Size Of Microdomains Research Articles

Light Induced Micro-Domains in Ferroelectrics

The model of the micro-domains formation in photorefractive crystals near the illuminated area polarized due to the screening effects is developed. The micro-domain shape and physical properties are studied in the phenomenological Ginsburg--Landau--Devonshire (GLD) theory framework with respect to the semiconductor properties of ferroelectric medium. The spontaneous electric induction distribution in the micro-domain is shown to depend on the surface charge distribution on the boundary between illuminated area and the other system. Owing to the surface density peculiarities the transversal micro-domain size is revealed to be much smaller than longitudinal one.

Effects of organoclays on morphology and thermal and rheological properties of polystyrene and poly(methyl methacrylate) blends

AbstractMorphology, thermal and rheological properties of polymer‐organoclay composites prepared by melt‐blending of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PS/PMMA blends with Cloisite® organoclays were examined by transmission electron microscopy, small‐angle X‐ray scattering, secondary ion mass spectroscopy, differential scanning calorimetry, and rheological techniques. Organoclay particles were finely dispersed and predominantly delaminated in PMMA‐clay composites, whereas organoclays formed micrometer‐sized aggregates in PS‐clay composites. In PS/PMMA blends, the majority of clay particles was concentrated in the PMMA phase and in the interfacial region between PS and PMMA. Although incompatible PS/PMMA blends remained phase‐separated after being melt‐blended with organoclays, the addition of organoclays resulted in a drastic reduction in the average microdomain sizes (from 1–1.5 μm to ca. 300–500 nm), indicating that organoclays partially compatibilized the immiscible PS/PMMA blends. The effect of surfactant (di‐methyl di‐octadecyl‐ammonia chloride), used in the preparation of organoclays, on the PS/PMMA miscibility was also investigated. The free surfactant was more compatible with PMMA than with PS; the surfactant was concentrated in PMMA and in the interfacial region of the blends. The microdomain size reduction resulting from the addition of organoclays was definitely more significant than that caused by adding the same amount of free surfactant without clay. The effect of organoclays on the rheological properties was insignificant in all tested systems, suggesting weak interactions between the clay particles and the polymer matrix. In the PS system, PMMA, and organoclay the extent of clay exfoliation and the resultant properties are controlled by the compatibility between the polymer matrix and the surfactant rather than by interactions between the polymer and the clay surface. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 44–54, 2003

Morphological Studies of Binary Mixtures of Block Copolymers. 2. Chain Organization of Long and Short Blocks in Lamellar Microdomains and Its Effect on Domain Size and Stability

We focus on chain organization of long and short block chains on lamellar microdomains developed in a series of binary mixtures denoted as as/si, which are composed of a long asymmetric polystyrene-block-polyisoprene (SI) and one of three short symmetric SI's denoted respectively as as and si (i = 1, 2, 3). We investigated the effect of chain organization on stability of the microdomain and on microdomain size as a function of blending composition and ratio of degree of polymerization of as to si. Comparisons of the results with some theoretical predictions indicated that the strong segregation theory of Birshtein, Zhulina, and Lyatskaya fits well with the experimental results.

Theoretical model of the porosity of copolymer membranes

A theoretical model is developed to explore the porosity and chemical morphology of copolymer membranes. The size of the leaving group during polycondensation of the cross-links is found to have unexpected effects on the porosity, leading to a nonuniform pore-size distribution. The size and formation of microdomains with different chemistries and porosities can be predicted using this model. Such knowledge of a membrane’s physical and chemical morphology is useful in the development of fouling-resistant filtration membranes. Reverse osmosis and nanofiltration membranes commonly used today frequently undergo degradation due to fouling and thus experience a diminishing water flux. Additional control over the properties of the membrane can be achieved by combining two or more polymers to form a heteropolymer network.

Detection and Characterization of Membrane Microheterogeneity by Resonance Energy Transfer

The application of resonance energy transfer (RET) in the study of heterogeneity in membrane systems is described. Useful formalisms for monophasic and biphasic systems are presented, together with quantitative studies. Evidence for reduction of dimensionality, probe segregation, and microdomain sizes in these systems is discussed. Selected examples of multicomponent systems (natural membranes or model systems including proteins) are also referred, as well as recent work using RET under the microscope.

Interplay between the vortex phase coherence and extended disorder defects in the vortex-liquid regime of thin films and superlattices of 123 superconductors

a-axis oriented (CuO_2 planes perpendicular to the substrate) films and superlattices grown on cubic substrates show a structure with 90° microdomains. The microdomains are grains with a 90° rotation of the c axis. In the vortex liquid region, this microstructure induces a change from the usual three-dimensional (3D) behavior of the anisotropy toward a 2D behavior, in a temperature range above the usual crossover from 2D to 3D. Moreover, when the thickness of the superconducting part of the multilayers becomes smaller (or of the same order as) than the microdomain size the 3D dimensional anisotropy behavior is recovered.

The ordered micro-domain in Ba1−xSrxTiO3 thin films and its effect on phase transition

It has been pointed out that the diffuse phase transition (DPT) of A(B′B′′)O3 perovskite ferroelectrics correlates with the size of micro-domains, which are characterized by B-site cation ordering [1]. Also, the regulations of B-site cation ordering were summarized based on the principle of crystal chemistry [2]. Comparatively, less similar work has been done on the DPT of (A′A′′)BO3 perovskite ferroelectrics. For the same ion charges on the A site cation, whether A′ and A′′ can be ordered remains unknown until King et al. reported the existence of 1/2{110}, 1/2{100} and 1/2{111} superlattice in (PbCa)TiO3 [3]. So far, no reports on superstructure of (Ba1−x Srx )TiO3 (BST) compounds has been found by authors. In this letter, the 1/2{201} ordered micro-domains in Ba0.7Sr0.3TiO3 thin film were observed by TEM and the characterization of DPT could been seen from the dependence of dielectric permittivity and polarization hysteresis on temperature, which were different from those of corresponding bulks. The Ba0.7Sr0.3TiO3 thin film with 500 nm in thickness was deposited onto Pt/Ti/SiO2/Si(100) substrates by sol-gel method [4]. The gold dot matrix with 0.5 mm in diameter was sputtered onto the film as upper electrodes, and MIM structure capacitors were formed. The capacitance was measured by HP-4192 with oscillation of 0.005 V. The polarization-field relationship (P-E) was measured by RT-6000HVS.TEM observa-

Reducing Substrate Pinning of Block Copolymer Microdomains with a Buffer Layer of Polymer Brushes

We study the range of orientational order of a single layer of cylindrical block copolymer microdomains annealed on several types of substrates. The orientational persistence length or nematic correlation length (ξ) is evaluated using recently developed imaging and analysis methods to measure the grain size of the block copolymer microdomains. We show that the substrate can lower ξ for block copolymers with a majority component that interacts strongly with the substrate, but this can be mitigated by attaching a buffer layer of polystyrene brushes to the substrate. In addition, we show that, for a block copolymer where the block that strongly interacts with the substrate is the minority component, the microdomain correlation length does not increase when substrates are treated with this buffer layer. We suggest that in this case the brushes do not increase ξ not only because of the lower volume fraction of the strongly interacting component but also because there are block copolymer wetting layers at the f...

Amphiphile micelles formed by polystyrene/poly(2-vinyl pyridine) heteroarm star copolymers in toluene

We report the micellar behavior of polystyrene/poly(2-vinyl pyridine) heteroarm star copolymers (PSnP2VPn) in toluene which is a selective solvent of polystyrene. A series of PSnP2VPn were synthesized by anionic polymerization and their micellar characteristics such as critical micelle concentrations (cmc), aggregation numbers, hydrodynamic dimensions and core–corona sizes were determined by the means of static and dynamic light scattering, viscometry and transmission electron microscopy. All these parameters were studied as a function of the insoluble arm length and the corresponding scaling relations were established. Our system seems to belong to the class of amphiphile micelles characterized by strong dependencies of the aggregation number and the microdomain sizes on the insoluble arm length. This behavior is also characteristic of strongly segregated diblock and triblock copolymer systems.

Disordered heteropolymers with cross-links – phase diagram and conformational transitions

The phase structure of globular random heteropolymers with quenched cross-links is studied by replica field theory. Our analysis predicts the occurrence of complex freezing patterns with few conformations sampled. The low cross-linking temperature phase is attributed to microphase separation of the pre-gel state with cross-links forming at the microphase interfaces. A first-order transition occurs at higher cross-linking temperatures by an increase of the microdomain size by statistical matching of microphases bounded by cross-links. At higher cross-linking temperatures, a second-order transition is predicted to a sequence-stabilized globular state.

Effect of cross-link density and hydrophilicity of PU on blood compatibility of hydrophobic PS/hydrophilic PU IPNs

To investigate the effect of the hydrophilic and hydrophobic microdomain structure on blood compatibility, a series of interpenetrating polymer networks (IPNs) composed of hydrophilic polyurethane (PU) and hydrophobic polystyrene (PS) was prepared. One series was prepared with varying cross-link densities of each network, the other with varying hydrophilicity of the PU component. All PU/PS IPNs exhibited microphase-separated structures that had dispersed PS domains in the continuous PU matrix. The domain size decreased with decreasing the hydrophilicity of the PU component and increasing the cross-link density of each network. As the cross-link density and hydrophobicity of the PU component was increased, an inward shift of Tgs was observed, which was due to the decrease in phase separation between the hydrophobic PS component and hydrophilic PU component. In the in vitro platelet adhesion test, as the microdomain size of PU/PS IPN surface decreased, the number of adhered platelets on the PU/PS IPN surface was reduced and deformation of the adhered platelets decreased. It could be concluded that blood compatibility of PU/PS IPN was mainly affected by the degree of mixing between PU and PS component, which was reflected by the domain size of PS rich phase.

Modulated differential scanning calorimetry: 13. Analysis of morphology of poly(ethyl methacrylate)/polyurethane interpenetrating polymer networks

The phase structure of poly(ethyl methacrylate)–polyurethane (PEMA/PUR) interpenetrating polymer networks (IPNs) has been investigated by means of modulated-temperature differential scanning calorimetry (M-TDSC), dynamic mechanical thermal analysis (DMTA) and small-angle X-ray scattering (SAXS). Experimental data from both M-TDSC and SAXS indicate that the morphologies of all the PEMA/PUR IPN samples (90 : 10 to 10 : 90 PUR/PEMA) are multi-phase structures. The scattering peaks from SAXS are quite broad, thereby indicating a distribution of microdomain sizes from 5 to 12 nm. This structure formation in IPNs is a competitive process between phase separation and the formation of cross-links which restricts segmental diffusion. An M-TDSC-based characterization method for IPNs has been developed using the differential of heat capacity signal, d C p/d T, to analyze phase structure and calculate the weight fraction of each component.

Meso-scale texture of mesophase pitch and its spun fiber

The mesoscopic textures of the mesophase pitch and its spun fiber were examined in the as-prepared and solvent extracted forms using high resolution scanning electron microscopy (HR-SEM). HR-SEM revealed spherical or elliptical grains of 10–50 nm size. Such units were defined as microdomains in the insoluble fraction of the mesophase pitch. The solvent of high dissolving activity reduced the size of the grains, while maintaining their basic shape. No porosity was found in the surface of the microdomain. The as-spun fiber showed a flat textureless plane on its surface along the fiber axis. The solvent extraction closed up the spherical micrograin of 10 nm, as viewed perpendicular to the surface. A tilt angle of 10 ° to the surface of the fiber revealed the pleat alignment of insoluble microdomains. The carbonization after the stabilization of the fiber provided pleat alignment of microdomains on the surface when the fiber was tilted to be observed. Pleat microdomains observed on the surfaces of as-extracted and carbonized fibers were basically the same. The insoluble fraction in the mesophase pitch forms the particular microdomains in the extracted pitch. Thus, the insoluble microdomains in the pitch were deformed into the pleat unit through the spinning. The soluble fraction which coats the mesoscopic units of the insoluble fraction to give the textureless surface of the as-spun fiber may shrink during carbonization to follow the shapes of the insoluble microdomains. The unique shape of the insoluble fraction may reflect the channel structure observed in polymer blends, since microdomains in the fiber reflect the shape and size of those in the pitch after the spinning. The shape, size and arrangement of microdomains in the fiber may be one of the key factors in finding ways to control the mechanical properties of mesophase pitch-based carbon fibers.

Super2- Structures in Polydisperse Multiblock-Copolymers

Microphase separation in multiblock (AB) n copolymer melts at equilibrium is considered theoretically. It is shown that any finite polydispersity of the block molecular weights results in a set of novel super 2 -structures which are characterized by two levels of microdomains, one on the top of the other. The typical size of the second-level microdomains is governed by the polydispersity degree δ, and is much larger than the size of ordinary microdomains if δ is small. The theoretical description involves the second order parameter field φ(r) (in addition to the normal order parameter ψ related to the local composition) which is proportional to the local excess of longer blocks over shorter blocks. A scaling picture including the main characteristics of the super 2 -structures is built for both weak and strong segregation regimes.

Energy Transfer Studies of Binary Block Copolymer Blends. 1. Effect of Composition on the Interface Area per Chain and the Lamellar Size

Binary blends of polyisoprene−poly(methyl methacrylate) PI−PMMA diblock copolymers with a common PMMA length and different lengths of polyisoprene blocks were prepared from samples containing a single fluorescent dye, either phenanthrene (donor) or anthracene (acceptor), at the junction point. The two pure block copolymers and their mixtures were studied by the direct energy transfer (DET) technique. All experiments point to intimate mixing of the samples over the entire composition range. These DET experiments yield the interphase volume per junction vj and/or the ratio R/δ of the microdomain size R to the interphase thickness δ, as a function of the composition of the block copolymer mixture. Since, for these strongly segregated chains, the interface thickness is invariant with chain length and should also be constant for this set of mixtures, we can calculate from vj and R/δ the interface area per chain and the period spacing R. Here we find that addition of up to 25 mol % of the second polymer has no ...

Crystallization and Intriguing Morphologies of Compatible Mixtures of Tetrahydrofuran−Methyl Methacrylate Diblock Copolymer with Poly(tetrahydrofuran)

The crystallization and unusual crystalline morphologies of compatible mixtures of tetrahydrofuran−methyl methacrylate diblock copolymer with tetrahydrofuran homopolymer were studied. It is shown that the PTHF [poly(tetrahydrofuran)] block of the copolymer cocrystalizes with the PTHF homopolymer in the PTHF microphase of the blend. However, the degree of crystallinity of the PTHF block is always lower than that of the PTHF homopolymer in the PTHF microphase. The crystallizability of the PTHF microphase increases appreciably with increasing PTHF microphase size and PTHF homopolymer weight fraction in the microphase. The morphology study of the blends shows that the crystalline morphology is strongly dependent on blend composition, copolymer composition and PTHF block length, as well as crystallization temperature. When alternating PTHF and PMMA [poly(methyl methacrylate)] lamellae are formed, the macroscopic crystalline morphology could be only observed when the thickness of the PTHF lamellae is large enough (∼20 nm). In the blend where PMMA spherical or cylindrical microphases are formed, the crystalline morphology changes dramatically with the change in the PTHF microdomain size and PMMA interdomain distance. Many unusual crystalline morphologies have been observed. A study of the solution-crystallized morphology of the blends at different temperatures shows that the morphology is also strongly dependent on the isothermal crystallization temperature, suggesting that the PMMA microdomains may have different effects on the morphology formation when the blend is crystallized at different rates.

Inhomogeneous structure of polyurethane networks based on poly(butadiene)diol: 2. Time-resolved SAXS study of the microphase separation

The process of the microphase separation leading to an inhomogenous structure of the polyurethanes prepared from poly(butadiene)diol (PBD), 4,4′-diphenylmethane diisocyanate (MDI) and poly(oxypropylene)triol (POPT) has been investigated by synchrotron small-angle X-ray scattering (SAXS). The development of the two-phase structure of the polyurethanes, consisting of microdomains of higher electron density dispersed in the matrix of PBD chains, was revealed. When POPT is not used in the preparation, the interdomain distance does not increase with time and it corresponds to the root-mean-square end-to-end distance of the PBD chains. In the presence of POPT a distinct growth in the microdomain size and interdomain distance is observed. The scattering data are discussed in terms of the modified Percus-Yevick hard sphere model. © 1997 Elsevier Science Ltd.

Direct Energy Transfer Studies of the Domain−Boundary Interface in Polyisoprene−Poly(methyl methacrylate) Block Copolymer Films

Direct nonradiative energy transfer (DET) experiments were carried out on five polyisoprene−poly(methyl methacrylate) diblock copolymers with polyisoprene volume fractions ranging from 0.07 to 0.5 (polyisoprene microdomains dispersed in a poly(methyl methacrylate) matrix). These experiments yield the ratio R/δ of the microdomain size R to the thickness of the domain−boundary interface δ as a function of the block copolymer overall chain length N. A plot of ln(R/δ) vs ln N indicates that the microdomain size varies as N0.65, close to the N2/3 predicted by theory, while the interfacial thickness δ (26 A) is independent of the degree of polymerization covered in this work. In addition, the Flory−Huggins interaction parameter χ for PI−PMMA was determined from the DET data (0.077). We conclude from these experiments that PI−PMMA belongs to the class of strongly segregated systems.

Effective Volume per Junction in Block Copolymer Interfaces Probed by Direct Energy Transfer

Direct nonradiative energy transfer (DET) experiments were carried out on a series of labeled polyisoprene-poly(methyl methacrylate) (PI-PMMA) and polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers spanning a range of molecular weights and compositions. In all samples with spherical or cylindrical morphology, PMMA represents the major component, with PI or PS microdomains dispersed within the PMMA phase. These DET experiments yield the ratio of the microdomain size R to the interface thickness δ. We relate the R/δ ratio to the volume per junction υ j at the block copolymer interface and show that υ j does not depend upon the microdomain geometry or the overall block copolymer molecular weight, but only on the length N B of the shorter component. We derive an expression which accommodates the observed dependence of υ j on N B 1/3 .

Effect of Ionic Chain Polydispersity on the Size of Spherical Ionic Microdomains in Diblock Ionomers

The effect of ionic chain polydispersity on the morphology of spherical ionic microdomains in the dry state is studied by SAXS and TEM for two systems of diblock ionomers, polystyrene-b-poly(4-vinylpyridinium methyl iodide) (PS-b-P4VPMeI) and polystyrene-b-poly(cesium methacrylate) (PS-b-PMACs). The polydispersity of the ionic block is controlled by blending diblock copolymers of constant polystyrene length but different ionic block lengths. The samples are mixed in appropriate ratios so that the number-average molecular weight is constant but a wide range of polydispersity in the ionic blocks is obtained. The samples are prepared by three different methods