Self-assembly Of Triblock Copolymers Research Articles

Self-assembly of rod-coil-rod block copolymers in a coil-selective solvent: coarse-grained simulation results.

The solution self-assembly of amphiphilic polymers provides a versatile approach to design novel nanostructured materials. Multiblock polymers, particularly those composed of liquid crystalline and coil blocks, are of significant interest due to the potential display of nematic ordering in liquid crystalline domains, offering intriguing optical and mechanical properties. In this study, dissipative particle dynamics is used to investigate the solution self-assembly of rod-coil-rod copolymers in a coil-selective solvent. Extensive molecular simulations were conducted to elucidate the impact of polymer composition, concentration and flexibility on the self-assembly behavior. A quantitative analysis was performed to investigate how polymer conformations varied with changes in composition, concentration, and rigidity. Simulation results show that, at small rod compositions, rod-coil-rod polymers self-assemble into micelles at low concentrations, transitioning to network formation as concentration increases. An increase in rod composition leads to the formation of larger aggregates, resulting in cylindrical micelles and membranes. The results reported here also offer insights into the role of flexibility in shaping the self-assembly behavior of rod-coil-rod triblocks in selective solvents, thus, contributing to a comprehensive understanding of the factors governing the formation of diverse structures in the solution self-assembly of triblock copolymers.

Reduction-sensitive flower-like magnetomicelles based on PCL-ss-PEG-ss-PCL triblock copolymer as anti-cancer drug delivery system

Introducing an intelligent pharmaceutical nanocarrier for targeted drug release and reducing the side effects of chemotherapy is the main goal of many researchers. In this area, we synthesized amphiphilic triblock copolymer PCL-ss-PEG-ss-PCL consisting of cystamine as a reduction sensitive linkage. The aqueous self-assembly of triblock copolymer in the presence of magnetic iron oxide nanoparticles (Fe3O4) and doxorubicin (DOX) led to the formation of reduction-sensitive flower like magnetomicelle containing DOX and Fe3O4. The innovative design based on intelligent flower like structure led to high drug loading content, reduce drug release in physiologic condition, fast degradation at targeted site and burst release of more content of drug at earlier time. The DOX loading content was about 19% and DOX- loaded magnetomicelles (D-LMM) showed more triggered release under redox conditions at pH = 5. The efficiency of D-LMM was compared with non-reduction sensitive control group (CD-LMM), free DOX and commercial product of liposomal DOX (LD) in vitro. The D-LMM showed significant improvement in cellular uptake and toxicity behavior on human breast adenocarcinoma MCF-7 cells in comparison to commercial LD and also displayed better results in the cytotoxicity and apoptosis/necrosis assays in comparison to CD-LMM.

Phase-Separation-Induced Porous Hydrogels from Amphiphilic Triblock Copolymer with High Permeability and Mechanical Strength

Porous hydrogels, possessing both high mechanical strength and high permeability, are sought after in energy storage, soft robotics, solar vapor generation, and tissue engineering. However, there is always a trade-off between mechanical strength and permeability. In general, high porosity promotes molecular mass transportation (permeability) but sacrifices mechanical strength. To address this issue, in this work, micro/nanoporous hydrogels with high mechanical strength are fabricated from the self-assembly of amphiphilic triblock copolymers consisting of hydrophilic end blocks and hydrophobic midblocks. The chemically distinct blocks induce the phase separation, yielding a hydrogel network consisting of nanopores dispersed in the micrometer-thick sponge-like base support with an ordered lamellar structure. The soft water-depleted phase is dynamic, forming a transient network that allows chain exchange and coalescence between different phases. This reversible process not only dissipates energy to toughen hydrogels but also enables self-recovery. By systematically altering the length of end blocks and midblocks, one can synthesize hydrogels with tunable mechanical properties, including an elastic modulus of 87–884 kPa, a fracture stress of 63–584 kPa, a fracture strain of 1–20, and work of extension of 217–2104 kJ/m3. The gels with a porous size in the range of 1–8 μm also exhibit self-recovery behavior and a high permeability of 10–12 and 10–11 m2. The porous hydrogels show a fracture energy of ∼2000 J/m2, several orders of magnitude higher than common porous hydrogels (gelatin, agarose, and polyacrylamide) and comparable to soft biological tissues. The preparation process also endows the foreseeable potential as injectable hydrogels for applications in soft robotics and 3D printing.

Fabrication of a robust superhydrophobic coating from the aqueous self-assembly of perfluoropolyether-based triblock copolymers

Five types of poly(hydroxyethyl methacrylate)m-perfluoropolyether-poly(hydroxyethyl methacrylate)m triblock copolymers (HFHm) with different poly(hydroxyethyl methacrylate) chain lengths were synthesized successfully. The as-synthesized HFHm can self-assemble into micelles in water with perfluoropolyether core surrounded by poly(hydroxyethyl methacrylate) corona under a dilute concentration. By casting the mixture of the HFHm micelles in water, hydrophilic silica nanoparticles and hydrophilic polyisocyanates as a cross-linking agent, a robust superhydrophobic surface can be obtained on smooth substrates. The addition of silica nanoparticles and polyisocyanates enhances the surface roughness and mechanical durability of the coatings. Due to the high surface roughness (Ra = 889 nm) and the high surface fluorine content (41.9 wt%), the cross-linked HFHm superhydrophobic coating can reach a water contact angle of 157.8 ± 0.7° and a water sliding angle of 3.5 ± 0.6°. After 30 abrasion cycles or immersion for 22 h in strong acid (pH 2) and weak alkaline (pH 9) solutions, the coating still maintains its superhydrophobicity. These phenomena indicate that the HFHm can be used as a kind of environment-friendly coatings with superhydrophobicity.

Dynamics of pearling instability in polymersomes: The role of shear membrane viscosity and spontaneous curvature

The stability of copolymer tethers is investigated theoretically. Self-assembly of diblock or triblock copolymers can lead to tubular polymersomes, which are known experimentally to undergo shape instability under thermal, chemical, and tension stresses. It leads to a periodic modulation of the radius, which evolves to assembly line pearls connected by tiny tethers. We study the contributions of shear surface viscosity and spontaneous curvature and their interplay to understand the pearling instability. The performed linear analysis of stability of this cylinder-to-pearls transition shows that such systems are unstable if the membrane tension is larger than a finite critical value contrary to the Rayleigh–Plateau instability, an already known result, or if the spontaneous curvature is in a specific range, which depends on membrane tension. For the case of spontaneous curvature-induced shape instability, two dynamical modes are identified. The first one is analog to the tension-induced instability with a marginal mode. Its wavenumber associated with the most unstable mode decreases continuously to zero as membrane viscosity increases. The second one has a finite range of unstable wavenumbers. The wavenumber of the most unstable mode tends to be constant as membrane viscosity increases. In this mode, its growth rate becomes independent of the bulk viscosity in the limit of high membrane viscosity and behaves as a pure viscous surface.

Self-assembly strategy for Co/N-doped meso/microporous carbon toward superior oxygen reduction catalysts

Proton-exchange-membrane fuel cells (PEMFCs) are of considerable interest as a sustainable, renewable, efficient, and eco-friendly electrochemical conversion systems of energy. Sluggish oxygen reduction reaction (ORR) as the cathodic reaction have mainly dragged down the PEMFCs in practical use. The most effective catalyst for ORR today is a Pt-based catalyst, which have a high scarcity value and low durability for methanol. Therefore, major efforts have recently been devoted to exploring transition metal and hetero-atom doped carbon materials in fuel cells for large-scale and commercial applications. Herein, we report a facile synthesis route of Co-N doped meso/microporous carbon catalysts (Co/N/MPC-act) via self-assembly of resorcinol-based resin, triblock co-polymer and Co containing ionic liquid followed by CO 2 activation. The obtained catalyst exhibited outstanding oxygen reduction activity in an alkaline medium. It yields an onset potential of 0.960 V (vs. RHE) and a limiting current density of 5.0 mA/cm 2 , which are comparable to that of the commercial Pt/C catalyst. This high activity is contributed by the combination of inter-connected meso/microporous structures and highly dispersed CoN x species with metallic Co. The Co/N/MPC-act catalyst exhibited excellent long-term operation stability and methanol tolerance, making it a promising non-precious metal-based ORR catalyst for PEMFCs. • Co/N doped meso-micro porous carbon (Co/N/MPC-act) was prepared by self-assembly process and CO 2 activation. • Co/N/MPC-act contains high content of pyridinic-N and Co-N. • Co/N/MPC-act exhibits an impressive high catalytic performance for ORR. • Co/N/MPC-act shows better durability and tolerance to methanol for ORR than 20 wt% Pt/C.

Recent Advances in Polyallenes: Preparation, Self-Assembly, and Stimuli-Responsiveness.

Polyallenes, as a typical type of reactive polymers, are of great significance and have aroused widespread interest because they contain double bonds that can be post-modified into other functionalities to afford varieties of functional materials. This Minireview firstly highlights the recent advances in the preparation of polyallenes, including preparation of helical polyallenes through directly polymerization of chiral allene monomers or helix-sense-selective polymerization (HSSP) of achiral allene monomers, synthesis of 1,2-regulated polyallenes and 2,3-regulated polyallenes via selective polymerization of allene monomers, polymerization of allene monomers catalyzed by Ni(II)-terminated poly(3-hexylthiophene) (P3HT), and so on. Then, latest progress on the self-assembly and stimuli-responses of polyallene-based diblock, ABA and ABC triblock copolymers is summarized. We hope this Minireview will inspire more interest in developing polyallenes and encourage further advances in functional materials.

Enhanced hydrophobicity of polyurethane with the self-assembly of perfluoropolyether-based triblock copolymers

The self-assemblies of poly(isobornyl methacrylate)m-b-perfluoropolyether-b-poly(isobornyl methacrylate)m (BCPm) in mixed 1,1,2-trichlorotrifluoroethane/N,N-dimethylformamide (F113/DMF) solvent were used to improve the surface hydrophobicity of polyether-based polyurethane (PU). With the loading of BCPm micelles into the PU, the surface roughness and the fluorine content in the surface were effectively enhanced, leading to the significant increase of water contact angle (WCA) from 73° to 140°. This improvement was much more pronounced than that of PU containing only perfluoropolyether units at the same fluorine content level due to higher surface roughness. For the hybrid coatings prepared from BCPm with different degrees of polymerization (DP) of poly(isobornyl methacrylate) blocks, the water repellency reached the maximum at the DP of 10. In addition, the hybrid coatings exhibited excellent mechanical durability and acid-alkali resistance, which is beneficial for broadening the application scenarios of cotton fabrics. Altogether, the self-assembly of perfluoropolyether based copolymers with high surface hydrophobicity shows potential applications in the protection of polymeric materials.

Ordered Mesoporous Alumina with Tunable Morphologies and Pore Sizes for CO2 Capture and Dye Separation.

We describe a versatile and scalable strategy toward long-range and periodically ordered mesoporous alumina (Al2O3) structures by evaporation-induced self-assembly of a structure-directing ABA triblock copolymer (F127) mixed with aluminum tri-sec-butoxide-derived sol additive. We found that the separate preparation of the alkoxide sol-gel reaction before mixing with the block copolymer enabled access to a relatively unexplored parameter space of copolymer-to-additive composition, acid-to-metal molar ratio, and solvent, yielding ordered mesophases of two-dimensional (2D) lamellar, hexagonal cylinder, and 3D cage-like cubic lattices, as well as multiscale hierarchical ordered structures from spinodal decomposition-induced macro- and mesophase separation. Thermal annealing in air at 900 °C yielded well-ordered mesoporous crystalline γ-Al2O3 structures and hierarchically porous γ-Al2O3 with 3D interconnected macroscale and ordered mesoscale pore networks. The ordered Al2O3 structures exhibited tunable pore sizes in three different length scales, <2 nm (micropore), 2-11 nm (mesopore), and 1-5 μm (macropore), as well as high surface areas and pore volumes of up to 305 m2/g and 0.33 cm3/g, respectively. Moreover, the resultant mesoporous Al2O3 demonstrated enhanced adsorption capacities of carbon dioxide and Congo red dye. Such hierarchically ordered mesoporous Al2O3 are well-suited for green environmental solutions and urban sustainability applications, for example, high-temperature solid adsorbents and catalyst supports for carbon dioxide sequestration, fuel cells, and wastewater separation treatments.

Enhanced Self-Assembly and Mechanical Properties of Cellulose-Based Triblock Copolymers: Comparisons with Amylose-Based Triblock Copolymers

Enhanced Self-Assembly and Mechanical Properties of Cellulose-Based Triblock Copolymers: Comparisons with Amylose-Based Triblock Copolymers

Open Porosity and Pore Size Distribution of Mesoporous Silica Films Investigated by Positron Annihilation Lifetime Spectroscopy and Ellipsometric Porosimetry.

Tunable mesoporous silica films were prepared though a sol-gel process directed by the self-assembly of various triblock copolymers. Positron annihilation γ-ray energy spectroscopy and positron annihilation lifetime spectroscopy (PALS) based on intense pulsed slow positron beams as well as ellipsometric porosimetry (EP) combined with heptane adsorption were utilized to characterize the open porosity/interconnectivity and pore size distribution for the prepared films. The consistency between the open porosities was examined by the variations of orthopositronium (o-Ps) 3γ annihilation fractions and the total adsorbed volumes of heptane. The average pore sizes deduced by PALS from the longest-lived o-Ps lifetimes are in good agreement with those by EP on the basis of the Barrett–Joyner–Halenda model, as indicated by a well fitted line of slope k = 1. The results indicate that the EP combined with heptane adsorption is a useful method with high sensitivity for calibrating the mesopore size in highly interconnected mesoporous films, whereas PALS is a novel, complementary tool for characterizing both closed and open pores in them.

The effect of topology of PEG chain on the stability of micelles in brine and serum

Polymeric micelles are promising vehicles for drug delivery these years. The stability of micelles in blood system is very important for the encapsulated therapeutic agents reaching the targeting area. However, generally, micelles are not stable in the presence of proteins and ions after being injected intravenously. The topology of polymer chain on the surface of micelles plays a key role on the stability of micelles. Here we have prepared flower micelles and the traditional micelles via self-assembly of triblock and diblock copolymer of polyethylene glycol (PEG) and poly(ε-caprolactone) (PCL) in water. The special PEG shell of flower micelles prevents micelles from ions and proteins, which endows the micelles with the ability to resist aggregation. The experiment results show that flower micelles are much more stable in the presence of serum and salt than traditional micelles, which indicates these micelles would be promising in drug delivery in the future.

Micro-scale hollow nanosphere as highly efficient ORR electrocatalyst derived from the self-assembly of triblock copolymer (L64)

The micro-scale hollow nanosphere with rich defect was synthesized by pyrolyzing the transparent film composed of the co-polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymer (L64) and Zn (OH)2, which formed in the mixture solution of ethanol and n-hexane. The content increase of n-hexane in the mixture solution would decrease the formation rate during self-assembly of block copolymers, which was beneficial for forming the uniformly distributed nano-carbon spheres obtained. As the ratio of ethanol and n-hexane is 1:1, the as-synthesized product (noted as C (1:1)) has an even pore size (7 nm) and hollow nanosphere morphology, which possessed the highest specific surface area (753 m2 g−1) and disorder (ID/IG, 3.4). In terms of ORR performance, C (1:1) exhibits not only superior cycle stability and methanol-tolerance than 20% Pt/C but also comparable half-wave potential (0.76 V vs. RHE) to that of commercial 20% Pt/C (0.80 V) in 0.1 M KOH solution.

Hydrogen-bonding mediated self-assembly of amphiphilic ABA triblock copolymers into well-defined giant vesicles

A straightforward and efficient access towards the generation of well-defined giant vesicles (∼3 μm in diameters), featured by Hydrogen-bonded DAP–DAP dimerization, and the amphiphilic interactions is reported.

From hierarchically porous carbon to Mn3O4/Carbon composites for high voltage aqueous supercapacitors

The energy density of aqueous supercapacitors can be enhanced by large capacitance and high operating voltage, which is mainly limited by the narrow stability window of the water. Herein, carbonaceous materials with nitrogen-doping and hierarchical porosity are successfully designed and prepared via a facile sol−gel route accompanied by the cooperative self-assembly of triblock copolymer and melamine-resorcinol-formaldehyde polymer, followed by carbonization and CO2 activation. Based on the as-prepared carbon material, symmetric supercapacitors achieve a high cell voltage of 1.8 V in 1 M Li2SO4, and exhibit a high energy density of 27.8 Wh kg−1 at power density of 0.23 kW kg−1. Taking advantage of the reversible redox reaction of Mn3+/Mn4+ accompanied with the insertion/extraction of Li+ of birnessite-type MnO2, the working potential of positive electrode is further expanded to 0–1.2 V (vs SCE). Then asymmetric supercapacitors with high cell voltage of 2.2 V have been successfully fabricated, exhibiting a higher energy density of 44.5 Wh kg−1 at power density of 0.27 kW kg−1 and an acceptable energy density of 21.8 Wh kg−1 even at a high power density of 5.6 kW kg−1.

Regulating Dynamics of Polyether-Based Triblock Copolymer Hydrogels by End-Block Hydrophobicity

The relaxation dynamics of poly(ethyl glycidyl ether-co-isopropyl glycidyl ether-b-ethylene oxide-b-ethyl glycidyl ether-co-isopropyl glycidyl ether) triblock copolymer hydrogels were investigated as a function of the end-block hydrophobicity and temperature primarily using the oscillatory rheometer, which is crucial to understand the unique viscoelastic behaviors including injectability and self-healing property of the self-assembled hydrogels. Lower critical solution temperature behavior of the poly(alkyl glycidyl ether) end-blocks was harnessed by random copolymerization of poly(ethyl glycidyl ether) (EGE) and poly(isopropyl glycidyl ether) (iPGE), resulting in the remarkable temperature responsiveness of the hydrogel. As the fraction of hydrophilic monomer (i.e., EGE) increases, the sol-to-gel transition occurs at higher temperature and higher polymer concentration. The hydrogel relaxation measured by the oscillatory rheometer becomes faster with decreasing temperature and increasing fraction of hydrophilic monomers. In particular, we observed that a small increment of the hydrophilic monomer fraction significantly reduces the unfavorable interaction between the end-block and aqueous media, resulting in faster hydrogel relaxation dynamics. All polyether-based hydrogels showed biocompatibility and injectability, indicating promising soft materials for biological and biomedical applications. The results are discussed in terms of the current understanding of self-assembled triblock copolymer hydrogels, and particular attention is paid to the issue of chain dynamics.

Synthesis of magnetite loaded fluorescence micelles of triblock copolymer

Abstract Magnetic micelles with fluorescence dyes were fabricated by self-assembly of triblock copolymer followed by in situ templated coprecipitation method. Nile red was encapsulated into the polystyrene core of the triblock copolymer confirmed by fluorescence measurement. The magnetic nanoparticles are selectively chemisorbed on the poly(acrylic acid) (PAA) shell of polymeric micelles due to ionic interaction between PAA and Fe ions. The negatively charged PAA also a platform to bind positively charged drug molecules. The hydrophilic poly(ethylene glycol) (PEG) corona stabilizes the micelles composites. The multifunctional polymeric micelles were well characterized by using different tools and techniques: dynamic light scattering, transmission electron microscope, UV–visible spectrophotometer, fluorescence spectroscope, and magnetometer.

Preparation and self-assembly of thermosensitive triblock copolymers with N-isopropylacrylamide and 3-methacryloxypropyltrimethoxysilane as monomers

Well-defined triblock copolymers poly(N-isopropylacrylamide)-b-poly(3-methacryloxypropyltrimethoxysilane)-b-poly(N-isopropylacrylamide) (PNIPAM-b-PMEMO-b-PNIPAM) with varying block ratios were successfully synthesized via reversible addition–fragmentation chain transfer polymerization. The amphiphilic triblock copolymers showed surfactant-like behavior in aqueous solution and could easily self-assemble into dendritic micelles with hydrophobic PMEMO as the core and hydrophilic PNIPAM as the shell when the copolymer concentration exceeded the critical micelle concentration (CMC). Transmittance measurements showed the triblock copolymers were thermosensitive, and it was worth noting that the lower critical solution temperature (LCST) values of copolymers exceeded pure PNIPAM to about 35.3 °C, which was very close to physiological temperature of human body. This was attributed to the effect of Si–O–CH3 hydrolysis in polymers. The effect of a series of inorganic salts on thermosensitivity of PNIPAM-b-PMEMO-b-PNIPAM was investigated, and our results suggested that the block copolymers maintained good thermosensitivity in all salt solutions. The LCST did not change significantly in different concentrations of NaCl, CaCl2 and MgCl2 solutions, which proved the polymer had good salt resistance. Dynamic light scattering experiments showed that the micelles were well dispersed at about 120 nm below LCST with a small polydispersity index. In addition, the drug-loading experiments of micelles showed high drug encapsulation efficiency indicating their potential as drug carriers.

Solvent-non-solvent rapid-injection for preparing nanostructured materials from micelles to hydrogels

Due to their distinctive molecular architecture, ABA triblock copolymers will undergo specific self-assembly processes into various nanostructures upon introduction into a B-block selective solvent. Although much of the focus in ABA triblock copolymer self-assembly has been on equilibrium nanostructures, little attention has been paid to the guiding principles of nanostructure formation during non-equilibrium processing conditions. Here we report a universal and quantitative method for fabricating and controlling ABA triblock copolymer hierarchical structures using solvent-non-solvent rapid-injection processing. Plasmonic nanocomposite hydrogels containing gold nanoparticles and hierarchically-ordered hydrogels exhibiting structural color can be assembled within one minute using this rapid-injection technique. Surprisingly, the rapid-injection hydrogels display superior mechanical properties compared with those of conventional ABA hydrogels. This work will allow for translation into technologically relevant areas such as drug delivery, tissue engineering, regenerative medicine, and soft robotics, in which structure and mechanical property precision are essential.

Assembling structurally customizable synthetic carriers of siRNA through thermodynamically self-regulated process

This study demonstrates that our previously reported polywraplex, a synthetic siRNA carrier consisting of a uni-molecular polyplex core of customizable size and a self-assembled tri-block copolymer envelop, may be constructed using dendrimers as the crosslinking junctions. Replacing the branched low molecular weight PEI with polyamidoamine (PAMAM) dendrimer in the zeta potential regulated polymerization resulted in the similar network structured cationic polymer with electron microscopically visible crosslinking junctions. This visibility may offer a convenient way to characterize the molecular structure of the rationally designed networked siRNA-packing cationic polymer without altering its chemical properties and biologic functions. A series of physical-chemical characterizations and biological assays, comprising size, zeta potential, pre-phagocytic siRNA leaking and degradation, and silencing of functional genes, confirmed that the advanced properties of polywraplexes remained with the dendrimer junctions. Although sixth generation PAMAM dendrimer was used as the crosslinking junctions in the size-customizable polymerization for electron microscopic observation, lower generation dendrimer should also work in case more practical and structurally defined cationic polymer is needed.