Undergo Microphase Separation Research Articles

Enzymes as Biodevelopers for Nano- And Micropatterned Bicomponent Biopolymer Thin Films.

The creation of nano- and micropatterned polymer films is a crucial step for innumerous applications in science and technology. However, there are several problems associated with environmental aspects concerning the polymer synthesis itself, cross-linkers to induce the patterns as well as toxic solvents used for the preparation and even more important development of the films (e.g., chlorobenzene). In this paper, we present a facile method to produce micro- and nanopatterned biopolymer thin films using enzymes as so-called biodevelopers. Instead of synthetic polymers, naturally derived ones are employed, namely, poly-3-hydroxybutyrate and a cellulose derivative, which are dissolved in a common solvent in different ratios and subjected to spin coating. Consequently, the two biopolymers undergo microphase separation and different domain sizes are formed depending on the ratio of the biopolymers. The development step proceeds via addition of the appropriate enzyme (either PHB-depolymerase or cellulase), whereas one of the two biopolymers is selectively degraded, while the other one remains on the surface. In order to highlight the enzymatic development of the films, video AFM studies have been performed in real time to image the development process in situ as well as surface plasmon resonance spectroscopy to determine the kinetics. These studies may pave the way for the use of enzymes in patterning processes, particularly for materials intended to be used in a physiological environment.

Structure of nanorod assembly in the gyroid phase of diblock copolymer.

Diblock copolymers undergo microphase separation to form various microstructures, for example, lamellar, gyroid, cylindrical, cubic phases depending on composition and segregation strength (Flory–Huggins parameter χ). Thus, it can act as template to organize doped nanomaterials into different 3D self-assembled structures located within the block copolymer matrix. Gyroid phase is one of the microstructures formed by block copolymer. It has a curved interfacial surface providing confinements throughout the matrix and thus can regulate the shape and sizes of self-assembled nanorods doped in it. Mesoscale simulation of model systems has been performed to explore the structure and dynamics of self-assembly of bundles formed by nanorods of different flexibilities in the gyroid phase of diblock copolymer matrix. Bundles of different shapes and sizes have been found to be formed depending on the nanorod bending flexibility and copolymer–nanorod interactions. The shape anisotropy (κ(2)) and radius of gyration (R(g)(2)) of bundles situated at different interfacial confining locations of block copolymer matrices have been investigated as a function of nanorod flexibility and nanorod–diblock copolymer miscibility.

Nanostructured poly(benzimidazole) membranes by N-alkylation

Modification of poly(benzimidazole) (PBI) by N-alkylation leads to polymers capable of undergoing microphase separation. Polymers with different amounts of C18 alkyl chains have been prepared. The polymers were analyzed by spec- troscopy, thermal analysis, electron microscopy and X-ray scattering. The impact of the amount of alkyl chains on the observed microphase separation was analyzed. Membranes prepared from the polymers do show microphase separation, as evidenced by scattering experiments. While no clear morphology could be derived for the domains in the native state, evi- dence for the formation of lamellar morphologies upon doping with phosphoric acid is provided. Finally, the proton con- ductivity of alkyl-modified PBI is compared with that of pure PBI, showing that the introduction of alkyl side chains does not result in significant conductivity changes.

Microrheology, microstructure, and aging of physically cross-linked poly(vinyl alcohol)/poly(ethylene glycol) blends

Physically cross-linked blends of concentrated poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) undergo microphase separation and gel as they age. We investigate the microrheology and microstructure of these materials by using particle tracking and dynamic light scattering to measure the thermal motion of small polystyrene spheres suspended in the blends. Dynamic light scattering probes the ensemble-averaged motion of all the probe particles over a wide range of time scales, while video-based particle tracking follows the motion of many individual tracer particles. Dynamic light scattering shows that the tracer particles move diffusively at short and long time scales, while their motion is restricted by material elasticity at intermediate time scales. The particle tracking experiments show a wide distribution of mean square displacements at a given lag time, indicating spatial heterogeneity on the micron length scale. We separate the particles into three populations according to their behavior. We extract information about the local microrheological environments probed by each population and study their dependence on PEG concentration and aging time. We find that addition of PEG to the PVA solutions influences the microrheological environment significantly, and that phase separation occurs prior to gelation as the blends age. The gelation time determined from the microrheological measurements is later than the bulk gel time, indicating that the different phase-separated regions age differently. Our results are consistent with a model in which the PVA/PEG blends consist of PVA-poor pores within a continuous PVA-rich domain.

Polystyrene–Poly(ethylene oxide) Diblock Copolymer: The Effect of Polystyrene and Spreading Concentration at the Air/Water Interface

Polystyrene-block-poly(ethylene oxide) (PS-PEO) is an amphiphilic diblock copolymer that undergoes microphase separation when spread at the air/water interface, forming nanosized domains. In this study, we investigate the impact of PS by examining a series of PS-PEO samples containing constant PEO (~17,000 g·mol(-1)) and variable PS (from 3600 to 200,000 g·mol(-1)) through isothermal characterization and atomic force microscopy (AFM). The polymers separated into two categories: predominantly hydrophobic and predominantly hydrophilic with a weight percent of PEO of ~20% providing the boundary between the two. AFM results indicated that predominantly hydrophilic PS-PEO forms dots while more hydrophobic samples yield a mixture of dots and spaghetti with continent-like structures appearing at ~7% PEO or less. These structures reflect a blend of polymer spreading, entanglement, and vitrification as the solvent evaporates. Changing the spreading concentration provides insight into this process with higher concentrations representing earlier kinetic stages and lower concentrations demonstrating later ones. Comparison of isothermal results and AFM analysis shows how polymer behavior at the air/water interface correlates with the observed nanostructures. Understanding the impact of polymer composition and spreading concentration is significant in leading to greater control over the nanostructures obtained through PS-PEO self-assembly and their eventual application as polymer templates.

The effect of Janus nanospheres on the phase separation of immiscible polymer blends via dissipative particle dynamics simulations

Using dissipative particle dynamics simulations, we have studied the effect of Janus nanospheres on the phase separation dynamics of polymer blends. We find that Janus nanospheres significantly impede domain growth and at a later stage the average domain size approaches saturation and the growth exponent n decays to near-zero. Additionally, compared with homogeneous nanospheres, the phase separation dynamics of ternary systems containing Janus nanospheres is slower and the average size of domains is smaller at later stages of the phase separation process. This mainly arises from the inherent equatorial adsorption and low desorption probability of Janus nanospheres at interfaces, which can greatly reduce the interfacial tension and hence the driving force towards macrophase separation. In particular, such a difference in the retardation effect becomes more pronounced for the systems containing small sized nanospheres with the preferential particle-matrix interaction. Furthermore, in the later-stage of the phase separation process there exists a dynamical self-similarity in the ternary systems that undergo microphase separation and the domain growth follows a crossover scaling form. Similarly, ternary systems containing Janus nanospheres are closer to saturation and the extracted crossover scaling exponent is closer to 1 than the counterpart ternary systems containing homogeneous nanospheres. Therefore, the Janus nanospheres can be used as a more effective emulsifying or stabilizing agent than homogeneous nanospheres for immiscible polymer blends.

Synthesis and self-assembly of diblock copolymers composed of poly(3-hexylthiophene) and poly(fluorooctyl methacrylate) segments

Regioregular poly(3-hexylthiophene)-b-poly(1H,1H-dihydro perfluorooctyl methacrylate) (P3HT-b-PFOMA) diblock copolymers were synthesized by atom transfer radical polymerization of fluorooctyl methacrylate using bromoester terminated poly(3-hexylthiophene) macroinitiators in order to investigate their morphological properties. The P3HT macroinitiator was previously prepared by chemical modification of hydroxy terminated P3HT. The block copolymers were well characterized by 1H NMR spectroscopy and gel permeation chromatography. Transmission electron microscopy was used to investigate the nanostructured morphology of the diblock copolymers. The block copolymers are able to undergo microphase separation and self-assemble into well-defined and organized nanofibrillar-like micellar morphology. The development of the morphology of P3HT-b-PFOMA block copolymers was investigated after annealing in solvent vapor and also in supercritical CO2. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Phase Transitions in Soft Matter Induced by Selective Solvation

Abstract We review our recent studies on selective solvation effects in phase separation in polar binary mixtures with a small amount of solutes. Such hydrophilic or hydrophobic particles are preferentially attracted to one of the solvent components. We discuss the role of antagonistic salt composed of hydrophilic and hydrophobic ions, which undergo microphase separation at water–oil interfaces leading to mesophases. We then discuss phase separation induced by a strong selective solvent above a critical solute density np, which occurs far from the solvent coexistence curve. We also give theories of ionic surfactant systems and weakly ionized polyelectrolytes including solvation among charged particles and polar molecules. We point out that the Gibbs formula for the surface tension needs to include an electrostatic contribution in the presence of an electric double layer.

Micro-phase separation and crystallization behavior of amorphous oriented PLLA/PVAc blends during heat treatment under strain

Amorphous oriented poly( l-lactide) (PLLA)/poly(vinyl acetate) (PVAc) 50/50 films were prepared by uniaxial drawing of melt-mixed blends at 65 °C. The morphology development and crystal organization of the blends during heat treatment under strain were investigated using small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). Equatorial scattering maxima in the SAXS patterns for samples annealed at 75 °C were observed before the appearance of crystal reflections. Further annealing of the samples at higher temperature induced two further discrete meridian scattering maxima. The observations indicated that homogenous oriented PLLA/PVAc film undergoes micro-phase separation first, followed by crystallization of PLLA in the PLLA-rich phase. The micro-phase separated PVAc nanodomains are aligned parallel to the stretching direction, whereas the crystallized PLLA lamellae are oriented perpendicular to the stretching direction (crystal c-axis along the stretching direction). Micro-phase separation was not observed when films were annealed at 120 °C, at which temperature the high crystallization rate of PLLA overwhelmed the micro-phase separation process.

High-Performance Field-Effect Transistors Based on Polystyrene-b-Poly(3-hexylthiophene) Diblock Copolymers

Polystyrene-b-poly(3-hexylthiophene) (PS-b-P3HT) block copolymers with fixed PS block length have been synthesized by combined atom transfer radical polymerization (ATRP) and Grignard metathesis (GRIM) polymerization. The self-assembled structures of these diblock copolymer thin films based on PS-b-P3HT have been studied by TEM, SAED, GIXD, AFM, and additionally by first principles modeling and simulation. These block copolymers undergo microphase separation and form nanostructured spheres, lamellae, nanofibers, or nanoribbons in the films dictated by the molecular weight of the P3HT block. Within the diblock copolymer thin film, PS blocks segregate to form amorphous domains, and the covalently bonded conjugated P3HT blocks exist as highly ordered crystalline domains through intermolecular packing with their alkyl side chains aligned normal to the substrate while the thiophene rings align parallel to the substrate through π-π stacking. The conjugated PS-b-P3HT block copolymers exhibited significant improvements in organic field-effect transistor (OFET) performance and environmental stability as compared to P3HT homopolymers, with up to a factor of 2 increase in measured mobility (0.08 cm(2)/(V·s)) for the P4 (85 wt % P3HT). Overall, this work demonstrates that the high degree of molecular order induced by block copolymer phase separation can improve the transport properties and stability of conjugating polymers, which are critical for high-performance OFETs and other organic electronics.

Octupole-like Supramolecular Aggregates of Conical Iron Fullerene Complexes into a Three-Dimensional Liquid Crystalline Lattice

The installation of three structural features into a fullerene molecule, a conical shape, a polar iron-ferrocene complex, and long alkyl chains, allowed dipolar molecules 1 and 2 to undergo microphase separation and to form a three-dimensional lattice in a crystalline and a thermotropic liquid crystalline phase. The key feature is a tetrameric octupole-like aggregate, in which four dipoles are arranged supramolecularly to cancel the molecular polarity, forming a sphere. In addition to this lattice formation mechanism, the molecules incorporate noteworthy features, such as redox active C(60)/ferrocene and luminescent cyclophenacene.

Bioinspired Block Copolymers: Translating Structural Features from Proteins to Synthetic Polymers

AbstractIn order to mimic a key functional feature of the transport protein serum albumin that disposes of several different simultaneous binding sites, new ternary linear block copolymers were synthesized. The block copolymers are made of one non‐ionic hydrophilic block based on derivatives of poly(oligoethyleneglycol), and of two mutually immiscible hydrophobic poly(acrylate) blocks, based on hydrocarbon and fluorocarbon esters of acrylic acid, respectively. The polymers self‐organize in aqueous solution to micellar aggregates, which undergo microphase separation within the hydrophobic micellar core. The different aggregate structures were imaged by transmission electron cryo‐microscopy (cryo‐TEM). Depending on the detailed polymer architecture, either core‐shell‐corona micelles, or micelles with a true multicompartment structure were formed, that are capable of selective solubilization.magnified image

Microphase Structure of Poly(N-isopropylacrylamide) Hydrogels As Seen by Small- and Wide-Angle X-ray Scattering and Pulsed Field Gradient NMR

Above the lower critical solution temperature T(c) (ca. 34 degrees C), poly(N-isopropylacrylamide) hydrogels become weakly hydrophobic and undergo microphase separation. Macroscopic deswelling, however, is extraordinarily slow, the out-of equilibrium state of the gel being conserved for many days. In this article the structure of the microphase-separated state above T(c) is probed by small-angle X-ray scattering and by pulsed field gradient NMR of the protons of water, both in the water phase and in the polymer-rich phase. Above T(c) the gel comprises two microphases, separated by smooth interfaces. The cavities occupied by the water phase form a connected network. The diffusion rate of the water molecules in this phase varies from one cavity to another and can be described by a Gaussian distribution. Water molecules belonging to the polymer-rich phase are also mobile, but their self-diffusion coefficient D is greatly diminished. Absence of compartmentalization of the water phase implies that the slow deswelling rate of the gel is not due to trapping of the water phase.

HyperMacs to HyperBlocks: A Novel Class of Branched Thermoplastic Elastomer

We demonstrate here the great versatility of the macromonomer approach for the synthesis of long chain hyperbranched polymers (HyperMacs) and describe the synthesis of HyperMacs from polybutadiene and poly(methyl methacrylate) using analogous yet modified synthetic strategies. Furthermore, we report the synthesis, morphology, and mechanical properties of an entirely new class of HyperMacs—HyperBlocks—prepared from the coupling of polystyrene−polyisoprene−polystyrene triblock copolymer macromonomers. Transmission electron microscopy (TEM) studies show that these unconventional block copolymers undergo microphase separation, but the resulting morphologies lack any long-range order. Tensile testing shows that these materials offer promise as a new class of branched thermoplastic elastomer (TPE). Finally, blends of HyperBlock (10%) with a commercial linear TPE produced by Kraton show both enhanced ultimate tensile stress and elongation at break.

Microphase separation induced by differential interactions in diblock copolymer/homopolymer blends

Phase behavior of diblock copolymer/homopolymer blends (AB/C) is investigated theoretically. The study focuses on a special case where all three binary pairs, A/B, B/C, and C/A, are miscible. Despite the miscibility of the binary pairs, a closed-loop immiscible region exists in the AB/C blends when the A/C and B/C pair interactions are sufficiently different. Inside the closed-loop, the system undergoes microphase separation, exhibiting different ordered structures. This phenomenon is enhanced when the homopolymer (C) interacts more strongly to one of the blocks (A or B).

Microphase separation and liquid-crystalline ordering of rod-coil copolymers

Microphase separation and liquid-crystalline ordering in diblock and triblock rod-coil copolymers (with rod-to-coil fraction f=0.5) were investigated using the dissipative particle dynamics method. When the isotropic disordered phases of these systems were cooled down below their order-disorder transition temperatures T(ODT), lamellar structures were observed. For rod-coil diblock copolymers, the lamellar layers were obtained below T=2.0. This temperature was found to be higher than the T(ODT) for normal coil-coil diblock copolymers. Significant ordering of the rods was observed only below T=0.9 which is the isotropic-nematic transition temperature for rodlike fluids. For the triblock rod-coil copolymers, both microphase separation and rod ordering occurred at T=0.9. Normal coil-coil triblock copolymers were found to undergo microphase separation at T=0.8, which is about half the T(ODT) of the normal diblock copolymers. Investigations of the mean square displacement and the parallel and the perpendicular components of the spatial distribution function revealed that at low temperatures, the rod-coil diblock copolymers exhibit smectic-A and crystalline phases, while the triblock copolymers show smectic-C and crystalline phases. No nematic phases were observed at the density and interaction parameters used in this study.

Single Chains of Block Copolymers in Poor Solvents: Handshake, Spiral, and Lamellar Globules Formed by Geometric Frustration

A single multiblock copolymer chain in poor solvent undergoes microphase separation within its own globule, driven by the same kind of forces operating in the bulk system. However, the necessity of packing a large AB interface into a small volume leads to novel convoluted geometries. Long block lengths form a double droplet. Very short block lengths exhibit bulk behavior, forming a lamellar globule. With intermediate block lengths, the AB interface buckles to form a hand shake or spiral dicluster. An order-disorder transition is reported for short block lengths.

Gel-size dependence of temperature-induced microphase separation in weakly-charged polymer gels

The gel-size dependence of microphase separation in weakly-charged gels of N-isopropylacrylamide (NIPA) and 1-vinylimidazole (VI) copolymers has been investigated using swelling measurement, small-angle neutron scattering (SANS), and dynamic and static light scattering (DLS/SLS). It is known that weakly-charged polymer gels undergo microphase separation in a poor solvent as a result of competing interactions involving hydrophobic attraction versus electrostatic repulsion. The microphase separation is characterized by a scattering maximum in SANS intensity functions of which Bragg spacing, Λ, is around 20–30nm. However, when gel size was reduced to the order of Λ, no microphase separation was observed. Instead, a typical scattering of isolated spherical particles was clearly observed. On the basis of the experimental evidence, we conclude that microphase separation has its own wavelength independent of gel size, and nanometer-order gels, i.e., nanogels, do not undergo microphase separation.

Phase Behavior of Near-Monodisperse Semifluorinated Diblock Copolymers by Atom Transfer Radical Polymerization

Well-defined diblock copolymers of pentafluorostyrene and methyl methacrylate with narrow molecular weight distributions (PDI < 1.15) were successfully synthesized by atom transfer radical polymerization (ATRP). Both polypentafluorostyrene and poly(methyl methacrylate) can serve as effective macroinitiators for the polymerization of the subsequent block. Because of thermodynamic immiscibility between the two blocks, these diblock copolymers undergo microphase separation upon annealing to form ordered nanostructures. The order−disorder transition temperatures for a series of symmetric, low molecular weight samples were determined to ascertain the temperature dependence of the Flory−Huggins interaction parameter (χ). Poly(pentafluorostyrene-b-methyl methacrylate) is only about twice as segregated as its nonfluorinated counterpart, poly(styrene-b-methyl methacrylate), or the quintessential poly(styrene-b-isoprene), at 440 K. Despite perfluorination of the ring, the symmetric placement of the C−F bonds on the benzene ring causes the polarities at the ortho and meta positions to cancel in polypentafluorostyrene. Replacing polystyrene with polypentafluorostyrene thus only leads to a small net polarity increase, which in turn results in a reduced polarity difference between polypentafluorostyrene and poly(methyl methacrylate), as compared to that predicted on the basis of the increase in fluorine content alone.

Effect of the Mobility of Charged Units on the Microphase Separation in Amphiphilic Polyelectrolyte Hydrogels

The effect of the migration of charged units on the structure of hydrophobically modified polyelectrolyte gels swollen by D(2)O was studied by small-angle neutron scattering on an example of gels of terpolymers of acrylic acid, n-dodecylacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid (quenched charged units) and gels of copolymers of partially neutralized acrylic acid and n-dodecylacrylate (annealed charged units). The content of charged units did not exceed 20 mol %, so that the electrostatic repulsion was too weak to disrupt the hydrophobic domains formed by self-assembled n-dodecyl chains, which was evidenced by NMR data. It was shown that upon increasing the charge content both types of gels undergo microphase separation with the formation of hydrophobic clusters consisting of several densely packed hydrophobic domains and hydrophilic regions swollen by water, where most of the charged repeat units and counterions are located. The dimensions of the nanostructure of the gels with quenched and annealed charged groups were compared. It was shown that the size of clusters in the gels with annealed charged units is much bigger than that in the gels with the same fraction of quenched charged units. This effect was attributed to a much weaker electrostatic repulsion in the corona of the hydrophobic clusters in the gels with annealed charged groups, because the charged units repelling each other are able to move farther apart.