurfactant effects (mixtures of small amounts of short diblocks in the long diblocks), 3−5,8,9,13,16,17,26,28−31,33,35,36,38 anomalous temperature behavior of the domain spacing, 11,19,24,27,29,31,35,39 elucidation of the effects of cast solvent on the morphology in thin films, 32,34 and examination of the grain boundary structure between the macroscopically phase-separated grains of thick and thin lamellae. 6 For these many purposes, a variety of AB/AB binary blends have been examined, such as [long symmetric AB]/[short symmetric AB] blends, 3−6,8,9,13,16,17,26,29,36 [long asymmetric AB]/[short symmetric AB] blends, 14,24,28,30,31,35,38 [asymmetric AB]/[symmetric AB] blends (with similar molecular weights), 15,25 and antisymmetric AB/AB blends (with similar molecular weights). 7,10−12,18−23,27,32−34,37,39 Furthermore, binary blends of AB/ABA 3,40−44 and ABA/ABA 45−47 have attracted interest from the viewpoint of mechanical properties because the ABA triblock copolymers possess good elastomeric property due to...…”