Phase Behavior Of Block Copolymers Research Articles

Phase Behavior of Charged Star Block Copolymers at Fluids Interface

AbstractThe phase behavior of block copolymers (BCPs) at the water‐oil interface is influenced by the segmental interaction parameter ( ) and chain architecture. We synthesized a series of star block copolymers (s‐BCPs) having polystyrene (PS) as core and poly(2‐vinylpyridine) (P2VP) as corona. The interaction parameters of block‐block ( PS‐P2VP) and block‐solvent ( P2VP‐solvent) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized‐P2VP (Q‐P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s‐BCP matrix, while nanotubes comprised Q‐P2VP as corona and PS as core. Control over pore size, d‐spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s‐BCPs. Large‐scale nanoporous films were obtained by freeze‐drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal‐packed rigid spherical micelles with Q‐P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well‐controlled pore structure.

Phase Behavior of Charged Star Block Copolymers at Fluids Interface.

The phase behavior of block copolymers (BCPs) at the water-oil interface is influenced by the segmental interaction parameter ( ) and chain architecture. We synthesized a series of star block copolymers (s-BCPs) having polystyrene (PS) as core and poly(2-vinylpyridine) (P2VP) as corona. The interaction parameters of block-block ( PS-P2VP ) and block-solvent ( P2VP-solvent ) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized-P2VP (Q-P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s-BCP matrix, while nanotubes comprised Q-P2VP as corona and PS as core. Control over pore size, d-spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s-BCPs. Large-scale nanoporous films were obtained by freeze-drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal-packed rigid spherical micelles with Q-P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well-controlled pore structure.

Discrete Linear–Branched Block Copolymer with Broken Architectural Symmetry

Rationally introducing chain length heterogeneity, such as binary blending, is a robust approach to regulate phase behavior of block copolymers. This work designed a library of discrete linear–branched block copolymers bearing two unequal branches. Diverse ordered nanostructures, including complex Frank–Kasper phases and quasicrystalline phase, were captured by tuning the compositional and architectural asymmetry. The precise chemistry rules out the interferences associated with statistical distribution, while the discrete feature decouples the intertwined variables. Compared with the symmetric counterparts, the synergies between the long and short chains effectively release the packing frustration during the formation of ordered structures, leading to a significant increase of lattice dimension and phase stability. The “built-in” chain length heterogeneity circumvents the shortcomings encountered by the conventional blending strategy, providing an excellent alternative for quantitatively assessing the effect of molecular symmetry on the self-assembly behaviors of block copolymers.

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

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

Unidirectional Perpendicularly Aligned Lamella-Structured Oligosaccharide (A) ABA Triblock Elastomer (B) Thin Films Utilizing Triazolium+/TFSI- Ionic Nanochannels.

We designed and synthesized high χ-low N-maltoheptaose-(triazolium+/N(SO2CF3)2–)-polyisoprene-(triazolium+/N(SO2CF3)2–)-maltoheptaose ABA triblock elastomers featuring triazolium+/N(SO2CF3)2– (TFSI–) counteranion ionic interfaces separating their constituting polymeric sub-blocks. Spin-coated and solvent-vapor-annealed (SVA) MH1.2k-(T+/TFSI–)-PI4.3k-(T+/TFSI–)-MH1.2k thin films demonstrate interface-induced charge cohesion through ca. 1 nm “thick” ionic nanochannels which facilitate the self-assembly of a perpendicularly aligned lamellar structure. Atomic force microscopy (AFM) and (grazing-incidence) small-angle X-ray scattering ((GI)SAXS) characterizations of MH1.2k-(T+/TFSI–)-PI4.3k-(T+/TFSI–)-MH1.2k and pristine triBCP analogous thin films revealed sub-10 nm block copolymer (BCP) self-assembly and unidirectionally aligned nanostructures developed over several μm2 areas. Solvated TFSI– counterions enhance the oligosaccharide sub-block packing during SVA. The overall BCP phase behavior was mapped through SAXS characterizations comparing di- vs triblock polymeric architectures, a middle PI sub-block with two different molecular masses, and TFSI– or I– counteranion effects. This work highlights the benefits of inducing single-point electrostatic interactions within chemical structures of block copolymers to master the long-range self-assembly of prescribed morphologies.

Random Forest Predictor for Diblock Copolymer Phase Behavior.

Physics-based models are the primary approach for modeling the phase behavior of block copolymers. However, the successful use of self-consistent field theory (SCFT) for designing new materials relies on the correct chemistry- and temperature-dependent Flory-Huggins interaction parameter χAB that quantifies the incompatibility between the two blocks A and B as well as accurate estimation of the ratio of Kuhn lengths (bA/bB) and block densities. This work uses machine learning to model the phase behavior of AB diblock copolymers by using the chemical identities of blocks directly, obviating the need for measurement of χAB and bA/bB. The random forest approach employed predicts the phase behavior with almost 90% accuracy after training on a data set of 4768 data points, almost twice the accuracy obtained using SCFT employing χAB from group contribution theory. The machine-learning model is notably sensitive toward the uncertainty in measuring molecular parameters; however, its accuracy still remains at least 60% even for highly uncertain experimental measurements. Accuracy is substantially reduced when extrapolating to chemistries outside the training set. This work demonstrates that a random forest phase predictor performs remarkably well in many scenarios, providing an opportunity to predict self-assembly without measurement of molecular parameters.

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Accelerated Pseudo-Spectral Method of Self-Consistent Field Theory via Crystallographic Fast Fourier Transform

Self-consistent field theory (SCFT) has been proven as one of the most successful methods for studying the phase behavior of block copolymers. In the past decades, a number of numerical methods hav...

Scalable Electrically Conductive Spray Coating Based on Block Copolymer Nanocomposites

Currently available conductive inks present a challenge to achieving electrical performance without compromising mechanical properties, scalability, and processability. Here, we have developed blends of carbon black and the commercially available triblock copolymer (BCP), poly(styrene-ethylene-butylene-styrene)-g-maleic anhydride (SEBS-g-MAH) (FG1924G, Kraton), that can be readily applied as a conductive coating via a spray-coating process, for a wide range of insulating materials (fabric, wood, glass, and plastic). Simple but effective mechanical and chemical modifications of the ingredients can increase the electrical conductivity (∼100 S/m) by an order of magnitude more than previously reported for carbon black composites; moreover, the coatings display excellent mechanical flexibility (tensile strain ε ∼ 5.00 mm/mm). To correlate electrical conductivity and nanoscale structural changes with mechanical deformation, small-angle X-ray scattering (SAXS) during in situ tensile testing was performed. We show that the nanocomposite can be produced using low-cost ingredients (∼$ 10/kg), ensuring scalability for fabrication of large-scale devices without specialized material synthesis. Equally important, the phase behavior of block copolymers can enable recovery from physical damage via thermal annealing, which is critical for product longevity.

Modulation of thermodynamic and kinetic inverted phase behavior of block copolymers by inorganic polyoxometalates.

The Keggin polyoxometalates (POM) H3PW12O40 (PW) electrostatically complexed with poly(styrene-block-2-vinyl pyridine) (PS-b-P2VP) in DMF, and ordered microphase separation occurred through solvent evaporation. The phase behaviors of PS-b-P2VP/PW in bulk were systematically investigated by using SAXS and TEM to discover the effect of POM content and molecular weight of the block copolymers. Computational simulation was also performed to reveal the same phase transition sequence as the experimental results. As the POM content increases, the PS-b-P2VP/PW complex with a low molecular weight changed from lamellar phase (LAM) to hexagonal cylindrical phase (HEX), and finally transited into spherical phase (SPH). Unexpectedly, PS-b-P2VP/PW complexes with a high molecular weight were inclined to form a kinetic-trapped intermediate phase (inverted HEX). The mechanism of formation of inverted phases was proposed based on simulation that asymmetric swelling in the concentrated DMF solution would result in the ultimate kinetic-trapped nanostructure in the bulk.

Closed-Loop Phase Behavior of Block Copolymers in the Presence of Competitive Hydrogen-Bonding and Coulombic Interaction

The closed-loop phase behavior, where a lower disorder-to-order transition (LDOT) takes place first, followed by an upper order-to-disorder transition (UODT) upon heating, is seldom observed in block copolymers (BCPs). In this work, we prepared a model BCP, LiClO4-doped poly(ethylene oxide)-b-poly(tert-butyl acrylate-co-acrylic acid) (PEO-b-P(tBA-co-AA)), in which the hydrogen (H)-bonding between the PEO and AA units and the Coulombic interaction in salt-doped PEO block have opposite effects on the miscibility of BCPs. The relative strength of the H-bonding and Coulombic interaction can be easily tuned by the hydrolysis degree (DH) of the PtBA block and the amount of doped salt. Various phase behaviors are observed by changing relative strength of different forces. Especially, the closed-loop phase behavior can be achieved when H-bonding, Coulombic interaction, and mixing entropy reach a delicate balance.

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.

Field-theoretic simulations of random copolymers with structural rigidity.

Copolymers play an important role in a range of soft-materials applications and biological phenomena. Prevalent works on block copolymer phase behavior use flexible chain models and incorporate interactions using a mean-field approximation. However, when phase separation takes place on length scales comparable to a few monomers, the structural rigidity of the monomers becomes important. In addition, concentration fluctuations become significant at short length scales, rendering the mean-field approximation invalid. In this work, we use simulation to address the role of finite monomer rigidity and concentration fluctuations in microphase segregation of random copolymers. Using a field-theoretic Monte-Carlo simulation of semiflexible polymers with random chemical sequences, we generate phase diagrams for random copolymers. We find that the melt morphology of random copolymers strongly depends on chain flexibility and chemical sequence correlation. Chemically anti-correlated copolymers undergo first-order phase transitions to local lamellar structures. With increasing degree of chemical correlation, this first-order phase transition is softened, and melts form microphases with irregular shaped domains. Our simulations in the homogeneous phase exhibit agreement with the density-density correlation from mean-field theory. However, conditions near a phase transition result in deviations between simulation and mean-field theory for the density-density correlation and the critical wavemode. Chain rigidity and sequence randomness lead to frustration in the segregated phase, introducing heterogeneity in the resulting morphologies.

Thermal stability of ester linkage in the presence of 1,2,3‐Triazole moiety generated by click reaction

ABSTRACTThe copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC), so‐called “click” reaction, is one of most useful synthetic strategies to connect two polymer chains. 1,2,3‐Triazole ring (TA) produced by the click reaction has good thermal and chemical stability. However, we observed that block copolymers synthesized by the click reaction showed thermal degradation to give homopolymers when they are thermally annealed at high temperature, which is required for obtaining equilibrium microdomain structure. To investigate the origin of thermal instability of block copolymers, we synthesized model polystyrenes (PSs) using systematically designed bi‐functional atom transfer radical polymerization (ATRP) initiators containing TA. PS including both ester and TA groups showed thermal decomposition at relatively low temperature (e.g., 140 °C). MALDI‐TOF analysis clearly demonstrated that the cleavage site is the ester group adjacent to TA. We also found that the bromine group located at the polymer chain end plays an important role in pyrolysis of ester groups at low temperature. The pyrolysis occurs by syn‐elimination of the ester group. This result implies that the phase behavior of block copolymer synthesized by click reaction should be carefully investigated when high temperature thermal annealing is required. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 427–436

Anomalistic Self-Assembled Phase Behavior of Block Copolymer Blended with Organic Derivative Depending on Temperature

Amphiphilic Pluronic block copolymers have attracted great attention in a broad spectrum of potential applications due to the excellent phase behaviors in an aqueous solution, and many efforts have been made to investigate their phase behaviors under various external conditions. With a variety of external conditions, however, the closed looplike phase behaviors of a Pluronic block copolymer in an aqueous solution have not been reported yet. Herein, we report the closed looplike (CLL) phase behavior of a Pluronic P65 triblock copolymer blended with an organic derivative, 5-methylsalicylic acid (5mS), in aqueous solution, which is very unique for block copolymers. As the 5mS concentration increases, the isotropic to ordered phase or back to isotropic phase transition temperature is decreased while the number of closed loops is increased to two. To the best of our knowledge, this is the first demonstration of a CLL phase transition of a Pluronic block copolymer in an aqueous solution, which is readily applic...

Synthesis and Self-Assembly of Discrete Dimethylsiloxane-Lactic Acid Diblock Co-oligomers: The Dononacontamer and Its Shorter Homologues.

Most of the theoretical and computational descriptions of the phase behavior of block copolymers describe the chain ensembles of perfect and uniform polymers. In contrast, experimental studies on block copolymers always employ materials with disperse molecular makeup. Although most polymers are so-called monodisperse, they still have a molecular weight dispersity. Here, we describe the synthesis and properties of a series of discrete length diblock co-oligomers, based on oligo-dimethylsiloxane (oDMS) and oligo-lactic acid (oLA), diblock co-oligomers with highly noncompatible blocks. By utilizing an iterative synthetic protocol, co-oligomers with molar masses up to 6901 Da, ultralow molar mass dispersities (Đ ≤ 1.00002), and unique control over the co-oligomer composition are synthesized and characterized. This specific block co-oligomer required the development of a new divergent strategy for the oDMS structures by which both bis- and monosubstituted oDMS derivatives up to 59 Si-atoms became available. The incompatibility of the two blocks makes the final coupling more demanding the longer the blocks become. These optimized synthetic procedures granted access to multigram quantities of most of the block co-oligomers, useful to study the lower limits of block copolymer phase segregation in detail. Cylindrical, gyroid, and lamellar nanostructures, as revealed by DSC, SAXS, and AFM, were generated. The small oligomeric size of the block co-oligomers resulted in exceptionally small feature sizes (down to 3.4 nm) and long-range organization.

Phase Behavior of Block Copolymers in Selective Supercritical Solvent

The phase behavior of a block copolymer and supercritical fluid system was investigated. When a particular block was selectively swollen by the supercritical fluid, the apparent volume fraction of one domain was controlled by the pressure of the supercritical fluid. The morphological variation of polystyrene-b-poly[2-(perfluorooctylethyl) methacrylate]s (PS–PFMAs) with different ratios of PS to PFMA and the total degree of polymerization were analyzed. Time-resolved small-angle neutron scattering measurement revealed that lamellar and hexagonal phases coexist metastably, which may be induced by fluctuation of the supercritical fluid.

Analytic Structure of the SCFT Energy Functional of Multicomponent Block Copolymers

AbstractThis paper concerns the analytic structure of the self-consistent field theory (SCFT) energy functional of multicomponent block copolymer systems which contain more than two chemically distinct blocks. The SCFT has enjoyed considered success and wide usage in investigation of the complex phase behavior of block copolymers. It is well-known that the physical solutions of the SCFT equations are saddle points, however, the analytic structure of the SCFT energy functional has received little attention over the years. A recent work by Fredrickson and collaborators [see the monograph by Fredrickson,The Equilibrium Theory of Inhomogeneous Polymers, (2006), pp. 203–209] has analysed the mathematical structure of the field energy functional for polymeric systems, and clarified the index-1 saddle point nature of the problem caused by the incompressible constraint. In this paper, our goals are to draw further attention to multicomponent block copolymers utilizing the Hubbard-Stratonovich transformation used by Fredrickson and co-workers. We firstly show that the saddle point character of the SCFT energy functional of multicomponent block copolymer systems may be high index, not only produced by the incompressible constraint, but also by the Flory-Huggins interaction parameters. Our analysis will be beneficial to many theoretical studies, such as the nucleation theory of ordered phases, the mesoscopic dynamics. As an application, we utilize the discovery to develop the gradient-based iterative schemes to solve the SCFT equations, and illustrate its performance through several numerical experiments takingABCstar triblock copolymers as an example.

Rheological Study of Order-to-Disorder Transitions and Phase Behavior of Block Copolymer–Surfactant Complexes Containing Hydrogen-Bonded Small Molecule Additives

Dynamic mechanical measurements were used to investigate the effect of small molecule additives on the order-to-disorder transitions (ODTs) of Pluronic, poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–PEO triblock copolymer surfactant melts. The small molecule additives contain multiple functional groups (carboxyl or hydroxyl), which selectively interact with the PEO component of Pluronic via hydrogen bonding, thereby effectively increasing χ of the system and leading to microphase separation in otherwise disordered melts. The ODTs of these Pluronic/small-molecule-additive complexes can be detected by rheology since, upon increasing temperature, crossing the order-to-disorder transition temperature (TODT) results in a sharp decrease in the low frequency storage and loss moduli (G′ and G″, respectively). The crystallization of the PEO component is suppressed with increasing additive loading due to strong hydrogen bond interactions. The TODT is strongly composition dependent and increases up to 145 °...

Study of the phase behavior of a diblock copolymer in an ionic liquid: Outlook for use of the integral-equation theory

It is shown that the integral-equation theory may be used to study the phase behavior of a diblock copolymer in an ionic liquid with allowance made for the solvent structure. Features of microphase separation are exemplified via calculation of the mean-field spinodal temperature and order-disorder transition temperature as functions of the copolymer concentration at two different lengths of the cationic tail of the ionic liquid. The need to allow for the solvent structure during construction of the theory of the phase behavior of block copolymers in ionic liquids is substantiated.