Microphase Separation Transition Research Articles

Lamellar Microphase Separation and Phase Transition of Hydrogen-Bonding/Crystalline Statistical Copolymers: Amide Functionalization at the Interface.

Microphase separation of random copolymers, as well as that of high χ-low N block copolymers, is promising to construct sub-10-nm structures into materials. Herein, we designed statistical copolymers consisting of 2-hydroxyethyl acrylate (HEA) and N-octadecylacrylamide (ODAAm) to produce crystallization and hydrogen bond-assisted lamellar structure materials. The copolymers not only formed a crystalline lamellar structure with 3-4 nm domain spacing but also maintained an amorphous lamellar structure via phase transition above the melting temperature up to approximately 100 °C. The key is to introduce hydrogen-bonding amide junctions between the octadecyl groups and the polymer backbones, by which the polymer chains are physically fixed at the interface of lamellar structures even above the melting temperature. The stabilization of the lamellar structure by the amide units is also supported by the fact that the lamellar structure of all-acrylate random copolymers bearing hydroxyethyl and crystalline octadecyl groups is disordered above the melting temperature. By spin-coating on a silicon substrate, the HEA/ODAAm copolymer formed a multilayered lamellar thin film consisting of a hydrophilic hydroxyethyl/main chain phase and a hydrophobic octadecyl phase. The structure and order-disorder transition were analyzed by neutron reflectivity.

Microphase-separated structure and mechanical properties of cycloaliphatic diisocyanate-based thiourethane elastomers

Polythiourethane (PTU) and polyurethane (PU) elastomers were prepared from poly(oxytetramethylene) glycol, 1,4-bis(isocyanatomethyl) cyclohexane and a dithiol or diol chain extender with two methylene numbers (tetramethylene (C4) and pentamethylene (C5)). The effect of dithiol and diol and the methylene length of the chain extenders on the microphase-separated structure and mechanical properties of PTU and PU were evaluated. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction measurements revealed that the degree of ordering of hard segment chains in PTUs is lower than that for PU elastomers. However, it was revealed from the DSC, small-angle X-ray scattering and temperature dependent dynamic viscoelasticity measurements that the degree of microphase separation in the PTUs became stronger than that for the PUs. As a result, the mechanical property of PTUs is comparable with PUs. Furthermore, the glass transition temperature for the soft segment of PTU became lower than that for PU. PTU and PU exhibited a larger degree of microphase separation and mechanical property when the chain extender was composed of a tetramethylene (C4) chain compared to a pentamethylene (C5) chain. Polythiourethane (PTU) elastomers, which are obtained by the reaction between polyol, diisocyanate, and dithiol, are expected to have some properties that polyurethanes (PUs) do not have. Herein, the microphase-separated structure and mechanical properties of the 1,4-bis(isocyanatomethyl) cyclohexane-based PTUs were investigated. It was revealed from the differential scanning calorimetry, small-angle X-ray scattering and dynamic viscoelasticity measurements that the PTUs possess a stronger degree of microphase separation and lower glass transition temperature of soft segment compared to that of PUs.

Ionic Transport, Microphase Separation, and Polymer Relaxation in Poly(propylene glycol) and Lithium Perchlorate Mixtures

By combining broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC), the ionic transport, microphase separation, and polymer relaxation in poly(propylene glycol) (PPG) and lithium perchlorate (LiClO4) mixtures have been systematically examined as a function of temperature, pressure, polymer molecular weight, and salt concentration. While the low molecular weight PPG–LiClO4 mixtures exhibit only a single phase, microphase separation is observed in the mixtures of higher molecular weight PPGs (1000 and 4000 g/mol). In the samples with microphase separation, BDS and DSC yield consistent glass transition temperatures for ion-rich and ion-depleted domains. Our Walden plot analysis indicates that the ionic transport in PPG–LiClO4 is controlled by the (slow) segmental relaxation, and the data of all PPG–LiClO4 fall close to the “ideal” Walden line. Last, the application of pressure not only suppresses the microphase separation, but also decouples the ionic transport from the segmenta...

Rheological and thermal properties of glycidyl azide polyol‐based energetic thermoplastic polyurethane elastomers

AbstractThe purpose of this study was to investigate the effects of polyol on glycidyl azide polyol (GAP)‐based energetic thermoplastic polyurethane elastomers (ETPEs). Briefly, a series of GAP/polyol‐based ETPEs (GAP/polyol ETPEs) with different copolyol ratios and hard segment contents were synthesized using GAP‐diol with common polyol and 4,4‐methylenebis(phenylisocyanate)‐extended 1,5‐pentanediol as soft and hard segments, respectively, by solution polymerization in dimethylformamide. The three types of polyols used were poly(tetramethylene ether) glycol (PTMG), polycarbonate‐diol (PCL‐diol) and polycaprolactone‐diol (PCD‐diol). The synthesized GAP/polyol ETPEs were identified and characterized using Fourier transform infrared and 1H NMR spectroscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and rheometric mechanical spectrometry. For GAP/PCL ETPEs with lower hard segment content, DSC results showed that the GAP segment failed to interact with either the PCL segment or PCL melting. In addition, the results of DMA showed that the presence of PCL segments in ETPEs improved the storage modulus below the melting temperature of the PCL block. Further, the crystalline PCL segments were attributed to reinforcing the ETPEs in a manner similar to that of the hard domain. As the hard segment content increased in the GAP/polyol ETPEs, both GAP/PTMG ETPEs and GAP/PCL ETPEs exhibited microphase separation transitions, while rheological experiments demonstrated a sudden decrease in complex viscosity in neighboring microphase separation transitions. © 2012 Society of Chemical Industry

Microphase separation induced by differentiating non-solvent in a semi-dilute solution studied by rheometry and SANS

We investigated microphase separation and order-order transition induced by a "differentiating non-solvent" in the semi-dilute solutions of a block copolymer (BCP) with an ultra-high-molecular-weight (UHMW). The microdomain structures formed were highly ordered. We used a diblock copolymer of polystyrene-block-poly (tert-butyl methacrylate) (PS-b-PtBuMA) and THF as a good solvent and water as a differentiating non-solvent. The rheological property of this semi-dilute solution at the polymer concentration of 11 wt % was investigated by the dynamic viscoelastic measurement. By the addition of a small amount of water up to 8 wt %, G′ and G′′ increased gradually except at the water concentration ϕw of ca. 6 wt % where the abrupt change of G′ was observed due to the morphological transition. At higher water concentrations at 9 and 10 wt %, plateau regions as general polymer melts were observed. This is due to the movement of THF and water into PtBuMA phase as revealed by small-angle neutron scattering measurement. This movement is the key to understand the microphase separation and the order-order transitions induced by the differentiating non-solvent.

Pressure‐ and Temperature‐Induced Phase Separation Transition in Homopolymer, Block Copolymer, and Protein in Water

AbstractEffects of temperature, T, and pressure, P, on phase behavior and structure are discussed on three types of polymeric systems, i.e., a homopolymer (HP), a block copolymer (BC), and a protein (PR) in water. Due to the presence of hydrophobic groups, each system underwent a T‐induced and P‐induced phase separation by increasing T and P, respectively. However, these transitions are different from each other depending on their molecular structures. Small‐angle neutron scattering investigations revealed that HP showed a macrophase separation transition (MaST) with respect to both T and P. BC underwent a microphase separation transition (MiST) followed by a MaST with increasing T, while only a MaST was observed with increasing P. In the case of PR, on the other hand, T‐induced and P‐induced denaturations led to densely‐packed aggregates of oligomers and fractal‐aggregates of primary particles, respectively. The results from all systems indicated that hydrophobic interactions become insignificant at high pressures.

Rheological behaviour of thermoplastic poly(ester-siloxane)s

Two series of thermoplastic elastomers (TPES) based on poly(dimethylsiloxane), (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were analyzed by dynamic mechanical spectroscopy. In the first TPES series the lengths of both hard and soft segments were varied while the mass ratio of the hard to soft segments was nearly constant (about 60 mass%). In the second series, the mass ratio of hard and soft segments was varied in the range from 60/40 to 40/60, with a constant length of soft PDMS segments. The influence of the structure and composition of TPESs on the rheological properties, such as complex dynamic viscosity, ?*, the storage, G?, and loss, G?, shear modulus as well as the microphase separation transition temperature, TMST, was examined. The obtained results showed that the storage modulus of the TPESs increased in a rubbery plateau region with increasing degree of crystallinity. The rheological measurements of TPESs also showed that a microphase reorganization occurred during the melting process. The microphase separation transition temperatures were in the range from 220 to 234 ?C. In the isotropic molten state, the complex dynamic viscosity increased with increasing both the content and lenght of hard PBT segments.

Tuning block copolymer phase behavior with a selectively associating homopolymer additive

AbstractWe use polymer random phase approximation (RPA) theory to calculate the microphase separation transition (MST) spinodal for an AB + C diblock copolymer–homopolymer blend where the C homopolymers are strongly attracted to the A segment of the copolymers. Our calculations indicate that one can shift the MST spinodal value of the A − B segmental interaction parameter (χABN)S to significantly lower values [i.e., (χABN)S < 10.5] upon the addition of a selectively attractive C homopolymer. For a sufficiently attractive C homopolymer, (χABN)S can be pushed to negative values, indicating microphase separation in what would appear to be a completely miscible diblock copolymer. Furthermore, we show that microphase separation can occur in diblock copolymer–homopolymer blends where the segmental interactions between all polymer constituents are attractive. By tuning the value of (χABN)S with a homopolymer additive, one is therefore able to tune the effective copolymer segregation strength and thus dramatically affect the blend phase behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2083–2090, 2009

Structure Development in Flexible Polyurethane Foam‐Layered Silicate Nanocomposites

AbstractSummary: Polyurethane foam nanocomposites were formed via in‐situ copolymerisations, in which polyether polyol/water‐montmorillonite mixtures were reacted with toluene diisocyanate. The unmodified Na+‐ montmorillonite (MMT) was swollen in polyol/water using an ultrasound technique resulting in intercalated layers with increased basal spacings of 2.3 ± 0.1 nm. Measurements of quasi‐adiabatic temperature rise showed higher reaction rates as MMT loading increased from 0 to 10 wt.‐%. Forced‐adiabatic FTIR spectroscopy was used to determine the kinetics of both the copolymerisation and of the microphase separation between poly(ether‐urethane) soft segments and polyurea hard segments. The apparent microphase‐separation transition time decreased from 70 ± 3 to 42 ± 2 s upon addition of ≤10 wt.‐% MMT, but at reaction times >100 s there was significant retardation of the development of hydrogen bonding in the urea groups of the hard‐segment phase.

Evolutionary Approach in Copolymer Sequence Design

AbstractSummary: In this work, we discuss a simple evolutionary algorithm that introduces a “selection pressure” under which two‐letter (AB) copolymer sequences can mutate and transform into the sequences tuned to microphase separation transition (MIST). In particular, we are interested in determining how a sequence of A and B units should be organized in order to reach maximum length scale for MIST at a given AB composition. It is found that such sequences are similar to those known for tapered or gradient copolymers exhibiting strong composition inhomogeneity along their chain. The problems of the evolution of copolymer sequences are considered from the viewpoint of emerging of information complexity in the sequences in the course of this evolution.

中性子散乱・光散乱による高分子水溶液・ゲルの圧力誘起相分離と疎水性相互作用の研究

The phase behavior and microscopic structure of polymer aqueous solutions and hydrogels were investigated by means of small-angle neutron scattering (SANS) and light scattering (LS). Attention was focused on pressure (P) and/or temperature (T) induced phase transitions, such as microphase and macrophase separation transitions. In the case of poly(N-isopropylacrylamide) solutions and gels, coexistence and spinodal curves in the P-T coordinate were found to be convex-upward functions. At the phase boundary, the correlation length of the solution diverged. When charges were introduced to the gels, a scattering maximum originating from charge interactions appeared. This peak disappeared and reappeared by scanning P, showing reentrancy with respect to P. In the case of block copolymer solutions consisting of thermosensitive and hydrophilic block chains, both microphase and macrophase separation transitions were observed depending on T and P. It was found that the phase behavior was classified into several regimes with respect to the strength of hydrophobic solvation. All of these facts indicate that the roles of T and P in the thermodynamics of hydrophobic interaction are quite different.

Rheological investigation of microphase separation transition of polyurethane elastomer

AbstractA technique of linear viscoelasticity measurements coupling with temperature scanning was found effective in the detection of microphase separation transition (MST) and in the determination of MST temperature. The validity and accuracy of the technique were confirmed and reinforced by atomic force microscopy and differential scanning calorimetry (DSC). The technique was applied to a study of the MST of a series of 13 polyurethane (PU) elastomers based on mixed toluene diisocyanate (TDI), 1,4 butadiol, and poly(tetramethylene oxide) (PTMO) of two different molecular weights; the MST temperatures of the PU elastomer samples were measured. Although each of the 13 polymer samples had distinct hard segment content and used PTMO of different chain lengths, or mixed PTMO, the MST temperatures of the 13 samples formed a linear master curve when the MST temperature was plotted against the fraction of hard segment. The master curve indicated that the MST temperature is independent of the length and type of PTMO. It was also found that 2,4 TDI prevailing over its isomer 2,6 TDI played a dominant role in the MST of this series of PU elastomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2107–2112, 2007

Block Copolymers Under Shear Flow

AbstractSummary: Microphase separation transition in block copolymer melts and solutions in equilibrium and under shear flow is reviewed. The non‐equilibrium molecular dynamics (NEMD) computer simulation methodology is presented in detail including the derivation of the SLLOD equations of motion, Gaussian thermostat, and operator‐splitting symplectic integrators. Results of our recent NEMD computer simulation studies of diblock copolymers in a selective solvent under shear flow are presented. Shear‐dependent structural, rheological, and microscopical properties are described. New phase transitions are discovered. The parallel‐perpendicular orientational transition in a weak‐strong flow is revealed. Theoretical approaches are reviewed including the Edwards Hamiltonian, Landau‐Ginzburg model, self‐consistent mean field theory, field‐theoretic simulation, as well as the time‐dependent Landau‐Ginzburg framework and its application to the studies of complex fluids. magnified image

Nature of slow dynamics in a minimal model of frustration-limited domains.

We present simulation results for the dynamics of a schematic model based on the frustration-limited domain picture of glass-forming liquids. These results are compared with approximate theoretical predictions analogous to those commonly used for supercooled liquid dynamics. Although model relaxation times increase by several orders of magnitude in a non-Arrhenius manner as a microphase separation transition is approached, the slow relaxation is in many ways dissimilar to that of a liquid. In particular, structural relaxation is nearly exponential in time at each wave vector, indicating that the mode-coupling effects dominating liquid relaxation are comparatively weak within this model. Relaxation properties of the model are instead well reproduced by the simplest dynamical extension of a static Hartree approximation. This approach is qualitatively accurate even for temperatures at which the mode-coupling approximation predicts loss of ergodicity. These results suggest that the thermodynamically disordered phase of such a minimal model poorly caricatures the slow dynamics of a liquid near its glass transition.

Theory of domain patterns in systems with long-range interactions of Coulomb type.

We develop a theory of the domain patterns in systems with competing short-range attractive interactions and long-range repulsive Coulomb interactions. We take an energetic approach, in which patterns are considered as critical points of a mean-field free energy functional. Close to the microphase separation transition, this functional takes on a universal form, allowing us to treat a number of diverse physical situations within a unified framework. We use asymptotic analysis to study domain patterns with sharp interfaces. We derive an interfacial representation of the pattern's free energy which remains valid in the fluctuating system, with a suitable renormalization of the Coulomb interaction's coupling constant. We also derive integro-differential equations describing stationary domain patterns of arbitrary shapes and their thermodynamic stability, coming from the first and second variations of the interfacial free energy. We show that the length scale of a stable domain pattern must obey a certain scaling law with the strength of the Coulomb interaction. We analyzed the existence and stability of localized (spots, stripes, annuli) and periodic (lamellar, hexagonal) patterns in two dimensions. We show that these patterns are metastable in certain ranges of the parameters and that they can undergo morphological instabilities leading to the formation of more complex patterns. We discuss nucleation of the domain patterns by thermal fluctuations and pattern formation scenarios for various thermal quenches. We argue that self-induced disorder is an intrinsic property of the domain patterns in the systems under consideration.

Theoretical Study of Hydrogen-Bonded Supramolecular Liquid Crystals

We propose a new theoretical method to study hydrogen-bonded supramolecular liquid crystals. It is based on our recent theory of associating polymer solutions combined with McMillan's molecular theory of liquid crystallization. We derive phase diagrams of supramolecular liquid crystals consisting of two different species of molecules, such as dimers and trimers. In such phase diagrams, liquid crystallization and two-phase separation coexist. There are two different types of phase separation: one is caused by the first-order transitions of liquid crystals, and the other is demixing by repulsive interaction between the different species of molecules. As a result, multicritical phenomena such as tricritical point, Flory's chimney type two-phase region, etc., appear. Comparison of phase diagrams of dimerized supramolecular liquid crystals with those of corresponding flexible polymers suggests that a new microphase separation transition may occur inside the layers of the smectic A phase.

Microphase Separation Transition and Rheology of Side-Chain Liquid-Crystalline Block Copolymers

Microphase separation was induced from homogeneous polystyrene-block-polyisoprene (SI diblock) copolymer by grafting of a liquid-crystalline (LC) monomer onto the polyisoprene (PI) block. The origin of the formation of microdomain structure in the side-chain LC block copolymer from a homogeneous SI diblock copolymer is explained in terms of a dramatic increase in repulsive segmental interactions between the constituent blocks. For the investigation, three homogeneous SI diblock copolymers with varying block length ratios (SI-5/6, SI-10/6, and SI-14/3) were synthesized via anionic polymerization in tetrahydrofuran as solvent. This resulted in PI blocks having the following microstructures: 34% 1,2-addition, 59% 3,4-addition, and 7% 1,4-addition. Subsequently, the PI blocks in each of the SI diblock copolymers were first hydroxylated via hydroboration/oxidation reactions to yield hydroxylated SI diblock copolymers (SI-5/6-OH, SI-10/6-OH, and SI-14/3-OH), and then a liquid-crystalline (LC) monomer, 6-[(4-cyano-4'-biphenyl)oxy]hexanoic acid (5CN-COOH), synthesized in our laboratory, was grafted onto the hydroxylated PI blocks (PI-OH), yielding side-chain LC diblock copolymers (SI-5/6-5CN, SI-10/6-5CN, and SI-14/3-5CN). The disappearance of the -COOH and -OH groups after coupling reaction was confirmed using 1 H nuclear magnetic resonance spectroscopy and infrared spectroscopy. Transmission electron microscopy revealed that at room temperature SI-5/6-5CN has spherical microdomains, SI-10/ 6-5CN has hexagonally packed cylindrical microdomains, and SI-14/3-5CN has lamellar microdomains. The LC phase of the side-chain block copolymers was identified using polarizing optical microscopy. The clearing temperature (T cl ), determined by differential scanning calorimetry, of the side-chain LC block copolymers is found to be ca. 84 °C, whereas the T cl of LC monomer 5CN-COOH is 170 °C. Oscillatory shear rheometry indicates that the sphere-forming block copolymer SI-5/6-5CN undergoes a lattice disordering/ordering transition at 140 °C and a demicellization/micellization transition at 155 °C, while both the cylinder-forming block copolymer SI-10/6-5CN and lamella-forming block copolymer SI-14/3-5CN undergo microphase separation transition at temperatures much higher than 240 °C, the highest experimental temperature employed. Binodal curves exhibiting upper critical solution temperature were constructed, via cloud point measurement, for four pairs of polystyrene (PS) and PI grafted with 5CN-COOH (PI-5CN). An expression for the temperature dependence of the Flory-Huggins interaction parameter X for the PS/(PI-5CN) pair was determined and compared with the X expression for the PS/PI pair. The origin of the formation of microdomain structure in the side-chain LC block copolymers SI-5CN from a homogeneous SI diblock copolymer is explained in terms of molecular weight, block composition, and X for the PS/(PI-5CN) pair.

Microphase segregation in molten randomly grafted copolymers

We study microphase ordering of molten randomly grafted copolymers (RGCs) by using a mean field theory and the replica method to calculate the quenched average. Our results illustrate that in the weak segregation limit (WSI), the optimal wave vector q* of the lamellar phase formed by molten RGCs, has a temperature dependence different from either linear random copolymers (LRCs) or diblock copolymers (DCPs): when close, but below the microphase separation transition (MST) temperature, q* increases sharply with decreasing temperature; then q* gradually acquires an asymptotic value determined by the length of the branch and the average distance between branch points on the backbone. Our results are compared with recent experiments, and the effects of chain architecture on the microphase separation characteristics of RGCs are delineated. Our results suggest a new method for controlling the microphase spacing by exploiting quenched disorder.

Microphase Separation upon Heating in Diblock Copolymer Melts

A mean-field Landau free energy is formulated for a compressible diblock copolymer melt that microphase separates upon heating. Finite compressibility, which induces microphase separation in such a copolymer, is incorporated into the free energy through interaction fields for describing effective interactions between constituent polymers. The condition of microphase separation transition and equilibrium microphase morphologies are determined for the diblock copolymer of deuterated polystyrene and poly(vinyl methyl ether) as a model system exhibiting the thermally induced microphase separation. The Landau analysis reveals that microphase separation transition for the given copolymer is of first order in the entire region of composition. The phase diagram for the copolymer including classical microphase morphologies is shown to be apparently different from that for typical diblock copolymers exhibiting microphase separation upon cooling. In addition, the fluctuations of free volume are analyzed after microphase separation. Excess free volume is shown to be present in the domains of a more compressible component.

Phase behavior of comblike copolymers: The integral equation theory

We study the phase behavior of self-assembling grafted comblike copolymers with strongly attractive side chains. An off-lattice, microscopic integral equation theory is applied to investigate intermolecular correlations, collective scattering intensities, and thermally induced macro- and microphase separation transitions in the systems of different comb models having various architectures and chain stiffness. The properties of these models are analyzed as a function of molecular density, the number of side chains, the length of the side chains and backbone. Detailed calculations reveal the main factors that control micro- versus macrophase separation and thereby yield guideline for controlling the phase behavior of comblike copolymer systems in solutions and in melts.