Microphase-separated Structure Research Articles

Synthesis of halogenated benzonorbornadiene monomer and preparation of self-crosslinking bisimidazole cationic functionalized benzonorbornadiene triblock copolymer anion exchange membrane

In this paper, a series of anion exchange membranes of bisimidazolium functionalized triblock copolymers were synthesized by ring-opening metathesis polymerization of alkyl bromide functionalized benzonorbornadiene derivatives, 1,2-dimethyl imidazole and epoxy functionalized norbornene under the action of Grubbs 2nd catalyst. The designed decomposition temperature of the triblock copolymer anion exchange membrane (AEM) exceeded 320 °C, which was much higher than the actual working temperature of anion exchange membrane fuel cell. TEM and AFM characterization proved that the AEM had formed an obvious microphase separation structure. The OH− conductivity of AEM-40 at 80 °C was as high as 56.09 mS cm−1. The single cell performance of the prepared AEM was tested at 60 °C, and we found that AEM-40 reached the highest power density of 189.1 mW cm−2 at 352.1 mA cm−2.

Flexible coatings with microphase separation structure attained by copolymers and ultra-fine nanoparticles for endurable antifouling

Incorporating antibacterial agent into biomimetic coating inspired by natural organisms with micro-nano structure surface has generated more interest for antifouling applications. In this work, poly(dimethylsiloxane) (PDMS)-based triblock copolymers and sub-20 nm nanoparticles Ag and heterogeneous Fe3O4-coated Ag (Fe3O4@Ag) were used to construct microphase separation topography with oriented copolymer blocks structure. The artificial surface was verified by atomic force microscopy and scanning electron microscopy images. Meanwhile, the surface exhibited relative stable hydrophobic property, which was demonstrated by the water contact angle and dynamic air-bubble contact angle measurements. Consequently, after immersed in BSA solution 24 h and 720 h, the actual BSA absorption amount of the surface with Fe3O4@Ag nanoparticles was as low as 10 % and 27 % that of the initial BSA amount, respectively. Moreover, the surface also showed remarkable antibacterial performance, which effectively suppressed the growth rate of Escherichia coli. The strategy of constructing the flexible microphase separation structure by introducing heterogeneous inorganic antibacterial nanoparticles into a block copolymer substrate opens up a new way to create an antifouling surface coating.

Effects of conditions in hot-melt coating process on microphase-separated structures and macroscopic deformation in coated layers composed of di- and triblock copolymer blends

Effects of the coating rate, the cooling temperature and the discharge rate in the hot-melt coating process on the microphase-separated structure and the macroscopic deformation have been revealed using blend specimens of MA/MAM where MA and MAM are a poly(methylmethacrylate)-block-poly(n-butylacrylate) diblock copolymer and a poly(methylmethacrylate)-block-poly(n-butylacrylate)-block-poly(methylmethacrylate) triblock copolymer, respectively. It was found that the hot-melt coated specimen had the anisotropic distribution of the spheres where the d spacing of the nanostructure in the machine direction (MD) is longer than that in the transverse direction (TD) and had a lower ordering regularity of the spherical microdomains in the MD due to shear and elongational deformation. The change of the macroscopic size upon the release of the coated layer from the substrate also confirmed the elongation of the soft-segment (poly (n-butylacrylate)) chains in the MD during the hot-melt coating by exhibiting the macroscopic shrinkage in the MD upon the release. However, the extent of the microscopic elongation (d spacing) was lower than the macroscopic elongation in the MD. This implies that the soft-segment chains are relaxed due to pulling-out of the poly (methylmethacrylate) chains from the hard spherical microdomains. As for the effects of the coating rate, the extent of the chain stretching of the soft segment was increased with the coating rate when the discharge rate (the flux of materials provided onto the substrate through the die lip) was kept constant. However, no effects were confirmed when the discharge rate was so controlled to maintain the thickness of the as-coated layer constant. Thus, the effects of the coating rate and the discharge rate were compensated, and the effects on the chain stretching of the soft segment can be recognized simply in terms of the thickness of the as-coated layer. As for the effects of the cooling-roll temperature, it was found that the extent of the chain stretching of the soft segment was decreased with an increase in the cooling-roll temperature.

Preparation of Branch Polyethyleneimine (BPEI) Crosslinked Anion Exchange Membrane Based on Poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) (SEBS)

AbstractAnion exchange membranes with chemical stability, high conductivity, and high mechanical properties play an important role in alkaline fuel cells. Here, a series of CPX anion exchange membranes based on poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) (SEBS) and branch polyethyleneimine (BPEI) are achieved by casting, in which BPEI acts as both a crosslinking agent and an OH− conducting functional group. The introduction of BPEI facilitates the formation of good hydrophilic/hydrophobic microphase separation structure, thus improving the ion transport channel of CPX membrane. The physicochemical and electrochemical properties of the CPX membrane are significantly improved when the mass ratio of SEBS to BPEI is within an appropriate range. The OH− conductivity of the CP2 membrane (the mass ratio of SEBS to BPEI is 2) can reach 66.63 mS cm−1 at 80 °C, and more than 80% initial OH− conductivity is maintained in 1.0 m NaOH solution for 20 d at 60 °C. The strategy of using a polymer with excellent alkali resistance and oxidation resistance as the main body and introducing a conductive group that can construct microphase separation can simultaneously improve the conductivity and membrane stability. This viable strategy is a promising construction method for anion exchange membranes that can be applied to fuel cells.

Constructing micro-phase separation structure to improve the performance of anion-exchange membrane based on poly(aryl piperidinium) cross-linked membranes

The ether-bond-free poly(biphenyl piperidine)s are prepared to improve the alkaline stability of the anion exchange membrane (AEMs). At the same time, the construction of micro-phase separation structure is a good way to solve the “trade-off” problem between ionic conductivity and stability of AEMs. In this study, we report a new method for constructing micro-phase separation structures based on “main-chain type” AEMs and a crosslinking strategy that does not sacrifice ion exchange capacity. A series of poly(biphenyl piperidine)s AEMs (PAP–OH–x) are prepared by introducing 2-bromoethanol and 1,6-dibromohexane to form piperidine cationic groups and cross-linked structure. The structure of hydrophilic/hydrophobic phase separation is confirmed by TEM images. The cross-linked membrane of poly(biphenyl piperidine)s (PAP–OH–8%) membrane exhibits high conductivity of 0.081 S/cm with a rational water absorption (55.6%) and low swelling ratio (11.8%) at 80 °C, and also preserves the hydroxide conductivity (89.2% retention) after testing in a 5 M NaOH aqueous solution at 80 °C for 30 days, exhibits high alkaline stability. Furthermore, a single H2/O2 fuel cell with poly(biphenyl piperidine)s (PAP–OH–8%) membrane exhibits the open circuit voltage of 1.02 V and the peak power density of 290 mW/cm2 at 60 °C.

Microphase separation/crosslinking competition-based ternary microstructure evolution of poly(ether-b-amide).

The temperature dependence of the rheological properties of poly(ether-b-amide) (PEBA) segmented copolymer under oscillatory shear flow has been investigated. The magnitude of the dynamic storage modulus is affected by the physical microphase separation and irreversible crosslinking network, with the latter spontaneously forming between the polyamide segments and becoming the dominant factor in determining the microstructural evolution at temperatures well above the melting point of PEBA. From the rheological results, the initial temperature of the rheological properties dominated by the microphase separation and crosslinking (Tcross) structures were determined, respectively. Based on the two obtained temperatures, the microstructure evolution upon the heating can be separated into the ternary microstructure domains: homogenous (temperature below ), microphase separation dominating (between and Tcross), and crosslinking dominating domains (above Tcross). When the PEBA is heated to above Tcross, the content of crosslinking network increases with time and temperature, leading to an irreversible and non-negligible influence on the rheological, crystallization, and mechanical properties. A more pronounced strain-hardening phenomenon during the uniaxial stretching is observed for the sample with a higher content of crosslinking network.

Bicontinuous Ion-Exchange Materials through Polymerization-Induced Microphase Separation.

Polymerization-induced microphase separation has been used to prepare solid cross-linked monoliths containing bicontinuous and nanostructured polymer domains. We use this process to fabricate a monolith containing either a negatively or positively charged polyelectrolyte domain inside of the neutral styrene/divinylbenzene-derived matrix. First, the materials are made with a neutral pre-ionic polymer containing masked charged groups. The monoliths are then functionalized to a charged state by treatment with trimethylamine; small-angle X-ray scattering shows no significant morphological change in the microphase-separated structure upon postpolymerization modification. By exchanging dyes with the counterions in the material, we corroborated the continuity of the charged domains. Using ion-exchange capacity measurements, we estimate the number of accessible charges within the material based on macro-chain transfer agent molar mass and loading.

Deep learning model for predicting phase diagrams of block copolymers

Block copolymers show various microphase-separated structures depending on their chain architecture and the interaction parameters between the different chemical structures of monomeric unit χ. Self-consistent field theory is a powerful tool to predict such phase-separated structures, and phase diagrams of block copolymers have been reported using self-consistent field theory. However, obtaining stable morphology of each polymer structure and the χ parameter requires intensive computational study. We applied deep learning to predict phase diagrams from metastable structures obtained by crude, cost-effective self-consistent field calculation. We used a 3D convolutional neural network for classification of the metastable structures, and a limited number of sets of block copolymer structures and χ parameters with stable phase labels were used for training. After the model was trained using the training set, it successfully assigned the metastable structures of a wide variety of diblock and triblock copolymers to the correct stable phases. This approach is capable of predicting the phase diagrams of block copolymers effectively without intensive self-consistent field calculation.

Highly hydroxide-conductive anion exchange membrane with PIL@MOF-assisted ion nanochannels

A highly hydroxide-conducting anion exchange membrane with well-organized multi ion channels were fabricated via incorporating poly ionic liquids modified MIL101 (PIL@MIL101) into imidazolated poly (2,6-dimethyl-1,4-phenylene oxide) (ImPPO). 1-Vinyl-3-ethylimidzolium bromine was first immobilized in MIL101 cages via supercritical fluid impregnation method. Afterwards, the rigid-assisted ion nanochannels were constructed by in-situ polymerization of ionic liquids within the long-range ordered pores of MIL101. Meanwhile, PPO was functionalized by 1-ethyl-2-methyimidzolium to prepare comb-shaped ImPPO with enhanced microphase separation structure. Then the PIL@MIL101 was combined with ImPPO to fabricate hybrid anion exchange membrane with well-organized multiple ion channels. The OH− conductivity of the hybrid membrane significantly reached 138mS/cm at 80°C (176% higher than that of pristine membrane). Furthermore, the stability and mechanical properties of the hybrid membranes were remarkably enhanced. The excellent performances render the hybrid membrane a good candidate for the application in anion exchange membrane fuel cells.

Synthesis and properties of styrenic triblock copolymers with dual structural asymmetry via RAFT emulsion polymerization

The polystyrene-block-poly(n-butyl acrylate)-block-polystyrene (PSt-b-PBA-b-PSt, SBAS) triblock copolymers (TBCPs) with dual structural asymmetry were synthesized via a reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. The dual structural asymmetry contained two asymmetric outer PSt blocks and a single short ionic block on one chain end while the SBAS TBCPs had the almost same molecular weight (~100 kDa) and composition (~70 wt% of PSt and ~30 wt% of PBA) excluding the short ionic block. The dual structural asymmetry with a synergistic effect was designed by locating the long PSt block near the short ionic block that was derived from ionic macromolecular RAFT agent. With the SBAS TBCPs having microphase separation structure, the structural asymmetry of two outer PSt blocks tailored the interaction of PSt and PBA blocks, further leading to the change of static tensile and dynamic mechanical properties, and rheology. Structural asymmetry will provide an alternative to tailor-made properties of TBCPs.

Polyurethane as smart biocoatings: Effects of hard segments on phase structures and properties

Development of smart polyurethane (PU) coatings for enhancing the biocompatibility of the metal scaffold has attracted great interest in the past few years, and the investigation of the relationship between phase structure and smart properties is necessary. Herein, two series of PU biocoatings with different hard segment structures and soft segment length were prepared, and the soft segments consist of the polycaprolactone diols (PCL) with different molecular weights, and the hard segments were made of 1, 4-butanediol (BDO) and hexamethylene diisocyanate (HDI) with linear structure, or BDO and isophorone diisocyanate (IPDI) with alicyclic structure, respectively. To understand the phase structures, the chemical structure, surface micromorphology, and segmental incompatibility of the PU films were characterized, which reveals that IPDI-based PU possesses a phase compatible structure with a single-phase transition above 0 °C. Besides, the IPDI-based PU shows the thermal-responsive deformation at the temperature of 45 °C, slightly higher than the human body temperature. In contrast, the HDI-based PU possesses the excellent shape memory property caused by the microphase separation structure, because of the crystallization of soft and hard segments from the melt. Further, based on the characteristics of phase structure, the potential application of the IPDI-based PU and HDI-based PU is explored, offering a useful approach to effectively design the structures and properties of PU coatings.

Frank-Kasper A15 Phase Formed in ABn Block-Graft Copolymers with Large Numbers of Graft Chains

Microphase-separated structures of a series of ABn block-graft copolymers were studied by transmission electron microscopy (TEM) coupled with small-angle X-ray scattering (SAXS). Five block-graft c...

Excellent film-forming, ion-conductive, zwitterionic graft copolymer electrolytes for solid-state supercapacitors

Polymer electrolytes with robust mechanical properties and high ionic conductivity are highly desirable for solid-state energy storage devices. Therefore, in this study, a polymer electrolyte based on a zwitterionic graft copolymer, poly(vinyl alcohol)-graft-poly(sulfobetaine methacrylate) (PVA-g-PSBMA), is developed. Herein, we designed a graft copolymer that utilizes the excellent film-forming nature of PVA main chains and ion-conductive properties of polyzwitterionic PSBMA side chains. The PVA-g-PSBMA electrolytes exhibited microphase separated structures, wherein H3PO4 interacted more strongly with the PSBMA domains. Therefore, the transport of proton ions was facilitated through the well-defined PSBMA-based ion channels, leading to a significant increase in the ionic conductivity. The polymer electrolyte was applied to the electric double-layer capacitor (EDLC) with activated carbon-based electrode. In comparison with the neat conventional PVA-based cell, the solid EDLC with PVA-g-PSBMA zwitterionic graft copolymer electrolytes showed improved specific capacitance (46.6 F g−1), energy density (3.67 Wh kg−1), and power density (186 W kg−1). The improved performance can be attributed to the higher ionic conductivity and better interfacial compatibility of electrode/electrolyte for the PVA-g-PSBMA electrolytes.

Hydrogen bonding and topological network effects on optimizing thermoplastic polyurethane/organic montmorillonite nanocomposite foam

Foaming behavior of thermoplastic polyurethane (TPU) is extremely difficult to be regulated due to the special microphase-separation structure. Therefore, organic montmorillonite (O-MMT) was applied in TPU foaming to regulate cell nucleation, growth and stabilization simultaneously: (1) strong interfacial interaction between O-MMT with TPU could not only facilitate O-MMTs’ nanoscale dispersion but also ensure a similar cell nucleation at various O-MMT loading, which effectively decoupled the complicated influences of cell nucleation and growth on TPU foam's shrinkage; (2) TPU/O-MMT topological network was constructed by O-MMT loading, regulating cell growth and corresponding decreasing cell size; (3) -OH group on O-MMT surface could hydrogen bond with TPU molecular chains in soft/hard segments, stabilizing TPU molecular chains and finally reducing foams' shrinkage. Combining hydrogen bonding and topological network resulted from O-MMT, it enables us to optimize TPU foam structure by controlling cell nucleation, growth and stabilization simultaneously, the optimal O-MMT loading was 1 wt%.

In Situ Synchrotron Radiation X-ray Scattering Investigation of a Microphase-Separated Structure of Thermoplastic Elastomers under Uniaxial and Equi-Biaxial Deformation Modes

Changes in the microphase-separated structure of the poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer (13 wt % polystyrene (PS) block) were investigated during mechanical deformation. In situ synchrotron radiation small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS) measurements were successfully performed for SEBS under equi-biaxial deformation as well as under uniaxial deformation. In situ SAXS/WAXS measurements revealed changes in (1) the shape of spherical PS domains, (2) the spacing of PS domains packed in the body-centered cubic structure in the initial state, (3) their ordering, and (4) the orientation of PEB chains during deformations. In terms of the microdomain structure, affine deformation was kept below a certain strain (εd-A), which are 4 and 1.2 for uniaxial and equi-biaxial deformation, respectively. In contrast, the ordering of the arranged PS domains decreased from the initial strain region. Above the εd-A value, deviation from affine deformation started to occur. This deviation is related to contact of PS domains under mechanical deformation. Uniaxial stretching still showed the plane-independent behavior, while equi-biaxial stretching did not. Moreover, the εd-A value for equi-biaxial deformation was smaller than that for uniaxial deformation and further smaller than expected. This might be because the entanglement effect was enhanced for equi-biaxial deformation. Furthermore, after contact of PS domains at around strains of 6 and 2, during uniaxial and equi-biaxial deformation, respectively, the ordering of PS domains suddenly increased with an increase in strain. It is inferred that the locked state between the PS domains and the extended PEB chains formed during deformation may have been released and repacked at a certain strain.

Prepared poly(aryl piperidinium) anion exchange membranes for acid recovery to improve dialysis coefficients and selectivity

The diffusion dialysis (DD) process based on AEM is considered for the acid recovery from acid effluents. In this work, the novel self-organized nanostructured cross-linked AEMs based on poly (aryl piperidinium) are synthesized for acid recovery. The cross-linked AEMs are designed by introducing 2-bromoethanol and 1,6-dibromohexane into the hydrophobic poly (biphenyl piperidine)s backbone via Menshutkin reaction, and the self-assembled nanostructure is confirmed by TEM imagines. The acid flux is improved by constructing a micro-phase separation structure and hydrogen bond network. The H-bond networks and cross-linking structure improve the selectivity between the acid and salt system without sacrificing IEC values of AEM. The IEC values of PBP-OH-x AEMs are in the range of 2.18–2.21 mmol/g. The AEMs exhibit high H+ dialysis coefficients (UH), ranging from 0.045 to 0.053 m/h, and have good separation factors (S) in the range of 32–56. The prepared PBP-OH-x AEMs have better DD performance, comparing with the commercial membrane DF-120 (UH = 0.009 m/h, S = 18.5). The novel AEMs based on poly (aryl piperidinium) showed the potential to be used in acid recovery via DD.

Self-assembly of amphiphilic poly(2-hydroxyethyl methacrylate)-containing block copolymers in the vicinity of cellulose fibres

Within this work, well-defined polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) and a non-polar model block copolymer (BCP) polystyrene-block-polybutadiene (PS-b-PB) have been prepared via sequential anionic polymerization and investigated with respect to their capability of microphase separation in the presence of cellulose fibres. Both the original morphologies in the bulk state as well as the microphase-separated structures in the vicinity of cellulose fibres were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) measurements. BCP series featuring molar masses below 70 kg mol−1 and higher molar masses up to 201 kg mol−1 have been subjected to solvent-casting and subsequent thermal annealing to elucidate the microstructures in the presence or absence of cellulose fibres with defined contents of water. Besides the classical morphologies comprising spheres, cylinders and lamellae, also gyroidal and helical-domains were observed. Moreover, a significant impact on the degree of domain order and orientation was found for the PHEMA-containing BCPs based on the hydroxyl moiety interactions of the cellulose fibres and respective PHEMA block segments.

Effects of Solubility Difference of Tackifier to Respective Components of Block Copolymers on Microphase-Separated Structures in Coated Layers of Pressure-Sensitive Adhesive Prepared by Solution Coating Process

Effects of solubility difference of tackifier to respective components of block copolymers on microphase-separated structures were examined using coated layers of the polystyrene-block-polyisoprene...

Microphase-separated structures of ion gels consisting of ABA-type block copolymers and an ionic liquid: A key to escape from the trade-off between mechanical and transport properties

Upon combination of an ionic liquid (IL) with an amphiphilic ABA-type triblock copolymer, the insoluble A blocks aggregate to form mechanical frameworks and the soluble B blocks form ion-transport paths by incorporating the IL. Consequently, a self-standing ion gel, exhibiting the characteristic high ionic conductivity of ILs, can be obtained. In this study, we investigated the effect of microstructures formed by the block copolymer (spherical, cylindrical, gyroid, and lamellar structures) on the ionic conductivity and mechanical properties of the ion gel by focusing on the microstructures. As a result, an ion gel that formed an isotropic bicontinuous structure was successfully obtained via a heat-induced order-order transition. The structure was maintained even at room temperature, and the ion gel having a bicontinuous structure exhibited favorable mechanical properties (storage modulus, G' ~ 1.0 MPa) and good ionic conductivity (σ ~ 0.1 mS cm−1). In contrast, the ion gels having anisotropic structures (cylindrical structure) exhibited weaker mechanical properties and lower ionic conductivity. The characteristics of bicontinuous structures may be the key to resolving the trade-off between mechanical and transport properties of electrolyte materials for electrochemical devices.

Morphologies of spherical bidisperse polyelectrolyte brushes in the presence of trivalent counterions

We study surface morphologies of a bimodal polyelectrolyte brush grafted onto a surface of spherical colloid in the presence of trivalent counterions, using molecular dynamics simulations. Both the good and poor solvent conditions are considered. Grafting density and charge fraction are varied to generate a series of microphase separated structures, which represents the competition between the excluded volume interaction and trivalent counterion mediated bridging. The short chains are more extended than the long counterparts under good solvent conditions, which are different with those under poor solvent conditions through a careful analysis on shape factor of grafted chains as well as distributions of monomers and counterions. Furthermore, the electrostatic bridging effect of trivalent counterions is analyzed carefully by classifying them into four states. Also, our simulation results can sever as a guide for improving the performance of polydisperse polyelectrolyte brushes as smart stimuli-responsive materials.