Molecular Weight Block Copolymers Research Articles

Constructing a Comprehensive Nanopattern Library through Morphological Transitions of Block Copolymer Surface Micelles via Direct Solvent Immersion.

This study establishes a comprehensive library of nanopatterns achievable by a single block copolymer (BCP), ranging from spheres to complex structures like split micelles, flower-like clusters, toroids, disordered micelle arrays, and unspecified unique shapes. The ordinary nanostructures of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) surface micelles deposited on a SiOx surface undergo a unique morphology transformation when immersed directly in solvents. Investigating parameters such as immersion solvents, BCP molecular weight, substrate interactions, and temperature, this work reveals the influence of these parameters on the thermodynamics and kinetics governing the morphology transformation. Additionally, the practical application of BCP nanopattern templates for fabricating metal nanostructures through direct solvent immersion of surface micelles is demonstrated. This approach offers an efficient and effective method for producing diverse nanostructures, with the potential to be employed in nanolithography, catalysts, electronics, membranes, plasmonics, and photonics.

Insights into the feature size required for the death of Pseudomonas fluorescens on nanostructured silicon fabricated by block copolymer lithography

It has been established that nanostructured surfaces can cause cell death for Gram-negative species; however, the exact mode of action has not yet been determined from among several agreed-upon possibilities. Herein, silicon nanospike arrays were fabricated via a combination of block copolymer lithography and plasma etching. Patterns were first developed on silicon substrates using tetrahydrofuran, chloroform, or acetic acid as annealing solvents with two different molecular weight block copolymers. Three silicon surface types (NSS, NSM and NSL) were fabricated after a hard mask development and plasma etching. These samples were designed to be “small, medium and large” versions of nanospike arrays regarding their height, diameter and pitch; maintaining the same approximate proportionality, while changing in size. NSS had structures of 28 nm in height, and 16 nm in base diameter, with a pitch of 36 nm. NSM structures were 140 nm in height, and 31 nm in diameter, with a pitch of 63 nm. NSL surface structures had a height of 272 nm, a diameter of 47 nm and a pitch of 99 nm. When suspensions of gentamicin-resistant P. fluorescens cells were interfaced with the arrays for 24 h, it was shown that the NSS had ∼76% less cell death than both NSM and NSL. To the best of our knowledge, this is the first study that etched silicon patterned using block copolymer lithography has been used to fabricate surfaces with antibacterial activity.

Reaction‐induced morphology control in block copolymers

AbstractControlling the self‐assembly behaviors of block copolymers (BCPs) is a focal point of many research thrusts due to their broad use in various applications. While BCP molecular weight, volume fraction, and chemical identities are key thermodynamic parameters to determine their morphology, an emergent method in this area is through reaction‐induced changes to the characteristics of a BCP in situ, which provides access to multiple morphologies and domain sizes from a single parent polymer, as well as enabling the formation of metastable morphologies which may be difficult to attain otherwise. This work provides a focused review about the current state of reaction‐induced morphology control in BCPs in both solution and solid states. Furthermore, we provide a forward‐looking perspective on the future opportunities of understanding and employing reaction engineering to manipulate and advance BCP self‐assembly. © 2023 Society of Industrial Chemistry.

Enhanced etching resolution of self-assembled PS-b-PMMA block copolymer films by ionic liquid additives

Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is one of the most widely studied block copolymers for direct self-assembly because of its excellent compatibility with traditional processes. However, pattern transfer of PS-b-PMMA block copolymers (BCPs) remains a great challenge for its applications due to the insufficient etching resolution. In this study, the effect of ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate (HMHF) additives on the line edge roughness (LER) performances of PS-b-PMMA self-assembled patterns was studied. Trace addition of HMHF kept the photolithography compatibility of PS-b-PMMA block copolymer films, but obviously increased their Flory–Huggins interaction parameter (χ) and enabled phase separation of disordered low molecular weight BCPs. LER value was effectively decreased by blending HMHF directly with PS-b-PMMA or from a supplying top layer of polyvinylpyrrolidone containing HMHF additives. This study shows an excellent strategy to improve the deficiencies of existing block copolymers.

A fast and efficient way of obtaining the average molecular weight of block copolymers via DOSY

Diffusion-ordered NMR spectroscopy (DOSY) allows for excellent determination of block copolymer molecular weights.

Multiple Pickering emulsions fabricated by a single block copolymer amphiphile in one-step

The mixture of emulsifiers with opposite amphiphilicity was often necessary in generating multiple emulsions, whereas multiple emulsions might be generated by a single-component copolymer amphiphile. In this work, the emulsification of amphiphilic block copolymers poly (lauryl methacrylate)-b-poly (N-(2-methacryloylxyethyl) pyrrolidone) (PLMAm-b-PNMPn) in the water/dodecane systems was systematically studied by the confocal laser scanning microscopy and dynamic light scattering techniques. Interestingly, multiple emulsions instead of single emulsions were generated by employing single-component block copolymer amphiphiles PLMAm-b-PNMPn as emulsifiers under certain conditions. In specifically, the formation of multiple emulsions was highly depended on the molar ratio (rPNMP/PLMA = n/m) between the PNMP and PLMA segments regardless of the molecular weight of block copolymers. Through introducing an aggregation-induced emission amphiphile poly (N-(2-methacryloyloxyethyl) pyrrolidone)-b-poly (lauryl methacrylate-co-1-ethenyl-4-(1,2,2-triphenylethenyl) benzene) (PNMP35-b-P(LMA42-co-TPE16) into emulsifiers, the interfacial characters of multiple emulsions were also clarified. The complex emulsification of PLMAm-b-PNMPn was explained by a concordant manner based on the in-situ formed emulsifier mixture composed of PLMAm-b-PNMPn molecules and micelles, which were confirmed by the quantitative fluorescent analysis. It was found out that the preferred continuous phase of emulsions was mainly determined by the hydrophilicity of PLMAm-b-PNMPn molecules. However, the agglomeration of hydrophobic aggregates on the interfacial layer might inverse the amphiphilicity of mixed emulsifiers, and thereby resulting in the formation of multiple emulsions.

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.

Rapid synthesis of sustainable poly(ethylene 2,5-furandicarboxylate)-block-poly(tetramethylene oxide) multiblock copolymers with tailor-made properties via a cascade polymerization route

Bio-based 2,5-furandicarboxylic acid (FDCA) is a promising monomer for the substitution of fossil-based terephthalic acid, yet its condensation polymerization with corresponding diols to high quality polyesters remains challenging due to the degradation and discolouration from side reactions. We report here a cascade polycondensation-coupling ring-opening polymerization (PROP) strategy towards the rapid synthesis of poly(ethylene 2,5-furandicarboxylate)-block-poly(tetramethylene oxide) multiblock copolymers (mBCPs), (PEF-b-PTMO-b-PEF)n, via the vacuum melt polymerization of cyclic oligo(ethylene 2,5-furandicarboxylate)s (COEFs) with PTMO diols. Due to the rapid cascade polymerization, the side reactions were suppressed and poly(ether ester) mBCPs with high number-average molecular weights (Mn > 30 kg/mol) were obtained within 60 min. The segmental length, block number and soft/hard weight ratio can be well-controlled by the polymerization conditions, and their structure-property relationship was investigated. In these double-crystalline mBCPs, the melting temperature and degree of crystallinity of PEF segments increase with PEF content, while those for PTMO are less affected. These mBCPs form bicontinuous disordered phase separation morphologies, with the domain size decreases with the increment of PTMO content, the total block copolymer molecular weight, and the reduced segmental length. With the crystalline PEF domains forming the physically-crosslinking points, these mBCPs show typical thermoplastic elastomer properties with elongations exceeding 400%. The strength and Young's modulus increase with PEF content, while the elongation at break decreases. Increment of block number enhances both the strength and elongation at break for mBCPs. In addition, these sustainable mBCPs show biodegradable properties controlled by the hard/soft weight ratio and crystallinity of PEF blocks. Our cascade polymerization method provides an efficient method for the rapid preparation of sustainable high value-added thermoplastic elastomers with tailor-made properties.

Electrospun nanofibers fromferrocene‐containingmultiblock copolymers prepared viaRAFTpolymerization withF127modified precursor

AbstractElectrospun nanofibers from copolymers composed of ferrocene side chains and PEO100‐PPO65‐PEO100(F127) were fabricated in chloroform andN,N–dimethyl formamide solutions (V/V = 95:5) at room temperature. Ferrocene‐containing multiblock copolymers (PFcMAn‐F127‐PFcMAn) were synthesized through reversible addition‐fragmentation chain transfer polymerization using s‐1‐dodecyl‐s''‐ (α, α'‐dimethyl‐α''‐acetic acid) trithiocarbonate (DDMAT) modified F127 with 2‐ (methacryloyloxy) ethyl ferrocencarboxylate (FcMA). The structures of as‐obtained chemicals were characterized by FTIR,1H NMR, and13C NMR. Additionally, the block copolymers molecular weight and polydispersity were measured using gel permeation chromatography. The electrochemical responsiveness of the polymers was investigated using cyclic voltammetry as well as the thermal stabilities of polymers and precursors were tested through DSC and TGA. The morphologies of electrospun fibers were observed through field emission scanning electronic spectroscopy and a fibrous diameter of 300–1100 nm was obtained. The results indicated that the suitable molecular weight of ferrocene ‐containing polymer would be processed in nanofibrous.

РЕЛАКСАЦИОННЫЕ СВОЙСТВА КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ НА ОСНОВЕ СМЕСЕЙ ЭПОКСИДНЫХ ПОЛИМЕРОВ И ТЕРМОЭЛАСТОПЛАСТОВ

The influence of thermoplastic elastomers, which are two-block statistical block copolymers based on polybutylene terephthalate and polytetramethylene oxide with a different ratio of rigid and elastic blocks, on the static and dynamic mechanical properties of epoxy polymers is studied. The initial compounds for the synthesis of block copolymers are dimethyl terephthalate, 1,4-butanediol and polytetramethylenoxide with a molecular weight of 2000. The tetrabutoxide is used as catalyst. The process of interaction of the initial components is carried out in two stages, the reaction of transesterification and copolycondensation is consistently carried out. The composition of BSP is set by the ratio of initial reagents. The total molecular weight of block copolymers is 30–40 thousand. The method of dynamic mechanical analysis shows that the introduction of modifiers leads to a decrease in molecular mobility in a wide temperature range from low-temperature (at 220K) to high-temperature (at 380K) relaxation transitions. The magnitude of the effect depends on the ratio of rigid and flexible blocks in the block copolymer. It is assumed that the decrease in the tangent of the angle of mechanical losses at temperatures below the glass transition temperature and especially in the region of the β-transition, may be associated with the slowdown of relaxation processes at the interface of the epoxide matrix with rigid blocks of thermoplastic elastomer. The observed effects in the region of high-temperature transition may be associated with the restriction of freedom of conformational rearrangements near the interface of the epoxy polymer with polybutylene terephthalate and polytetramethylene oxide blocks and an increase in the cross-linking density of the epoxy. A noticeable decrease in the magnitude and creep rate of epoxy composites is found when thermoelastoplast is introduced.

Wet Brush Homopolymers as “Smart Solvents” for Rapid, Large Period Block Copolymer Thin Film Self-Assembly

The spontaneous formation of periodic nanopatterns through the self-assembly of block copolymer (BCP) thin films offers an enticing path to engineer functional material properties over large areas, but the prohibitively slow ordering of ultrahigh molecular weight BCPs that generate large pattern periods (>100 nm) severely restricts the design space in which BCPs may be used. Here, we demonstrate that blending lamellae-forming polystyrene-block-poly(methyl methacrylate) diblock copolymers with very low molecular weight polystyrene and poly(methyl methacrylate) homopolymers can reduce by an order-of-magnitude the times required to form ordered large period patterns through solvent vapor annealing. Using in situ grazing-incidence small-angle X-ray scattering and ex situ electron microscopy, we show that the added homopolymer plasticizers act as a “smart solvent”: They increase the mobility of the long BCP chains by amplifying the dilution effect during solvent vapor annealing but segregate to like domains du...

Nanopatterns with a Square Symmetry from an Orthogonal Lamellar Assembly of Block Copolymers.

A nanosquare array is an indispensable element for the integrated circuit design of electronic devices. Block copolymer (BCP) lithography, a promising bottom-up approach for sub-10 nm patterning, has revealed a generic difficulty in the production of square symmetry because of the thermodynamically favored hexagonal packing of self-assembled sphere or cylinder arrays in thin-film geometry. Here, we demonstrate a simple route to square arrays via the orthogonal self-assembly of two lamellar layers on topographically patterned substrates. While bottom lamellar layers within a topographic trench are aligned parallel to the sidewalls, top layers above the trench are perpendicularly oriented to relieve the interfacial energy between grain boundaries. The size and period of the square symmetry are readily controllable with the molecular weight of BCPs. Moreover, such an orthogonal self-assembly can be applied to the formation of complex nanopatterns for advanced applications, including metal nanodot square arrays.

Annealing treatments of cylindrical siloxane-based block copolymers optimized for nanomanufacturing

Abstract Ultra high resolution lithography (sub-15 nm) could be developed using the directed self-assembly of block copolymers (BCPs), for which a high incompatibility – i.e. high-χ – between the blocks is necessary. Here we present an industrial compatible scheme of the annealing processes performed on different PS-b-PDMS BCPs, presenting the horizontal cylindrical morphology to form line/space patterns by graphoepitaxy. For BCPs with a larger molecular weight (period 15 nm), we compare the annealing performances of different solvents with an emphasis on solvents satisfying the manufacturing requirements, where butylacetate appears to be well suited. Furthermore, we show that a lower molecular weight BCP (period 10 nm) presents a good self-assembly by thermal annealing. Both annealing processes developed here are fully integrable in a microelectronics environment for high resolution lithography.

Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed.

Aspect Ratio-Controlled Synthesis of Uniform Colloidal Block Copolymer Ellipsoids from Evaporative Emulsions

Block copolymers (BCPs) confined in evaporative emulsions can assemble into ellipsoidal particles when solvent evaporation is faster than polymer diffusion within the droplet. Here, we report the synthesis of monodisperse, ellipsoidal polystyrene-block-1,4-polybutadiene (PS-b-PB) BCP particles with tunable aspect ratios (ARs) ranging from 1.0 to 2.2 and particle sizes ranging from 0.1 to 5 μm by membrane emulsification and subsequent solvent evaporation. The ratio of the propagation distance (lp) of ordered BCP domains perpendicular to the particle surface to the particle size (rBCP), or lp/rBCP, was found to be a critical parameter dictating the particle shape, where lp/rBCP > 1 yielded ellipsoids. We show that the AR of colloidal BCP ellipsoids can be precisely controlled by varying particle size (i.e., membrane pore size) and BCP molecular weight, as predicted by theoretical calculations of the free energy of particle elongation including three terms: (1) the interfacial energy between the two blocks o...

In Situ Synthesis of Ternary Block Copolymer/Homopolymer Blends for Organic Photovoltaics.

A detailed investigation of in situ-synthesized all-conjugated block copolymer (BCP) compatibilized ternary blends containing poly(3-hexylthiophene) (P3HT) and poly{[ N, N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dibcarboximide)-2,6-diyl]- alt-5,5'-(2,2'-bithiophene)} (PNDIT2) as donor and acceptor polymers, respectively, is presented. Both polymers are incompatible and show strong segregation in blends, which renders compatibilization with their corresponding BCPs promising to enable nanometer-phase-separated structures suitable for excitonic devices. Here, we synthesize a ternary block copolymer/homopolymer blend system and investigate the phase behavior as a function of block copolymer molecular weight and different annealing conditions. The device performance decreases on increasing annealing temperatures. To understand this effect, morphological investigations including atomic force microscopy, high-resolution transmission electron microscopy (HR-TEM), and grazing incidence wide- and small-angle X-ray scattering (GIWAXS/GISAXS) are carried out. On comparing domain sizes of pristine and compatibilized blends obtained from GISAXS, a weak compatibilization effect appears to take place for the in situ-synthesized ternary systems. The effect of thermal annealing is most prevalent for all samples, which, for the highest annealing temperature above the melting point of PNDIT2 (310 °C), ultimately leads to a change from the face-on to edge-on orientation of PNDIT2, as seen in GIWAXS. This effect dominates and decreases all photovoltaic parameters, irrespective of whether a pristine or compatibilized blend is used.

Perpendicular Structure Formation of Block Copolymer Thin Films during Thermal Solvent Vapor Annealing: Solvent and Thickness Effects.

Solvent vapor annealing of block copolymer (BCP) thin films can produce a range of interesting morphologies, especially when the perpendicular orientation of micro-domains with respect to the substrate plays a role. This, for instance, allows BCP thin films to serve as useful templates for nanolithography and hybrid materials preparation. However, precise control of the arising morphologies is essential, but in most cases difficult to achieve. In this work, we investigated the solvent and thickness effects on the morphology of poly(styrene-b-2 vinyl pyridine) (PS-b-P2VP) thin films with a film thickness range from 0.4 L0 up to 0.8 L0. Ordered perpendicular structures were achieved. One of the main merits of our work is that the phase behavior of the ultra-high molecular weight BCP thin films, which hold a 100-nm sized domain distance, can be easily monitored via current available techniques, such as scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM). Systematic monitoring of the self-assembly behavior during solvent vapor annealing can thus provide an experimental guideline for the optimization of processing conditions of related BCP films systems.

Effect of surfactant chain length on drug release kinetics from microemulsion-laden contact lenses

The effect of surfactant chain lengths [sodium caprylate (C8), Tween 20 (C12), Tween 80 (C18)] and the molecular weight of block copolymers [Pluronic F68 and Pluronic F 127] were studied to determine the stability of the microemulsion and its effect on release kinetics from cyclosporine-loaded microemulsion-laden hydrogel contact lenses in this work. Globule size and dilution tests (transmittance) suggested that the stability of the microemulsion increases with increase in the carbon chain lengths of surfactants and the molecular weight of pluronics. The optical transmittance of direct drug-laden contact lenses [DL-100] was low due to the precipitation of hydrophobic drugs in the lenses, while in microemulsion-laden lenses, the transmittance was improved when stability of the microemulsion was achieved. The results of in vitro release kinetics revealed that drug release was sustained to a greater extent as the stability of microemulsion was improved as well. This was evident in batch PF127-T80, which showed sustained release for 15days in comparison to batch DL-100, which showed release up to 7days. An in vivo drug release study in rabbit tear fluid showed significant increase in mean residence time (MRT) and area under curve (AUC) with PF-127-T80 lenses (stable microemulsion) in comparison to PF-68-SC lenses (unstable microemulsion) and DL-100 lenses. This study revealed the correlation between the stability of microemulsion and the release kinetics of drugs from contact lenses. Thus, it was inferred that the stable microemulsion batches sustained the release of hydrophobic drugs, such as cyclosporine from contact lenses for an extended period of time without altering critical lens properties.

Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers.

The incorporation of structural color into 3D printed parts is reported, presenting an alternative to the need for pigments or dyes for colored parts produced through additive manufacturing. Thermoplastic build materials composed of dendritic block copolymers were designed, synthesized, and used to additively manufacture plastic parts exhibiting structural color. The reflection properties of the photonic crystals arise from the periodic nanostructure formed through block copolymer self-assembly during polymer processing. The wavelength of reflected light could be tuned across the visible spectrum by synthetically controlling the block copolymer molecular weight and manufacture parts that reflected violet, green, or orange light with the capacity to serve as selective optical filters and light guides.

Morphological Evolution of Block Copolymer Particles: Effect of Solvent Evaporation Rate on Particle Shape and Morphology.

Shape and morphology of polymeric particles are of great importance in controlling their optical properties or self-assembly into unusual superstructures. Confinement of block copolymers (BCPs) in evaporative emulsions affords particles with diverse structures, including prolate ellipsoids, onion-like spheres, oblate ellipsoids, and others. Herein, we report that the evaporation rate of solvent from emulsions encapsulating symmetric polystyrene-b-polybutadiene (PS-b-PB) determines the shape and internal nanostructure of micron-sized BCP particles. A distinct morphological transition from the ellipsoids with striped lamellae to the onion-like spheres was observed with decreasing evaporation rate. Experiments and dissipative particle dynamics (DPD) simulations showed that the evaporation rate affected the organization of BCPs at the particle surface, which determined the final shape and internal nanostructure of the particles. Differences in the solvent diffusion rates in PS and PB at rapid evaporation rates induced alignment of both domains perpendicular to the particle surface, resulting in ellipsoids with axial lamellar stripes. Slower evaporation rates provided sufficient time for BCP organization into onion-like structures with PB as the outermost layer, owing to the preferential interaction of PB with the surroundings. BCP molecular weight was found to influence the critical evaporation rate corresponding to the morphological transition from ellipsoid to onion-like particles, as well as the ellipsoid aspect ratio. DPD simulations produced morphologies similar to those obtained from experiments and thus elucidated the mechanism and driving forces responsible for the evaporation-induced assembly of BCPs into particles with well-defined shapes and morphologies.