Blends Of Diblock Copolymers Research Articles

Directed Self-Assembly of Binary AB/AB Diblock Copolymer Blends for Dense Nanopatterns with Density Multiplication

Directed Self-Assembly of Binary AB/AB Diblock Copolymer Blends for Dense Nanopatterns with Density Multiplication

Particle Dynamics in a Diblock-Copolymer-Based Dodecagonal Quasicrystal and Its Periodic Approximant by X-Ray Photon Correlation Spectroscopy.

Temperature-dependent x-ray photon correlation spectroscopy (XPCS) measurements are reported for a binary diblock-copolymer blend that self-assembles into an aperiodic dodecagonal quasicrystal and a periodic Frank-Kasper σ phase approximant. The measured structural relaxation times are Bragg scattering wavevector independent and are 5 times faster in the dodecagonal quasicrystal than the σ phase, with minimal temperature dependence. The underlying dynamical relaxations are ascribed to differences in particle motion at the grain boundaries within each of these tetrahedrally close-packed assemblies. These results identify unprecedented particle dynamics measurements of tetrahedrally coordinated micellar block polymers, thus expanding the application of XPCS to ordered soft materials.

Bicontinuous microemulsion in binary blends of complementary diblock copolymers.

The phase behavior of binary blends of AB diblock copolymers of compositions f and 1 - f is examined using field-theoretic simulations. Highly asymmetric compositions (i.e., f ≈ 0) behave like homopolymer blends macrophase separating into coexisting A- and B-rich phases as the segregation is increased, whereas more symmetric diblocks (i.e., f ≈ 0.5) microphase separate into an ordered lamellar phase. In self-consistent field theory, these behaviors are separated by a Lifshitz critical point at f = 0.2113. However, its lower critical dimension is believed to be four, which implies that the Lifshitz point should be destroyed by fluctuations. Consistent with this, it is found to transform into a tricritical point. Furthermore, the highly swollen lamellar phase near the mean-field Lifshitz point disorders into a bicontinuous microemulsion (BμE), consisting of large interpenetrating A- and B-rich microdomains. BμE has been previously reported in ternary blends of AB diblock copolymer with its parent A- and B-type homopolymers, but in that system the homopolymers have a tendency to macrophase separate. Our alternative system for creating BμE is free of this macrophase separation.

Reaction-induced morphological transitions in a blend of diblock copolymers and reactive monomers: dissipative particle dynamics simulation.

The dissipative particle dynamics (DPD) method is applied to the morphological transitions of microphase-separated domains in a mixture of symmetric AB-diblock copolymers and reactive C-monomers, where polymerization and cross-linking reactions take place among C-monomers. The initial structure for the DPD simulation is an equilibrated cylindrical domain structure prepared by the density-biased Monte Carlo method with density profiles obtained from the self-consistent field theory. By introducing a cross-linking reaction among reactive C-monomers, we confirmed that the DPD simulation reproduces the morphological transitions observed in experiments, where the domain morphology changes due to segregation between A-blocks of diblock copolymers and cross-linking networks of C-monomers. When the cross-linking reaction of C-monomers is sufficiently fast compared to the deformation of the domains, the initial cylindrical domains are preserved, while the distance between the domains increases. On the other hand, when the formation of the cross-linking network is slow, the domains can deform and reconnect with each other in the developing cross-linking network. In this case, we observe morphological transitions from the initial domain morphology with a large-curvature interface to another domain morphology with a smaller-curvature interface, such as the transition from the cylindrical phase to the lamellar phase. We calculated the spatial correlations in the microphase-separated domains and found that such correlations are affected by the speed of the formation of the cross-linking network depending on whether the bridging between microphase-separated domains occurs in a nucleation and growth process or in a spinodal decomposition process.

Phase Behavior of Binary Blends of Diblock Copolymers: Progress and Opportunities.

The phase behavior of binary blends of diblock copolymers has been examined extensively in the past decades. Experimental and theoretical studies have demonstrated that mixing two different block copolymers provides an efficient and versatile route to regulate their self-assembled morphologies. A good understanding of the principles governing the self-assembly of block copolymer blends has been obtained from the study of A1B1/A2B2 diblock copolymer blends. The second (A2B2) diblocks could act synergistically as fillers and cosurfactants to regulate the domain size and interfacial properties, resulting in the formation of ordered phases not found in the parent (A1B1 or A2B2) diblock copolymer melts. The study of A1B1/A2B2 block copolymer blends further provides a solid foundation for future research on more complex block copolymer blends.

Semi-conductive micellar networks of all-conjugated diblock and triblock copolymer blends.

The crystallization-driven self-assembly of the blends of the all-conjugated block copolymers of poly(3-hexylthiophene) (P3HT) and poly(3-ethylhexylthiophene) (P3EHT) results in the cross-linking of the one-dimensional nanowires of P3HT-b-P3EHT, which is achieved by intercalating P3HT-b-P3EHT-b-P3HT into the nanowire cores. The micellar networks constitute flexible and porous materials that conduct electricity upon doping.

Confined crystallization in the binary blends of diblock copolymers bearing stereoisomeric isotactic and syndiotactic polypropylene

The morphology and crystallization behavior of the binary blends of two crystalline-amorphous diblock copolymers bearing stereoisomeric crystalline blocks have been investigated. A polystyrene-block-isotactic polypropylene (S-iPP) and a polystyrene-block-syndiotactic polypropylene (S-sPP) were used to prepare a series of blends forming lamellar morphology. In the melt state, the PS blocks from these two diblock copolymers mixed intimately in the PS lamellar microdomains; meanwhile, the iPP and sPP blocks were found to form a miscible mixture in the PP domains. Under the effects of nanoscale confinement and the constraint imposed by the junction points, the iPP and sPP blocks exhibited the crystallization behavior greatly deviated from that in the neat diblock copolymers. A local demixing between a fraction of iPP and sPP chains was found to occur in the S-sPP-rich blend at low crystallization temperatures, which yielded the defective crystalline domains composed of alternately intervened iPP and sPP crystallites. This crystalline species displayed a significant depression of melting point located at the temperature around 10°C higher than the corresponding Tc due to an excess surface free energy at the interface between the alternately intervened iPP and sPP crystallites.

Frank–Kasper Phases in Block Polymers

The discovery of the Frank–Kasper σ phase in diblock copolymer and tetrablock terpolymer melts catalyzed a renewed interest over the past decade in understanding particle-forming phases in block polymer systems. This Perspective provides a concise overview of the Frank–Kasper phases seen to date in block polymers (A15, σ, and the C14 and C15 Laves phases) and mechanisms known to produce them: conformational asymmetry in neat diblock copolymer melts, interfacial segregation effects in diblock copolymer blends, particle swelling in diblock copolymer/homopolymer blends, and matrix segregation effects in neat tetrablock terpolymer melts. While a qualitative understanding of the emergence of Frank–Kasper phases in block polymer systems has been achieved, a number of outstanding questions remain, in particular those arising from the low degree of polymerization used in experiments, nonequilibrium effects during thermal processing, and the large design space available in blends and multiblock systems. This Perspective discusses potential avenues for future research related to these areas as well as overarching issues underlying the connections between Frank–Kasper phase formation in block polymers to other soft matter and metals.

Binary Blends of Diblock Copolymers: An Efficient Route to Complex Spherical Packing Phases

AbstractThe phase behavior of binary blends composed of AB and AB diblock copolymers is systematically studied using the polymeric self‐consistent 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 phase, complex spherical packing phases including the Frank–Kasper A15, and the Laves C14, C15 phases could be stabilized by the addition of longer AB‐copolymers to asymmetric AB‐copolymers. Stabilizing the complex spherical packing phases requires that the added AB‐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 intra‐domain segregation of different copolymers, which depends sensitively on the copolymer length ratio and composition. The predicted phase behaviours of the AB/AB diblock copolymer blends are in good agreement with previous experimental and theoretical results. The study demonstrates that binary blends of diblock copolymers provide an efficient route to regulate the emergence and stability of complex spherical packing phases.

Complex Phase Behavior in Particle-Forming AB/AB′ Diblock Copolymer Blends with Variable Core Block Lengths

Complex Phase Behavior in Particle-Forming AB/AB′ Diblock Copolymer Blends with Variable Core Block Lengths

Field-Theoretic Simulations for Block Copolymer Melts Using the Partial Saddle-Point Approximation.

Field-theoretic simulations (FTS) provide an efficient technique for investigating fluctuation effects in block copolymer melts with numerous advantages over traditional particle-based simulations. For systems involving two components (i.e., A and B), the field-based Hamiltonian, , depends on a composition field, , that controls the segregation of the unlike components and a pressure field, , that enforces incompressibility. This review introduces researchers to a promising variant of FTS, in which fluctuates while tracks its mean-field value. The method is described in detail for melts of AB diblock copolymer, covering its theoretical foundation through to its numerical implementation. We then illustrate its application for neat AB diblock copolymer melts, as well as ternary blends of AB diblock copolymer with its A- and B-type parent homopolymers. The review concludes by discussing the future outlook. To help researchers adopt the method, open-source code is provided that can be run on either central processing units (CPUs) or graphics processing units (GPUs).

Supramolecular Self-assembly Behaviors of Asymmetric Diblock Copolymer Blends with Hydrogen Bonding Interactions between Shorter Blocks Modelled by Yukawa Potentials

We employed the extended self-consistent field theory to investigate the supramolecular self-assembly behaviors of asymmetric diblock copolymer blends (AB/B’C) with hydrogen bonding interactions between shorter B and B’ blocks. The hydrogen bonding interactions are described by Yukawa potentials, where the hydrogen bonding donors and acceptors were modelled as two blocks smeared with opposite screened charges. The hierarchical microstructures with parallelly packed lamellae-in-lamellae (Lam) and 4.8.8 Archimedean tilting pattern (4.8.8) were observed at lower and higher hydrogen bonding density (θ), respectively. The hierarchy of Lam and 4.8.8 were demonstrated by the one- and two-dimensional density profiles and the underlying order of the large-length-scale and small-length-scale microstructures were also clarified. It was found that the 4.8.8 is favorable to the stronger hydrogen bonding density or interactions. As θ increases, the microphase transition from Lam to 4.8.8 occurs at θ =0.34, which is mainly attributed to the optimization of the electrostatic energy and conformational entropy with sacrificing the interfacial energy. This work can provide a new strategy to understand the supramolecular self-assembly as well as the mechanism behind the formation of complex hierarchical microstructures.

Binary Blends of Diblock Copolymers: An Effective Route to Novel Bicontinuous Phases

AbstractThe formation of various bicontinuous phases from binary blends of linear AB diblock copolymers (DBCPs) is studied using the polymeric self‐consistent field theory. The theoretical study predicts that the double diamond and the “plumber's nightmare” phases, which are metastable for neat DBCPs, could be stabilized in block copolymers with designed dispersity, namely, binary blends composed of a gyroid‐forming DBCP and a homopolymer‐like DBCP. The spatial distribution of different monomers reveals that these two types of DBCPs are segregated such that the homopolymer‐like component is localized at the nodes to relieve the packing frustration. Simultaneously, the presence of a local segregation of the two DBCPs on the AB interface regulates the interfacial curvature. These two mechanisms could act in tandem for homopolymer‐like DBCPs with proper compositions, resulting in larger stable regions for the novel bicontinuous phases.

Self-assembly of rod-coil diblock copolymer-nanoparticle composites in thin films: dissipative particle dynamics.

In this study, the assembled structures of rod-coil diblock copolymer and nanoparticle blends were studied via dissipative particle dynamics (DPD). Thin films were composed of soft confinement DPD fluid beads and the fluctuating film structure was maintained during the simulation process. Analysis of the position of nanoparticles was done in the smectic lamellar phase of the rod-coil polymer matrix, and density distributions of rods, coils, and nanoparticles were obtained as functions of the size of the nanoparticle and the DPD repulsion constant between the rod and the nanoparticle. The distribution of nanoparticles was explained by using the concept of translational entropy of nanoparticles, stretching energy of the polymer chain, relative repulsion enthalpy of nanoparticles to rods or coils, and the effect of the liquid crystalline rod.

Stereocomplex Crystallization in Asymmetric Diblock Copolymers Studied by Dynamic Monte Carlo Simulations

Stereocomplex crystallization in asymmetric diblock copolymers was studied using dynamic Monte Carlo simulations, and the key factor dominating the formation of stereocomplex crystallites (SCs) was uncovered. The asymmetric diblock copolymers with higher degree of asymmetry exhibit larger difference between volume fractions of beads of different blocks, and local miscibility between different kinds of beads is lower, leading to lower SC content. To minimize the interference from volume fraction of beads, the SC formation in blends of asymmetric diblock copolymers was also studied. For the cases where the volume fractions of beads of different blocks are the same, similar local miscibility between beads of different blocks and similar SC content was observed. These findings indicate that the volume fraction of beads of different blocks is a key factor controlling the SC formation in the asymmetric diblock copolymers. The SC content can be regulated by adjusting the difference between the contents of beads of different blocks in asymmetric diblock copolymers.

Instability of the Microemulsion Channel in Block Copolymer-Homopolymer Blends.

Field theoretic simulations are used to predict the equilibrium phase diagram of symmetric blends of AB diblock copolymer with A- and B-type homopolymers. Experiments generally observe a channel of bicontinuous microemulsion (BμE) separating the ordered lamellar (LAM) phase from coexisting homopolymer-rich (A+B) phases. However, our simulations find that the channel is unstable with respect to macrophase separation, in particular, A+B+BμE coexistence at high T and A+B+LAM coexistence at low T. The preference for three-phase coexistence is attributed to a weak attractive interaction between diblock monolayers.

Regulation Mechanism of Bubbling Deformation and Fracture Toughness of the Membrane by Asymmetric Phospholipids: A Model System Study.

Dynamic regulation of the deformation modulus and fracture toughness of a membrane is critical to organelles and cells for matching their conflicting needs of resilient and fractured behaviors. These properties implement the protection of the function in the normal condition and the fission function in the endocytosis condition of a membrane. Naturally, a membrane contains phospholipids that have different hydrophilic and hydrophobic group length. The diffusion and aggregation of the phospholipids with asymmetry of the hydrophilic-hydrophobic ratio on the membrane play a key role in regulating the mechanical behaviors passively to the external force. In present work, the effects of the asymmetry of phospholipids on the bubbling deformation and fracture toughness of the membrane to external stretching are investigated in a model system. A disk-shaped micelle formed from the blend of symmetric and asymmetric diblock copolymers in a selective solvent is considered as the membrane sheet. Its mechanically responsive behaviors are investigated by self-consistent field theory. By analyzing the evolution of different components during the stretching process, the mechanism of formation of the bubbling structure is revealed. Moreover, the fracture toughness depending on the asymmetry of the phospholipids is determined quantitatively.

Thermal and Morphological Properties of Poly(L-Lactic Acid)/Poly(D-Lactic Acid)-B-Polycaprolactone Diblock Copolymer Blends.

Due to the brittle nature of poly(lactic acid) many attempts have been made to flexibilize this polyester for applications such as thin films and foils. However, due to complex phase behavior, many drawbacks for plasticizer and blend components are described. To overcome miscibility, post crystallization and migration issues a principle of click-chemistry was employed to change the molecular characteristics from external to internal plasticization by fixation of a plastisizing unit with help of a stereocomplex crystallization. Hydroxyl terminated polycaprolactone oligomers were used as a macroinitiator for the ring opening polymerization of d-lactide, resulting in blockcopolymers with plasticizing unit polycaprolactone and compatibilizing poly(d-lactic acid)-blocks. The generated block copolymers were blended with a poly(l-lactic acid)-matrix and formed so called stereocomplex crystals. In comparison to unbound polycaprolactone the polycaprolactone blocks show a lower migration tendency regarding a solution test in toluene. Besides that, trapping the plasticizing units via stereocomplex also improves the efficiency of the plasticizer. In comparison to polymer blends with the same amount of non-bonded polycaprolactone oligomers of the same molecular weight, block copolymers with poly(d-lactic acid) and polycaprolactone can shift the glass transition temperature to lower values. This effect can be explained by the modulated crystallization of the polycaprolactone-blocks trapped into the matrix, so that a higher effective amount can interact with the poly(l-lactic acid)-matrix.

Partitioning of the components into two-demixed-macrophases from a solution blend emulating high impact polystyrene close to the phase inversion region

Blends of a butadiene rich-tapered diblock copolymer (DC) with polystyrene (PS) and/or polybutadiene (PB) in ethylbenzene (EB) were investigated to better understand the phenomena occurring during the synthesis of high impact polystyrene (HIPS). For the first time, the apparent partitioning of components between the demixed-phases of quaternary blends PS/PB/DC/EB was determined, involving variations of DC concentration, PS molar mass, simulated conversion of styrene and temperature. The new methodology combines FTIR, solvent extraction, TLC and mass balances and verifies important results by TEM and SEC. During demixing, a molecular fractionation occurs which depends on the DC composition distribution, the ratio between the molar masses of each of the copolymer blocks and the respective homopolymers and the viscosity ratio between the continuous and dispersed phases. The affinity between the low molar mass PS and the PS block in DC favors the stabilization of PS domains in the PB-rich phase.

A15, σ, and a Quasicrystal: Access to Complex Particle Packings via Bidisperse Diblock Copolymer Blends.

A renewed focus on the phase behavior of nominally single-component, compositionally asymmetric diblock copolymers has revealed a host of previously unanticipated Frank-Kasper (FK) and quasicrystalline phases. However, these periodic and aperiodic particle packings have thus far only been reported in low molecular weight, highly conformationally asymmetric diblock copolymers, leaving researchers with a relatively small library of polymers in which these phases can be studied. In this work, we report on a simple approach to access these morphologies: blending two diblock copolymers with the same corona block length and varied core block lengths. Compositionally symmetric and asymmetric polystyrene-b-1,4-polybutadiene (SB) diblock copolymers with constant corona block lengths were blended together and shown via small-angle X-ray scattering and transmission electron microscopy to order into the FK A15 and σ phases, as well as a dodecagonal quasicrystal, providing a route to various particle packings in high molecular weight diblock copolymer melts.