Block Copolymer Composition Research Articles

Effects of neat and silver coated fly ash cenospheres on the properties of styrene-butadiene-styrene block copolymer composites obtained by a solution mixing method

Utilization of industrial by-products to develop novel value-added materials while mitigating their environmental impact is a crucial issue. Fly ash (FA) microparticles are a common component of power plant waste. This work aims to investigate the impact of varying concentrations of neat/silver-coated FA on the morphology and thermal properties of styrene-butadiene-styrene/FA composites. Composite materials based on styrene-butadiene styrene triblock copolymer (SBS) with various volume fractions of as-received and silver-coated FA were prepared using a solution mixing method. Silver-coated cenosphere particles were prepared using an electroless plating method. Scanning electron microscopy and optical microscopy showed that the solution mixing method obtains composite materials characterized by uniform dispersion of filler without large particle aggregates and predominantly unbroken cenospheres. The tensile strength of the composite with 10% of both as-received and silver-coated fly ash remains at the level of the unfilled SBS sample. However, at higher filler concentrations (20% and 30%), a decrease in strength by 27% and 42% respectively is observed, possibly due to the agglomeration of FA, which leads to a poorer interface and dispersion at higher filler weights. Additionally, thermal analysis in an oxygen atmosphere showed that the introduction of both as-received and metallized cenospheres in the same quantity increased the thermal stability of the tested composition. The temperatures at 5% mass loss of SBS/FA composites were on average 70°C higher than those of the original SBS.

Electrical Double-Layer Transistors Comprising Block Copolymer Electrolytes for Low-Power-Consumption Photodetectors.

Electrical double-layer transistors (EDLTs) have received extensive research attention owing to their exciting advantages of low working voltage, high biocompatibility, and sensitive interfacial properties in ultrasensitive portable sensing applications. Therefore, it is of great interest to reduce photodetectors' operating voltage and power consumption by utilizing photo-EDLT. In this study, a series of block copolymers (BCPs) of poly(4-vinylpyridine)-block-poly(ethylene oxide) (P4VP-b-PEO) with different compositions were applied to formulate polyelectrolyte with indigo carmine salt in EDLT. Accordingly, PEO conduces ion conduction in the BCP electrolyte and enhances the carrier transport capability in the semiconducting channel; P4VP boosts the photocurrent by providing charge-trapping sites during light illumination. In addition, the severe aggregation of PEO is mitigated by forming a BCP structure with P4VP, enhancing the stability and photoresponse of the photo-EDLT. By optimizing the BCP composition, EDLT comprising P4VP16k-b-PEO5k and indigo carmine provides the highest specific detectivity of 2.1 × 107 Jones, along with ultralow power consumptions of 0.59 nW under 450 nm light illumination and 0.32 pW under dark state. The results indicate that photo-EDLT comprising the BCP electrolyte is a practical approach to reducing phototransistors' operating voltage and power consumption.

Effect of Thermo- and pH-Sensitive Block Copolymer Structure and Composition on the Synthesis and Stabilization of Gold Nanoparticles.

Homopolymers of poly[N-(2-(diethylamino)ethyl) acrylamide] exhibit the ability to adsorb onto the surface of preformed or growing gold nanoparticles. The resulting hybrid materials possess a pH and thermo-sensitive nature. Consequently, their optical properties can be modulated by manipulating either the temperature or the pH. Moreover, introducing monomers based on poly(N-isopropyl acrylamide) into block or random statistical polymers enables further modulation of the thermosensitive properties. These copolymers, employed for the in-situ synthesis and/or stabilization of gold nanoparticles, lead to hybrid materials whose properties and/or particle size depend on the polymer composition and microstructure: statistical polymers emerge as superior stabilizing agents compared to their block counterparts at a constant composition.

Polymersomes as the Next Attractive Generation of Drug Delivery Systems: Definition, Synthesis and Applications.

Polymersomes are artificial nanoparticles formed by the self-assembly process of amphiphilic block copolymers composed of hydrophobic and hydrophilic blocks. They can encapsulate hydrophilic molecules in the aqueous core and hydrophobic molecules within the membrane. The composition of block copolymers can be tuned, enabling control of characteristics and properties of formed polymersomes and, thus, their application in areas such as drug delivery, diagnostics, or bioimaging. The preparation methods of polymersomes can also impact their characteristics and the preservation of the encapsulated drugs. Many methods have been described, including direct hydration, thin film hydration, electroporation, the pH-switch method, solvent shift method, single and double emulsion method, flash nanoprecipitation, and microfluidic synthesis. Considering polymersome structure and composition, there are several types of polymersomes including theranostic polymersomes, polymersomes decorated with targeting ligands for selective delivery, stimuli-responsive polymersomes, or porous polymersomes with multiple promising applications. Due to the shortcomings related to the stability, efficacy, and safety of some therapeutics in the human body, polymersomes as drug delivery systems have been good candidates to improve the quality of therapies against a wide range of diseases, including cancer. Chemotherapy and immunotherapy can be improved by using polymersomes to deliver the drugs, protecting and directing them to the exact site of action. Moreover, this approach is also promising for targeted delivery of biologics since they represent a class of drugs with poor stability and high susceptibility to in vivo clearance. However, the lack of a well-defined regulatory plan for polymersome formulations has hampered their follow-up to clinical trials and subsequent market entry.

Soft optical materials based on the integration of perovskite nanostructures and block copolymers.

Metal halide perovskites and their nanostructures have efficient optical absorption and emission in the visible range with high external quantum efficiency. They have been at the forefront of next-generation photovoltaics and optoelectronics applications. But several intrinsic limitations of perovskites including low stability and incompatibility with lithography-based patterning constrains their broader applications. In recent years, the integration of perovskites with polymers especially multifunctional block copolymers (BCPs) has provided a new approach to overcome those issues. The chemical composition and chain architecture of BCPs are critical for achieving synergistic effects with perovskites in their hybrid systems. In this Highlight review article, we provide an overview and critical summary of the recent progress in the creation of perovskite-BCP hybrid structures, with a focus on the different roles of BCPs. The major categories include: (i) BCPs act as the nanopattern template for the spatial control and patterning of perovskite; (ii) BCP micelles or stars act as the template for perovskite nanostructure crystallization; (iii) BCPs act as the macromolecular ligands for perovskite NCs during its solution synthesis; (iv) BCP encapsulation of perovskite NCs into hierarchical composite particles; and (v) BCP incorporation into bulk perovskite and forming bulk composite films. The applications of perovskite-BCP hybrid structures in various fields and the major current challenges are also identified and discussed.

Emergent structures in active block copolymer composites.

Block copolymer melts offer unique templates to control the position and alignment of nanoparticles due to their ability to self-assemble into periodic ordered structures. Active particles are shown to coassemble with block copolymers leading to emergent organized structures. The block copolymer acts as a soft template that can control the self-propulsion of active particles, both for interface-segregated and selective nanoparticles. At moderate activities, active particles can form organized structures such as polarized trains or rotating vortices. At high activity, the contrast in the polymeric and colloidal timescales can lead to particle swarms with distorted block copolymer morphology, due to the competition between polymeric self-assembly and active Brownian self-propulsion.

Improving damage resistance of solid-state battery cathodes with block copolymers: A non-linear diffusion-mechanics study at the microscale

Minimizing interfacial failure in the composite cathode remains a crucial challenge to unravel the full potential of all solid-state batteries (ASSBs). Polymer-based ASSBs offer promising means of minimizing those damage effects due to their high ductility. However, multicomponent polymers such as block copolymers (BCPs) are needed to meet requirements for both ionic conductivity and mechanical resistance. This study aims to provide a new insight into the combined effects of block copolymer composition (soft-to-hard phase ratio) and interfacial strength on the coupled diffusion-mechanics response of an ASSB cathode, achieved by proposing a non-linear computational micromechanics approach. The approach combines a pressure-dependent diffusion process, interfacial gap-dependent diffusivity, and advanced elasto-viscoplastic constitutive model for a BCP, and it is implemented numerically within a non-linear finite element framework. Two cathode design concepts are explored here, with and without the BCP coating. Results from these case studies suggest that there is a strong interplay between the interface strength (between active particles and the BCP matrix), the BCP material composition, and the interfacial diffusivity. It is found that interfacial damage can be minimized by increasing both the interfacial strength and the amount of the soft component in the BCP system. If the diffusivity across the interface is damage-dependent, the latter is reduced when the BCP is predominantly made of the hard phase. Ultimately, a simple sensitivity analysis reveals that interfacial strength plays a vital role in minimizing interfacial damage, while the coating thickness is the least influential design parameter.

Crystallization, structure and properties of PP-b-PE block copolymer

In recent years, a commercialized polypropylene (PP) and polyethylene (PE) block copolymer has been synthesized using chain-shuttling polymerization, but its molecular structure and properties are still limitedly understood. In this work, we analyzed the chain composition, mechanical properties, and structural transformations occurring during the deformation of commercial PP-PE block copolymer obtained via chain-shuttle technology. The chain composition and crystallization properties of PP-PE block copolymers obtained by chain shuttling technique were analyzed using nuclear magnetic resonance (NMR), temperature-rising elution fractionation (TREF), and differential scanning calorimetry (DSC) techniques. The sample has a mass ratio of 49:51 of PE chains to PP chains, but the crystallinity of the two components differs significantly. The PP displays limited crystallinity, indicating short PP chain segments. Some PE sequences are incorporated into the PP matrix as random copolymers, resulting in elastomeric behavior. We investigated the In-situ structural changes of crystals during stretching using synchrotron radiation 2D X-ray diffraction/scattering. In the elastic deformation region, the strain has a significant influence on the orientation of PE crystals but has little effect on the orientation of PP crystals. After the yield point, the strain-induced PE crystal failure resulting in a decrease in stress. In the strain hardening region, the orientation of PE induces recrystallization, forming a layered structure with tensile orientation. At the same time, the PP crystals are disoriented under the action of strain until they break. The results from this work provide significant insight into the design of PP-PE block copolymer products to meet the performance requirements needed for engineering applications.

Effect of block ratios on self-assembly morphologies of poly(ε-caprolactone)-block-poly(tert-butyl acrylate) block copolymer

Crystalline-coil block copolymer compositions, determined by block ratios, play a vital role in the construction of different self-assembly morphologies. Here, we synthesized a series of crystalline-coil block copolymers with different block ratios, namely poly (ε-caprolactone)-block-poly (tert-butyl acrylate) (PCL-b-PtBA), to explore the impact of polymer compositions on self-assembly morphologies via crystallization-driven self-assembly (CDSA). It was found that the PCL-b-PtBA can self-assemble into various morphologies including lozenges, quadrilaterals, elongated hexagons, hexagonal platelets, saw blade platelets and spindle micelles. Additionally, transmission electron microscopes (TEM) imaging indicated a gradual morphological transformation from quadrilateral to lozenge platelets, and then to elongated-hexagon platelets with high aspect ratios as the sampling time was prolonged. We hypothesize that variations in polymer composition lead to changes in the self-assembly morphology primarily due to differences in the reduced tethering density of PtBA segments with varying chain lengths, which subsequently impacts the crystallization of PCL. Our work reveals that adjusting block ratios of the PCL-contained block copolymer for self-assembly is a facile way to construct diverse morphologies of polymer materials, and the corresponding materials may have potential applications in fields such as drug delivery, antibacterial treatments and other fields.

3D Printing Hierarchically Nano-Ordered Structures.

Natural materials are composed of a limited number of molecular building blocks and their exceptional properties are governed by their hierarchical structure. However, this level of precision is unattainable with current state-of-the-art materials for 3D printing. Herein, new self-assembled printable materials based on block copolymers (BCPs) enabling precise control of the nanostructure in 3D are presented. In particular, well-defined BCPs consisting of poly(styrene) (PS) and a polymethacrylate-based copolymer decorated with printable units are selected as suitable self-assembled materials and synthesized using controlled radical polymerization. The synthesized library of BCPs are utilized as printable formulations for the fabrication of complex 3D microstructures using two-photon laser printing. By fine-tuning the BCP composition and solvent in the formulations, the fabrication of precise 3D nano-ordered structures is demonstrated for the first time. A key point of this work is the achievement of controlled nano-order within the entire 3D structures. Thus, imaging of the cross-sections of the 3D printed samples is performed, enabling the visualization also from the inside. The presented versatile approach is expected to create new avenues for the precise design of functional polymer materials suitable for high-resolution 3D printing exhibiting tailor-made nanostructures.

Thermo‐Responsive Ultrafiltration Block Copolymer Membranes Based on Polystyrene‐block‐poly(diethyl acrylamide)

AbstractWithin the present work, a thermo‐responsive ultrafiltration membrane is manufactured based on a polystyrene‐block‐poly(diethyl acrylamide) block copolymer (BCP). The poly(diethyl acrylamide) block segment features a lower critical solution temperature (LCST) in water, similar to the well‐known poly(N‐isopropylacrylamide), but having increased biocompatibility and without exhibiting a hysteresis of the thermally induced switching behavior. The BCP is synthesized via sequential “living” anionic polymerization protocols and analyzed by 1H‐NMR spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The resulting morphology in the bulk state is investigated by transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS) revealing the intended hexagonal cylindrical morphology. The BCPs form micelles in a binary mixture of tetrahydrofuran and dimethylformamide, where BCP composition and solvent affinities are discussed in light of the expected structure of these micelles and the resulting BCP membrane formation. The membranes are manufactured using the non‐solvent induced phase separation (NIPS) process and are characterized via scanning electron microscopy (SEM) and water permeation measurements. The latter are carried out at room temperature and at 50 °C revealing up to a 23‐fold increase of the permeance, when crossing the LCST of the poly(diethyl acrylamide) block segment in water.

Cycling of block copolymer composites with lithium-conducting ceramic nanoparticles.

Solid polymer and perovskite-type ceramic electrolytes have both shown promise in advancing solid-state lithium metal batteries. Despite their favorable interfacial stability against lithium metal, polymer electrolytes face issues due to their low ionic conductivity and poor mechanical strength. Highly conductive and mechanically robust ceramics, on the other hand, cannot physically remain in contact with redox-active particles that expand and contract during charge-discharge cycles unless excessive pressures are used. To overcome the disadvantages of each material, polymer-ceramic composites can be formed; however, depletion interactions will always lead to aggregation of the ceramic particles if a homopolymer above its melting temperature is used. In this study, we incorporate Li0.33La0.56TiO3 (LLTO) nanoparticles into a block copolymer, polystyrene-b-poly (ethylene oxide) (SEO), to develop a polymer-composite electrolyte (SEO-LLTO). TEMs of the same nanoparticles in polyethylene oxide (PEO) show highly aggregated particles whereas a significant fraction of the nanoparticles are dispersed within the PEO-rich lamellae of the SEO-LLTO electrolyte. We use synchrotron hard x-ray microtomography to study the cell failure and interfacial stability of SEO-LLTO in cycled lithium-lithium symmetric cells. Three-dimensional tomograms reveal the formation of large globular lithium structures in the vicinity of the LLTO aggregates. Encasing the SEO-LLTO between layers of SEO to form a "sandwich" electrolyte, we prevent direct contact of LLTO with lithium metal, which allows for the passage of seven-fold higher current densities without signatures of lithium deposition around LLTO. We posit that eliminating particle clustering and direct contact of LLTO and lithium metal through dry processing techniques is crucial to enabling composite electrolytes.

Effect of SIS block copolymers on damping properties of natural rubber/AO-80 and the performance enhancement mechanism: experimental study and molecular dynamics simulation

Natural rubber/blocked phenol/styrene-isoprene block copolymer (NR/AO-80/SIS) composites were prepared by using hindered phenolic polar small molecules (AO-80) and styrene isoprene block copolymer (SIS) as damping performance-enhancing components and (NR) as rubber substrate to overcome the problems of narrow effective damping temperature range, unsatisfactory damping effect and subpar mechanical properties in NR/AO-80 rubber applications.The effects of SIS and AO-80 on the morphology, structure, mechanical properties, aging resistance, and damping properties of the NR/AO-80/SIS composite were investigated. Molecular dynamics simulations (MD) were employed to investigate the intermolecular forces, and interaction mechanisms of the rubber composites. SIS exhibited compatibility with the NR/AO-80 matrix and can significantly enhanced the mechanical, aging, and damping properties of the NR/AO-80 matrix. The effective damping temperature range can be extended to a maximum of 114.5 °C, demonstrating its notable improvement to the damping performance of NR/AO-80. The primary mechanisms of enhancing damping performance involve the more van der Waals forces, electrostatic interactions in NR/AO-80/SIS composites,which is beneficial for increasing the internal friction of rubber and improving the damping performance of NR/AO-80 /SIS.

Controlling Morphological Transitions of Polymeric Nanoparticles via Doubly Responsive Block Copolymers

We report on a dual-responsive block copolymer system that exhibits a pH-dependent cloud point (Tcp) and allows for precise control over the size and morphology of self-assembled nanostructures. By incorporating 2-(dimethylamino)ethyl methacrylate (DMAEMA), a pH- and temperature-responsive monomer, within the corona of a nanoparticle, the relative hydrophilic/hydrophobic block volumes can be controlled. Capitalizing on this phenomenon, we explore the temperature response of block copolymer assemblies at acidic, neutral, and basic pH, where the DMAEMA units are 99, 60, and 2% protonated. In general, as pH decreases, the corona was observed to swell due to charge repulsion and increased hydration, attenuating temperature sensitivity. By systematically varying the pH, temperature, and content of DMAEMA, we develop several systems that can readily form micelles, worms, and vesicles from a single block copolymer composition.

Synthesis and microphase separation of dendrimer-like block copolymers by anionic polymerization strategies

Anionic polymerization for the preparation of polystyrene-b-polybutadiene is well-established and leads to thermoplastic elastomers on industrial scale. The classical ABA block copolymer (BCP) architecture and composition usually forms a cylindrical morphology in the bulk state. Their anisotropic mechanical properties are, however, unfavorable for many applications. The gyroid microphase is entirely isotropic, but it is only formed in a narrow compositional area of around 35 vol% of the minority polymer block. In the present study, a second-generation dendrimer-like block copolymer structure ((AB)2B)3 is described. This BCP architecture is expected to show a higher curvature on the microphase boundaries, which leads to a larger morphological range for the gyroid phase. Three compositionally different polymers are synthesized by living anionic polymerization strategies and the resulting morphology is analyzed via transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The dendrimer-like BCPs are compared to their less branched analogues, namely the asymmetric star polymers and H-shape stars. The expected influence of the dendrimer-like BCP architecture on the microphase separation is investigated paving the way to a promising synthetic platform for interesting mechanical and optical properties.

Encapsulation of phenylacetic acid in block copolymer nanoparticles during polymerization induced self‐assembly

AbstractPolymerization induced self‐assembly (PISA) is an in situ method for producing block copolymer nanoparticles. Performing PISA in the presence of a pharmaceutical drug causes the nanoparticles to encapsulate the drug. While this approach is straightforward, the effects of drug loading and block copolymer composition remain unclear. Here, we investigate encapsulation of the drug phenylacetic acid (PA) in poly(glycerol monomethacrylate)‐block‐poly(2‐hydroxypropyl methacrylate) (PGMA‐PHPMA) nanoparticles during PISA. Nanoparticle morphology is characterized by electron microscopy and light scattering, while encapsulation efficiency () is quantified using nuclear magnetic resonance diffusometry. Increasing the PA loading shifts the nanoparticle morphology from spherical micelles cylindrical micelles vesicles. At a 32 mg/ml PA loading, maximizes at ~80%. Increasing the PHPMA degree of polymerization minimally impacts . The invariance of toward core block length suggests that PA binds to the nanoparticle corona, highlighting the importance of the hydrophilic block for drug encapsulation during PISA.

Sustainable, Alternative Conductive Fillers for Flexible Electronics: Investigation of Filler Size on Morphological and Electrical Properties of Styrene-[Ethylene-(Ethylene-Propylene)]-Styrene Block Copolymer (SEEPS) Composites

Sustainability is getting popular for many engineering applications from packaging to textiles, energy to electronics. Since renewable, environmental friendly sources lowers the negative impacts of the end product on ecology, sustainability studies generally start with the raw materials. The sustainability of electronic materials has gained importance because of limited amount of resources and increasing costs as well as environmental restrictions. In this study, pistachio shell waste was used to synthesize conductive fillers for the fabrication of sustainable flexible electronics. Pistachio shell waste was carbonized. After carbonization, two different grounding settings were used to obtain different filler sizes. In order to compare the effects of filler size on electrical and morphological properties of the composites, six different samples were prepared based on filler concentration with styrene-[ethylene-(ethylene-propylene)]-styrene block copolymer. Homogeneous filler distribution and good filler-matrix interface were observed for both composite sets. Filler size was found significant in terms of the electrical conductivity of the composites. For larger fillers, the percolation region was found to shift to lower concentration compared to smaller filler size.

An efficient thermal interface material with anisotropy orientation and high through-plane thermal conductivity

The rapid development of integrated circuits and electronic devices with increased power density and heat flux, requires effective heat dissipation for thermal management. Constructing a directional thermal pathway from the vertically aligned thermal conductive fillers in the thickness-direction of polymer-based thermal interface materials (TIMs) is a desirable strategy to form materials with high thermal conductivity. However, due to the complexity of vertical orientation technology, fillers with the poor orientation degree weaken the enhancement of through-plane thermal conductivity. In this work, we prepared short carbon fiber (CF)/olefin block copolymer (OBC) composites with high orientation degree via the melting extrusion method on a basis of sharing force induce alignment. Attributed to the high orientation degree of CF in the vertical direction, the as-prepared material shows a through-plane thermal conductivity (κ⊥) up to 15.06 W/m K at a 30 vol% CF content, which is ∼10 times that of a parallel structure. The operating temperature difference between vertical and random reached 35.2 °C, surpassing the characters in most works of literature. This study provides an effective way to develop high-oriented degree and electrical insulation polymer composites with superior κ⊥ for scalable thermal management applications in electronic devices.

In Situ Hydrolysis of Block Copolymers at the Water‐Oil Interface

In situ manipulation of the chemical composition of block copolymers at the fluid interfaces affords a route by which the interfacial tension, the packing of the copolymers, and the penetration of the blocks into the two liquids can be manipulated. Here, a series of linear block copolymers of poly(solketal methacrylate- b -styrene) (PSM- b -PS) are used, converting hydrophobic PSM block into a hydrophilic glycerol monomethacrylate (GM) block, that results in a marked decrease in the liquid-liquid interfacial tension. The kinetics of the first-order hydrolysis reaction was analyzed by monitoring the time-dependent interfacial tension as a function of pH, polymer concentration, molecular weight, and composition. Fluorescence recovery after photobleaching (FRAP) was used to measure the in-plane dynamics of the copolymers before and after hydrolysis. Overall, this work provides insight into a quantitative pathway by which in situ interfacial reactions may be performed and monitored in real time, with complete alteration of the interfacial activity of the molecule.

In Situ Hydrolysis of Block Copolymers at the Water‐Oil Interface

AbstractIn situ manipulation of the chemical composition of block copolymers at the fluid interfaces affords a route by which the interfacial tension, the packing of the copolymers, and the penetration of the blocks into the two liquids can be controlled. Here, a series of linear block copolymers of poly(solketal methacrylate‐b‐styrene) (PSM‐b‐PS) are used, converting hydrophobic PSM block into a hydrophilic glycerol monomethacrylate (GM) block, that results in a marked decrease in the liquid‐liquid interfacial tension. The kinetics of the first‐order hydrolysis reaction was analyzed by monitoring the time‐dependent interfacial tension as a function of pH, polymer concentration, molecular weight, and composition. Fluorescence recovery after photobleaching (FRAP) was used to measure the in‐plane dynamics of the copolymers before and after hydrolysis. This work provides insights into a quantitative pathway by which in situ interfacial reactions may be performed and monitored in real time, completely changing the interfacial activity of the molecule.