Morphology Of Block Copolymers Research Articles

Stabilization of complex morphologies in highly disperse AB diblock copolymers

Block copolymers have the unique property to self-assemble into ordered microstructures with well-defined periodicity. Among the various attainable microdomain morphologies, complex morphologies with inherent structural connectivity are highly desirable. While such structures are difficult to obtain in monodisperse block copolymers, they may be stabilized by increasing block dispersity. In this study, we prepare poly (styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers where dispersity of both PS and PMMA blocks are varied independently. Morphology examination of the diblocks reveals that at fixed block composition, dispersity dictated phase transition is observed. In particular, in the case where dispersity of both blocks are high, the polymers are found to exhibit perforated lamellae and disordered bicontinuous morphologies. Dissipative particle dynamics (DPD) simulations are also carried out to confirm the stability of the observed morphologies. These results show that control of block dispersity can effectively stabilize energetically disfavored complex morphologies in block copolymers.

Influence of pore morphology on the diffusion of water in triblock copolymer membranes.

Understanding the transport properties of water in self-assembled block copolymer morphologies is important for furthering the use of such materials as water-purifying membranes. In this study, we used coarse-grained dissipative particle dynamics simulations to clarify the influence of pore morphology on the self-diffusion of water in linear-triblock-copolymer membranes. We considered representative lamellar, cylindrical, and gyroid morphologies and present results for both the global and local diffusivities of water in the pores. Our results suggest that the diffusivity of water in the confined, polymer-coated pores differs from that in the unconfined bulk. Explicitly, in confinement, the mobility of water is reduced by the hydrodynamic friction arising from the hydrophilic blocks coating the pore walls. We demonstrate that in lamella and cylindrical morphologies, the latter effects can be rendered as a universal function of the pore size relative to the brush height of the hydrophilic blocks.

Tuning the morphology of segmented block copolymers with Zr-MOF nanoparticles for durable and efficient hydrocarbon separation membranes

PU/UiO66-NH2membranes demonstrate exceptional C4H10/CH4selectivity due to the enhanced gas solubility associated with MOFs and tuning the polymer morphology.

Correlations of Morphology and Optoelectronic Property of a DB1fA Type Block Co-Polymer

Correlations of Morphology and Optoelectronic Property of a DB1fA Type Block Co-Polymer

Nanofiller Dispersion, Morphology, Mechanical Behavior, and Electrical Properties of Nanostructured Styrene-Butadiene-Based Triblock Copolymer/CNT Composites.

A nanostructured linear triblock copolymer based on styrene and butadiene with lamellar morphology is filled with multiwalled carbon nanotubes (MWCNTs) of up to 1 wt% by melt compounding. This study deals with the dispersability of the MWCNTs within the nanostructured matrix and its consequent impact on block copolymer (BCP) morphology, deformation behavior, and the electrical conductivity of composites. By adjusting the processing parameters during melt mixing, the dispersion of the MWCNTs within the BCP matrix are optimized. In this study, the morphology and glass transition temperatures (Tg) of the hard and soft phase are not significantly influenced by the incorporation of MWCNTs. However, processing-induced orientation effects of the BCP structure are reduced by the addition of MWCNT accompanied by a decrease in lamella size. The stress-strain behavior of the triblock copolymer/MWCNT composites indicate higher Young’s modulus and pronounced yield point while retaining high ductility (strain at break ~ 400%). At a MWCNT content of 1 wt%, the nanocomposites are electrically conductive, exhibiting a volume resistivity below 3 × 103 Ω·cm. Accordingly, the study offers approaches for the development of mechanically flexible functional materials while maintaining a remarkable structural property profile.

Anionic Grafting to Strategies for Functional Polymethacrylates: Convenient Preparation of Stimuli‐Responsive Block Copolymer Architectures

Front Cover: Functional block copolymers are promising candidates for many important applications. In article number 1800548 by Markus Gallei and co-workers, a convenient postmodification strategy for responsive poly(methacrylate)s (PMA) to an existing block copolymer (BCP) architecture is reported by application of a “grafting to” strategy. The grafted BCPs are capable of undergoing microphase separation in the bulk state or they can form stimuli-responsive micelles in various solvents. The switching capabilities and the BCP morphology can be fine-tuned by the amount and kind of the grafted PMA. This article is dedicated to Reimund Stadler, inspiring us with his seminal work on block copolymers.

Influence of Molecular Architecture and Chain Flexibility on the Phase Map of Polystyrene-block-poly(dimethylsiloxane) Brush Block Copolymers

We report the microphase-separated morphologies of model bottlebrush block copolymers (BBCPs) over a wide range of architectural design parameters. Densely grafted polystyrene-block-poly(dimethylsi...

Controlled morphological transition of ABC triblock copolymer aided by oleic acid via hydrogen bonding

A facile method is introduced to tune the aggregate morphologies of ABC triblock copolymer in selective media by combining the self-assembly and hydrogen bonding. Poly(styrene)-block-poly(1,4-butadiene)-block-poly(2-vinyl pyridine), abbreviated for PS-b-PBd-b-P2VP and used as an ABC triblock copolymer, self-assembles in toluene and methanol mixture to form discoid micelles with PBd as the disk containing part of PS domains in the core, other PS as bumps and P2VP as corona, respectively. When oleic acid (OA) is added in the assembly system, supramolecular polymer PS-b-PBd-b-P2VP(OA) is prepared by the hydrogen bonding between OA and P2VP of triblock copolymer. As a result, biscuit-like and mushroom-like micelles are formed with assistance of hydrogen bonding. Interestingly, the biscuit-like and mushroom-like micelles can transform reciprocally by fission and fusion mechanism through varying the volume ratio of toluene and methanol. Thus, it provides a simple and convenient approach to control the aggregate morphologies of block copolymers by tuning the hydrogen bonding and selective solvent content. The multicompartment micelles from ABC triblock copolymer may present potential applications in drug delivery, targeting, catalysis and others.

Complex core-shell morphologies of block copolymers revealed beneath the surface

This paper identifies and characterizes complex core-shell morphologies in thin films of a polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) (BVT) triblock terpolymer. The spin-coated BVT film develops into two distinct microphase separated structures with thickness variation during solvent annealing in a well-controlled atmosphere of THF vapor. Cylinders parallel to the film plane are found in thinner terraces and featureless areas that are characteristic of the lying lamella phase, or disordered structures are found in thicker terraces. Underneath the surface, we found that these microphase separated structures exhibit core-shell morphologies, i.e. surface ablation revealed core-shell cylinders and core-shell perforated lamellae under a cover layer in each terrace. Time-resolved study upon solvent annealing shows that the dynamics of microdomain evolution are affected by the extent of annealing time. The structural development in the BVT terpolymer films on corrugated supports demonstrates flow-field-induced sequenced ordering of the microdomains.

Solvent mediated inclusion of metal oxide into block copolymer nanopatterns: Mechanism of oxide formation under UV-Ozone treatment

Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time.

Tuneable Metamaterial-like Platforms for Surface-Enhanced Raman Scattering via Three-Dimensional Block Co-polymer-Based Nanoarchitectures.

Surface-enhanced Raman spectroscopy (SERS) pushes past the boundaries and inherent weaknesses of Raman spectroscopy, with a great potential for a broad range of applications particularly, for sensing. Yet, current real world applications are limited due to poor reproducibility, low-throughput, and stability issues. Here, we present the design and fabrication of self-assembly guided structures based on adjustable block co-polymer (BCP) nanomorphologies and demonstrate reproducible SERS enhancement across large areas. Golden three-dimensional (3D) nanostructured morphologies with controllable dimensions and morphologies exhibit high chemical stability, enhanced plasmonic properties and are highly suitable for SERS substrates due to the strong enhancement of the electromagnetic field. Adjustable, free standing porous nanostructures, continuous in 3D space are achieved by removal of selected BCP constituents. Four BCP morphologies and the corresponding achievable enhancement factors are investigated at 633 and 785 nm excitation wavelengths. The choice of excitation laser is shown to greatly affect the observed signal enhancement, highlighting the sensitivity of the technique to the underlying surface architecture and length scales. By using BCP assemblies, it is possible to reliably tune these parameters to match specific applications, thus bridging the gap toward the realization of applied metamaterials. The fabricated SERS platforms via three-dimensional block co-polymer-based nanoarchitectures provide a recipe for intelligent engineering and design of optimized SERS-active substrates for utilization in the Raman spectroscopy-based devices toward enabling the next-generation technologies fulfilling a multitude of criteria.

Reaction: Size Distribution in Olefin Block Copolymers: Not Bad at All

Hongyu Chen completed his PhD in macromolecular science at Case Western Reserve University in 2010. He is a fellow of the Dow Chemical Company, where he focuses on developing new products. He is also a fellow of the American Physical Society and American Chemical Society. Valeriy Ginzburg completed his PhD in polymer physics at the Moscow Institute of Physics and Technology in 1992. He is a senior scientist at the Dow Chemical Company and a fellow of the American Physical Society.

Confined Self-Assembly Enables Stabilization and Patterning of Nanostructures in Liquid-Crystalline Block Copolymers

Various pathways have been utilized to manipulate microphase separation (MPS) of block copolymers, but the obtained MPS nanostructures are often suffering from poor thermal stability. Here, confined self-assembly is first adopted to thermally stabilize and conveniently pattern the MPS morphologies of an amphiphilic liquid-crystalline block copolymer (LCBC) composed of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic azobenzene-containing polymethacrylate. The MPS nanostructures are thermally stabilized by top coating a layer of water-soluble polymer, sodium polystyrenesulfonate (PSSNa), as a result of coordination interaction between PEO and PSSNa. Interestingly, both thermal annealing and rubbing-treated polyimide film caused reorientation of mesogens in the PSSNa-coated LCBC film; however, the orientation of PEO nanocylinders remained unchangeable. This indicates that the PEO nanocylinders are selectively anchored by the PSSNa covering layer, regardless of the changes of mesogenic orientation. Thus, complicated hierarchical nanostructures can be fabricated effortlessly and preserved nondestructively by selected-area confined self-assembly or noncontact photopatterned technology due to the existence of photoresponsive azobenzene moieties.

Self-assembly morphology of block copolymers in sub-10 nm topographical guiding patterns

Fabrication of sub-10 nm topographical guiding patterns, block copolymer directed self-assembly, thorough morphology analysis and free energy modelling.

Block copolymer microparticles comprising inverse bicontinuous phases prepared via polymerization-induced self-assembly.

Traditionally, post-polymerization processing routes have been used to obtain a wide range of block copolymer morphologies. However, this self-assembly approach is normally performed at rather low copolymer concentration, which precludes many potential applications. Herein, we report a facile method for the preparation of block copolymer particles exhibiting complex internal morphology via polymerization-induced self-assembly (PISA). More specifically, a series of diblock copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) alternating copolymerization of styrene (St) with N-phenylmaleimide (NMI) using a poly(N,N-dimethylacrylamide) (PDMAC) stabilizer as a soluble precursor. Conducting such PISA syntheses in a 50 : 50 w/w ethanol/methyl ethyl ketone (MEK) mixture leads directly to the formation of micrometer-sized PDMAC-P(St-alt-NMI) diblock copolymer particles at 20% w/w solids. Adjusting the degree of polymerization (DP) of the core-forming P(St-alt-NMI) block to target highly asymmetric copolymer compositions provides convenient access to an inverse bicontinuous phase. TEM studies of intermediate structures provide useful insights regarding the mechanism of formation of this phase. SEM studies indicate that the final copolymer particles comprise perforated surface layers and possess nanostructured interiors. In addition, control experiments using 1,4-dioxane suggest that the high chain mobility conferred by the MEK co-solvent is essential for the formation of such inverse bicontinuous structures. One-pot PISA formulations are reproducible and involve only cheap, commercially available starting materials, so they should be readily amenable to scale-up. This augurs well for the potential use of such nanostructured micrometer-sized particles as new organic opacifiers for paints and coatings.

Dependence of Block Copolymer Domain Spacing and Morphology on the Cation Structure of Ionic Liquid Additives

We find that the topology of phase diagrams for block copolymer/ionic liquid (IL) blends and the scaling of the phase-separated domains are significantly influenced by the cation structure of the IL. We have varied the cation structure of bis(trifluoromethane sulfonyl)imide ILs and investigated the influence of these changes on the thermodynamics of blends with polystyrene-b-poly(methyl methacrylate). Effective χ parameters (χeff) were determined and used to plot phase diagrams, where significant differences were observed, suggesting that the balance of Coulombic and van der Waals interactions was influencing the topology of the phase diagrams. The relationship between IL structure and scaling of domain spacing was also investigated. These important findings shed additional light on the thermodynamic-driven properties of IL-containing block copolymers and have practical implications for how they can be used in nanotemplating or block copolymer lithography applications.

Diffusion in Lamellae, Cylinders, and Double Gyroid Block Copolymer Nanostructures.

We study transport of penetrants through nanoscale morphologies motivated by common block copolymer morphologies, using confined random walks and coarse-grained simulations. Diffusion through randomly oriented grains is 1/3 for cylinder and 2/3 for lamellar morphologies versus an unconstrained (homopolymer) system, as previously understood. Diffusion in the double gyroid structure depends on the volume fraction and is 0.47-0.55 through the minority phase at 30-50 vol % and 0.73-0.80 through the majority at 50-70 vol %. Thus, among randomly oriented standard minority phase structures with no grain boundary effects, lamellae is preferable for transport.

Static miscible vapor environment controlled honeycombed morphology in polystyrene–b–poly(methyl methacrylate) films

Breath figure (BF) technology involves a concise process to obtain large sized honeycombed morphology in polymer film. The vapor condensability and the affinity between the condensed vapor and the polymer play key roles in the film morphology. A static breath figure technology was introduced here to control the porous film morphologies of homo-polystyrene (homo-PS), homo-polymethyl methacrylate (homo-PMMA), and block copolymer polystyrene-block-polymethyl methacrylate (PS–b–PMMA) with different total molecular weights and PS contents by using miscible vapor consisting of ethanol/water or acetone/water as atmospheric environment. The results showed that the vapor including component with low evaporation enthalpy led to larger droplets and favored to form regular honeycombed morphologies. The pore size depended strongly on the total block copolymer molecular weights and PS contents: the larger the total molecular weight and the lower the hydrophobic PS content, the larger the pore size.

Synthesis of diblock copolymer nano-assemblies: Comparison between PISA and micellization

RAFT dispersion polymerization following the formulation of polymerization induced self-assembly (PISA) and micellization of pre-prepared amphiphilic block copolymers in block-selective solvents are generally used to prepare block copolymer nano-assemblies. Herein, we make a comparison between these two methods by employing two typical block copolymers of poly(acrylic acid)-block-polystyrene (PAA-b-PS) and poly(ethylene glycol)-block-polystyrene (PEG-b-PS). It is found that the block copolymer nano-assemblies prepared by these two methods are similar with each other when the solvophilic block is relatively long and the solvophobic block is relatively short. Otherwise, the block copolymer nano-assemblies by these two methods are different. The possible reasons leading to the difference between PISA and micellization are discussed, and the kinetic factors including temperature, polymer concentration and solvent are ascribed. It is thought that the present study is helpful to clarify how the kinetic factors beyond the block copolymer itself affecting block copolymer morphology.

Topology Affecting Block Copolymer Nanoassemblies: Linear Block Copolymers versus Star Block Copolymers under PISA Conditions

Linear and star block copolymer (BCP) nanoassemblies of [poly(4-vinylpyridine)-block-polystyrene]n ([P4VP-b-PS]n) with different arm numbers have been synthesized by RAFT dispersion polymerization under formulation of polymerization-induced self-assembly (PISA). All RAFT dispersion polymerizations employing mono- and multifunctional macromolecular chain transfer agents proceed with similar polymerization kinetics. The size and/or morphology of [P4VP-b-PS]n nanoassemblies are firmly correlative to arm number n, and star [P4VP-b-PS]n BCPs have more complex morphology than the linear counterpart. Several interesting morphologies of star BCPs including small-sized vesicles and porous nanospheres have been synthesized, and they are compared with those of the linear counterpart. Our research indicates that topology is a significant parameter to dedicate the size and morphology of star BCP nanoassemblies under PISA conditions.