Increase In Domain Size Research Articles

Liquid phase demixing in ferroelectric/semiconducting polymer blends: An experimental and theoretical study

AbstractThis article describes a combined experimental and theoretical study on nanophase structure development as a result of liquid phase demixing in solution‐cast blends of the organic semiconductor poly(9,9′‐dioctyl fluorene) (PFO) and the ferroelectric polymer poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)). Blend layers (200 nm) are prepared by spin coating a 1:9 (w/w) PFO:P(VDF‐TrFE) blend solution in a common solvent on a poly(ethylenedioxy thiophene)/poly(styrene sulfonate) substrate. Owing to the pronounced incompatibility between the two polymers, a strong phase‐separated morphology is obtained, characterized by disk‐like nanodomains of PFO embedded in a P(VDF‐TrFE) matrix, as revealed by scanning electron microscopy. By varying the processing conditions, we find the average domain size and standard deviation to increase with spinning time. The considerable increase in domain size suggests the coarsening process not to be impeded by a steep rise in viscosity. This indicates solvent evaporation to be only moderate within the experimental time frame. The evolution of the observed phase morphology is modeled using ternary diffuse interface theory integrated with a modified Flory–Huggins (FH) treatment of the homogeneous (bulk) free energy of mixing, to account for significant molecular differences between the active blend components. Using calculated FH interaction parameters, the model confirms the phase separation to occur via spinodal decomposition of the blend solution during spin coating, as suggested by experimental observations. The simulated phase morphologies as well as the modeled trends in domain growth and standard deviation compare favorably with the experimental data. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1255–1262, 2011

Observation of Continuous and Quantized Domain Size and Shape Evolution in Monolayers at Air–Water Interface

Langmuir monolayers of pentadecanoic acid (C15) and dipalmitoyl phosphatidylcholine (DPPC) are investigated in liquid expanded–liquid condensed (LE–LC) phase co-existence region in order to study evolution of circular and undulating LC domains. The Brewster angle microscopy is analyzed to evaluate LC domain size and shape for various average molecular areas. For C15 monolayer circular domain shape and continuous increase of domain size are observed. In contrast, for DPPC monolayer undulating domain shapes are observed, where the mode of oscillations m is quantized depending on the average molecular area. Surprisingly, also the average domain size is quantized and depends on m. These observations are discussed in accordance with the phase rule modified for the monolayer phase co-existence region and observed levels of domain sizes are compared with theories of m-fold distortion.

Observation of Continuous and Quantized Domain Size and Shape Evolution in Monolayers at Air–Water Interface

Langmuir monolayers of pentadecanoic acid (C15) and dipalmitoyl phosphatidylcholine (DPPC) are investigated in liquid expanded–liquid condensed (LE–LC) phase co-existence region in order to study evolution of circular and undulating LC domains. The Brewster angle microscopy is analyzed to evaluate LC domain size and shape for various average molecular areas. For C15 monolayer circular domain shape and continuous increase of domain size are observed. In contrast, for DPPC monolayer undulating domain shapes are observed, where the mode of oscillations m is quantized depending on the average molecular area. Surprisingly, also the average domain size is quantized and depends on m. These observations are discussed in accordance with the phase rule modified for the monolayer phase co-existence region and observed levels of domain sizes are compared with theories of m-fold distortion.

Dynamics of Crystallization and Disorder during Annealing of P3HT/PCBM Bulk Heterojunctions

A real-time crystallographic analysis of P3HT/PCBM films during thermal annealing is reported, detailing the temporal variation of crystallization, disorder, and orientational spread during the annealing. Five P3HT/PCBM chlorobenzene solutions with different P3HT concentrations (0, 33, 50, 67, 100 wt %) were spin coated on SiO2 substrates. The thick films (100 nm) were studied during annealing (50 min at 140 °C), with in situ synchrotron grazing incidence X-ray diffraction (GI-XRD) and a sampling time <8 s. For the first time, the evolution of the crystal structure is analyzed taking into account P3HT paracrystallinity. The following were observed: a predominance of edge-on P3HT lamellae in the as-spun and annealed films; changes in concentration-dependent edge-on lamellar orientation spread along the alkyl-stacking direction and paracrystalline disorder after annealing; a permanent lamellar stretching just along the alky-stacking direction after annealing; an increase in the P3HT domain size along only the alkyl-stacking direction for the edge-on lamellae, with dynamics consistent with PCBM acting as a plasticizer for P3HT; and finally, an increase in the PCBM concentration at the sample−air interface. We show that the paracrystalline correction is important to calculate correctly the domain size as deduced from GI-XRD.

Kinetics of the cellular Potts model revisited

The relaxation kinetics of cell sorting are studied with the cellular Potts model. In contrast to previous reports, the increase in domain size is found to obey a power law (R(t)∝tn). The growth exponent turns out to be n=1/3 for an even mixture of two cell types, where the domains for each cell type are interconnected and the kinetics are dominated by smoothing of the domain boundary. The exponent is n=1/4 for uneven mixtures where cell sorting proceeds via the diffusion–coalescence of circular cell domains. The exponent is explained by the decrease in motility of a cell cluster as a function of its size according to D(R)∝R−2. Our results provide a theoretical framework for elucidating how cell populations migrate within tissue.

Triton X −100 and TM Helices Increase Ordered Domain (lipid Raft) Size

It has been postulated that the formation of co-existing liquid ordered (Lo) domains rich in sphingolipids and cholesterol and liquid disordered (Ld) domains rich in unsaturated lipids, has an important role in cell membrane structure and function. Detergent TX-100 favorably partitions into and dissolves the Ld phase. It is used to isolate insoluble Lo-like membranes known as detergent resistant membrane (DRM) from cells. The relationship between DRM and pre-existing Lo domains in cells is not clear. We carried out experiments to find out how TX-100, and TM helices (which are cell membranes components), change membrane properties by investigating their effect on liposomes composed of brain sphingomyelin/1-palmitoyl-2-oleoyl-phosphatidylcholine/cholesterol. As measured by anisotropy and tempo quenching, methods that detect local environment at the nearest neighbor level, neither TX-100 nor TM helices affected the thermal stability of membrane order. In contrast, FRET, which detects proximity at longer length scales, detected that ordered domains disappeared at a lower temperature than that estimated from anisotropy or quenching, both with and without TX-100 and TM helices. FRET detected domains at higher temperatures in the presence of TX-100 or TM peptides than in their absence. The amount of ordered domains and their thermal stability appeared to increase as the interaction distance (Ro) of the FRET pair decreased. These differences are most easily explained by a difference in the size-sensitivity of the detection techniques, such that FRET is unable to detect Lo domains smaller than Ro in size, and by the conclusion that TX-100 increases ordered domain size. However, in presence of TM peptides, this increase in domain size is less evident, as the TM peptide by itself already increases domain size. Thus, in natural membranes the effect of TX-100 upon domain formation may not be significant.

Graphene Films with Large Domain Size by a Two-Step Chemical Vapor Deposition Process

The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.

Regulation of Local Structure and Composition of Binary Disulfide and Thiol Self-Assembled Monolayers Using Nanografting

Nanografting is used to create spatial confinement, which enables regulation of self-assembly reaction pathways and outcome. The degree and outcome of this regulation is revealed using binary self-assembled monolayers (SAMs) of organothiols and disulfides. In naturally grown systems, these SAMs have more complex morphology when compared with corresponding binary alkanethiol SAMs. Taller molecules form nanodomains of ellipsoidal cap in shape. These domains arrange in various irregular geometries, including 1D worm-like and 2D branches. This observation differs from binary alkanethiol SAMs, where nanodomains are separated and randomly dispersed. During nanografting, more homogeneous morphology was observed compared with naturally grown layers. By varying nanoshaving speed, the nanodomain structure can be regulated from randomly dispersed to more heterogeneous and, finally, to near natural growth. This trend is very similar to mixed alkanethiol systems, where the domain size and separation increase with increasing speed. Different from the alkanethiol systems, the observed structural variations are due to the changes in surface composition, in addition to domain size, shape, and arrangement.

On the Correlation between Nanoscale Structure and Magnetic Properties in Ordered Mesoporous Cobalt Ferrite (CoFe2O4) Thin Films

In this work, we report the synthesis of periodic nanoporous cobalt ferrite (CFO) that exhibits tunable room temperature ferrimagnetism. The porous cubic CFO frameworks are fabricated by coassembly of inorganic precursors with a large amphiphilic diblock copolymer, referred to as KLE. The inverse spinel framework boasts an ordered open network of pores averaging 14 nm in diameter. The domain sizes of the crystallites are tunable from 6 to 15 nm, a control which comes at little cost to the ordering of the mesostructure. Increases in crystalline domain size directly correlate with increases in room temperature coercivity. In addition, these materials show a strong preference for out-of-plane oriented magnetization, which is unique in a thin film system. The preference is explained by in-plane tensile strain, combined with relaxation of the out-of-plane strain through flexing of the mesopores. It is envisioned that the pores of this ferrimagnet could facilitate the formation of a diverse range of exchange coupled composite materials.

Temperature-induced structure and microstructure evolution of nanostructured Ni0.9Zn0.1O

The crystal structure and microstructure of as-prepared and annealed Ni0.9Zn0.1O were refined at room temperature in both theFm{\overline 3}mandR{\overline 3}mspace groups. It is shown that below the Néel point (458 K), where magnetic ordering triggers the presence of a trigonal strain, the common usage of a higher-symmetry non-admissible space group for crystal structure and microstructure analysisviathe Rietveld method may result in both an incorrect structure description and incorrect microstructure parameters (size and strain). More realistic microstructure data can be obtained by whole powder pattern modelling of the powder diffraction data. Increasing the annealing temperature causes a reduction of the trigonal distortion as well as an increase in domain size. Simultaneously, the Raman spectra become less resolved, a clear indication of domain growth and structural evolution of the structure towards cubic symmetry (R{\overline 3}m→Fm{\overline 3}m).

Magnetic properties of granular CoCrPt:SiO2 films as tailored by Co+ irradiation

We report on an approach to tailor the magnetic exchange in a conventional granular CoCrPt:SiO2 recording medium by irradiation with Co+ ions. Irradiation at low fluences enhances the intergranular exchange resulting in a narrowing of the switching field distribution (SFD). The modification of magnetic exchange coupling was evidenced by measuring the angular dependence of the switching field and is supported by an increase in the magnetic domain size. Further, micromagnetic simulations of a granular magnetic medium confirm the correlation between intergranular exchange and SFD. At high fluences, however, the irradiation damages lead to the degradation of the magnetic layer as magnetic anisotropy and saturation magnetization decrease. Ion irradiation simulations suggest that this is caused by strong intermixing at the grain and layer interfaces.

Rotating spiral waves in [formula omitted] systems on circular domains

λ – ω systems are reaction–diffusion systems whose reaction kinetics admit a stable limit cycle. It is known that λ – ω systems can possess various types of solutions. Among them, spiral waves are the most fascinating pattern. However, the effects of the diffusivity, the sizes of the domains, and the reaction kinetics on spiral waves are largely unknown. In this paper, we investigate how these quantities affect the properties of m -armed spiral waves in a generalized class of λ – ω system on a circular disk with no-flux boundary condition. First we derive a criterion for the existence of m -armed spiral waves. Specifically, we show that m -armed spiral waves do not exist for d ≥ λ 0 R 2 / j m 2 , while for d ∈ ( 0 , λ 0 R 2 / j m 2 ) , there exists an m -armed spiral wave if the twist parameter q is small. Here d is the diffusivity for the λ – ω system, R is the radius of the circular disk, λ 0 is the value of the function λ ( A ) at A = 0 , and j m is the first positive zero of the first derivative of the Bessel function of the first kind of order m . We also show that the critical diffusivity d = λ 0 R 2 / j m 2 is a bifurcation point. Next we use the numerical simulation to show that, for small twist parameter, the rotational frequency increases with increasing domain size, while for large twist parameter, the dependence of the rotational frequency on the domain size is not monotonic. Moreover, small circular domains may change the properties of spiral waves drastically. These numerical results are in contrast to those in excitable media. Finally, the stability of spiral waves is investigated numerically.

Performance and Characterization of ALD Vanadium Oxide Catalytic Nanoliths

Supported vanadium oxide species are active catalysts for the selective, oxidative conversion of hydrocarbons to useful chemicals. Both the catalytic vanadium oxide and the supporting oxide were synthesized by ALD on high surface powders and anodic aluminum oxide (AAO) nanoliths. The nanoliths were prepared by anodic oxidation of aluminum. 1 nm of ALD aluminum oxide acts as the support for vanadium oxide loaded by 1 to 18 ALD cycles of vanadyltri-isopropoxide/H2O2. Ultraviolet-visible absorption edges red shift as the vanadia loading increases. The edge energy of 1-cycle ALD VOx corresponds to isolated, tetrahedral VO4 in agreement with Raman spectroscopy. V-O-V bonds form with additional cycles producing a gradual increase in VOx domain size. Reaction rate coefficients for the oxidative dehydrogenation of cyclohexane show increased overall activity in the high loading catalysts but a higher specific activity in the low loading catalysts for cyclohexene formation.

Temperature-dependent behavior of lysozyme within the reverse hexagonal mesophases (H II)

This manuscript is the second part of a study on the structural behavior of lysozyme-loaded reverse hexagonal mesophases. In the current paper we focused mainly on the mutual temperature-dependency relationship between the protein and the mesophase. The conformational stability of the enzyme and the structural effects on the host system were characterized using small-angle X-ray scattering (SAXS), ATR-FTIR spectroscopy, fluorescence, and rheological measurements. It was found that the mesophase does not change the solubilized lysozyme (LSZ) active site conformation. The obtained data suggested that LSZ embedment within the H II mesophase improved its thermal stability by hampering its helical structure destruction, apparently due to hydrogen bonding of the protein with monoolein polar heads. Examination of the structural parameters of the hexagonal carrier revealed a strong thermal dependency. The lattice parameter of both empty and LSZ-loaded systems had a similar temperature-dependent behavior. However, comparing the domain size of the LSZ-loaded system to the empty system showed different trends. LSZ incorporation induced a decrease in crystal size and lower order at room temperature. Nevertheless, an increase in domain size was triggered by the enzyme at elevated temperatures, in contrast to its decrease in the empty carriers. Rheological measurements showed concentration-dependent elasticity in the presence of LSZ compared to the empty system, which took place in a concentration-dependent manner at all examined temperatures. Up to 60 °C, the elasticity of the LSZ-loaded hexagonal systems decreased with temperature increase. This finding was interpreted in the context of weakening and/or cleaving of the monoolein hydroxyls’ interactions with the protein, leading to partial reconstitution of the initially low domain size and elasticity decrease. However, in the range of 60–75 °C (in most systems), the prevailing effect was thermally induced dehydration of the monoglyceride hydrophilic heads, which imposed elasticity increase, owing to enhanced flow ability of the liquid crystalline structure.

Single Polyelectrolyte Layers Adsorbed at High Salt Conditions: Polyelectrolyte Brush Domains Coexisting with Flatly Adsorbed Chains

AFM is used to measure the surface forces and to image sodium poly(styrenesulfonate) (PSS) layers physisorbed from 1 M NaCl solution on different length scales within one experiment. Domains of PSS brushes coexist with flatly adsorbed PSS. For degree of polymerization N = 380, the brush area fraction is 6%. With increasing degree of polymerization, brush area fraction and domain size increase, whereby the domain radii vary between 50 nm and 1.5 μm. Lateral homogeneous brush layers are found for a degree of polymerization exceeding 1100. The colloidal probe technique reveals that the surface forces are a superposition of steric and electrostatic forces; their respective contribution is determined by the brush area fraction. A comparison with literature demonstrates that adsorbed PSS brushes show the same scaling behavior as end-grafted PSS brushes. We develop a model for the adsorption of polyelectrolytes in which not the whole chain but only a fraction of the monomers adsorbs onto the surface. Thereby, we show that partial adsorption can lead to stable conformations and calculate scaling laws for the fraction of adsorbed monomers and the distance between the chains dangling into solution.

Inducible activation of Akt increases skeletal muscle mass and force without satellite cell activation

A better understanding of the signaling pathways that control muscle growth is required to identify appropriate countermeasures to prevent or reverse the loss of muscle mass and force induced by aging, disuse, or neuromuscular diseases. However, two major issues in this field have not yet been fully addressed. The first concerns the pathways involved in leading to physiological changes in muscle size. Muscle hypertrophy based on perturbations of specific signaling pathways is either characterized by impaired force generation, e.g., myostatin knockout, or incompletely studied from the physiological point of view, e.g., IGF-1 overexpression. A second issue is whether satellite cell proliferation and incorporation into growing muscle fibers is required for a functional hypertrophy. To address these issues, we used an inducible transgenic model of muscle hypertrophy by short-term Akt activation in adult skeletal muscle. In this model, Akt activation for 3 wk was followed by marked hypertrophy ( approximately 50% of muscle mass) and by increased force generation, as determined in vivo by ankle plantar flexor stimulation, ex vivo in intact isolated diaphragm strips, and in single-skinned muscle fibers. No changes in fiber-type distribution and resistance to fatigue were detectable. Bromodeoxyuridine incorporation experiments showed that Akt-dependent muscle hypertrophy was accompanied by proliferation of interstitial cells but not by satellite cell activation and new myonuclei incorporation, pointing to an increase in myonuclear domain size. We can conclude that during a fast hypertrophic growth myonuclear domain can increase without compromising muscle performance.

Effect of external electrostatic charge on condensed phase domains at the air-water interface: Experiment and shape equation analysis

The effect of external electrostatic charge on the shapes of liquid condensed (LC) phase domains in monolayer at the air/water interface was investigated. For this reason the thermodynamic properties, domain size, and spontaneous polarization were analyzed by surface pressure-area isotherms, Brewster angle microscopy (BAM), and Maxwell displacement current technique. The analysis indicated magnesium ions preferred to bond with dipalmitoyl phosphatidylcholine negative head group in liquid expanded phase and/or at domain boundary at low ion concentration and got an access to binding with molecules inside of the LC domains for higher ion concentration. Domain size increase characterized by BAM was discussed in respect to the shape equation on the basis of electrostatic energy contribution. Although molecular repulsive force increased by adding of ions into subphase, the growth of domain size exceeded this tendency. Following shape equation analysis it was suggested that this effect corresponded to change in dipole moment orientation represented by increase in spontaneous polarization in normal projection. This demonstrated impact of local electrostatic field on molecular dipoles and free energy of LC domains.

Computational fluid dynamics prediction of the air-core in hydrocyclones

The air-core diameter was successfully predicted by large eddy simulation and volume of fluid models. The dynamics of the flow for 75- and 250-mm hydrocyclones was evaluated in 11 cases in which the spigot diameter, conical length, vortex finder diameter, diameter of the hydrocyclone and viscosity of the fluid were changed. FLUENT™ 6.0 code was used to compute the dynamics of the flow. The air-core profiles demonstrated the accuracy of the simulations. A reduction in the spigot increases tangential velocity and hence air-core diameter is increased. An increase in hydrocyclone diameter also increases air-core diameter, while the vortex finder or an increase in fluid viscosity inversely influences it. The vortex finder influences inversely air-core diameter. The increase in viscosity of the fluid reduces air-core diameter. The computational time required to reach the solution increases as the domain size increases. The LES model cannot be used in everyday cases to optimise hydrocyclones, but it is an outstanding tool to study new designs.

Modulated and Localized States in a Finite Domain

A subcritical pattern-forming (Turing) instability of a uniform state, in an infinite domain, produces two branches of spatially localized states that bifurcate from the pattern-forming instability along with a uniform spatially periodic pattern. In this paper we demonstrate that branches of localized states persist as strongly amplitude-modulated patterns in large, but finite, domains with periodic boundary conditions. Our analysis is carried out for a model Swift–Hohenberg equation with a cubic-quintic nonlinearity. If the domain size exceeds a critical value, modulated states appear in secondary bifurcations from the primary branch of spatially periodic solutions. Multiple-scales analysis indicates that these secondary bifurcations occur close to the primary instability and close to the saddle-node bifurcation on the spatially periodic solution branch. As the domain size increases, extra “turns” on the snaking curve arise through a repeating sequence of saddle-node bifurcations and mode interactions between periodic patterns of nearby wavenumbers. With periodic boundary conditions, the crosslinks in the “snakes and ladders” structure identified by previous authors in the infinite domain case also persist in finite domains. However, the imposition of either Dirichlet or Neumann boundary conditions preserves one of the two branches of localized states that exist in the infinite domain case and causes the other to fragment.

Effect of Growth Temperature on Bamboo-shaped Carbon–Nitrogen (C–N) Nanotubes Synthesized Using Ferrocene Acetonitrile Precursor

This investigation deals with the effect of growth temperature on the microstructure, nitrogen content, and crystallinity of C–N nanotubes. The X-ray photoelectron spectroscopic (XPS) study reveals that the atomic percentage of nitrogen content in nanotubes decreases with an increase in growth temperature. Transmission electron microscopic investigations indicate that the bamboo compartment distance increases with an increase in growth temperature. The diameter of the nanotubes also increases with increasing growth temperature. Raman modes sharpen while the normalized intensity of the defect mode decreases almost linearly with increasing growth temperature. These changes are attributed to the reduction of defect concentration due to an increase in crystal planar domain sizes in graphite sheets with increasing temperature. Both XPS and Raman spectral observations indicate that the C–N nanotubes grown at lower temperatures possess higher degree of disorder and higher N incorporation.