Microphase Separation Of Block Copolymers Research Articles

Propagator-Biased Chain Generation: Accurately Reverse Mapping Microphase-Separated Block Copolymers

Propagator-Biased Chain Generation: Accurately Reverse Mapping Microphase-Separated Block Copolymers

Liquid Crystal Promoted Self-Assembly of Statistical Copolymers into Diverse Nanostructures with Precise Dimensions.

In both natural and synthetic systems, the segregation of multicomponent entities is vital for regulating functions and the ultimate usage of materials. To accomplish the desired properties via nanosegregation or microphase separation, great effort is usually demanded in the synthesis. For example, microphase-separated block copolymers rely on the delicate controlled/living polymerization of different monomers in sequence. Here, we demonstrate that a facile one-pot copolymerization can generate statistical side-chain copolymers exhibiting well-defined and diverse nanostructures. Two hemiphasmidic (or wedge-shaped) cyclooctene monomers were designed, differing in the peripheral tails of the wedges (dodecyl vs. tetraethylene glycol), with lengths of ca. 1 nm. When combining the two monomers together, the statistical copolymers can show columnar liquid crystal (LC) phase and microphase-separated structures of the two monomers, including sphere, cylinder, double gyroid, and lamella. To the best of our knowledge, this is the first time the gyroid phase has been achieved in statistical copolymers. We further demonstrate that changing the side chains to calamitic (or rod-like) mesogens or the backbone to less flexible polynorbornene, the statistical copolymers can also undergo microphase separation of the side chains. The intrinsic self-assembly scheme of statistical copolymers with mesogenic side chains, which are chemically accurate, affords the resultant nanostructures with precise periodicities at the 10- or sub-10-nm scale. Given the small chemical difference between the side-chain tails, microphase separation is promoted by the anisotropic packing of mesogens. It is validated that the statistical side-chain LC copolymers can be a versatile platform for creating nanostructured materials with tailored functionalities.

Vacuum-driven orientation of Nanostructured polystyrene-block-Poly(L-lactide) block copolymer thin films for Nanopatterning

Herein, we demonstrate a simple approach to control the orientation of cylinder-forming nanostructures in polystyrene-block-poly(L-lactide) (PS-b-PLLA) BCP thin films through thermal annealing under a high-vacuum environment. Surface tension discrepancy between the constituent blocks is critical in controlling the aimed orientation of self-assembled nanostructures in block copolymer (BCP) thin films. For BCP self-assembly, temperature has been widely utilized as a thermodynamic state variable under ambient pressure conditions, whereas the use of high vacuum (low pressure) for thermal annealing is limited. It has been observed that temperature can alter the surface tension only marginally with increasing temperature for polymeric materials; as a result, the pressure dependence of surface tension for PS and PLLA was investigated. By increasing the vacuum degree during thermal annealing, the surface tension discrepancy between the PS and PLLA blocks can be reduced significantly. Accordingly, during thermal annealing under high vacuum degree, a neutral air polymer interface can be generated for the BCP thin films, resulting in the formation of perpendicular cylinders from the neutral surface of the thin film through BCP microphase separation.

Solvent-induced microphase separation membranes of block poly (aryl ether sulfone) copolymer with high selectivity of O2/N2 separation

Gas separation membranes have a wide range of applications in industry, and there are two important factors in judging membrane standards permeability and selectivity. How to improve the selectivity of gas separation membranes while improving permeability is a challenge. In this study, poly (aryl ether sulfone) (PES) block copolymers were synthesized from fluorine-terminated polysulfone (PSF–F) and hydroxyl-terminated cardo PES containing phenyl substituted isoindolinone side group (PES-PPI-OH). Large side groups can enlarge the free volume and hinder chain movement to improve gas permeation behavior. Solvent-induced microphase separation of block copolymers by casting membranes with solvent benzyl alcohol (BA) can improve selectivity. The PSF-b-PES-PPI (10:10) BA membrane maintain good mechanical properties and tensile strength up to 93 MPa which compared to random polymer membrane rises to 14 MPa. Gas permeation at 23 °C showed that the O2/N2 selectivity of PSF-b-PES-PPI (5:15)BA membrane was 10.6, which was the 2008 Robeson upper bound. Thus, poly (aryl ether sulfone) materials showed great potential application for O2/N2 separation.

The permeability of diamond and other microphase-separated morphologies in copolymer films.

A method is proposed for the theoretical assessment of potential membrane properties in materials based on microphase-separated block copolymer films subjected to the etching of one of the components. The concepts of topological permeability and connectivity contrast introduced by the authors are used to compare the percolation characteristics of simple cubic, diamond, and diamond-like morphologies compatible with the slit geometry and specified by a given distribution of the order parameter. The diamond-like morphology, which has the most promising transport characteristics, can be formed in a thin film of diblock copolymer AB placed on a chemically structured substrate. For this case, the quantitative analysis of permeability for certain parameters of the model system is carried out using the local distribution of A and B units calculated with the self-consistent field theory of microphase separation. The results obtained may be useful for the design of isoporous membranes based on block copolymers.

Strategy to simulate and fit 2D grazing-incidence small-angle X-ray scattering patterns of nanostructured thin films.

Grazing-incidence small-angle X-ray scattering (GISAXS) is a widely used method for the characterization of the nanostructure of supported thin films and enables time-resolved in situ measurements. The 2D scattering patterns contain detailed information about the nanostructures within the film and at its surface. However, this information is distorted not only by the reflection of the X-ray beam at the substrate-film interface and its refraction at the film surface but also by scattering of the substrate, the sample holder and other types of parasitic background scattering. In this work, a new, efficient strategy to simulate and fit 2D GISAXS patterns that explicitly includes these effects is introduced and demonstrated for (i) a model case nanostructured thin film on a substrate and (ii) experimental data from a microphase-separated block copolymer thin film. To make the protocol efficient, characteristic linecuts through the 2D GISAXS patterns, where the different contributions dominate, are analysed. The contributions of the substrate and the parasitic background scattering - which ideally are measured separately - are determined first and are used in the analysis of the 2D GISAXS patterns of the nanostructured, supported film. The nanostructures at the film surface and within the film are added step by step to the real-space model of the simulation, and their structural parameters are determined by minimizing the difference between simulated and experimental scattering patterns in the selected linecuts. Although in the present work the strategy is adapted for and tested with BornAgain, it can be easily used with other types of simulation software. The strategy is also applicable to grazing-incidence small-angle neutron scattering.

Polymerization Induced Microphase Separation for the Fabrication of Nanostructured Materials.

Polymerization induced microphase separation (PIMS) is a strategy used to develop unique nanostructures with highly useful morphologies through the microphase separation of emergent block copolymers during polymerization. In this process, nanostructures are formed with at least two chemically independent domains, where at least one domain is composed of a robust crosslinked polymer. Crucially, this synthetically simple method is readily used to develop nanostructured materials with the highly coveted co-continuous morphology, which can also be converted into mesoporous materials by selective etching of one domain. As PIMS exploits a block copolymer microphase separation mechanism, the size of each domain can be tightly controlled by modifying the size of block copolymer precursors, thus providing unparalleled control over nanostructure and resultant mesopore sizes. Since its inception 11 years ago, PIMS has been used to develop a vast inventory of advanced materials for an extensive range of applications including biomedical devices, ion exchange membranes, lithium-ion batteries, catalysis, 3D printing, and fluorescence-based sensors, among many others. In this review, we provide a comprehensive overview of the PIMS process, summarize latest developments in PIMS chemistry, and discuss its utility in a wide variety of relevant applications.

Polymerization Induced Microphase Separation for the Fabrication of Nanostructured Materials

AbstractPolymerization induced microphase separation (PIMS) is a strategy used to develop unique nanostructures with highly useful morphologies through the microphase separation of emergent block copolymers during polymerization. In this process, nanostructures are formed with at least two chemically independent domains, where at least one domain is composed of a robust crosslinked polymer. Crucially, this synthetically simple method is readily used to develop nanostructured materials with the highly coveted co‐continuous morphology, which can also be converted into mesoporous materials by selective etching of one domain. As PIMS exploits a block copolymer microphase separation mechanism, the size of each domain can be tightly controlled by modifying the size of block copolymer precursors, thus providing unparalleled control over nanostructure and resultant mesopore sizes. Since its inception 11 years ago, PIMS has been used to develop a vast inventory of advanced materials for an extensive range of applications including biomedical devices, ion exchange membranes, lithium‐ion batteries, catalysis, 3D printing, and fluorescence‐based sensors, among many others. In this review, we provide a comprehensive overview of the PIMS process, summarize latest developments in PIMS chemistry, and discuss its utility in a wide variety of relevant applications.

Single-molecule tracking of dye diffusion in synthetic polymers: A tutorial review

Single-molecule tracking (SMT) methods have been widely employed to offer a high-resolution characterization of synthetic polymers under ambient conditions and, thus, have advanced our understanding of their unique material properties. SMT is based on the systematic monitoring of the diffusive motions of individual fluorescent dye molecules in the as-prepared polymer thin films or thicker monoliths. Quantitative assessment of the recorded SMT video data involves the systematic analysis of the generated diffusion trajectories of a single molecule using well-established and reported methods. The results have offered a wealth of new information on the structural alignment, orientational order, and long-range continuity of the polymer microdomains; the nanoscale material heterogeneities governed by defects, misalignment, and ill-controlled preparation conditions; as well as the various forms of probe–host interactions on the single-molecule level. In the first part of this Tutorial review, we describe the fundamental principles and instrumentation of SMT, before offering interested readers and potential future SMT users a practical guidance on the selection of fluorescent probe molecules, preparation of suitable samples, and optimization of experimental conditions and imaging parameters. Then, we highlight several representative SMT studies in microphase-separated block copolymers, and semicrystalline and amorphous homopolymers to further emphasize the usefulness of SMT methods for polymer characterization without neglecting some of their shortcomings. This Tutorial review is written with the motivation to attract new researchers to the fast-growing field and assist them in starting their own SMT research of synthetic polymers and other technologically useful soft matter systems.

Dual sugar and temperature responsive isoporous membranes for protein sieving with improved separation coefficient and decreased denaturation

Sugar dissolved in solution is found to stabilize native structure of proteins and notably decrease their denaturation. To better utilization of this unique performance, we herein studied the preparation and application of a novel isoporous membrane with dual sugar and temperature responsiveness that offered both decreased protein denaturation and improved separation efficiency. New block copolymers (BCPs) with poly (N-isopropyl acrylamide-co-acrylamidophenyl boronic acid) P(NIPAM-co-APBA) as pore forming blocks were synthesized and adopted to prepare isoporous membranes via the SNIPS method. The boronic acid moieties in P(NIPAM-co-APBA) were found to endow membranes with adoptive changes of pore size with the variation of sugar concentrations. The microphase separation of BCPs in concentrated solutions and thin film were carefully studied, observing that APBA attached to pore-forming segment greatly increased the phase separation strength for BCPs. Composition analysis indicated that membranes with uniform pore structures showing higher contents of APBA groups on surface, uncovering an interesting structure-composition relationship that segments with higher fractions of APBA moieties segregated much stronger to pores and surface. Sugar dependent permeability and protein sieving were also determined, observing that the separation coefficient increased sharply from 4.2 to 11 for protein mixture of Hemoglobin/Lysozyme, suggesting that prepared isoporous membranes had enabled a faster separation of proteins in the presence of sugars. It was finally found that sugar in solution simultaneously reduced membrane fouling as it decreased protein denaturation during the separation. Our results demonstrate that novel isoporous membranes fabricated from bio-responsive BCPs with specifically designed functionality will enable protein separation with reduced denaturation, decreased membrane fouling and higher separation selectivity, which remain a big challenge for traditional isoporous membranes produced from well-explored BCPs.

Fabrication of Block Copolymer Templated Extended Surface Model Electrocatalysts By Atomic Layer Deposition and Physical Vapor Deposition

Templating platinum group metal (PGM) nanostructures from microphase separated block copolymers (BCPs) allows for electrocatalytic activity to be studied on highly ordered, model surfaces with precisely controlled feature sizes and morphologies, thereby allowing catalyst electroactivity and stability to be probed as a function of nanoscale geometry. In our previous work [1], BCP templated electrocatalysts fabricated via incipient wetness impregnation of PGM precursors were tested for hydrogen oxidation/evolution and water-splitting activity on interdigitated electrodes using liquid and solid polymer electrolytes. This talk presents the fabrication of such electrocatalysts via Atomic Layer Deposition (ALD) and Physical Vapor Deposition (PVD) techniques (e-beam evaporation and sputtering). Self-assembled lamellae of poly-(styrene-block-methylmethacrylate) (PSbPMMA) thin films on Si wafer and glassy carbon substrates were subjected to 5 - 15 ALD cycles with trimethylaluminium (TMA) precursor to induce selective growth of alumina in the PMMA domains via Sequential Infiltration Synthesis. Thereafter, the polymer template was removed via Reactive Ion Etching (RIE) with oxygen plasma. The resultant alumina nanostructures templated from self-assembled PSbPMMA was then used as a substrate either for Platinum ALD with (trimethyl)methylcyclopentadienylplatinum(IV) precursor atop a Titanium Nitride adhesive layer, or for sputtering of Pt atop a Ti adhesive layer to obtain conformal Pt coatings of up to 20 nm in thickness. When e-beam evaporation was used, The PMMA domains were selectively removed by successive wet and dry etch steps, followed by deposition and lift-off. The PGM electrocatalyst nanostructures were characterized via a combination of electron microcopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and the Pt content of the catalysts were determined via microwave leaching and digestion of the electrocatalyst thin film followed by Inductively Coupled Plasma Mass Spectroscopy. The nanostructured electrocatalysts were tested for oxygen reduction (ORR) activity in a conventional rotating disk electrode setup using 0.1 M perchloric acid electrolyte, and the ORR mass activities and active surface area were obtained.[1] Bhattacharya, D., Arges, C. G., et al., Small, 2021, 17, 2100437

Tailor‐Made Vinylogous Urethane Vitrimers Based on Binary and Ternary Block and Random Copolymers: An Approach toward Reprocessable Materials

AbstractVitrimers are promising reprocessable materials. To tune their properties, microphase separated block copolymers as backbones play an essential role in the thermal and mechanical properties of the resulting nanostructured networks. In this study, various narrow disperse di‐ and triblock copolymers containing a hydroxyethyl methacrylate block and, for comparison, random copolymers of the same comonomers are synthesized in a controlled manner by photoiniferter reversible addition‐fragmentation chain transfer polymerization. Subsequently, the copolymers are modified by acetoacetate groups and cross‐linked with diamines. After curing, the di‐ and triblock copolymer‐based vitrimers exhibit excellent thermal and mechanical properties compared to random ones; moreover, their characteristic properties can be adjusted by different types and amounts of diamines. As the transamination reaction is a thermoreversible exchange reaction, the resulting vitrimers are reprocessable and therefore are recyclable materials. The combining of two of these classes of soft materials, namely vitrimers and block copolymers, leads to materials with a broad spectrum of adjustable mechanical properties for various applications with an improved end‐of‐life management, when compared to permanently crosslinked thermosets.

Induced Circular Dichroism and Circularly Polarized Luminescence for Block Copolymers with Chiral Communications.

Many sophisticated chiral materials are found in living organisms, giving specific functions and required complexity. Owing to the remarkable optical properties of chiral materials, they have drawn significant attention for the development of synthetic materials to give optical activities for appealing applications. In contrast to a top-down approach, the bottom-up approach from self-assembled systems with chiral host-achiral guest and achiral guest-chiral host for induced circular dichroism and induced circularly polarized luminescence has greatly emerged because of its cost-effective advantage with easy fabrication for mesoscale assembly. Self-assembled hierarchical textures with chiral sense indeed give significant amplification of the dissymmetry factors of absorption and luminescence (gabs and glum ), resulting from the formation of well-ordered superstructures and phases with the building of chromophores and luminophores. By taking advantage of the microphase separation of block copolymers via self-assembly, a variety of well-defined chiral nanostructures can be formed as tertiary superstructures that can be further extended to quaternary phases in bulk or thin film. In this article, a conceptual perspective is presented to utilize the self-assembly of chiral block copolymers with chiral communications, giving quaternary phases with well-ordered textures at the nanoscale for significant enhancement of dissymmetry factors.

Atomic insights into shock-induced spalling of polyurea by molecular dynamics simulation

Some block-copolymer elastomers are regarded as competitors to metal for lightweight impact protection design. However, the microscopic spalling mechanism of polymer is still unclear owing to the complex macromolecule structure. Molecular dynamics (MD) can overcome the drawback in the experiment and reveal the nature of dynamic damage at the microscale. In this work, the spalling of polyurea under different impact velocity is analyzed using MD method and coarse-grained molecular dynamics model. The simulation results show that spalling failure originates from the nucleation and development of void-damage. The flow stress has a plateau in the early and middle stages of void flow. The Hugoniot relation is obtained. Furthermore, the free surface velocity is calculated, which shows the typical characteristics observed in the experiment. The spalling strength is calculated by the direct and indirect methods, respectively. The non-monotonic variation of spalling strength with impact velocity is the result of the competition between the strain-rate strengthening and temperature weakening. The molecular mechanism is further analyzed, which indicates that the molecules are oriented during void flow, and the hard segments are more rigid and hysteretic. Besides, microphase-separated block copolymers have a special fibril toughening mechanism. The relationship between the flow stress and deformation of a fibril is quantitatively analyzed. Finally, the unit cell simulation, which represents one point in macroscopic, is compared with the spalling simulation.

Polyply; a python suite for facilitating simulations of macromolecules and nanomaterials

Molecular dynamics simulations play an increasingly important role in the rational design of (nano)-materials and in the study of biomacromolecules. However, generating input files and realistic starting coordinates for these simulations is a major bottleneck, especially for high throughput protocols and for complex multi-component systems. To eliminate this bottleneck, we present the polyply software suite that provides 1) a multi-scale graph matching algorithm designed to generate parameters quickly and for arbitrarily complex polymeric topologies, and 2) a generic multi-scale random walk protocol capable of setting up complex systems efficiently and independent of the target force-field or model resolution. We benchmark quality and performance of the approach by creating realistic coordinates for polymer melt simulations, single-stranded as well as circular single-stranded DNA. We further demonstrate the power of our approach by setting up a microphase-separated block copolymer system, and by generating a liquid-liquid phase separated system inside a lipid vesicle.

Full parameter space exploration of microphase separation of block copolymer brushes within a single simulation framework

Microphase separation of block copolymer brushes on a wide range system variable space is systematically explored using efficient coarse-grained simulations. Enriched phases behaviors and their internal structures are investigated.

Macroscopic Regulation of Hierarchical Nanostructures in Liquid-crystalline Block Copolymers towards Functional Materials

The great potential of liquid-crystalline block copolymers (LCBCs) containing photoresponsive mesogens toward novel applications in photonics and nanotechnology has been attracting increasing attention, due to the combination of the inherent property of microphase separation of block copolymers and the hierarchically-assembled structures of liquid-crystalline polymers (LCPs). The periodically ordered nanostructures in bulk film of LCBCs can be acquired by supramolecular cooperative motion, derived from the interaction between liquid-crystalline elastic deformation and microphase separation, which are able to improve physical properties of polymer film toward advanced functional applications. Moreover, various micro/nano-patterned structures have been fabricated via light manipulation of photoresponsive LCBCs with good reproducibility and mass production. Thanks to recent developments in synthesis and polymerization techniques, diverse azobenzene-containing LCBCs have been designed, resulting in the creation of a wide variety of novel functions. This review illustrates recent progresses in macroscopic regulation of hierarchical nanostructures in LCBCs towards functional materials. The existing challenges are also discussed, showing perspectives for future studies.

Homocrystalline mesophase formation and multistage structural transitions in stereocomplexable racemic blends of block copolymers

Polymer crystallization is a multi-stage process and generally takes place through the metastable intermediate structure or mesophase. However, mesopahse is difficult to be experimentally detected during crystallization and its formation mechanism is not well understood. Herein, we find that the formation of mesopahse is facilitated in the crystallization of stereocomplexable block polymers. We use the poly(L-lactic acid)-poly(ethylene glycol)-poly(L-lactic acid) (PLLA-PEG-PLLA) and poly(D-lactic acid)-poly(ethylene glycol)-poly(D-lactic acid) (PDLA-PEG-PDLA) as the stereocomplexable pair and investigate the synergetic effects of copolymer composition and PLLA/PDLA stereocomplexation on the mesophase formation in the PLLA-PEG-PLLA/PDLA-PEG-PDLA 1/1 blends. Intriguingly, the stereocomplexable blend having the high PEG fraction forms the unique homocrystalline mesophase at the low crystallization temperature (Tc, 70–120 °C) but the usual α-form homocrystals (HCs) at high Tc (120–160 °C), except for the stereocomplexes (SCs). However, the crystalline structure of PLLA-PEG-PLLA/PDLA-PEG-PDLA blend with low PEG fraction is similar as the PLLA/PDLA blend; it crystallizes in the mixture of α(α′)-HCs + SCs at Tc = 70–160 °C. The homocrystalline mesophase formed in stereocomplexable blend is metastable and reorganizes into the more thermally-stable α-HCs and SCs during heating. We propose that the mesophase formation in enantiomeric blend is resulted by the constrained effects induced by the stereocomplexation and microphase separation of block copolymers.

Characterisation of the PS-PMMA Interfaces in Microphase Separated Block Copolymer Thin Films by Analytical (S)TEM.

Block copolymer (BCP) self-assembly is a promising tool for next generation lithography as microphase separated polymer domains in thin films can act as templates for surface nanopatterning with sub-20 nm features. The replicated patterns can, however, only be as precise as their templates. Thus, the investigation of the morphology of polymer domains is of great importance. Commonly used analytical techniques (neutron scattering, scanning force microscopy) either lack spatial information or nanoscale resolution. Using advanced analytical (scanning) transmission electron microscopy ((S)TEM), we provide real space information on polymer domain morphology and interfaces between polystyrene (PS) and polymethylmethacrylate (PMMA) in cylinder- and lamellae-forming BCPs at highest resolution. This allows us to correlate the internal structure of polymer domains with line edge roughnesses, interface widths and domain sizes. STEM is employed for high-resolution imaging, electron energy loss spectroscopy and energy filtered TEM (EFTEM) spectroscopic imaging for material identification and EFTEM thickness mapping for visualisation of material densities at defects. The volume fraction of non-phase separated polymer species can be analysed by EFTEM. These methods give new insights into the morphology of polymer domains the exact knowledge of which will allow to improve pattern quality for nanolithography.

Short and Soft: Multidomain Organization, Tunable Dynamics, and Jamming in Suspensions of Grafted Colloidal Cylinders with a Small Aspect Ratio.

The yet virtually unexplored class of soft colloidal rods with a small aspect ratio is investigated and shown to exhibit a very rich phase and dynamic behavior, spanning from liquid to nearly melt state. Instead of the nematic order, these short and soft nanocylinders alter their organization with increasing concentration from isotropic liquid with random orientation to small domains with preferred local orientation and eventually a multidomain arrangement with a local orientational order. The latter gives rise to a kinetically suppressed state akin to structural glass with detectable terminal relaxation, which, on further increasing concentration, reveals features of hexagonally packed order as in ordered block copolymers. The respective dynamic response comprises four regimes, all above the overlapping concentration of 0.02 g/mL:(I) from 0.03 to 0.1 g/mol, the system undergoes a liquid-to-solidlike transition with a structural relaxation time that grows by 4 orders of magnitude. (II) From 0.1 to 0.2 g/mL, a dramatic slowing-down is observed and is accompanied by an evolution from isotropic to a multidomain structure. (III) Between 0.2 and 0.6 g/mol, the suspensions exhibit signatures of shell interpenetration and jamming, with the colloidal plateau modulus depending linearly on concentration. (IV) At 0.74 g/mL, in the densely jammed state, the viscoelastic signature of hexagonally packed cylinders from microphase-separated block copolymers is detected. These properties set short and soft nanocylinders apart from long colloidal rods (with a large aspect ratio) and provide insights for fundamentally understanding the physics in this intermediate soft colloidal regime and for tailoring the flow properties of nonspherical soft colloids.