Block Copolymer Blends Research Articles

Computational Phase Discovery in Block Polymers.

Self-consistent field theory (SCFT), the mean-field theory of polymer thermodynamics, is a powerful tool for understanding ordered state selection in block copolymer melts and blends. However, the nonlinear governing equations pose a significant challenge when SCFT is used for phase discovery because converging an SCFT solution typically requires an initial guess close to the self-consistent solution. This Viewpoint provides a concise overview of recent efforts where machine learning methods (particle swarm optimization, Bayesian optimization, and generative adversarial networks) have been used to make the first strides toward converting SCFT from a primarily explanatory tool into one that can be readily deployed for phase discovery.

Porous polylactide membranes with high piezo-catalytic efficiency for organic wastewater treatment

Piezo-catalysis has been emerged as a green and promising wastewater treatment technology for efficient removal of persistent organic pollutants (POPs), such as 4-nitrophenol (4-NP). However, it remains challenging to achieve advanced materials with combined advantages of high piezo-catalytic efficiency, good hydrophilicity, and environmental friendliness. In this work, highly crystalline porous polylactide (PLA) membranes possessing such exceptional advantages have been successfully prepared from biodegradable poly(L-lactide)/poly(D-lactide)/polyethylene glycol/polyoxyethylene-polyoxypropylene block copolymer (PLLA/PDLA/PEG/PEO-PPO-PEO) blends by melt processing and subsequent water etching. During the melt-processing, the two PLA enantiomers co-crystallize into stereocomplex (SC) crystals and simultaneously the PEG used as a porogen is expelled from the crystalline regions. The results show that the prepared PLA membranes have not only abundant micro-porous structures but also good hydrophilicity due to the preferential localization of PEO-PPO-PEO copolymer on the pore walls, thus giving rise to an extremely high water flux of 2400 L/m2h. More interestingly, the PLA membranes exhibit remarkable piezoelectric activity and the piezo-catalytic degradation efficiency of 4-NP can reach as high as 96 % under the triggering of water flow involved in vacuum filtration. In addition, the membranes show excellent reusability and the high catalytic efficiency can be well-maintained after five repeated uses. These findings suggest broad application prospects of our porous SC-PLA membranes in organic wastewater treatment.

Diverse Strategies to Develop Poly(ethylene glycol)-Polyester Thermogels for Modulating the Release of Antibodies.

In this work, we present basic research on developing thermogel carriers containing high amounts of model antibody immunoglobulin G (IgG) with potential use as injectable molecules. The quantities of IgG loaded into the gel were varied to evaluate the possibility of tuning the dose release. The gel materials were based on blends of thermoresponsive and degradable ABA-type block copolymers composed of poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) or poly(lactide-co-caprolactone)-b-poly(ethylene glycol)-b-(lactide-co-caprolactone) (PLCL-PEG-PLCL). Primarily, the gels with various amounts of IgG were obtained via thermogelation, where the only factor inducing gel formation was the change in temperature. Next, to control the gels' mechanical properties, degradation rate, and the extent of antibody release, we have tested two approaches. The first one involved the synergistic physical and chemical crosslinking of the copolymers. To achieve this, the hydroxyl groups located at the ends of the PLGA-PEG-PLGA chain were modified into acrylate groups. In this case, the thermogelation was accompanied by chemical crosslinking through the Michael addition reaction. Such an approach increased the dynamic mechanical properties of the gels and simultaneously prolonged their decomposition time. An alternative solution was to suspend crosslinked PEG-polyester nanoparticles loaded with IgG in a PLGA-PEG-PLGA gelling copolymer. We observed that loading IgG into thermogels lowered the gelation temperature (TGEL) value and increased the storage modulus of the gels, as compared with gels without IgG. The prepared gel materials were able to release the IgG from 8 up to 80 days, depending on the gel formulation and on the amount of loaded IgG. The results revealed that additional, chemical crosslinking of the thermogels and also suspension of particles in the polymer matrix substantially extended the duration of IgG release. With proper matching of the gel composition, environmental conditions, and the type and amount of active substances, antibody-containing thermogels can serve as effective IgG delivery materials.

The study on the micromechanical mechanism of PP/EPDM blends and PP/SEBS blends using atomic force microscopy-based nanomechanics

Using atomic force microscope-based nanomechanics to measure the micromechanical properties of different polymer blends, we found that the miscibility of the blend system affects the phase structure and micromechanical properties at the nanoscale, which further affects macroscopic mechanical properties of materials. In the immiscible polypropylene/ethylene propylene diene rubber blends, the microscopic phase structure is connected to the macroscopic mechanical properties of the material, since the microscopic modulus of elasticity of the phases remains constant even if the blend ratio is changed. On the other hand, in the partially miscible polypropylene/styrene-ethylene-butylene-styrene block copolymer blends, the macroscopic mechanical properties of the material are determined by the combination of the microscopic phase structure and the microscopic elastic modulus, because the microscopic elastic modulus of each phase changes with the blending ratio.

Synthesis of Self‐assembled Star/Linear Block Copolymer Blends via Aqueous RAFT Dispersion Polymerization

Comprehensive SummaryReversible addition‐fragmentation chain transfer (RAFT)‐mediated polymerization‐induced self‐assembly (PISA) of star block copolymer and linear block copolymer using a binary mixture of a star‐like macro‐RAFT agent and a linear macro‐RAFT agent is reported. With this formulation, star block copolymer and diblock copolymer were formed simultaneously to generate colloidally stable star/linear block copolymer assemblies. Size exclusion chromatography (SEC) analysis confirmed the presence of two types of polymers in the final samples. The molar ratio of the star‐like macro‐RAFT agent and the linear macro‐RAFT agent has a significant impact on the morphology of polymer assemblies. It was found that increasing the amount of star‐like macro‐RAFT agent facilitated the formation of higher‐order morphologies. Additionally, effects of other reaction parameters including the length/number of the arm of the star‐like macro‐RAFT agent, degree of polymer (DP), monomer concentration on the morphology of star/linear block copolymer assemblies were also investigated. We expect that this work will offer new possibilities for the scalable preparation of polymer assemblies with unique structures and functions.

Nanostructures and toughening mechanisms in lightly cross-linked all-methacrylate copolymer/functional block copolymer blends

Nanostructures and toughening mechanisms in lightly cross-linked all-methacrylate copolymer/functional block copolymer blends

Investigation of Crystallization, Morphology, and Mechanical Properties of Polypropylene/Polypropylene-Polyethylene Block Copolymer Blends.

Polyethylene (PE)-based elastomers are the ideal choice for enhancing the compatibility of polypropylene/polyethylene (PP/PE) blends and improving the mechanical properties of PP-based materials. However, the issue of blend systems lies in the interplay between the crystallization processes. Therefore, we investigated the crystallization behavior during the cooling process of a new generation of PP/PE block copolymers (PP-b-PE) and random polypropylene (PPR, a copolymer of propylene and a small amount of ethylene or an alpha-olefin) blends using in-situ X-ray diffraction/scattering and differential scanning calorimetry (DSC) techniques. We also conducted mechanical performance tests on PPR/PP-b-PE blends at room temperature and low temperature (-5 °C). The results indicate that during the cooling process, the PP phase of PP-b-PE will follow the PPR to crystallize in advance and form a eutectic mixture, thereby enhancing the compatibility of PP/PE. Moreover, the PPR/PP-b-PE blend will form stable β-(300) crystals with excellent mechanical properties. Due to the improved compatibility of PP/PE with PP-b-PE, PE crystals are dispersed within PP crystals, providing bonding that improves the toughness of PPR under the low stiffness failure conditions of PPR/PP-b-PE blends, thereby enhancing their impact performance at low and room temperatures. This research has great significance for both recycling waste plastics and enhancing the low-temperature toughness of PPR.

Rheological, morphological and solid-state viscoelastic properties of ethylene vinyl acetate copolymer/olefin block copolymer (EVA/OBC) blends

Rheological, morphological and solid-state viscoelastic properties of ethylene vinyl acetate copolymer/olefin block copolymer (EVA/OBC) blends

Phase Behavior of Binary Blends of Diblock Copolymers: Progress and Opportunities.

The phase behavior of binary blends of diblock copolymers has been examined extensively in the past decades. Experimental and theoretical studies have demonstrated that mixing two different block copolymers provides an efficient and versatile route to regulate their self-assembled morphologies. A good understanding of the principles governing the self-assembly of block copolymer blends has been obtained from the study of A1B1/A2B2 diblock copolymer blends. The second (A2B2) diblocks could act synergistically as fillers and cosurfactants to regulate the domain size and interfacial properties, resulting in the formation of ordered phases not found in the parent (A1B1 or A2B2) diblock copolymer melts. The study of A1B1/A2B2 block copolymer blends further provides a solid foundation for future research on more complex block copolymer blends.

Regulating the self‐assembly of AB/CD diblock copolymer blends via secondary interactions

AbstractDesigned multiblock copolymers with complex architectures offer unlimited opportunities to obtain novel nanostructured phases, however, their synthesis could be challenging and expensive. An alternative approach to access desired nanostructures is to use blends of block copolymers with simple chain architectures and designed block‐block interactions. We use binary blends composed of AB and CD diblock copolymers as a model system to establish design principles of polymeric blends containing block copolymers. Specifically, we explore the phase behavior of AB/CD blends by using the polymeric self‐consistent field theory to construct phase diagrams of the blends focusing on the sphere‐forming regions in the phase space. We predict the formation of various spherical packing phases composed of either core‐shell‐structured spheres or binary spheres resembling metallic alloys. We demonstrate that the equilibrium morphology can be regulated by adjusting the blend composition and molecular parameters such as block fractions, conformational asymmetry, and segment‐segment interactions. The strategy of using secondary interaction in polymeric blends to control the phase behavior explored in the current study can also be generalized to other soft matter systems.

Tetragonally Packed Inverted Cylindrical Microdomains from Binary Block Copolymer Blends with Enhanced Hydrogen Bonding

Tetragonally Packed Inverted Cylindrical Microdomains from Binary Block Copolymer Blends with Enhanced Hydrogen Bonding

Cross-Linking, Morphology, and Physico-Mechanical Properties of GTR/SBS Blends: Dicumyl Peroxide vs. Sulfur System.

In this work, ground tire rubber and styrene-butadiene block copolymer (GTR/SBS) blends at the ratio of 50/50 wt%, with the application of four different SBS copolymer grades (linear and radial) and two types of cross-linking agent (a sulfur-based system and dicumyl peroxide), were prepared by melt compounding. The rheological and cross-linking behavior, physico-mechanical parameters (i.e., tensile properties, abrasion resistance, hardness, swelling degree, and density), thermal stability, and morphology of the prepared materials were characterized. The results showed that the selected SBS copolymers improved the processability of the GTR/SBS blends without any noticeable effects on their cross-linking behavior-which, in turn, was influenced by the type of cross-linking agent used. On the other hand, it was observed that the tensile strength, elongation at break, and abrasion resistance of the GTR/SBS blends cured with the sulfur system (6.1-8.4 MPa, 184-283%, and 235-303 mm3, respectively) were better than those cross-linked by dicumyl peroxide (4.0-7.8 MPa, 80-165%, and 351-414 mm3, respectively). Furthermore, it was found that the SBS copolymers improved the thermal stability of GTR, while the increasing viscosity of the used SBS copolymer also enhanced the interfacial adhesion between the GTR and SBS copolymers, as confirmed by microstructure evaluation.

Anisotropically conductive phase change composites enabled by aligned continuous carbon fibers for full-spectrum solar thermal energy harvesting

Solar thermal energy harvesting with phase change materials (PCMs) can overcome the intermittent nature of solar energy through thermal energy storage to provide uninterruptible heat supply. However, the PCMs' intrinsically low thermal conductivities and weak solar absorptances pose considerable challenges to achieving high photothermal efficiency, and most PCMs also suffer from leakage and poor stability. Herein, we propose a simple and scalable approach to develop anisotropically conductive phase change composites (PCCs) by fabricating and embedding aligned continuous carbon fibers (CFs) in paraffin wax (PW)/olefin block copolymer (OBC) blends. The aligned CFs provide continuous and directional thermal conduction paths within the PCCs, enabling a high lengthwise thermal conductivity of 5.63 W·K−1·m−1 and a low transverse thermal conductivity of 0.77 W·K−1·m−1 with a rather high anisotropic degree of 7.31. The excellent anisotropic thermal conductivity can enhance the lengthwise heat transfer from the PCC surface to the deep inside and reduce the transverse heat loss from PCC to the surroundings. Furthermore, to enhance the solar absorption, carbon black is coated on the PCC surface to boost the full-spectrum solar absorptance up to 0.988. Because of the synergetic effects of the excellent anisotropic thermal conductivity and high full-spectrum solar absorptance, the PCC can achieve high photothermal efficiencies of 79.17 %-98.31 % under 1 sun-3 suns. Moreover, the PCC also demonstrates excellent thermal, cyclic and shape stability. This work offers a promising strategy for fabricating anisotropically conductive PCCs for efficient solar thermal energy harvesting.

Autonomous discovery of emergent morphologies in directed self-assembly of block copolymer blends.

The directed self-assembly (DSA) of block copolymers (BCPs) is a powerful approach to fabricate complex nanostructure arrays, but finding morphologies that emerge with changes in polymer architecture, composition, or assembly constraints remains daunting because of the increased dimensionality of the DSA design space. Here, we demonstrate machine-guided discovery of emergent morphologies from a cylinder/lamellae BCP blend directed by a chemical grating template, conducted without direct human intervention on a synchrotron x-ray scattering beamline. This approach maps the morphology-template phase space in a fraction of the time required by manual characterization and highlights regions deserving more detailed investigation. These studies reveal localized, template-directed partitioning of coexisting lamella- and cylinder-like subdomains at the template period length scale, manifesting as previously unknown morphologies such as aligned alternating subdomains, bilayers, or a "ladder" morphology. This work underscores the pivotal role that autonomous characterization can play in advancing the paradigm of DSA.

Responsive blends of block copolymers stabilize the hexagonally perforated lamellae morphology.

Blends of block copolymers can form phases and exhibit features distinct from the constituent materials. We study thin film blends of cylinder-forming and lamellar-forming block copolymers across a range of substrate surface energies. Blend materials are responsive to interfacial energy, allowing selection of pure or coexisting phases based on surface chemistry. Blending stabilizes certain motifs that are typically metastable, and can be used to generate pure hexagonally perforated lamellar thin films across a range of film thicknesses and surface energies. This tolerant behavior is ascribed to the ability of blend materials to redistribute chains to stabilize otherwise high-energy defect structures. The blend responsiveness allows the morphology to be spatially defined through multi-tone chemical surface patterns.

Semi-conductive micellar networks of all-conjugated diblock and triblock copolymer blends.

The crystallization-driven self-assembly of the blends of the all-conjugated block copolymers of poly(3-hexylthiophene) (P3HT) and poly(3-ethylhexylthiophene) (P3EHT) results in the cross-linking of the one-dimensional nanowires of P3HT-b-P3EHT, which is achieved by intercalating P3HT-b-P3EHT-b-P3HT into the nanowire cores. The micellar networks constitute flexible and porous materials that conduct electricity upon doping.

Hydrogen Bonding-Induced Crystal Orientation Changes in Confined Microdomains Constructed by Block Copolymer Blends

This study examined crystal orientation confined within a lamellar microdomain morphology formed by the blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA) through wide-angle X-ray diffraction. The hydrogen-bonding interaction between PEO and PAA molecules enabled block copolymers to co-organize into a microphase-separated morphology without inducing macrophase separation, but it hampered PEO crystallization. PEO crystallization that occurred at −20 °C resulted in the nucleation mechanism to be dominant, thus leading to the formation of small crystals. Small crystals allowed them to be free from spatial confinement, and they tended to be oriented with their c-axis parallel to the microdomain interface. By contrast, when PEO was crystallized at 40 °C, the high temperature facilitated PEO crystals to exhibit large crystallite sizes, which aligned perpendicularly to the microdomain interface. An increase in the PS-b-PAA concentration considerably reduced the crystallizability of PEO. The presence of a low amount of crystals and additional lateral confinement formed by hydrogen-bonded PEO/PAA reduced the degree of orientation regardless of the crystallization temperature.

Hydrogen bonding induced microphase and macrophase separations in binary block copolymer blends

This study investigated the macrophase and microphase transitions of blends comprising polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA). PEO and PAA molecules formed hydrogen bonds that enabled the two block copolymers to organize into a single microphase-separated morphology composed of two PS block chains in a common PS microdomain and PEO and PAA block chains in a coexisting PEO/PAA microdomain. Increasing temperature weakened the hydrogen-bonding interaction through the formation of PAA monomers and anhydride, causing the blends to macrophase separate into PS-b-PEO-rich and PS-b-PAA-rich phases. Further increasing the temperature weakened the repulsive interactions between both the PS and PEO segments and the PS and PAA segments, inducing order-to-disorder transitions in the PS-b-PEO-rich and PS-b-PAA-rich phases. However, the increasing repulsive interaction between the PEO and PAA segments with increasing temperature prevented the blends from forming an isotropic phase. The unique phase transformation of each block copolymer in the blend with an upper critical ordering transition (UCOT)-type interaction parameter, which caused the formation of a lower-critical-solution-temperature-type phase diagram, was attributed to the hydrogen-bonding interaction between PEO and PAA, which outweighed the UCOT behaviors of PS-b-PEO and PS-b-PAA and reversed the phase behaviors of their blends.

Chain Redistribution Stabilizes Coexistence Phases in Block Copolymer Blends.

The nanoscale morphologies of block copolymer (BCP) thin films are determined by chain architecture. Experimental studies of thin film blends of different BCP chain types have demonstrated that blending can stabilize new motifs, such as coexistence phases. Here, we deploy coarse-grained molecular dynamics (MD) simulations in order to better understand the self-assembly behavior of BCP blend thin films. We consider blends of lamella- and cylinder-forming BCP chains, studying their morphological makeup, the chain distribution within the morphology, and the underlying polymer chain conformations. Our simulations show that there are local concentration deviations at the scale of the morphological objects that dictate the local structure, and that BCP chains redistribute within the morphology so as to stabilize the structure. Underlying these effects are measurable distortions in the BCP chain conformations. The conformational freedom afforded by BCP blending stabilizes defects and allows coexistence phases to appear, while also leading to kinetic trapping effects. These results highlight the power of blending in designing the morphology that forms.

Development of material extrusion 3D printing compatible tailorable thermoplastic elastomeric materials from acrylonitrile butadiene styrene and styrene‐(ethylene‐butylene)‐styrene block copolymer blends

AbstractCurrently, material extrusion‐based additive manufacturing (MEAM) is an advanced fabrication technique for polymeric materials. However, MEAM feedstocks typically rely on amorphous thermoplastics and hence it suffers from limitation of compatible polymers. The current work reports the manufacturing of MEAM compatible new thermoplastic elastomers (TPEs) from acrylonitrile butadiene styrene (ABS) and styrene‐(ethylene‐butylene)‐styrene (SEBS) block copolymer blends which allow the designing of tailorable TPEs. Printability and mechanical properties of several ABS/SEBS (w/w) compositions were investigated. Interestingly, it was revealed that only 40 ABS/60 SEBS (w/w) blend possesses elastomeric properties in terms of strain at break (~550%) and tension set values (~10%). The effect of print layer thickness, orientation of printing, and infill degree on mechanical and TPE properties of the printed parts were studied theoretically by exploiting the Taguchi method. The infill degree has a significant influence on the mechanical performance whereas a slight effect was found by varying the layer thickness. Finally, the performance of the additive manufactured TPE were compared with conventional compression molded TPE specimens. As expected, lower values of ultimate tensile strength, Young's modulus, and strain at break of the additive manufactured sample were obtained as compared to the molded samples. However, no major variation could be found in the dynamic moduli, loss tangent, and absolute value of complex viscosity.