Linear ABC Triblock Research Articles

Self-assembly of ABC-type patchy nanoparticles formed by crosslinking triblock copolymer micelles

Hierarchical self-assembly is efficient in transferring functionality from small to large scales. Polymer nanoparticles with regularity are highly desirable because they are ideal units of hierarchical self-assembly. Herein, we proposed a crosslinking strategy for generating nanoparticles from ABC linear triblock copolymers and conducted a computational study on the self-assembly of the nanoparticles. The effect of nanoparticle symmetry on aggregation behaviors was examined. We found that the symmetric patchy nanoparticles can form various low-curvature aggregates tuned by the crosslinking numbers and A/C block lengths. Increasing the asymmetry of patchy nanoparticles causes the increased curvature of assemblies, forming well-defined structures such as loops, vesicles, and wavy ribbons. Furthermore, the self-assembly kinetics reveals a step-growth nature, resembling the step polymerization for one-dimensional growth. The work demonstrates that ABC-type polymeric nanoparticles are versatile units for building hierarchical assemblies, considerably enriching the self-assembly strategies.

Self‐Assembly of Nonfrustrated ABCBA Linear Pentablock Terpolymers

AbstractThe effects of compositions, interaction parameters, and number of blocks on the self‐assembly of nonfrustrated ABCBA linear pentablock terpolymer melts are investigated and compared with the corresponding ABC linear triblock terpolymers using the self‐consistent field theory. For the case of symmetric interaction parameters (χABN = χBCN) and majority B‐blocks, both ABC triblocks and ABCBA pentablocks can form intriguing A‐ and C‐domains embedded in the B‐matrix. While these morphologies persist in the ABC systems when the segregation strength is decreased, the A blocks tend to mix with the B blocks in the ABCBA pentablocks due to the chain topology, resulting in the formation of C‐domains embedded in the AB‐mixed matrix. Different phase behavior is observed for the case of asymmetric interaction parameters (χABN < χBCN). Aside from the core–shell type structures, a number of morphologies arise due to the separation between C and AB‐mixed domains in ABCBA pentablock copolymers. The theoretical results not only capture the self‐assembling behavior of poly(isoprene‐b‐styrene‐b‐ethylene oxide‐b‐styrene‐b‐isoprene) pentablocks, but also provide concrete suggestions for designing diverse microstructures in the linear ABC‐type terpolymers.

Effect of Molecular Asymmetry on the Formation of Asymmetric Nanostructures in ABC-Type Block Copolymers

Because domain geometry is dictated by the volume fraction of the block constituting it, an ABC linear triblock copolymer with unequal volume fractions of A and C blocks can form asymmetric ordered...

Regulate the Stability of Gyroids of ABC-Type Multiblock Copolymers by Controlling the Packing Frustration.

We propose to regulate the stability of gyroids of ABC-type multiblock copolymers by controlling the packing frustration of majority-component B-blocks. Accordingly, we investigate the self-assembly behaviors of the BABCB linear terpolymer with a variable length ratio τ of the middle B-block relative to the total B-blocks using self-consistent field theory. It is observed that the gyroid region exhibits a maximal width with respect to τ, which is attributed by the nonmonotonical change of the packing frustration of three B-blocks in the morphology of discrete domains, for example, cylinders. Then we further purposely design another ABC-type copolymer composed of an ABC linear triblock tethered by another B-block at the middle of the B-block. In contrast, the packing frustration of B-blocks of the second terpolymer drops down continuously as the middle B-block shortens, thus, expanding the stable regions of cylinders and spheres while contracting those of lamella and gyroid.

Surface-Induced Nanostructures and Phase Diagrams of ABC Linear Triblock Copolymers under Spherical Confinement: A Self-Consistent Field Theory Simulation.

We investigate the nanostructures and phase diagrams of ABC linear triblock copolymers confined in spherical cavities by using real-space self-consistent field theory. Various 3D morphologies, such as spherical concentric lamellae, dumbbell-like cylinder, and rotational structures, are identified in the phase diagrams, which are constructed on the basis of the diameters of spherical cavities and the interaction between the polymers and preferential surfaces. We designate specific monomer-monomer interactions and block compositions, with which the polymers spontaneously form a cylindrical morphology in bulk, and firstly study morphology transformation with a neutral surface when a confining radius progressively increases. We then focus on phase morphologies under the preferential surfaces and consolidate them into phase diagrams. The spherical radius and the degree of preferential interactions can obviously induce the formation of a cylindrical morphology. Theoretical results correspond to an amount of recent experimental observations to a high degree and contribute to synthesising functional materials.

Complex liquid-crystal nanostructures in semiflexible ABC linear triblock copolymers: A self-consistent field theory.

We show that two series of ABC linear triblock copolymers possess sequences of order-to-order phase transitions between microphase-separated states, as the degree of flexibility of the semiflexible middle B-blocks varies. The spatial and orientational symmetries of these phases, some of them containing liquid-crystal ordering, are analysed in comparison with related structures previously determined experimentally and theoretically. A theoretical framework based on the self-consistent field treatment of the wormlike-chain model, which incorporates the Flory-Huggins and Maier-Saupe interactions in the free energy, is used here as a basic foundation for numerical calculations. We suggest that tuning the flexibility parameter, which reduces to the concept of degree of polymerization in the coil-like limit and characterizes the chain-persistency in the rod-like limit, provides a promising approach that can be used to design the resulting microphase-separated structures in semiflexible copolymer melts.

Enhancing Gelation of Doubly Thermosensitive Hydrophilic ABC Linear Triblock Copolymers in Water by Thermoresponsive Hairy Nanoparticles

A method is reported for enhancing the gelation of doubly thermosensitive hydrophilic linear ABC triblock copolymers in water using thermoresponsive polymer brush-grafted nanoparticles (hairy NPs). A linear ABC triblock copolymer (ABC-Q) composed of a hydrophilic, charged middle block, and two thermosensitive outer blocks with different LCSTs, LCSTA of the lower LCST A block and LCSTC of the higher LCST C block, and two batches of hairy NPs with distinct thermoresponsive properties were prepared. When the temperature was raised from 0 °C to above the LCSTA but below the LCSTC, ABC-Q self-assembled into micelles in water with the lower LCST A block forming the core; further heating to above the LCSTC triggered the collapse of the C block, producing a two-compartment 3-D network micellar hydrogel when the polymer concentration was sufficiently high. Rheological studies showed that adding thermoresponsive hairy NPs with a LCST similar to the LCSTC of ABC-Q led to a significant increase in dynamic storage mod...

Synthesis and self-assembly of ABC linear triblock copolymers to target CO2-responsive multicompartment micelles

A series of ABC triblock copolymers were synthesized by tailoring the block length, suggesting polymers in a narrow composition window (0.34 ≤ fF ≤ 0.38) might transform from spherical micelles to multicompartment micelles upon stimulation of CO2.

Emergence of ordered network mesophases in kinetic pathways of order-order transition for linear ABC triblock terpolymers.

Applying the string method to the self-consistent field theory (SCFT) of ABC linear triblock copolymers, we developed a new strategy to design kinetic pathways for the formation of stable or metastable network mesophases in order-order transition (OOT) processes. The design principle regarding the kinetic pathways between distinct mesophases is based on the matching relationships of both domain spacing and dominant Fourier components of the density distributions. The results suggest that complex ordered network mesophases, such as alternating diamond (DA) and alternating plumber's nightmare (PA) could be obtained in kinetic pathways between simple phases covering lamellae, cylinders and spheres. By virtue of the minimal free energy pathway (MEP) obtained, we could acquire the epitaxial relationship and phase transition mechanism. Furthermore, we managed to regulate the MEP by changing the block composition to adjust packing frustration. Two new metastable networks, core-shell five-pronged and six-pronged morphologies, were found in the kinetic pathways, further demonstrating the regulating mechanism. The results will contribute to a better understanding of the kinetic relationship between simple phases and complex networks, thus providing a platform for soft materials design via the OOT route and guiding experimental procedures to fabricate ordered network mesophases.

Polymeric Janus nanoparticles from triblock terpolymer micellar dimers

Well-defined polymeric Janus nanoparticles have been synthesized by a novel method of combining self-assembly of simple ABC linear triblock terpolymers into nanostructured dimers and crosslinking of the conjunction between the opposite hemispheres.

Complex Multicompartment Micelles from Simple ABC Linear Triblock Copolymers in Solution

For the simple ABC linear terpolymer composed of a solvophilic A block and two solvophobic B and C blocks, the solution‐state self‐assembly is systematically investigated by dissipative particle dynamics (DPD) simulations, and several complex multicompartment micelles beyond the conventional wisdom, such as helix‐on‐sphere, cage, ring, bowl, raspberry‐onion and so on, are predicted from the simulations. The detailed phase diagrams clearly point out the regions of building these complex multicompartment micelles. Thus, the complex multicompartment micelles can be obtained from the simple linear ABC terpolymers. This work advances the molecular‐level understanding of multicompartment micelles from the simple linear ABC terpolymers, which will be useful for the future application of novel micelles.

Simulation study of co-assembly of ABC triblock copolymer/nanoparticle into multicompartment hybrids in selective solvent

Co-assembly of ABC linear triblock copolymer/nanoparticle into bump-surface multicompartment hybrids in selective solvent was studied through self-consistent field theory (SCFT) simulation. Results from three-dimensional SCFT simulation showed that the hybrid morphology depended on the length and number of grafted chains, whereas the number and shape of bumps relied on nanoparticle size. Moreover, the simulation results showed that the length and number of grafted chains had equivalent effect on hybrid morphology. Calculated results indicated that entropy was a more important factor than enthalpy in the co-assembly.

Theoretical Study of Phase Behavior of Frustrated ABC Linear Triblock Copolymers

The self-assembling behavior of ABC linear triblock copolymer melts is systematically studied using the self-consistent field theory, focusing on the emergence and stability of the knitting-pattern (KP) phase. The KP is one of the most intriguing unconventional phases formed from ”frustrated” linear triblock copolymers, where the interaction between the two end blocks is much weaker than those between neighboring blocks. Specifically phase diagrams for linear ABC triblock copolymer melts are constructed by comparing the free energy of about 10 candidate structures, including the knitting patterns, three-color lamellae (L3), core–shell cylinders (CSC), perforated lamellae (PL), cylinders-within-lamellae (LC), triple/quadruple cylinders-on-cylinders (C3/C4), double/triple helices-on-cylinders (H2C/H3C), and perforated circular lamella-on-cylinders (PC). The results of the phase behavior are presented for three cases with increasing complexity of the block copolymers. First of all, we investigate the stable region of the KP phase in triblock copolymers with a uniform segment size. Second, we study the impact of the conformational parameters as well as the interaction asymmetry between neighboring blocks on the stability of the KP phase. Finally, we examine the stability region of the KP phase surrounded by LC, PL, L3, CSC, PC, and C4 phases for a model system with a specific set of parameters corresponding to those of the polystyrene–poly(ethylene-co-butylene)–poly(methyl methacrylate) (PS–PEB–PMMMA) samples.

Phase diagrams of ABC linear triblock copolymers under nanopore confinements

The phase diagrams of triblock copolymers in cylindrical nanopores are investigated using the real-space self-consistent field theory in a two-dimensional space. We concentrate on pores with neutral surfaces and invariable diameters, whose rich variety of phases are considered to originate from pure geometric frustration. A series of triangular phase diagrams are constructed by varying the volume fractions for several sets of interaction parameters. These diagrams are sorted into three categories according to their interaction parameters. The confined phase diagrams exhibit several characteristic features that differ from those observed in the bulk. First, a rich variety of geometric frustration phases with strong symmetries, such as cylindrical and square, are observed in the triangular phase space because of the symmetry constraint in the geometric boundary. Second, the frustrated phases present some novel and complex features compared with those in the bulk, demonstrating that the confined morphologies much more sensitively depend on the subtle variation in the binary interaction parameters than those in the bulk. Meanwhile, the entropic energies of the symmetric melts with equal end block volume fractions are investigated to further understand the geometric frustration phase behaviors in the triangular phase diagrams. The reasonable formation mechanisms of the frustration phases are also discussed.

Emergence and Stability of Helical Superstructures in ABC Triblock Copolymers

The emergence and stability of superstructured cylindrical phases in frustrated ABC linear triblock copolymers are investigated by the self-consistent field theory. Our results reveal that the complex single/double/triple helices-on-cylinder phases are formed when the straight cylinders-on-cylinder and rings-on- cylinder phases are frustrated due to packing constraints. A free energy comparison indicates that the double and triple helical phases are stable, whereas the other cylinders-on-cylinder phases are metastable. In addition, the chirality and rotation for the helical supercylinders are considered in our calculations. Our theoretical prediction is consistent with a number of experimental observations.

Stealth properties of poly(ethylene oxide)-based triblock copolymer micelles: A prerequisite for a pH-triggered targeting system

Evaluation of the biocompatibility of pH-triggered targeting micelles was performed with the goal of studying the effect of a poly(ethylene oxide) (PEO) coating on micelle stealth properties. Upon protonation under acidic conditions, pH-sensitive poly(2-vinylpyridine) (P2VP) blocks were stretched, exhibiting positive charges at the periphery of the micelles as well as being a model targeting unit. The polymer micelles were based on two different macromolecular architectures, an ABC miktoarm star terpolymer and an ABC linear triblock copolymer, which combined three different polymer blocks, i.e. hydrophobic poly(ε-caprolactone), PEO and P2VP. Neutral polymer micelles were formed at physiological pH. These systems were tested for their ability to avoid macrophage uptake, their complement activation and their pharmacological behavior after systemic injection in mice, as a function of their conformation (neutral or protonated). After protonation, complement activation and macrophage uptake were up to twofold higher than for neutral systems. By contrast, when P2VP blocks and the targeting unit were buried by the PEO shell at physiological pH, micelle stealth properties were improved, allowing their future systemic injection with an expected long circulation in blood. Smart systems responsive to pH were thus developed which therefore hold great promise for targeted drug delivery to an acidic tumoral environment.

ABC triblock copolymer hamburger-like micelles, segmented cylinders, and Janus particles

An ABC linear triblock copolymer with a carboxyl-containing terminal C block and a photocrosslinkable middle B block was synthesized and characterized. In a poor solvent for the B block and in the presence of a diamine, (−)-sparteine, which complexed with the C block and made it insoluble, the triblock copolymer self-assembled into hamburger-like micellar aggregates and segmented cylinders. In a “hamburger”, the “buns” were made of the B block, the filling was made of the complexed C block, and the soluble A chains stretched out from the bun surface into the solvent phase. The main body of the segmented cylinders was made of stacking alternating B and C stubs. The cylinders were dispersed in solvent by the A chains stretching out from the surfaces of the B stubs. After the photocrosslinking of the buns of the hamburgers and the removal of (−)-sparteine by dialysis, we were able to separate the buns of the hamburgers to yield presumably Janus particles.

Simulation study of aggregate morphologies formed by ABC linear triblock copolymers in a selective solvent through the self‐consistent field theory

AbstractThe effect of the hydrophobic properties of blocks B and C on the aggregate morphologies formed by ABC linear triblock copolymers in selective solvent was studied through the self‐consistent field theory. Five typical micelles, such as core‐shell‐corona, hamburger‐like, segmented‐wormlike, were obtained by changing the hydrophobic properties of blocks B and C. The simulation results indicate that the shape and size of micelle are basically controlled by the hydrophobic degree of the middle block B, whereas the type of micelle is mainly determined by the hydrophobic degree of the end block C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 484–492, 2009

Self-assembling of ABC linear triblock copolymers in nanocylindrical tubes

By employing Monte Carlo simulations for various tube diameters and preferences of the tube surface for the A, B, and C segments, the morphologies of A(5)B(5)C(5), A(5)B(10)C(5), and A(5)B(5)C(10) triblock copolymer melts confined in nanocylindrical tubes were examined. The interaction parameters between different segments were considered constant epsilon(AB)=epsilon(AC)=epsilon(BC)=0.3k(B)T, the tube diameter was changed from d=9xlattice parameter to d=33xlattice parameter, and the preferences of the tube surface for the segments A, B, and C (-epsilon(AS),-epsilon(BS), and -epsilon(CS)) were varied between 0.05k(B)T and k(B)T. ABCCBA alternately stacked disks were generated in most tubes when the preference of the tube surface for any of the segments was weak, and the morphologies tended to transform into curved lamellae in tubes with large diameters when the preference for one of the segments was high. Numerous novel morphologies, such as ABC double helixes, AB single helix+C double helixes, AB double helixes+C quadruple helixes, plate morphologies with fins, dendrites, etc., which were located in the phase diagram between the stacked disks and the curved lamellar structures, were identified. Additionally, the orientation parameters indicating the alignments of the polymer chains were calculated and correlated with the morphologies.

Effect of Architecture on the Tensile Properties of Triblock Copolymers in a Lamellar Phase

We have used self-consistent field theory to calculate the tensile moduli of triblock copolymers in lamellar microstructures prepared from linear and star architectures. The extensional moduli K(33) are the main contributors to the tensile moduli, and the contribution of K(U)33 (the internal energy contribution to K(33)) is the main component of the value of K(33). We find that the tensile moduli of ABC three-miktoarm star terpolymers are smaller than those of ABC linear triblock copolymers having identical components, presumably for two main reasons. First, for the ABC three-miktoarm star terpolymers, the contributions of K(U)33 are larger than those of the linear triblock copolymers; we attribute this phenomenon to the star terpolymers having smaller lamellar domain sizes at equilibrium relative to those of the linear triblock copolymers. Second, conformational entropies play an important role in affecting the tensile moduli, mainly because of the different degrees of freedom of the various chains. In contrast, the shear moduli contribute negligibly to the tensile moduli.