Block Copolymer Blends Research Articles

Unusual Self-Assembly of Amphiphilic Block Copolymer Blends Induced by Control of Hydrophobic Interaction.

Block copolymer blend systems have been of great interest for a wide range of potential applications, such as nanobuilding blocks or guidance materials, because they can provide a rich phase behavior according to external conditions. However, a new and unique phase behavior of block copolymers, which can give us their more extended potential applications, has not yet been reported. Herein, we report the unusual self-assembly of two different types of Pluronic P65 and PE6200 triblock copolymer blends dependent on temperature and PE6200 concentration, which is unique for the block copolymer blends in aqueous solution. As the temperature and concentration of PE6200 (as an additive) increased, the Pluronic P65/PE6200 copolymer blends sequentially self-assembled into an isotropic micellar-hexagonal-isotropic micellar or isotropic micellar-hexagonal-isotropic micellar-lamellar phase, which is a discontinuous ordered phase (called a closed looplike phase transition), and their phase transition temperature could be controlled. To the best of our knowledge, this is the first report of a closed looplike phase transition of Pluronic block copolymer blends in aqueous solution, which can be easily applied to nanosized templates for temperature-selective highly ordered structures and optical devices such as optoelectronics or optical sensors.

Morphological Diversity from the Solution Self‐Assembly of Block Copolymer Blends Containing High Molecular‐Weight Hydrophobic Blocks

Morphological Diversity from the Solution Self‐Assembly of Block Copolymer Blends Containing High Molecular‐Weight Hydrophobic Blocks

Nanosphere size control by varying the ratio of poly(ester amide) block copolymer blends

HypothesisBlending amphiphilic triblock (A-B-A) and diblock (A-B) copolymers comprised of the same hydrophobic tyrosine-derived oligomeric B-block and hydrophilic poly(ethylene glycol) methyl ether (mPEG) A-block can provide highly tunable self-assembled nanosphere particle sizes suitable for biomedical applications. ExperimentTriblock and diblock copolymers were synthesized via carbodiimide chemistry and were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The amount of free PEG present in the purified copolymers was determined using a standard addition calibration curve and GPC peak deconvolution methods. Nanospheres were prepared by co-precipitation of each copolymer and of copolymer blends over a range of mole ratios. Nanospheres were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and % polymer recovery post-preparation. FindingPrecise synthesis control produced triblock and diblock copolymers with narrow molecular weight distributions and minimal residual reactants. Self-assembled nanosphere particle sizes were 33 nm for the triblock and 129 nm for the diblock, and the size of their blends increased continuously as a function of mole ratio within that biomedically relevant range. Addition of unreacted PEG had minimal impact on either triblock or diblock nanosphere particle sizes whereas addition of unreacted oligomeric B-block increased nanosphere sizes.

Morphological Diversity from the Solution Self-Assembly of Block Copolymer Blends Containing High Molecular-Weight Hydrophobic Blocks.

Self-assembled structures of high molecular-weight block copolymers (BCPs) can prematurely settle to local energy minima without reaching a time-averaged equilibrium, resulting in the emergence of intriguing morphologies, such as 3D micellar networks. This nonergodic behavior is evident in binary blends of BCPs with different molecular weights. This study reports the solution self-assembly of the blends of two branched-linear BCPs with similar block chemistries but different molecular weights of the hydrophobic blocks. A progressive transition of morphologies from hexosomes and cubosomes to 3D micellar networks, short cylinders, and spherical micelles is demonstrated, which is driven by the increase in the composition of low-molecular-weight BCP in the blend. The labeling of the micellar networks using Au nanoparticles confirms that lower molecular-weight BCP concentrates at the surface of micellar networks.

Photonic Crystal Palette of Binary Block Copolymer Blends for Full Visible Structural Color Encryption (Adv. Funct. Mater. 1/2022)

Block Copolymer Blends In article number 2103697, Cheolmin Park and co-workers develop a palette of block copolymer photonic crystal inks, enabling convenient modulation of the structural color in the full visible range via solution blending of two lamellar-forming block copolymers. The binary blend photonic crystals are applicable to various solution processes and offer efficient reflection-mode pattern encryption suitable for emerging vision encryption technology requiring ultra-thin, mechanically flexible, and thus skin-patchable performance.

The effects of the cross‐linking mechanism of low doses of gamma irradiation on the mechanical, thermal, and viscoelastic properties of the natural rubber latex/poly(styrene‐block‐isoprene‐block‐styrene) block copolymer blend

AbstractNatural rubber latex (NRL) is a natural polymer with versatile properties. However, uncured NRL has low strength and limited practical use. Therefore, we utilized low‐dose gamma irradiation to induce cross‐linking in blended NRL/poly(styrene‐block‐isoprene‐block‐styrene) (SIS). Blends were prepared in various ratios, and the 70NRL/30SIS blend gave optimal mechanical properties. The 70NRL/30SIS blend was then irradiated from 4 to 16 kGy. An exposure of 12 kGy led to the highest tensile strength (4.49 MPa), Young's modulus (0.41 MPa), gel content (45%), and cross‐link density (12.18 × 10−5 mol·cm−3). The results of study show irradiation has improved the crystallinity of the polymer blend, which has been determined by the formation of a new NRL crystal peak at 31.2° and the decrease of the crystallization temperature from 58 to 19°C due to strain‐induced crystallization. Moreover, the radiation has transformed the 70NRL/30SIS blend irradiated at 12 kGy from liquid‐like to an elastic state that degraded at a higher temperature (392.01°C). The presence of a singlet alkyl radical peak was detected in the electron spin resonance. Therefore, the cross‐links are proposed to be C‐C bonds formed via the radiation technique. Irradiation is an effective technique to improve the performance of NRL/SIS blends without introducing any chemical cross‐linking additive.

Self-assembled nanostructured viscoelastic and thermally stable high performance epoxy based nanomaterial for aircraft and automobile applications: An experimental and theoretical modeling approach

Nanostructured self-assembled and high-performance epoxy/epoxidized poly(styrene-block-butadiene-block-styrene) block copolymer blends with 55 mol% epoxidation degree [eSBS 55 ]- 0,5,10 and 20 phr- 4, 4′diaminodiphenyl methane (DDM) material were successfully synthesized by using solvent casting method. The role of the highest epoxidized SBS (eSBS 55 ) as a modifier and its concentration on the effect of nanostructured morphology, viscoelastic properties, reaction induced phase separation and thermal degradation kinetics of epoxy/eSBS 55 system were investigated in detail. Various theoretical models such as Coats-Redfern method, Broido method and Horowitz- Metzger method were applied for the first time on epoxy/eSBS systems to calculate the thermodynamic parameters and correlate experimental results. These highly enhanced viscoelastic & thermal properties and nanoscale morphology of as synthesized novel epoxy/eSBS 55 material have proved that ‘eSBS 55 ’is an outstanding modifier to epoxy resin for creating superior high-performance properties required for various coating and structural applications such as in aircrafts, floorings, automobiles and constructions. Viscoelastic and thermal properties of nanostructured epoxy/eSBS 55 systems • Nanostructured and high performance epoxy-amphiphilic blends were synthesized. • eSBS 55 wt% act as an excellent modifier and produced good compatibility with epoxy. • Excellent viscoelastic properties and thermal properties of blends were achieved. • Correlation of TGA experimental results with theoretical models for the first time. • eSBS 55 wt% produced superior performance properties for various coating applications.

Inverted Cylindrical Microdomains from Binary Block Copolymer Blends Capable of Hydrogen Bonding

Inverted Cylindrical Microdomains from Binary Block Copolymer Blends Capable of Hydrogen Bonding

Structural, thermal, mechanical and viscoelastic properties of ethylene vinyl acetate (EVA)/olefin block copolymer (OBC) blends

In this study, ethylene vinyl acetate and olefin block copolymer (OBC) blends were prepared by melt-compounding. The effect of vinyl acetate (VA:12 and 28 wt%) and OBC (10–50 wt%) content on the morphological, thermal, and mechanical properties of EVA/OBC blends were studied in detail. Short-term flexural creep tests were also reported to investigate the time-dependent behavior of the blends. Non-isothermal crystallization results showed that, fractionated crystallization around 75C was observed in EVA (28%) blends. The creep study showed that the creep behavior of the blends significantly improves with the addition of OBC. The four-element Burgers model and the two parameter power law (Findley’s) model were fitted creep curves of the blends well. The addition of OBC promoted significant gains in terms of the mechanical and solid-state viscoelastic properties.

Effect of Block Copolymer Composition and Homopolymer Molecular Weight on Ordered Bicontinuous Double-Diamond Structures in Binary Blends of Polystyrene–Polyisoprene Block Copolymer and Polyisoprene Homopolymer

We investigated the effect of block copolymer composition and homopolymer molecular weight on the stability of ordered bicontinuous double-diamond (OBDD) phases in polystyrene-rich polystyrene–polyisoprene block copolymer (PS–PI) and polyisoprene (PI) blend using small-angle X-ray scattering. PS–PI with PI volume fractions (fPI) of 31–40 vol % and a degree of polymerization of ca. 320 were prepared. Stable OBDD regions could be observed at fPI = 31–35 vol %, but no OBDD could be observed at fPI = 40 vol %. Moreover, OBDD morphology was formed only when the chain length of the homopolymer was greater than that of the same constituent chain in the copolymer (dry-brush conditions). Furthermore, OBDD formation required a homopolymer content of at least 11 wt % in the blend. These results indicate that the added homopolymer localized in the middle of the microdomains and relieved packing frustration inside the four-fold nodes of OBDD, resulting in a stable OBDD structure.

Thermo-Responsive Shape Memory Behavior of Methyl Vinyl Silicone Rubber/Olefin Block Copolymer Blends via Co-Crosslinking

Abstract Shape memory polymers (SMPs) are developed by blending and cross-linking polymers which include crystalline domains and cross-linked networks. In this paper, we describe the morphology, thermal and shape memory behavior of methyl vinyl silicone rubber (MVMQ)/olefin block copolymer (OBC) blends prepared by a melt-blending and chemical cross-linking method. MVMQ without crystalline domains could not hold its temporary shape. After introducing the OBC, the obtained blends exhibited excellent dual shape memory properties. The cross-linking networks of MVMQ acted as reversible domains, while crystalline regions of OBC worked as fixed domains. When the blending ratio of MVMQ/OBC was 50/ 50, the blend had both a high shape fixity ratio and shape recovery ratio.

Frank-Kasper σ and A-15 Phases Formed in Symmetry and Asymmetry Block Copolymer Blend System

Frank-Kasper σ and A-15 Phases Formed in Symmetry and Asymmetry Block Copolymer Blend System

Hyperbolic Metamaterials via Hierarchical Block Copolymer Nanostructures

AbstractHyperbolic metamaterials (HMMs) offer unconventional properties in the field of optics, enabling opportunities for confinement and propagation of light at the nanoscale. In‐plane orientation of the optical axis, in the direction coinciding with the anisotropy of the HMMs, is desirable for a variety of novel applications in nanophotonics and imaging. Here, a method for creating localized HMMs with in‐plane optical axis, based on block copolymer (BCP) blend instability, is introduced. The dewetting of BCP thin film over topographically defined substrates generates droplets composed of highly ordered lamellar nanostructures in hierarchical configuration. The hierarchical nanostructures represent a valuable platform for the subsequent pattern transfer into a Au/air HMM, exhibiting hyperbolic behavior in a broad wavelength range in the visible spectrum. A computed Purcell factor as high as 32 at 580 nm supports the strong reduction in the fluorescence lifetime of defects in nanodiamonds placed on top of the HMM.

Molecular Stereocomplexation for Enhancing the Stability of Nanoparticles Encapsulated in Polymeric Micelles for Magnetic Resonance Imaging.

A generalizable approach for improving the stability of polylactide-based (PLA-based) micelles for encapsulating nanoparticles (NPs) is demonstrated, using stereocomplexation between a pair of poly (ethylene glycol)-b-poly(d-lactide)/poly(ethylene glycol)-b-poly(l-lactide) block copolymer blends. Three different superparamagnetic ferrite-based NPs with distinct nanostructures are first prepared by the high-temperature pyrolysis method, including spherical MnFe2O4, cubic MnFe2O4, and core-shell MnFe2O4@Fe3O4. The diameters of these NPs are approximately 7-10 nm as revealed by transmission electron microscopy. These hydrophobic NPs can be encapsulated within self-assembled, stereocomplexed PLA (sc-PLA) micelles. All sc-PLA micelle systems loaded with three different NPs exhibit enhanced stability at elevated temperatures (20-60 °C) and with extended storage time (∼96 h) compared with analogous samples without stereocomplex formation, confirmed by dynamic light scattering measurements. The magnetic NP-loaded micelles with mean diameters of approximately 150 nm show both biocompatibility and superparamagnetic property. Under a 1.5 T magnetic field, cubic MnFe2O4 (c-MnFe2O4)-loaded micelles exhibit an excellent negative contrast enhancement of MR signals (373 mM-1·s-1), while core-shell MnFe2O4@Fe3O4-loaded micelles show a slightly lower signal for MR imaging (275 mM-1·s-1). These results suggest the potential of using sc-PLA-based polymer micelles as universal carriers for magnetic resonance imaging contrast agents with improved stability for different applications such as cancer diagnosis.

Transition between tetragonal and hexagonal pattern in binary blends of ABC block copolymers with different chain lengths

The thin film morphology of binary blends of triblock copolymers (poly(isoprene - block - styrene - block - (2-vinylpyridine)) ISP after solvent vapor annealing (SVA) was investigated using AFM, GISAXS and TEM. Although bulk samples of binary ISP blends exhibit tetragonal pattern, thin films led either to tetragonal pattern or hexagonal pattern, depending on the annealing time. These transitions were attributed to the formation of non-synchronized wetting layers of I and P, leading to a variation of the inner composition in I and P during SVA. Surprisingly, the hexagonal morphology exhibited centered hexagons of I and surrounding hexagons of P, which is not predicted nor observed for neat block copolymer samples. Although the system must adopt the lowest P/S interface, our results suggest that the effect of chain length with marked difference in the studied blends is playing a major role. Particularly, the presence of long chains of I favors the formation of I domains with bigger size, in order to keep their conformation entropy loss as small as possible.

Formation of a C15 Laves Phase with a Giant Unit Cell in Salt-Doped A/B/AB Ternary Polymer Blends.

Salt-doped A/B/AB ternary polymer blends, wherein an AB copolymer acts as a surfactant to stabilize otherwise incompatible A and B homopolymers, display a wide range of nanostructured morphologies with significant tunability. Among these structures, a bicontinuous microemulsion (BμE) has been a notable target. Here, we report the surprising appearance of a robust C15 Laves phase, at compositions near where the BμE has recently been reported, in lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass poly(ethylene oxide) (PEO)/polystyrene (PS)/symmetric PS-b-PEO block copolymer blends. The materials were analyzed by a combination of small-angle X-ray scattering (SAXS), 1H NMR spectroscopy, and impedance spectroscopy. The C15 phase emerges at a high total homopolymer volume fraction ϕH = 0.8 with a salt composition r = 0.06 (Li+/[EO]) and persists as a coexisting phase across a large area of the isothermal phase diagram with high PS homopolymer compositions. Notably, the structure exhibits a huge unit cell size, a = 121 nm, with an unusually high micelle core volume fraction (fcore = 0.41) and an unusually low fraction of amphiphile (20%). This unit cell dimension is at least 50% larger than any previously reported C15 phase in soft matter, despite the low molar masses used, unlocking the possibility of copolymer-based photonic crystals without compromising processability. The nanostructured phase evolution from lamellar to hexagonal to C15 along the EO60 isopleth (ϕPEO,homo-LiTFSI/ϕH = 0.6) is rationalized as a consequence of asymmetry in the homopolymer solubility limit for each block, which leads to exclusion of PS homopolymer from the PS-b-PEO brush prior to exclusion of the PEO homopolymer, driving increased interfacial curvature and favoring the emergence of the C15 Laves phase.

Morphology Evolution of Block Copolymer Blend Thin Films Induced by Solvent Vapor Annealing

ABSTRACT Self-assembly of binary block copolymer blends in thin film induced by solvent vapor annealing has been systematically studied. The diblock copolymers polystyrene-b-poly(2-vinylpyridine) with different molecular weights and volume fractions were blended with different molar ratios to cast thin films on silica substrate by spin coating. The films were annealed separately in the vapor of ethanol or toluene over time to induce morphology transformations from spheres, gyroids, and bicontinuous nanostructures, depending on the blending ratio, solvent selectivity, and annealing time, as investigated by atomic force microscopy and X-ray photoelectron spectroscopy. The formation and transformation mechanism of the self-assembly structure are discussed in the context of solvent-copolymer interactions. This study provides new insights into the simple manipulation of self-assembled nanostructures of block copolymer thin films.

Effect of low dose gamma irradiation on the tensile and thermal properties of natural rubber-based blend

Natural rubber (NR) is a renewable natural resource that has been utilized in many applications. Due to its low tensile strength, NR is commonly blended with another polymer to improve the properties of NR. However, most of the blended NR has miscibility issue, leading to poor mechanical properties. Gamma irradiation (GR) is a safe and green alternative than conventional chemical method for inducing crosslinking in blended NR. This study was aimed at investigating the mechanical and thermal properties of NR/liquid natural rubber/polystyrene-block-polyisoprene block copolymer (NR/LNR/PS-b-PI) blend using GR method. The polymer blend is prepared according to the ratio of NR:LNR:PS-b-PI of 6:1:3 using an internal mixer. The NR/LNR/PS-b-PI blends are irradiated with gamma ray at doses of 0, 5, 6, 7, 8 and 9 kGy. Tensile and thermal tests are conducted to evaluate the properties of unirradiated and irradiated polymer blend. The tensile strength and modulus of the irradiated blend are increased with increasing irradiation dose before decrease at 9 kGy. Lower melting point of blend indicates that PS-b-PI are compatible in NR/LNR blend. The improvement in tensile properties of irradiated NR/LNR/PS-b-PI blend is related to the radiation-induced crosslinking.

Wormlike Nanovector with Enhanced Drug Loading Using Blends of Biodegradable Block Copolymers.

The application of nanoparticles comprising amphiphilic block copolymers for the delivery of drugs is a subject of great interest as they hold promise for more effective and selective therapies. In order to achieve this ambition, it is of critical importance to develop our understanding of the self-assembly mechanisms by which block copolymers undergo so that we can control their morphology, tune their ability to be loaded with biofunctional cargoes, and optimize their interactions with target cells. To this end, we have developed a strategy by which blends of (biocompatible) amphiphilic block copolymers generate nonspherical nanovectors, simultaneously enhancing drug loading without the need for subsequent purification owing to the use of the biocompatible direct hydration approach. The principal morphology achieved using this blending strategy are wormlike nanovectors (nanoworms, NWs), with an elongated form known to have a profound effect on flow behavior and interactions with cells. Unloaded nanoworms are not toxic toward human retinal (ARPE-19) cells and can be effectively endocytosed even after varying the surface charge. In terms of drug loading, we demonstrate that uptake of dexamethasone (DEX; a clinically relevant therapeutic agent) in nanoworms (DEX@NWs) can be enhanced using this process, increasing drug content up to 0.5 mg/mL (10 wt % in particles). Furthermore, such nanoworms are stable for at least 5 months and are, therefore, a promising platform for nanomedicine applications.

Hierarchically ordered hybrid nanostructures via spontaneous self-assembly of block copolymer blends

Directed self-assembly of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) can serve as a strategy to creation of spatially-ordered nanostructures below tens of nanometer scale in a simple and cos-effective manner, eliminating the need for external force and conventional lithographic techniques. However, this approach still suffers from expansion of geometrical shapes and materials choices. In the present study, we offer a simple and facile route to formation of scalable nanostructures with hierarchical order via the rapid microphase separation of blends consisting of A-B/B-C diblock copolymers. Such this hierarchically ordered nanostructures (i.e., nanostructure in nanostructure), which cannot be evenly obtained from microphase separation of a single BCP, shed a light on the potential applications such as electronic, optical, and bio-devices. The strategy proposed in this paper can also benefit construction of more diverse and complicated nanostructures by securing control over blending of various BCPs.