Block Copolymer Phase Research Articles

Tuning the Double Gyroid Phase Window in Block Copolymers via Polymer Chain Conformation Near the Interface

Block copolymer network morphologies have been proven interesting for applications ranging from mechanical to transport and optical properties. The shape of the polymer chain and its ability to stretch across an interface can be used as handles to target these network morphologies. Here, we show that the double gyroid phase window is broadened when there is a flexible segment near the interface and narrowed when a more constrained segment is placed there by using a series of poly(styrene-b-peptoid) block copolymers in which the polypeptoid block chain conformation can be tuned to adopt either a helical or a coil conformation (NRpe6 vs Npe6). The double gyroid phase is accessed in both block copolymer series, while the phase boundaries are shifted toward larger polypeptoid volume fractions in the helix-forming PS–(NRpe6Nmey) series, due to the more compact helix segment (i.e., the helix segment has the same chain volume as its random coil counterpart but occupies less space). The space-filling difference between the helix and coil segment is further confirmed by the smaller domain spacing of PS–(NRpe6Nme39) compared to PS–(Npe6Nme36) (13.9 nm vs 14.3 nm) despite the former having a longer polypeptoid block. Furthermore, a broadened double gyroid phase window is accessed in the PS–(Npe6Nmey) series that has a flexible coil segment near the interface. These results demonstrate the possibility of tuning the double gyroid phase in linear block copolymers by chain conformation near the interface alone, highlighting chain conformation as a versatile handle in block copolymer design.

Late Stage Domain Coarsening Dynamics of Lamellar Block Copolymers

Block copolymer (BCP) phase separation dynamics can be expected to differ significantly from that of the polymer blends due to the constraint of chain connectivity. BCP phase separation dynamics has been studied theoretically, but there has been little experimental evidence to confirm the BCP domain growth scaling laws put forward theoretically. Here, we investigate the dynamics of late-stage lamellar BCP domain coarsening and find that the scaling exponent for lamellar domain growth is ≈1/6 (0.17), irrespective of the annealing temperature, a value close to the scaling exponent of 0.2 predicted by theoretical studies. Furthermore, we show that the prefactors in the domain coarsening equation show Arrhenius dependence on temperature, indicating that the BCP domain growth dynamics is Arrhenius over the temperature range investigated.

Reversible Micrometer‐Scale Spiral Self‐Assembly in Liquid Crystalline Block Copolymer Film with Controllable Chiral Response

AbstractThe spiral is a fundamental structure in nature and spiral structures with controllable handedness are of increasing interest in the design of new chiroptical materials. In this study, micrometer‐scale spiral structures with reversible chirality were fabricated based on the assembly of a liquid crystalline block copolymer film assisted by enantiopure tartaric acid. Mechanistic insight revealed that the formation of the spiral structures was closely related to the liquid crystalline properties of the major phase of block copolymer under the action of chiral tartaric acid. The chiral spiral structures with controllable handedness were easily erased under ultraviolet light irradiation and restored via thermal annealing. This facile thermal treatment method provides guidance for fabrication of chiral micrometer‐scale spiral structures with adjustable chiral properties.

Reversible Micrometer-Scale Spiral Self-Assembly in Liquid Crystalline Block Copolymer Film with Controllable Chiral Response.

The spiral is a fundamental structure in nature and spiral structures with controllable handedness are of increasing interest in the design of new chiroptical materials. In this study, micrometer-scale spiral structures with reversible chirality were fabricated based on the assembly of a liquid crystalline block copolymer film assisted by enantiopure tartaric acid. Mechanistic insight revealed that the formation of the spiral structures was closely related to the liquid crystalline properties of the major phase of block copolymer under the action of chiral tartaric acid. The chiral spiral structures with controllable handedness were easily erased under ultraviolet light irradiation and restored via thermal annealing. This facile thermal treatment method provides guidance for fabrication of chiral micrometer-scale spiral structures with adjustable chiral properties.

Влияние способа переработки на теплостойкость вторичного блок-сополимера пропилена и этилена, наполненного рисовой шелухой

Polymer composites based on secondary thermoplastic polymers filled with biodegradable components of plant origin was developed. Repeated thermal and mechanical action on polymers during their processing in the presence of dispersed phase particles leads to a change in the thermophysical and strength characteristics of finished products. The paper studies the regularities of changes in the heat resistance of polymer composites based on a secondary block copolymer of propylene and ethylene, and rice husks, processed by injection molding and pressing. It is shown that filling the secondary polymer with rice hulls leads to an increase in the heat resistance of composites, which is characterized by an increase in the bending temperature under load, Vicat softening temperature, and decomposition temperature during thermogravimetric analysis in an inert atmosphere. Compared to the injection molding method, the processing of polymer composites by pressing makes it possible to obtain more heat-resistant plastic products. Obviously, this is due to the different degrees of crystallinity of the polymer phase. The high cooling rate of the polymer composite melt during the filling of the injection mold reduces the time required for the corresponding change in the conformation of macromolecules and the formation of the crystalline phase. As a consequence, an increase in the content of the amorphous phase of the secondary block copolymer of propylene and ethylene decreases the heat resistance of the prototypes.

Rapid Generation of Block Copolymer Libraries Using Automated Chromatographic Separation.

A versatile and scalable strategy is reported for the rapid generation of block copolymer libraries spanning a wide range of compositions starting from a single parent copolymer. This strategy employs automated and operationally simple chromatographic separation that is demonstrated to be applicable to a variety of block copolymer chemistries on multigram scales with excellent mass recovery. The corresponding phase diagrams exhibit increased compositional resolution compared to those traditionally constructed via multiple, individual block copolymer syntheses. Increased uniformity and lower dispersity of the chromatographic libraries lead to differences in the location of order-order transitions and observable morphologies, highlighting the influence of dispersity on the self-assembly of block copolymers. Significantly, this separation technique greatly simplifies the exploration of block copolymer phase space across a range of compositions, monomer pairs, and molecular weights (up to 50000 amu), producing materials with increased control and homogeneity when compared to conventional strategies.

Stabilizing Phases of Block Copolymers with Gigantic Spheres via Designed Chain Architectures.

It is generally believed that the spherical domains self-assembled from AB-type block copolymers are composed of the minority A blocks with a volume fraction of fA < 1/2. Breaking this generic rule so that the spherical domains are formed by the majority A blocks (fA > 1/2) requires mechanisms to drastically expand the stable region of spherical packing phases. Self-consistent field theory predicts that dendron-like AB-type block copolymers, composed of G - 1 generations of A blocks connected with the outermost generation of B blocks, exhibit a stable region of spherical packing phases extending to fA ∼ 0.7. The extremely expanded spherical regions shed light on the mechanisms governing the self-assembly of amphiphilic macromolecules, as well as provide opportunities to engineer complex spherical packing phases.

Confinement-induced ordering of grafted nanoparticles aided by diblock copolymers

Self-assembly behavior of polymer grafted nanoparticles in ordered phases of geometrically confined diblock copolymers is studied using self-consistent field theory. Entropy loss and structural frustration introduced by physical confinement significantly alter the morphology of ordered phases from the bulk behavior. In particular, a rich variety of three-dimensional microstructures, for example, helical structures, are obtained under confinement. In the present study, we demonstrate that ordered microstructures of diblock copolymers can be employed as promising structural scaffolds to host and self-assemble nanoparticles within the selective domain. Templated self-assembly of nanoparticles offers a potential route to fabricate advanced nanomaterials with superior properties. Analysis reveals various stable equilibrium phases of block copolymers embedded with nanoparticles with a high degree of nanoscale ordering. The arrangement of nanoparticles is controlled by tuning various parameters such as block fraction in diblock copolymers, particle loading, size and number of grafted chains, and degree of confinement. At a low volume fraction, nanoparticles self-organize into chiral microstructures, such as single and double helices, even though the system contains only achiral species. Upon enhancing particle loading, the helical structure becomes less favorable and various other three-dimensional phases such as ring and disk morphologies are obtained. The regions of helical, ring, disk, and concentric lamellar phases are identified in terms of parameters related to grafted particles. Understanding the factors affecting localization of nanoparticles enables us to control the particulate self-assembly behavior of nanoparticles to design novel and advanced nanocomposites with desirable properties.

3D Micromachined Polyimide Mixing Devices for in Situ X-ray Imaging of Solution-Based Block Copolymer Phase Transitions.

Advances in modern interface- and material sciences often rely on the understanding of a system's structure-function relationship. Designing reproducible experiments that yield in situ time-resolved structural information at fast time scales is therefore of great interest, e.g., for better understanding the early stages of self-assembly or other phase transitions. However, it can be challenging to accurately control experimental conditions, especially when samples are only available in small amounts, prone to agglomeration, or if X-ray compatibility is required. We address these challenges by presenting a microfluidic chip for triggering dynamics via rapid diffusive mixing for in situ time-resolved X-ray investigations. This polyimide/Kapton-only-based device can be used to study the structural dynamics and phase transitions of a wide range of colloidal and soft matter samples down to millisecond time scales. The novel multiangle laser ablation three-dimensional (3D) microstructuring approach combines, for the first time, the highly desirable characteristics of Kapton (high X-ray stability with low background, organic solvent compatibility) with a 3D flow-focusing geometry that minimizes mixing dispersion and wall agglomeration. As a model system, to demonstrate the performance of these 3D Kapton microfluidic devices, we selected the non-solvent-induced self-assembly of biocompatible and amphiphilic diblock copolymers. We then followed their structural evolution in situ at millisecond time scales using on-the-chip time-resolved small-angle X-ray scattering under continuous-flow conditions. Combined with complementary results from 3D finite-element method computational fluid dynamics simulations, we find that the nonsolvent mixing is mostly complete within a few tens of milliseconds, which triggers initial spherical micelle formation, while structural transitions into micelle lattices and their deswelling only occur on the hundreds of milliseconds to second time scale. These results could have an important implication for the design and formulation of amphiphilic polymer nanoparticles for industrial applications and their use as drug-delivery systems in medicine.

A finite element method of the self-consistent field theory on general curved surfaces

Block copolymers provide a wonderful platform in the study of soft condensed matter systems. Many fascinating ordered structures have been discovered in bulk and confined systems. Among various theories, the self-consistent field theory (SCFT) has been proven to be a powerful tool for studying the equilibrium ordered structures. Many numerical methods have been developed to solve the SCFT model. However, most of these focus on the bulk systems, and little work on the confined systems, especially on general curved surfaces. In this work, we developed a linear surface finite element method, which has a rigorous mathematical theory to guarantee numerical precision, to study the self-assembled phases of block copolymers on general curved surfaces based on the SCFT. Furthermore, to capture the consistent surface for a given self-assembled pattern, an adaptive approach to optimize the size of the general curved surface has been proposed. To demonstrate the power of this approach, we investigate the self-assembled patterns of diblock copolymers on several distinct curved surfaces, including five closed surfaces and an unclosed surface. Numerical results illustrate the efficiency of the proposed method. The obtained ordered structures are consistent with the previous results on standard surfaces, such as sphere and torus. More significantly, the proposed numerical framework can be applied to study the phase behaviors of block copolymers on general surfaces accurately.

Stability of Two-Dimensional Dodecagonal Quasicrystalline Phase of Block Copolymers

Quasicrystalline (QC) phases have been observed in various condensed matter systems including self-assembling block copolymer (BCP) melts. Theoretical study of the thermodynamic stability of QC phases presents a long-standing unsolved problem because of the aperiodic nature of the structures. Here, we report a combination method to study the thermodynamic stability of two-dimensional dodecagonal quasicrystalline (DDQC) phase with both ideal tiling and random tiling patterns formed by ABCB tetrablock terpolymers. This method applies the self-consistent field theory coupled with the Stampfli self-similarity construction to accurately calculate the free energy of the periodic DDQC approximants and then uses a cluster model to predict the stability of aperiodic DDQC phase. Surprisingly, we find a stable DDQC approximant but metastable ideal tiling DDQC structures. Moreover, the random tiling DDQC structures as a mesoscopic coexistence of two neighboring periodic substructures of DDQC might become stable.

Self-Assembly of an Ultrahigh-χ Block Copolymer with Versatile Etch Selectivity

We report the successful synthesis of previously inaccessible poly(3-hydroxystyrene)-block-poly(dimethylsiloxane) (P3HS-b-PDMS) block copolymers (BCPs) with varying volume fractions, molecular weights, and narrow dispersities by sequential living anionic polymerization. The chemical structure and molecular weight were fully characterized by 1H NMR and gel permeation chromatography. The BCP phase behavior was investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy. Temperature-resolved SAXS measurements from symmetric disordered sample were used to determine the interaction parameter (χ) using mean-field theory. The results provide an estimate for interaction parameter, χHS/DMS(T) = 33.491/T + 0.3126, with an upper bound value of 0.39 at 150 °C. The calculated χ for P3HS-b-PDMS is approximately 4 times higher than that observed in a commonly studied high-χ system, PS-b-PDMS. The ultrahigh interaction parameter observed here affords the formation of well-ordered materials...

Control over Molecular Architectures of Carbohydrate-Based Block Copolymers for Stretchable Electrical Memory Devices

We synthesized a series of new intrinsically stretchable block copolymers (BCPs) in linear AB-type, ABA-type, and star-shaped architectures composed of oligosaccharide (MH) and flexible poly(n-butyl acrylate) (PBA) blocks for the application in field-effect transistor memory. The BCP thin films are used as the charge trapping layers in the memory devices where the BCPs phase separate into ordered MH microdomains in soft PBA matrices. The MH microdomain works as the charge-trapping sites while the soft PBA matrix provides a stretchability. In particular, the BCPs of the ABA-type and star-shaped architectures with the end MH blocks not only show superior memory performances but also form physical networks that impart mechanical resilience to the thin films such that they can endure 100% strain without formation of cracks. The mobilities and the memory windows of the devices are nearly constant even when the charge trapping layers are stretched and released at 50% strain for 1000 cycles. This work highlights...

Molecular Weight Distribution Shape as a Versatile Approach to Tailoring Block Copolymer Phase Behavior.

The molecular weight distributions (MWDs) of block copolymers significantly impact their morphological phase behavior, but exploiting these features as a means to tune material properties has been limited to the MWD breadth, or dispersity (Đ). Manipulation of the entire MWD has promising potential to address this challenge by providing a convenient and versatile route toward tailoring polymer nanostructure. Herein, we describe the self-assembly of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) where the PS blocks have systematically deviating compositions of molecular weights. We find that controlling the MWD shape, breadth and skew, afforded access to different morphologies in samples with the same molecular characteristics, including Đ. As such, we illustrate the generality and effectiveness of this strategy and anticipate that it will facilitate the increased deployment of disperse polymer compositions in advanced materials applications.

Intradomain phase transitions in flexible block copolymers with self-aligning segments.

We study a model of flexible block copolymers (BCPs) in which there is an enlthalpic preference for orientational order, or local alignment, among like-block segments. We describe a generalization of the self-consistent field theory of flexible BCPs to include inter-segment orientational interactions via a Landau-de Gennes free energy associated with a polar or nematic order parameter for segments of one component of a diblock copolymer. We study the equilibrium states of this model numerically, using a pseudo-spectral approach to solve for chain conformation statistics in the presence of a self-consistent torque generated by inter-segment alignment forces. Applying this theory to the structure of lamellar domains composed of symmetric diblocks possessing a single block of "self-aligning" polar segments, we show the emergence of spatially complex segment order parameters (segment director fields) within a given lamellar domain. Because BCP phase separation gives rise to spatially inhomogeneous orientation order of segments even in the absence of explicit intra-segment aligning forces, the director fields of BCPs, as well as thermodynamics of lamellar domain formation, exhibit a highly non-linear dependence on both the inter-block segregation (χN) and the enthalpy of alignment (ε). Specifically, we predict the stability of new phases of lamellar order in which distinct regions of alignment coexist within the single mesodomain and spontaneously break the symmetries of the lamella (or smectic) pattern of composition in the melt via in-plane tilt of the director in the centers of the like-composition domains. We further show that, in analogy to Freedericksz transition confined nematics, the elastic costs to reorient segments within the domain, as described by the Frank elasticity of the director, increase the threshold value ε needed to induce this intra-domain phase transition.

Complex Morphology of the Intermediate Phase in Block Copolymers and Semicrystalline Polymers As Revealed by 1H NMR Spin Diffusion Experiments

Nanostructured multiphase polymers exhibiting a mobile and a rigid phase also contain a phase of intermediate mobility that is usually assumed to be a continuous, uninterrupted interphase layer. This assumption is contrary to recent molecular-resolution micrographs and contradicts results from NMR spin diffusion experiments, all of which suggest a nontrivial interface structure. In this contribution, we reconsider our previous 1H NMR spin diffusion data sets (Roos Colloid. Polym. Sci. 2014, 292, 1825) and perform optimized 2D and 3D numerical spin diffusion calculations to characterize the basic intermediate-phase morphological pattern, thus overcoming previous inconsistencies in data fitting. For the diblock copolymer poly(butadiene)-poly(styrene), PS-b-PB, we demonstrate that the interphase region comprises nanometer-size intermixed immobile, intermediate and mobile subregions. In contrast, for the semicrystalline polymer poly(e-caprolactone), PCL, the spin diffusion data are best reproduced by an inter...

Nonclassical Spherical Packing Phases Self-Assembled from AB-Type Block Copolymers.

Among the various ordered morphologies self-assembled from block copolymers, the spherical packing phases are particularly interesting because they resemble the familiar atomic crystals. The commonly observed spherical morphology of block copolymers is the body-centered-cubic phase. Recently, a number of novel spherical packing phases, i.e., the complex Frank-Kasper phases originally obtained in metallic alloys, have been observed in block copolymer melts. Theoretical studies have revealed that conformational asymmetry of the different blocks provides a key mechanism to stabilize the Frank-Kasper phases. Furthermore, local segregation of different copolymers in blends of diblock copolymers and copolymer architectures provides additional mechanisms to enhance the stability of the complex ordered phases. In this Viewpoint we summarize recent advances in our understanding of the formation of the nonclassical spherical packing phases in AB-type block copolymers, emphasizing the formation mechanisms of these fascinating complex ordered structures.

Metal‐containing ionic liquid‐based, uncharged–charged diblock copolymers that form ordered, phase‐separated microstructures and reversibly coordinate small protic molecules

Metal‐containing ionic liquid‐based, uncharged–charged diblock copolymers that form ordered, phase‐separated microstructures and reversibly coordinate small protic molecules

Self-assembly of maltoheptaose-b-PMMA block copolymer systems: 10 nm Resolution in thin film and bulk states

This paper describes the self-assembly of oligosaccharide-based hybrid block copolymers (BCPs) consisting of maltoheptaose (MH) and poly(methyl methacrylate) (PMMA) into 10nm scale lamellar and cylindrical phases depending on the volume fractions of MH (ϕMH) and the annealing process. Time resolved SAXS study of the BCP bulk samples during thermal annealing indicated that the BCPs phase separate into 10nm scale periodical structures. The solvent vapor annealing induced self-organizations of the BCP into different phases depending on ϕMH and the weight fraction of THF/H2O. BCPs with relatively higher ØMH, MH-b-PMMA3k (ϕMH=0.27) and MH-b-PMMA5k (ϕMH=0.16) self-organized into lamellar phases while the BCP sample with relatively lower ϕMH, MH-b-PMMA9k (ϕMH=0.10), self-organized into cylindrical phase by using THF/H2O=1/4 (w/w). On the other hand, the solvent vapor annealing with larger fraction of THF, i.e. THF/H2O=2/3 (w/w), induced cylindrical phases for MH-b-PMMA3k and MH-b-PMMA5k.

Trade-Off Between Transport and Mechanical Properties in Ion-Containing Block Copolymers with Different Self-Assembled Morphologies: A Comparison Study Between Lamellar and Inverse-Hexagonal

Both transport and mechanical performances are required for ion-containing polymers to be successfully used in ion-conducting applications such as fuel cells, actuators and electrodialysis. Phase-separated structure with ion and non-ion domains has been proposed to meet this requirement because these two domains can accommodate the ion and solvent transport and provide mechanical support respectively. The self-assembling nature of block copolymers is therefore used to create ion-containing polymers with well-defined phase-separated morphologies. The morphologies with continuous ion-domain are usually designed to enhance ion transport (1), however more attention may be needed on the trade-off between transport and mechanical properties. We have found out that the mechanical property is poor for some morphologies with continuous ion domain even though the ion domain is still the minor phase compared to the non-ion domain. Due to the electrostatic ion interaction, ion-containing block copolymers display more complicated phase behaviors and generate morphologies beyond that of neutral copolymers (2). Among them, inverse-hexagonal (HEX) structures have been widely prepared (3-5). It has the major non-ion block form the ‘bulk-like’ cylinders residing in the ‘surface-like’ minor ion phase. Our experimental observation indicated that this inverse-HEX morphology may suffer from excessive water swelling when placed in liquid water environment. In our work, the ion-containing block copolymer under study was supposed to form lamellar morphology according to the block copolymer phase diagram, however it generated a mixture of lamellar and inverse-HEX morphologies when casting from a polar solvent. The formation of inverse-HEX was suppressed when adding a little nonpolar solvent for casting. These two morphologies were imaged by TEM as shown in Figure 1. They are both in principle ‘percolating’ structures for ion transport. Although the membrane with a mixture of lamellar and HEX structures did display higher ion-domain connectivity than the pure-lamellar one as per our preliminary dynamic tension test, its ion conductivity under low water activity (in water vapor) and its water vapor transport flux are very close to the pure-lamellar one. This inconsistency may be because of the larger ion to non-ion interface within the inverse-HEX structure, resulting in more interface resistance. Only under high water activities (more than 0.95), the one with inverse-HEX displayed larger conductivity than the pure-lamellar one, probably due to more effective swelling of the hydrophilic phase for the former. And if the water vapor transport was measured with liquid water contacting one side of the membrane, the one with inverse-HEX had larger flux. Water sorption experiment showed that the one with HEX morphology swell more than the pure-lamellar one. And we actually observed the HEX membrane broke apart after placed in liquid water for 2 month while the pure-lamellar one was still intact. Thermodynamic swelling model considering both interface energy and elastic energy is being developed to explain the difference between inverse-HEX and lamellar morphologies. (1) Arges, C. and Kambe, Y. et. al. Realizing the Potential of Micro-Phase Separated Block Copolymer Electrolytes: Ion Domain Connectivity Plays a Prominent Role in Ion Conduction. ECS Transactions. 2016, 75(14), 1013-1020 (2) Sing, C.; Zwanikken, J.; Cruz, M. D. La. Electrostatic Control of Block Copolymer Morphology. Nat. Mater. 2014, 13(7), 694–698 (3) Kim, O.; Shin, T. J.; Park, M. J. Fast Low-Voltage Electroactive Actuators Using Nanostructured Polymer Electrolytes. Nat. Commun. 2013, 4, 2208 (4) Mineart, K. P.; Lee, B.; Spontak, R. J. A Solvent-Vapor Approach toward the Control of Block Ionomer Morphologies. Macromolecules 2016, 49 (8), pp 3126–3137 (5) Zheng, W.; Cornelius, C. J. Solvent Tunable Multi-Block Ionomer Morphology and Its Relationship to Modulus, Water Swelling, Directionally Dependent Ion Transport, and Actuator Performance. Polymer. 2016, 103, 104–111 Figure 1