Block Copolymer Nanostructures Research Articles

SEPS functionalized PEG copolymer for improved toughness without obvious plasticization in epoxy resin

AbstractThe effects of grafting level of polyethylene glycol (PEG) grafted styrene ethylene propylene styrene (SEPS) on the intrinsic brittleness of epoxy thermosets were studied. The SEPS‐g‐PEG block copolymer (BCP) was synthesized by grafting various grafting degree of PEG (i.e., 10%, 20%, 30%, and 40%) on polystyrene (PS) blocks of SEPS following Williamson ether synthesis method. A total of 10 wt% of the BCP modifiers were dispersed in epoxy thermosets. PEG side chains were miscible in the epoxy which formed a uniform BCP dispersion within the epoxy thermoset matrix. As the degree of PEG grafting was increased, the BCP phase was absorbed in the epoxy matrix. This absorption occurred because the increase in PEG grafting provided more miscible PEG chains to bind the BCP and epoxy nanostructures together. The differential scanning calorimeter and dynamic mechanical thermal analysis analyses indicated that BCP toughened epoxy exhibited an improved glass transition temperature (Tg). At a 40% PEG grafting degree in the BCP, the critical stress intensity factor (KIC) and critical strain energy release rate (GIC) increased up to 80% and 180%, respectively. This trend suggested that the energy associated with fractures could be absorbed through the deformation of the softer phases when a load was applied to them.

Photoresponsive Block Copolymer Nanostructures through Implementation of Arylazopyrazoles.

Responsive nanomaterials that can undergo reversible changes in morphology are interesting for the development of functional materials that interact with and respond to their environment. Amphiphilic block copolymers are well-known for their ability to create a wide range of supramolecular nanostructures in solution. Arylazopyrazoles (AAPs) are versatile molecular photoswitches, which change their configuration and hydrophobicity upon irradiation with UV light (365 nm, Z isomer, less hydrophobic) and green light (520 nm, E isomer, more hydrophobic). In this work, photoswitchable block copolymers containing arylazopyrazole tetraethylene glycol methacrylate (AAPMA) and oligo(ethylene glycol) methacrylate (OEGMA) forming amphiphilic POEGMA-b-PAAPMA with varying block lengths are prepared by RAFT polymerization. The photochemical properties of AAP persist in the polymers. Due to their amphiphilic structure, the polymers self-assemble into supramolecular morphologies in water. Remarkably, photoisomerization results in a reversible change in the self-assembly behavior. Specifically, spherical and cylindrical micelles are observed for POEGMA33-b-PAAPMA47 when illuminated with green or UV light during assembly. Furthermore, the morphology of assembled structures can be reversibly switched by subsequent irradiation with UV and green light.

Lithium iodide transport in double gyroid nanochannels formed by zwitterion‐containing solid polymer electrolytes

AbstractThe fabrication of nanostructured block copolymer (BCP) films endowed with lithium ion‐conducting gyroid (GYR) nanochannels is an appealing solution to build solid polymer electrolytes (SPEs) that combines high ionic conductivity (IC) with suitable mechanical properties. However, the formation of a well‐developed GYR structure remains challenging to achieve from the self‐assembly of polyelectrolyte BCP chains. To overcome this issue, large ion conducting gyroid grains were produced within freestanding polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐b‐P2VP‐b‐PEO) films by combining a solvent vapor annealing (SVA) treatment with an infiltration process. Here, the SVA treatment enabled the manufacture of SPEs entirely composed of a GYR structure while the infiltration process allowed for the incorporation of an appropriate Li salt (i.e., lithium iodoacetate, LiIAc) within the 3D‐interconected nanochannels via a Menshutkin reaction. By using this SVA‐Infiltration strategy, it has been demonstrated that the creation of ion conducting GYR nanochannels enhances the ion transportation capacity of pyridine‐containing SPEs since substantially lower ICs were measured from analog PS‐b‐P2VP‐b‐PEO/LiIAc films having a nominally disordered as‐cast state. Remarkably, zwitterionic pyridinium‐based moieties formed inside the interpenetrated nanochannels enable an efficient migration of Li+ and I3− species, leading to an IC as high as 10−4 S cm−1 at 70°C.

Stimuli-Responsive Control over Self-Assembled Nanostructures in Sequence-Specific Functional Block Copolymers.

The precise sequence of a protein's primary structure is essential in determining its folding pathways. To emulate the complexity of these biomolecules, functional block copolymers consisting of segmented triblocks with distinct functionalities positioned in a sequence-specific manner are designed to control the polymer chain compaction. Triblock polymers P- b -C- b -F and P- b -F- b -C and random diblock copolymer P- b -C- r -F consist of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block with coumarin (C) and ferrocene (F) moieties that are grafted in a sequence-specific or random manner onto the hydrophilic block. External stimuli such as UVB light, redox, and chemical cues influence the functional hydrophobic block to alter the packing parameters that are monitored with spectroscopic and scattering techniques. Interestingly, the positioning of the stimuli-responsive moiety within the hydrophobic block of P- b -C- b -F, P- b -F- b -C, and P- b -C- r -F affects the extent of the hydrophobic-hydrophilic balance in block copolymers that renders orthogonal control in stimuli-responsive transformation of self-assembled vesicles to micelles.

Toughening epoxy by nano-structured block copolymer to mitigate matrix microcracking of carbon fibre composites at cryogenic temperatures

The incorporation of rigid nanoparticles has proven to enhance microcracking resistance in carbon fibre reinforced polymer (CFRP) composites at cryogenic temperatures, enabling CFRP tanks to store cryogenic liquid like hydrogen without requiring liners. Herein, we investigate efficacy of low-modulus soft nanoparticles in addressing the microcracking challenges inherent in CFRP at cryogenic temperatures. By incorporating a tri-block copolymer (BCP) into an epoxy, nano-structured fillers with an average diameter of approximately 100 nm are formed. Experimental results reveal that, at a 2.5 wt% loading, the BCP significantly increase the fracture energy of the nanocomposite by 392% at −196 °C while maintaining stiffness and strength. More importantly, composite laminates made with the BCP-modified nanocomposite matrix can withstand cryogenic temperatures without matrix microcracking, even when they contain multiple plies with the same orientation, such as [04/904]s, which are known to be highly susceptible to matrix microcracking at cryogenic temperatures. An advanced high-fidelity micromechanical model revealed that the observed toughening effect of nanostructured block copolymer at cryogenic temperatures can be attributed to the increased fracture resistance of the nanocomposite matrix. The findings of this research demonstrate that low concentration of block copolymer can effectively mitigate the initiation and propagation of matrix microcracks in carbon fibre composites at ultra-cold temperatures.

Exploration of complex nanostructures in block copolymers

The exploration of nanoscale morphologies with three-dimensional spatial arrangements in block copolymers involves the manipulation of compositional fluctuations at interfaces, induction of conformational asymmetry, and design of complex architectures. Despite the abundance of triply periodic minimal surfaces identified to date, the experimental demonstration of thermodynamically stable complex nanostructures with high-packing frustration remains limited. This research update focuses on the importance of molecular interactions for stabilizing complex nanostructures and proposes the use of end-group chemistry as a versatile method for realizing thermodynamically stable network structures with high-packing frustration in simple linear diblock copolymers. The proposed approach substantially alters phase diagrams and reveals unprecedented network structures in block copolymers. Ongoing research has the potential to generate even more diverse and stable nanostructures, thereby advancing nanotechnology and expanding our understanding of polymers and materials science. Published by the American Physical Society 2024

Microscopic Origins of the Distinct Mechanical Response of ABA and ABC Block Copolymer Nanostructures.

It has been commonly believed that the ordered thermoplastic elastomers formed by the ABC triblock copolymer should have better mechanical performance than that by the ABA counterpart due to the higher bridging fraction. However, the thermoplastic elastomer of ABA was often observed to perform better than that of ABC. To compare the performance of two kinds of thermoplastic elastomers and unveil the underlying microscopic mechanism, we have calculated their stress-strain curves using coarse-grained molecular dynamics simulations in conjunction with self-consistent field theory. It is revealed that the stretching degree of the bridging blocks and the network connectivity play important roles in determining the mechanical properties in addition to the bridging fraction. The higher degree in the stretching of bridging blocks and network connectivity of the structure formed by the ABA triblock copolymer enables its superior mechanical performance over the ABC block copolymer.

Amphiphilic Block Copolymer Nanostructures as a Tunable Delivery Platform: Perspective and Framework for the Future Drug Product Development.

Nanoformulation of active payloads or pharmaceutical ingredients (APIs) has always been an area of interest to achieve targeted, sustained, and efficacious delivery. Various delivery platforms have been explored, but loading and delivery of APIs have been challenging because of the chemical and structural properties of these molecules. Polymersomes made from amphiphilic block copolymers (ABCPs) have shown enormous promise as a tunable API delivery platform and confer multifold advantages over lipid-based systems. For example, a COVID booster vaccine comprising polymersomes encapsulating spike protein (ACM-001) has recently completed a Phase I clinical trial and provides a case for developing safe drug products based on ABCP delivery platforms. However, several limitations need to be resolved before they can reach their full potential. In this Perspective, we would like to highlight such aspects requiring further development for translating an ABCP-based delivery platform from a proof of concept to a viable commercial product.

Ultrafast Xanthate‐Mediated Photoiniferter Polymerization‐Induced Self‐Assembly (PISA)

AbstractPolymerization‐induced self‐assembly (PISA) is a powerful technique for preparing block copolymer nanostructures. Recently, efforts have been focused on applying photochemistry to promote PISA due to the mild reaction conditions, low cost, and spatiotemporal control that light confers. Despite these advantages, chain‐end degradation and long reaction times can mar the efficacy of this process. Herein, we demonstrate the use of ultrafast photoiniferter PISA to produce polymeric nanostructures. By exploiting the rapid photolysis of xanthates, near‐quantitative monomer conversion can be achieved within five minutes to prepare micelles, worms, and vesicles at various core‐chain lengths, concentrations, or molar compositions.

Ultrafast Xanthate-Mediated Photoiniferter Polymerization-Induced Self-Assembly (PISA).

Polymerization-induced self-assembly (PISA) is a powerful technique for preparing block copolymer nanostructures. Recently, efforts have been focused on applying photochemistry to promote PISA due to the mild reaction conditions, low cost, and spatiotemporal control that light confers. Despite these advantages, chain-end degradation and long reaction times can mar the efficacy of this process. Herein, we demonstrate the use of ultrafast photoiniferter PISA to produce polymeric nanostructures. By exploiting the rapid photolysis of xanthates, near-quantitative monomer conversion can be achieved within five minutes to prepare micelles, worms, and vesicles at various core-chain lengths, concentrations, or molar compositions.

Directed self‐assembly of block copolymer thin films via momentary thickness gradients

AbstractIn this study, a novel method to fabricate highly aligned lamellar nanostructures in a millimeter‐scale large area was demonstrated by directing the self‐assembly of block copolymer (BCP) thin films with a temporary thickness‐gradient micropattern via simple two‐step thermal annealing. In the first step of thermal annealing, the BCP nanostructure is latently guided by a phenomenon known as “geometric anchoring” for the area with a thickness gradient. The second annealing step causes thermal reflow of the height gradient micropattern with a sufficiently large curvature to flatten the micropattern. The shear stress generated by thermal reflow enlarged the grain of the BCP nanostructure, resulting in a highly aligned lamellar pattern over the entire area. Finally, the formation of periodic nanopatterns in large area was ensured by performing grazing‐incidence small‐angle x‐ray scattering. This innovative approach in directing the BCP self‐assembly promotes the fabrication of highly aligned nanostructures in large areas through cost‐effective and simple thermal imprinting method and designed two‐step heat treatment.

Nanostructured block copolymer single-ion conductors for low-temperature, high-voltage and fast charging lithium-metal batteries

Herein, a single-ion polymer electrolyte is reported for high-voltage and low-temperature lithium-metal batteries that enables suppressing the growth of dendrites, even at high current densities of 2 mA cm-2. The nanostructured electrolyte was introduced into the cell by mechanically processing the polymer powder via an easily scalable process. Important for the potential application in commercial battery cells is the finding that it does not induce aluminum corrosion at high voltages and leads to low interfacial resistance with lithium metal. These beneficial characteristics, in combination with its high single-ion conductivity and its high anodic stability, allow for the stable cycling of state-of-the-art lithium-ion cathodes, such as NMC111 and NMC622, in combination with a lithium metal anode at 20 °C and even 0 °C for several hundred cycles.

Interfacial Engineering of Block Copolymer Nanostructures: Morphology and Solvent Stability.

Interfacial engineering is a critical pathway for modulating the self-assembled nanostructures of block copolymers (BCPs) during solvent exchange. Herein, we demonstrated the generation of different stacked lamellae of polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) nanostructures during solvent exchange by using phosphotungstic acid (PTA) or PTA/NaCl aqueous solution as the nonsolvent. The participation of PTA in the confined microphase separation of PS-b-P2VP in droplets increases the volume fraction of P2VP and decreases the tension at the oil/water interface. Moreover, the addition of NaCl to the PTA solution can further increase the surface coverage of P2VP/PTA on droplets. All factors impact the morphology of assembled BCP nanostructures. In the presence of PTA, ellipsoidal particles composed of alternatively stacked lamellae of PS and P2VP were formed (named BP), whereas, in the coexistence of PTA and NaCl, they changed to stacked disks with PS-core-P2VP-shell (called BPN). The different structures of assembled particles induce their different stabilities in solvents and different dissociation conditions as well. The dissociation of BP particles was easy because PS chains were only entangled together which can be swollen in toluene or chloroform. However, the dissociation of BPN was hard, requiring an organic base in hot ethanol. The structural difference in BP and BPN particles further extended to their dissociated disks, which makes the cargo (like R6G) loaded on these disks to show a different stability in acetone. This study demonstrated that a subtle structural change can greatly affect their properties.

Utilizing in-situ construction of tailored block copolymer nanostructures to enhance CF/epoxy composites compressive properties

The imbalance in the compressive strength to tensile strength ratio of carbon fiber reinforced polymer (CFRP) composites is a key factor that limits its lightweight application. Increasing the tenacity and strength of resin matrix has been evidenced as an effective method to address this problem. In this work, an interesting strategy that block copolymer nanostructures built in-situ in epoxy to simultaneously increase its tensile strength and fracture toughness, is provided. Benefitting from the nanostructures, the tensile strength and fracture toughness of epoxy matrix are increased by 19% and 236%, respectively, without lowering its Tg. Block copolymers’ impact on the morphologies and transformation of nanostructures, the relationship between nanostructures and epoxy properties, and the strengthening and toughening mechanism are systematically studied. Meanwhile, these epoxy resins with excellent tensile properties and toughness are selected for the verification of the CFRP composite performance. The compression properties and interfacial properties of CFRP composites were 34.5% and 17.8% improved, demonstrating that in-situ constructing nanostructures in resin matrix is an effective strategy to enhance the compressive and interfacial properties of composites. Our research is anticipated to offer some fresh suggestions for creating high-performance CFRP composites.

Block copolymer particles with tunable and robust internal nanostructures by combining hydrogen-bonding and crosslinking

Nanostructured block copolymer (BCP) particles are attractive due to their ordered internal structures, unique shape and surface patterns; however, their structural integrity can be easily lost because of weak intermolecular interactions, which limits their practical applications. In this study, we present a simple and reliable method to fabricate nanostructured particles of polystyrene-block-poly(4-vinylpyridine) with tunable and robust nanostructures by employing hydrogen-bonding and cross-linking strategies. The key feature of poly(4-vinylpyridine) is the presence of reactive pyridyl moieties, which allow precise regulation of internal nanostructures via hydrogen bonds and locking of the structural integrity via quaternarization by feeding hydrogen bond donors and cross-linkers, respectively. The solvent resistance is well proven by immersing the particles in either selective solvents of the continuous phase or good solvent of the BCP. Furthermore, mesoporous BCP particles derived from the cross-linked particles are obtained simply by a swelling/deswelling treatment. This study provides a way to improve the structural robustness of BCP particles and could be a key step that advances the functionalization and subsequent applications of such nanostructured BCP colloidal particles.

Phase‐Purified Ruddlesden–Popper Perovskites Vertically Oriented in Block Copolymer Nanostructures for Environmentally Stable Light Conversion and Charge Trapping

Abstract2D Ruddlesden–Popper perovskites (RPPs) with 2D layer‐tunable optoelectronic properties suffer from randomly oriented multiple phases. Herein, an efficient method for developing RPP films with controlled phase purity and crystal orientation via a one‐step synthesis of RPPs in a self‐assembled block copolymer (BCP) film is demonstrated. RPP crystals with a target phase <n = 2 or 3> are preferentially embedded in the poly(ethylene oxide) domains of a polystyrene‐block‐poly(ethylene oxide) nanostructured film. Interestingly, rapid self‐assembly with the BCP results in phase‐purified n = 2 and 3 targeted RPPs with a target phase percentage two and four times higher, respectively, than that of pristine RPP. Furthermore, RPP crystals synthesized within BCP are preferentially oriented with their b‐axis parallel to the surface normal. The photoluminescence of the composite film is significantly enhanced, allowing environmentally stable ultraviolet‐to‐blue color conversion. Moreover, semiconducting RPP crystals nanopatterned in the BCP are successfully used as charge‐trapping floating nanogates, resulting in a non‐volatile field‐effect transistor memory.

Direct Visualization of the Self-Alignment Process for Nanostructured Block Copolymer Thin Films by Transmission Electron Microscopy

Herein, this work aims to directly visualize the morphological evolution of the controlled self-assembly of star-block polystyrene-block-polydimethylsiloxane (PS-b-PDMS) thin films via in situ transmission electron microscopy (TEM) observations. With an environmental chip, possessing a built-in metal wire-based microheater fabricated by the microelectromechanical system (MEMS) technique, in situ TEM observations can be conducted under low-dose conditions to investigate the development of film-spanning perpendicular cylinders in the block copolymer (BCP) thin films via a self-alignment process. Owing to the free-standing condition, a symmetric condition of the BCP thin films can be formed for thermal annealing under vacuum with neutral air surface, whereas an asymmetric condition can be formed by an air plasma treatment on one side of the thin film that creates an end-capped neutral layer. A systematic comparison of the time-resolved self-alignment process in the symmetric and asymmetric conditions can be carried out, giving comprehensive insights for the self-alignment process via the nucleation and growth mechanism.

Trilayered Block Copolymer Nanostructures Formed by an Iterative Layering Strategy

AbstractNanostructured block copolymer (BCP) thin films enable the formation on‐demand of a variety of periodic patterns at the nanometer scale by tuning the macromolecular BCP characteristics and annealing processes. Significant progress in the control of the self‐assembly has been witnessed over the past decade with the implementation of robust directed self‐assembly methods. However, the self‐assembled structural patterns obtained at equilibrium are limited and methods to expand the range of structural configurations are required to harness additional functionalities. Here, this work demonstrates how polystyrene‐b‐poly(methyl methacrylate) BCP thin layers can be stacked to produce a library of complex 3D hierarchical heterostructures. In this iterative assembly process based on simple building bricks (i.e., immobilized BCP patterns forming Holes, Lines and Dots), the stacking configuration (i.e., self‐assembly and registration) of a BCP thin film is directed with respect to the previous layer using confinement effects and interfacial energy tuning. This responsive layering can lead to intricate 3D Al2O3 structures and opens the way to a broad variety of structural designs toward functional applications.

Polymorphism of self-assembled colloidal nanostructures of comblike and bottlebrush block copolymers

Polymorphism of self-assembled colloidal nanostructures of comblike and bottlebrush block copolymers

Effect of Polymer Composition and Morphology on Mechanochemical Activation in Nanostructured Triblock Copolymers.

The effect of composition and morphology on mechanochemical activation in nanostructured block copolymers was investigated in a series of poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA) triblock copolymers containing a force-responsive spiropyran unit in the center of the rubbery PnBA midblock. Triblock copolymers with identical PnBA midblocks and varying lengths of PMMA end-blocks were synthesized from a spiropyran-containing macroinitiatior via atom transfer radical polymerization, yielding polymers with volume fractions of PMMA ranging from 0.21 to 0.50. Characterization by transmission electron microscopy revealed that the polymers self-assembled into spherical and cylindrical nanostructures. Simultaneous tensile tests and optical measurements revealed that mechanochemical activation is strongly correlated to the chemical composition and morphologies of the triblock copolymers. As the glassy (PMMA) block content is increased, the overall activation increases, and the onset of activation occurs at lower strain but higher stress, which agrees with predictions from our previous computational work. These results suggest that the self-assembly of nanostructured morphologies can play an important role in controlling mechanochemical activation in polymeric materials and provide insights into how polymer composition and morphology impact molecular-scale force distributions.