Mixtures Of Diblock Copolymers Research Articles

Dissipative particle dynamics study on the interfacial structure and tension for polymer blends of different copolymer chemical composition distributions

A dissipative particle dynamics (DPD) simulation is used to study the interfacial structure and tension for the polymer blends of different copolymer chemical composition distributions. Four chain lengths of diblock copolymers NAB = 10, 20, 40, and 60 with different microstructures are utilized for simulation. As the copolymer microstructure varied from the nondispersed symmetric diblock copolymer to the bidisperse asymmetric diblock copolymer mixtures, the asymmetry of the copolymer varied from f = 0.5 to 0.9. Our simulations show that (i) increasing the copolymer chain length NAB will significantly enhance the interfacial tension, which indicates that the chain length of the diblock copolymer is the most important factor affecting the compatibilization efficiency. Only when the copolymer chain length NAB = 10 can the asymmetry significantly affect the compatibilization efficiency, and the length of the shorter block is the decisive factor in the compatibilization efficiency of asymmetric diblock copolymers; (ii) with an increase in the asymmetry of the diblock copolymer from f = 0.5 to 0.9, the effective chain length of the diblock copolymer with compatibilization decreases, which results in a reduced number of compatibilized beads of copolymers. Thus, the symmetric block copolymer AB is more effective in reducing the interfacial tension than the asymmetric diblock copolymer mixtures at the same concentration; and (iii) The symmetric diblock copolymers enrich faster at the interfaces when elevating the copolymer concentration, which results in a faster reduction in the interfacial tension than that of the asymmetric bidisperse diblock copolymer mixtures. Our research work expands the understanding of polymer blends containing bidisperse asymmetric diblock copolymer mixtures.

Alternating Gyroid in Block Polymer Blends.

Alternating gyroid is a lower symmetry variant of the double gyroid morphology, where the left-handed and right-handed chiral networks are physically distinct. This structure is of particular interest for photonic applications owing to predictions of a complete photonic band gap subject to the requirement of a large dielectric contrast between the individual networks and sufficient optical matching between one of the networks and the matrix. We provide evidence, via self-consistent field theory (SCFT), that stoichiometric blends of double-gyroid-forming AB and BC diblock copolymers with relatively immiscible A and C blocks should form an alternating gyroid morphology with complementary three-dimensional A and C networks that have a free energy that is nearly degenerate with two phase-separated double gyroid states. Solvent casting offers the potential for trapping this binary mixture of diblock copolymers in this metastable alternating gyroid phase. Theory further predicts that the addition of a minuscule amount (<1%) of ABC triblock terpolymer will open an alternating gyroid stability window in the resulting ternary-phase diagram. The surfactant-like stabilization produced by the triblock is relatively insensitive to its exact composition provided the B-block forms a sufficiently long bridge between the A-rich and C-rich networks. This blending strategy provides significant synthetic and material processing advantages compared to prevailing methods to produce an alternating gyroid phase in block polymers.

Hydrogen bonding mediated self‐assembled structures from block copolymer mixtures to mesoporous materials

AbstractThe self‐assembled structures formed through hydrogen bonding interaction of block copolymers in polymeric materials are interesting materials because of their potential applications in biomedicine, nanopatterning and photonics, taking advantage of their responsive and tunable properties. In this review, we discuss the self‐assembled nanostructures that can be obtained from hydrogen‐bonded diblock copolymer/homopolymer (A‐b‐B/C) and diblock copolymer (A‐b‐B/C‐b‐D) mixtures in the bulk and how these block copolymer mixtures can then be used to synthesize mesoporous silica, phenolic and carbon materials. © 2021 Society of Industrial Chemistry.

Distinctive Dielectric Permittivity of Hierarchical Nanostructures with Ordered Nanoparticle Networks Self-Assembled from AB-g-NP/AC Block Copolymer Mixtures.

Directing nanoparticles into ordered organization in polymer matrix to improve macroscopic properties of nanocomposites remains a challenge. Herein, by means of theoretical simulations, we show the high permittivity of hybrid nanostructures designed with mixtures of AB block copolymer-grafted nanoparticles and lamella-forming AC diblock copolymers. The grafted nanoparticles self-assemble into parallel stripes or highly ordered networks in the lamellae of the AC diblock copolymers. The ordered nanoparticle networks, including honeycomb-like and kagomé networks, provide bending and conductive pathways for concentrating electric fields, which results in the improvement of the permittivity. We envisage that this strategy will open a gateway to prepare hierarchically ordered functional nanocomposites with distinctive dielectric properties.

Micellization through complexation of oppositely charged diblock copolymers: Effects of composition, polymer architecture, salt of different valency, and thermoresponsive block

AbstractThe structural and electrical characteristics of polyelectrolyte complex micelles (PCMs) formed by mixing of oppositely charged double hydrophilic copolymers are studied by means of molecular dynamics simulations. In mixtures of linear diblock copolymers we found that the preferential aggregation number Np of PCMs is a universal function of the ratio γ± of the total positive to total negative charges of the mixture. The addition of divalent salts ions induces a secondary micellization. In mixtures of copolymers bearing a common neutral thermoresponsive block, micelles with contracted corona consisting of thermoresponsive blocks and complex polyelectrolyte core are formed at low salt concentration and temperature far away the biphasic regime. At high salt concentration and temperature in the biphasic regime, reversed micelles are obtained. In equimolar mixtures of linear copolymers with miktoarm stars we found that Np of PCMs decreases as the number of charged branches of miktoarm copolymer increases. The shape of micelles progressively changes from spherical to worm‐like with the increase of number of branches of miktoarm copolymers. Our findings are in full agreement with existing experimental and theoretical predictions and provides new and additional insights.

Self-Assembly of Polymer Grafted Nanoparticles within Spherically Confined Diblock Copolymers.

Geometric confinement plays an important role in the generation of interesting microstructures on account of structural frustration and confinement-induced entropy loss. In the present study, self-consistent field calculations have been performed to examine the self-assembly behavior of a mixture of diblock copolymers and polymer grafted nanoparticles within a spherical confinement. The analysis is aimed at obtaining the equilibrium distribution of nanoparticles with a high degree of order. The ordered mesophases of diblock copolymers provide useful templates to achieve ordering of nanoparticles in a selective domain. Self-assembly of nanoparticles within frustrated diblock copolymers is found to be very different from the bulk. A rich variety of equilibrium morphologies are observed depending on the degree of confinement and the extent of particle loading. In addition, the role of particle size and selectivity along with the length and the number of polymer chains grafted onto the surface of nanoparticles are analyzed to understand the self-assembly behavior. The specific interest is to obtain the chiral structures out of achiral block copolymers subjected to spherical confinement. The realization of various captivating microstructures, such as chiral ordering of nanoparticles, is highly essential to produce advanced nanomaterials with superior physical properties.

Improved reverse osmosis thin film composite biomimetic membranes by incorporation of polymersomes

Biomimetic aquaporin-based membranes offer great promise as a disruptive water treatment technology, due to their potential of improving membrane permeability without compromising solute rejection. However, fabrication upscaling is challenging and therefore the technological potential of biomimetic membranes remains unused. We propose an easily upscalable process based on bulk hydration of diblock and triblock copolymer mixture for preparation of polymersomes which can reconstitute aquaporin proteins. Such polymersomes are incorporated into biomimetic membranes via polyamide active layer synthesis based on interfacial polymerization. By incorporation of blank polymersomes, it was possible to improve water permeability of the membrane by 30%, and by incorporation of aquaporin reconstituting polymersomes by 50%, compared to the membranes without polymersomes. In both cases NaCl rejection was not affected. X-ray photoelectron spectroscopy measurements confirmed incorporation of copolymers prepared with aquaporins into the active polyamide layer without affecting the thickness of the membrane's active layer and surface zeta-potential.

Micellization of Binary Diblock Co-polymer Mixtures in an Ionic Liquid

The structure of mixed diblock co-polymer micelles in the aprotic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI], was investigated by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and small-angle neutron scattering. The diblock co-polymers are poly(methyl methacrylate)-block-poly(n-butyl methacrylate) (PMMA-b-PnBMA), where PMMA is solvent selective and forms the corona of the micelles, whereas PnBMA segregates into the micelle core. In these experiments, a pair of diblocks with the same corona block length but distinct core block lengths (Ncore) was first mixed homogeneously and then allowed to self-assemble into well-defined mixed micelles. DLS and SAXS measurements show that the hydrodynamic radius (Rh) and core radius (Rc) increase monotonically with the fraction of the longer diblock in the mixture. Interestingly, the dimensions of the binary mixed micelles are significantly larger than those formed by a single diblock with the same numb...

Hierarchical Self-Assembled Structures from Diblock Copolymer Mixtures by Competitive Hydrogen Bonding Strength.

In this work we prepared poly(styrene–b–vinylphenol) (PS-b-PVPh) by sequential anionic living polymerization and poly(ethylene oxide-b-4-vinylpyridine) (PEO-b-P4VP) by reversible addition fragmentation chain transfer polymerization (RAFT) by using poly(ethylene oxide) 4-cyano-4-(phenylcarbonothioylthio)pentanoate (PEO-SC(S)Ph) as a macroinitiator with two hydrogen bonded acceptor groups. When blending with disordered PEO-b-P4VP diblock copolymer, we found the order-order self-assembled structure transition from lamellar structure for pure PS-b-PVPh to cylindrical, worm-like, and finally to PEO crystalline lamellar structures. Taking the advantage of the ΔK effect from competitive hydrogen bonding strengths between PVPh/P4VP and PVPh/PEO domains, it could form the hierarchical self-assembled morphologies such as core–shell cylindrical nanostructure.

Copolymer Nanocomposite Thin‐Films Under Shear

By means of molecular dynamics simulations, we study the behaviour of lamellae forming diblock copolymer and nanoparticle mixtures in thin‐film geometry under stationary shear. In particular, we investigate the system under transverse mode of shear considering both nonselective and selective types of nanoparticles. We find that the presence of nanoparticles affects the critical shear rate at which the lamellar morphology is not stable during transverse shear and orientation transition sets in. We also study the spatial distribution of nanoparticles in the presence of flow field and its effect on the macroscopic response of the system.

Tunable and noncytotoxic PET/SPECT-MRI multimodality imaging probes using colloidally stable ligand-free superparamagnetic iron oxide nanoparticles.

Physiologically stable multimodality imaging probes for positron emission tomography/single-photon emission computed tomography (PET/SPECT)-magnetic resonance imaging (MRI) were synthesized using the superparamagnetic maghemite iron oxide (γ-Fe2O3) nanoparticles (SPIONs). The SPIONs were sterically stabilized with a finely tuned mixture of diblock copolymers with either methoxypolyethylene glycol (MPEG) or primary amine NH2 end groups. The radioisotope for PET or SPECT imaging was incorporated with the SPIONs at high temperature. 57Co2+ ions with a long half-life of 270.9 days were used as a model for the radiotracer to study the kinetics of radiolabeling, characterization, and the stability of the radiolabeled SPIONs. Radioactive 67Ga3+ and Cu2+-labeled SPIONs were also produced successfully using the optimized conditions from the 57Co2+-labeling process. No free radioisotopes were detected in the aqueous phase for the radiolabeled SPIONs 1 week after dispersion in phosphate-buffered saline (PBS). All labeled SPIONs were not only well dispersed and stable under physiological conditions but also noncytotoxic in vitro. The ability to design and produce physiologically stable radiolabeled magnetic nanoparticles with a finely controlled number of functionalizable end groups on the SPIONs enables the generation of a desirable and biologically compatible multimodality PET/SPECT-MRI agent on a single T2 contrast MRI probe.

Polymersomes with Asymmetric Membranes Based on Readily Accessible Di- and Triblock Copolymers Synthesized via SET-LRP.

One of the hallmarks of nature is compartmentalization, and natural cell membranes are often asymmetric in terms of the inner and outer side. This communication describes work toward synthesizing such an asymmetric membrane from the bottom-up. A family of amphiphilic di- and triblock copolymers were synthesized via Cu(0)-mediated single electron transfer-living radical polymerization with the aim to generate polymer vesicles, or polymersomes, with an asymmetric membrane. Self-assembly of these polymeric amphiphiles in aqueous media was investigated using asymmetric field-flow fractionation and cryo-electron microscopy. Utilizing mixtures of diblock copolymers with differing hydrophilic moieties resulted in the formation of vesicles with an asymmetric segregation of charge between the inner and outer leaflet, confirmed by zeta potential measurements. These polymers, synthesized in good yields and using a biologically compatible method to induce self-assembly, have a promising range of applications from nanomedicine to synthetic cell research.

Stabilizing the Frank-Kasper Phases via Binary Blends of AB Diblock Copolymers.

The emergence of the complex Frank-Kasper phases from binary mixtures of AB diblock copolymers is studied using the self-consistent field theory. The relative stability of different ordered phases, including the Frank-Kasper σ and A15 phases containing nonspherical minority domains with different sizes, is examined by a comparison of their free energy. The resulting phase diagrams reveal that the σ phase occupies a large region in the phase space of the system. The formation mechanism of the σ phase is elucidated by the distribution of the two diblock copolymers with different lengths and compositions. In particular, the segregation of the two types of copolymers, occurring among different domains and within each domain, provides a mechanism to regulate the size and shape of the minority domains, thus enhancing the stability of the Frank-Kasper phases. These findings provide insight into understanding the formation of the Frank-Kasper phases in soft matter systems and a simple route to obtain complex ordered phases using block copolymer blends.

PH-Controlled Rheological Properties of Mixed Amphiphilic Triblock Copolymers

Aqueous mixtures of pH-sensitive block random BAB triblock copolymers with different hydrophobic B blocks connected to the same hydrophilic A block were studied in order to investigate comicellization and the impact on the dynamic mechanical properties. The B blocks were statistical copolymers of acrylic acid (AA) and n-butyl acrylate (nBA) with varying AA contents, whereas the A block was a pure PAA. Neat triblocks self-assembled into transient networks for which the mechanical relaxation time depended both on the AA content within the B blocks and on the pH, which affected the ionization of the AA units. Static and dynamic light scattering measurements were done on mixtures of equivalent AB diblock copolymers that showed that comicellization occurred only at conditions at which both copolymers considered separately self-assemble. When comicellization occurred, the characteristic escape time of both types of B blocks from the mixed hydrophobic cores impacted the rheological properties of the binary triblock mixture. Using binary mixtures of BAB triblock copolymers exhibiting pH-controlled dynamics thus allows control and fine-tuning of the viscoelastic properties at constant pH by formulation without the need to synthesize a large number of different polymers. Moreover, the more dynamic B blocks were slowed down in the presence of the less dynamic ones, and vice versa, so that a frozen network could be transformed into a transient one by coassembly with very dynamic chains.

The electrostatic co-assembly in non-stoichiometric aqueous mixtures of copolymers composed of one neutral water-soluble and one polyelectrolyte (either positively or negatively charged) block: a dissipative particle dynamics study.

The electrostatic co-assembly in non-stoichiometric aqueous mixtures of diblock copolymers composed of a neutral water-soluble block and an either positively or negatively charged polyelectrolyte (PE) block has been studied by dissipative particle dynamics (DPD) simulations. The employed DPD variant includes explicit electrostatics and enables the investigation of the role of small ions in the co-assembly. The properties of core-shell associates containing insoluble interpolyelectrolyte complex cores and protective neutral shells were investigated as functions of the ratio of positive-to-negative charges in the system. This ratio was varied by increasing the number of positively charged PE chains of the same length as those of negatively charged chains, and by changing the PE length and charge density. The simulation results show that the associates formed in non-stoichiometric mixtures differ from those formed in stoichiometric mixtures: their association numbers are lower, their cores are charged and a fraction of excess chains remain free in the non-associated state. The study demonstrates the important role of the compatibility of the counterions with the polymer blocks. It simultaneously emphasizes the necessity of including the electrostatic interaction of all the charged species in the DPD computational scheme.

Nano-structured micelle particles of polylactide-poly(oxyethylene) block copolymers with different block sequences: Specific influence of stereocomplex formation of the polylactide blocks

Triblock copolymers consisting of poly(oxyethylene) (PEG), poly(d-lactide) (PDLA), and poly(l-lactide) (PLLA) were successfully prepared by the two-step ring-opening polymerization of d- and l-lactides via PEG-PDLA diblock copolymers. These triblock copolymers as well as the diblock copolymer PEG-PDLA and a mixture of enantiomeric diblock copolymers PEG-PDLA/PEG-PLLA were emulsified to make their aqueous micelle solutions. It was found out that the triblock copolymers and the diblock copolymer mixture can form sc crystals in the core to highly stabilize the core–shell particles. In particular, the micelle of a triblock copolymer having a short middle PDLA block gave the smallest particles covered with thin layer of PEG coronas, because the sc crystals had formed around the core–shell interface. These results suggested that the micelle particle morphology can be tuned by changing the core structure even at constant hydrophilic/hydrophobic balance of the block chains.

Boundary Tension Between Coexisting Phases of a Block Copolymer Blend

Self-consistent field theory (SCFT) is used to evaluate the excess free energy per unit area (i.e., tension) of different boundaries (or interfaces) between the coexisting phases of a block copolymer blend. In this first study of its kind, we focus on the boundaries separating the short- and long-period lamellar phases that form in mixtures of small and large symmetric diblock copolymers of polymerizations Ns and Nl, respectively, when Ns ≪ Nl. According to strong-segregation theory (SST), the tension is minimized when both sets of lamellae orient parallel to the boundary, but experiments [Hashimoto, , Macromolecules 1994, 27, 1562] tend to observe kink boundaries instead, where the domains of one lamellar phase evolve continuously into those of the other lamellar phase. Our more refined SCFT calculations, on the other hand, do predict a lower tension for the kink boundary consistent with the experimental observations. For completeness, we also examine the boundaries that form when the short-period lamellar phase disorders, and again the SCFT results are in agreement with experiment.

Isothermal Microphase Separation Kinetics in Blends of Asymmetric Styrene–Isoprene Block Copolymers

The microphase separation behavior of Kraton D1161, a highly asymmetric styrene–isoprene triblock and diblock copolymer mixture often used as the base polymer in pressure-sensitive adhesives, was studied using time-resolved small-angle X-ray scattering (SAXS) and oscillatory rheological analysis during temperature ramp and temperature quench experiments. The total scattering intensity obtained from SAXS was represented as a sum of the scattering from disordered and ordered polystyrene domains. A modified Percus–Yevick hard-sphere model was used to describe the scattering from disordered spheres, while Gaussian functions were used to model scattering from ordered domains. The temperature- and time-dependent SAXS experiments suggest a sequence of four stages in the development of the copolymer morphology during the isothermal phase separation kinetics experiments. Avrami analysis of the shear modulus evolution following a temperature quench indicates that domain growth is preceded by nucleation process. The ordering of polystyrene domains as observed during rheological and SAXS analysis is dominated by polymer chain mobility, which resulted in slower kinetics at lower temperatures.

Correction to Dissipative Particle Dynamics Study of Electrostatic Self-Assembly in Aqueous Mixtures of Copolymers Containing One Neutral Water-Soluble Block and One Either Positively or Negatively Charged Polyelectrolyte Block

The paper describes the general features and trends of the electrostatic assembly (EA) of block polyelectrolytes. We performed computer simulations of the associative behavior of aqueous mixtures of diblock copolymers containing one neutral water-soluble block and one either positively or negatively charged polyelectolyte (PE) block. While the neutral block is readily soluble in water, the hydrophilic vs hydrophobic nature of the neutral backbone of the PE block and the compatibility of the blocks vary in a broad range. We investigated the role of (i) electrostatics, (ii) solvophobicity of the PE block, (iii) compatibility of the polymer blocks, and also (iv) compatibility of small ions with the polymer blocks. We employed the dissipative particle dynamics (DPD) method and used the generally recognized formula (J. Chem. Phys. 1997, 107, 4423) for recalculating the Flory–Huggins interaction parameters in DPD parameters of soft coarse-grained repulsion forces. The Coulomb interactions are described by the r...

Synthesis of Multicompartment Nanoparticles of Block Copolymer through Two Macro-RAFT Agents Co-Mediated Dispersion Polymerization.

A new and efficient strategy to synthesize multicompartment block copolymer nanoparticles (MCBNs) by two macro-RAFT agents comediated dispersion polymerization is proposed. By simultaneously employing two macro-RAFT agents in dispersion RAFT polymerization, one-pot synthesis of well-defined MCBNs constructed with two diblock copolymers of poly(tert-butyl methyl acrylate)-block-polystyrene (PtBMA-b-PS) and poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-polystyrene (PVEA-b-PS) is achieved. These MCBNs contain a PS core and discrete PVEA and/or PtBMA nodules on the PS core. By changing the ratio of the two macro-RAFT agents or the polymerization degree of the solvophobic block in the two diblock copolymer mixture, the structure of MCBNs can be tuned. Our strategy overcomes the inconvenience and difficulty in synthesis of MCBNs, and it introduces a valid way to prepare well-defined MCBNs constructed with two or more diblock copolymers.