Lateral Phase Research Articles

Modifying polyester surfaces with incompatible polymer additives

Surface modification of amorphous PET in incompatible blends is demonstrated using fluorocarbon end-functional polystyrenes. Contact angles with water and decane were consistent with high levels of surface fluorocarbon, even for spin-cast films with no further processing required. Hydrophobicity and lipophobicity were further increased by annealing above the glass transition temperature. High resolution depth profiling using complementary ion beam analysis and specular neutron reflectometry has enabled accurate characterisation of the composition profile of the additive including the minimum in additive concentration found just below the surface enriched layer. This analysis quantified the very low compatibility between the modifying polymer and the amorphous PET and was consistent with the highly segregated nature of the adsorbing species and its sharp interface with the subphase. For these incompatible polymer blends, surfaces enriched with the surface active polymer could coexist at equilibrium with extremely low (∼0.4%) bulk loadings of the additive. This suggests that for thicker films at even lower additive concentrations than the minimum 1% that we studied, it may be possible to achieve efficient surface modification. However, at this concentration, the efficiency of surface modification is limited by the processing conditions. Finally we note that in higher loadings of surface active additive there is clear evidence for lateral phase separation into patterned domains of differing composition. The enhancement in surface properties is due to local reorganisation rather than bulk redistribution of the components within the film, as the composition versus depth distributions of the polymer blend components was observed to be relatively unaffected by annealing.

Vocal Fold Vibration in Vocal Fold Atrophy: Quantitative Analysis With High-Speed Digital Imaging

Vocal fold vibrations of vocal fold atrophy (VFA), a rapidly increasing voice disorder owing to worldwide societal aging, have not been clarified by high-speed digital imaging (HSDI). The HSDI method was performed on 46 patients (33 males and 13 females) with VFA and 20 vocally healthy subjects (8 males and 12 females), and the obtained data were quantitatively evaluated by frame-by-frame analysis, laryngotopography, single- and multi-line kymography, and glottal area waveform. Overall, patients with VFA revealed larger open quotients, larger lateral phase difference, larger integral glottal width (the average glottal width over a glottal cycle), and smaller speed index than vocally healthy subjects. Some gender difference was noted: in males, lateral phase difference was not significant; and in females, integral glottal width and speed index were not significant. Correlation study revealed moderate correlations between HSDI-derived parameters and conventional acoustic or aerodynamic parameters. The combination of multiple HSDI analysis methods was effective in documenting the characteristics of vocal fold vibrations in VFA. The knowledge of general vibratory characteristics and gender difference is beneficial for the appropriate clinical care of VFA.

Nutritional assessment of amyotrophic lateral sclerosis in routine practice: value of weighing and bioelectrical impedance analysis.

We evaluated clinical and bioelectrical impedance (BIA) parameters at the time of diagnosis and during follow-up and associated these parameters with survival in amyotrophic lateral sclerosis (ALS) patients. One hundred seventeen patients were enrolled and were evaluated prospectively every 3 months. All patients underwent at least 1 BIA-based assessment, and 73 underwent at least 2 assessments. Data regarding the site of onset, age at onset, weight, body mass index (BMI), amyotrophic lateral sclerosis functional rating scale score (ALSFRS), fat-free mass (FFM), fat mass (FM), and phase angle (PA) were collected. At the time of diagnosis, weight loss exceeding 5% of the premorbid weight and low PA were poor prognostic factors. During follow-up, a decrease of PA and FFM were associated with shorter survival, regardless of weight loss. These results confirm that BIA is useful to identify poor prognostic factors at the time of diagnosis and during follow-up and thus could be used to monitor patients during follow-up. Early identification of poor prognostic factors enables nutritional management and might improve patient survival.

Budding of domains in mixed bilayer membranes.

We propose a model that accounts for the budding behavior of domains in lipid bilayers, where each of the bilayer leaflets has a coupling between its local curvature and the local lipid composition. The compositional asymmetry between the two monolayers leads to an overall spontaneous curvature. The membrane free energy contains three contributions: the bending energy, the line tension, and a Landau free energy for a lateral phase separation. Within a mean-field treatment, we obtain various phase diagrams which contain fully budded, dimpled, and flat states. In particular, for some range of membrane parameters, the phase diagrams exhibit a tricritical behavior as well as a three-phase coexistence region. The global phase diagrams can be divided into three types and are analyzed in terms of the curvature-composition coupling parameter and domain size.

Device and morphological engineering of organic solar cells for enhanced charge transport and photovoltaic performance

Conjugated polymers are potential materials for photovoltaic applications due to their high absorption coefficient, mechanical flexibility, and solution-based processing for low-cost solar cells. A bulk heterojunction (BHJ) structure made of donor–acceptor composite can lead to high charge transfer and power conversion efficiency. Active layer morphology is a key factor for device performance. Film formation processes (e.g., spray-coating, spin-coating, and dip-coating), post-treatment (e.g., annealing and UV ozone treatment), and use of additives are typically used to engineer the morphology, which optimizes physical properties, such as molecular configuration, miscibility, lateral and vertical phase separation. We will review electronic donor–acceptor interactions in conjugated polymer composites, the effect of processing parameters and morphology on solar cell performance, and charge carrier transport in polymer solar cells. This review provides the basis for selection of different processing conditions for optimized nanomorphology of active layers and reduced bimolecular recombination to enhance open-circuit voltage, short-circuit current density, and fill factor of BHJ solar cells.

Morphology of Ferroelectric/Conjugated Polymer Phase-Separated Blends Used in Nonvolatile Resistive Memories. Direct Evidence for a Diffuse Interface

The morphology of blends made of a ferroelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene), and a cross-linkable conjugated polymer, an oxetane-functionalized poly(9,9-dioctylfluorene-alt-bithiophene), is investigated. Making use of the insolubility of the conjugated polymer, we were able to selectively remove the ferroelectric copolymer and analyze the remaining material. Atomic force microscopy studies show a lateral phase separation, consistent with columns of the conjugated polymer surrounded by a matrix of the ferroelectric. X-ray photoelectron spectroscopy showed that even after a very long washing time (120 h), there was still ferroelectric polymer on the remaining film, which we conclude to correspond to ferroelectric chains trapped within the conjugated polymer domains. This fact suggests the existence of a diffuse interface between the two polymer domains. Resistive memories were fabricated with this blend, though exhibiting limited nonvolatility. This behavior is discussed in terms of the presence of a wetting layer and the use of poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid) as electrode.

The lateral diffusion and fibrinogen induced clustering of platelet integrin αIIbβ3 reconstituted into physiologically mimetic GUVs.

Platelet integrin αIIbβ3 is a key mediator of platelet activation and thrombosis. Upon activation αIIbβ3 undergoes significant conformational rearrangement, inducing complex bidirectional signalling and protein recruitment leading to platelet activation. Reconstituted lipid models of the integrin can enhance our understanding of the structural and mechanistic details of αIIbβ3 behaviour away from the complexity of the platelet machinery. Here, a novel method of αIIbβ3 insertion into Giant Unilamellar Vesicles (GUVs) is described that allows for effective integrin reconstitution unrestricted by lipid composition. αIIbβ3 was inserted into two GUV lipid compositions that seek to better mimic the platelet membrane. First, "nature's own", comprising 32% DOPC, 25% DOPE, 20% CH, 15% SM and 8% DOPS, intended to mimic the platelet cell membrane. Fluorescence Lifetime Correlation Spectroscopy (FLCS) reveals that exposure of the integrin to the activators Mn(2+) or DTT does not influence the diffusion coefficient of αIIbβ3. Similarly, exposure to αIIbβ3's primary ligand fibrinogen (Fg) alone does not affect αIIbβ3's diffusion coefficient. However, addition of Fg with either activator reduces the integrin diffusion coefficient from 2.52 ± 0.29 to μm(2) s(-1) to 1.56 ± 0.26 (Mn(2+)) or 1.49 ± 0.41 μm(2) s(-1) (DTT) which is consistent with aggregation of activated αIIbβ3 induced by fibrinogen binding. The Multichannel Scaler (MCS) trace shows that the integrin-Fg complex diffuses through the confocal volume in clusters. Using the Saffman-Delbrück model as a first approximation, the diffusion coefficient of the complex suggests at least a 20-fold increase in the radius of membrane bound protein, consistent with integrin clustering. Second, αIIbβ3 was also reconstituted into a "raft forming" GUV with well defined liquid disordered (Ld) and liquid ordered (Lo) phases. Using confocal microscopy and lipid partitioning dyes, αIIbβ3 showed an affinity for the DOPC rich Ld phase of the raft forming GUVs, and was effectively excluded from the cholesterol and sphingomyelin rich Lo phase. Activation and Fg binding of the integrin did not alter the distribution of αIIbβ3 between the lipid phases. This observation suggests partitioning of the activated fibrinogen bound αIIbβ3 into cholesterol rich domains is not responsible for the integrin clustering observed.

Multi-Level Lateral Phase Change Memory Based on N-Doped Sb70Te30 Super-Lattice like Structure

Lateral phase change memory (PCM) has attracted a lot of interest due to its simpler fabrication process and lower current. Researchers are trying to increase the storage capacity of lateral PCM. This paper proposed a novel super-lattice like (SLL) structure for lateral PCM to achieve multi-level storage. Lateral PCM with SLL structure incorporated with N-doped Sb70Te30 and ZnS-SiO2 has been fabricated and tested. Both tested static I-V curve and dynamic pulse mode R-V curve show multi states existing in the device. Electrical and thermal simulations have been done for this device. Simulation results show that different resistance level can be found in this device with different states of phase change bridges. With increasing periods of SLL structure, more states can be achieved.

Lateral Phase Separation between Phospholipids and Adhesion Macromolecules on Two Adhering Membranes

We study analytically the lateral phase separation produced between phospholipids and adhesion macromolecules on two adhering membranes from a static point of view. In this letter, the adhesion macromolecules are assumed as long-flexible polymer chains anchored by two extremities on the inner monolayer of the two adjacent plasma membranes by anchors-segments, which are big amphiphilic molecules. The aim is to quantify how these polymer chains can be driven from a dispersed phase to a dense one, under the variation of a suitable parameter such as temperature and membrane environment.... To investigate this demixtion transition, we elaborate a new field theory that allows us to derive the expression for the mixing free energy. From this, we extract the complete shape of the associated phase diagram in the composition-temperature plane. The essential conclusion is that the anchored polymer chains experience the significant attractive forces directly result from the shape deformations of two parallel membranes a mean-distance apart. Also, the solvent quality and the structure (length) of adhesion macromolecules have a strong influence on the compatibility domain of the mixture.

Growth-Dominant Superlattice-Like Medium and Its Application in Phase Change Memory

Lateral PCM is one structure with good thermal confinement and low RESET current. Ideal growth-dominant (GD) phase change material is needed for lateral Phase change memory (PCM). We propose the concept of GD superlattice-like (SLL) phase change structure. GeTe and Sb7Te3 were selected to form the GD SLL structure. Crystallization temperature and resistivity of GeTe and Sb7Te3 were thickness dependent. The crystallization temperature of GeTe/Sb7Te3 SLL phase change structure increase with increasing thickness ratio of GeTe/Sb7Te3. GeTe/Sb7Te3 SLL structure built with a thickness ratio of 1.6:1 (GeTe to Sb7Te3) exhibited the lowest melting temperature compared to other thickness ratio. For a typical lateral PCM employing such GeTe/Sb7Te3 SLL phase change structure, stable SET/RESET operations with a low RESET current of 1.5 mA, SET and RESET speed of 30 nanoseconds, a good endurance above 106 cycles and a high RESET/SET resistance ratio window of 20 were achieved, demonstrating strong potentials in next generation non-volatile memory application.

Ordering phenomena and formation of nanostructures inInxGa1−xNlayers coherently grown on GaN(0001)

We study the impact that local strain effects have on the spatial distribution of In in coherent ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ grown epitaxially on GaN(0001) using an effective crystal growth modeling technique that combines a semi-grand-canonical Monte Carlo simulation with an ab initio parametrized empirical force field. Our calculations show that ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ epitaxial layers exhibit a strong tendency towards ordering, as highlighted by the formation of a vertical stack of the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ patterned layers along the $\ensuremath{\langle}c\ensuremath{\rangle}$ direction. The ordering phenomena are identified as a key factor that determines lateral phase separation in ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ epitaxial layers at the nanometer scale. Consequences of this nanophase separation for the enhanced radiative emission through carrier localization in ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ of $x<1/3$ are discussed.

Pattern formation in polymer blend thin films: surface roughening couples to phase separation.

We introduce a model for thin films of multicomponent fluids that includes lateral and vertical phase separation, preferential component attraction at both surfaces, and surface roughening. We apply our model to thin films of binary polymer blends, and use simulations of different surface-blend interaction regimes to investigate pattern formation. We demonstrate that surface roughening couples to phase separation. For films undergoing lateral phase separation via a transient wetting layer, this results in distinct stages of roughening as the film evolves between different phase equilibria.

Ultra-high-speed lateral solid phase crystallization of GeSn on insulator combined with Sn-melting-induced seeding

To produce high-performance devices on flexible plastic substrates, it is essential to form Ge-based group IV semiconductors on insulating substrates at low temperatures (≤250 °C). We have developed a technique for solid phase crystallization of amorphous GeSn (≤220 °C) enhanced by Sn doping, and combined with a seeding technique induced by Sn melting (∼250 °C). This combination produces lateral crystallization of amorphous GeSn from seed arrays with no incubation time. As a result, extremely high growth velocities at 220 °C, depending on Sn concentration, e.g., 0.13 μm/h (14% Sn) and 1100 μm/h (23% Sn), are achieved. These velocities are 104–108 times higher than that of pure Ge. This technique enables growth of crystalline GeSn island arrays (diameters: 50–150 μm) at low temperatures (≤250 °C) at controlled positions on insulating substrates.

Melittin disruption of raft and non-raft-forming biomimetic membranes: A study by quartz crystal microbalance with dissipation monitoring

In this work we examine the role of lateral phase separation in cholesterol-containing biomimetic membranes on the disrupting action of melittin using a label-free surface-sensitive technique, quartz crystal microbalance with dissipation monitoring (QCM-D). Melittin disruption mechanisms depend strongly on the geometry of the lipid layer; however, despite the interplay between layer geometry/thickness and melittin activity, results indicate that the presence of lipid heterogeneity and lateral phase separation greatly influences the disrupting efficiency of melittin. In homogeneous non-raft forming membranes with high cholesterol content, melittin spontaneous activity is strongly delayed compared to heterogeneous raft-forming systems with the same amount of cholesterol. These results confirm the importance of lateral phase separation as a determinant factor in peptide activity. The information provided can be used for the design of more efficient antimicrobial peptides and the possibility of using a label-free approach for tailored-membranes and interactions with other types of peptides, such as amyloid peptides.

Formation of cholesterol-rich supported membranes using solvent-assisted lipid self-assembly.

This paper describes the application of a solvent-exchange method to prepare supported membranes containing high fractions of cholesterol (up to ∼57 mol %) in an apparent equilibrium. The method exploits the phenomenon of reverse-phase evaporation, in which the deposition of lipids in alcohol (e.g., isopropanol) is followed by the slow removal of the organic solvent from the water-alcohol mixture. This in turn induces a series of lyotropic phase transitions successively producing inverse-micelles, monomers, micelles, and vesicles in equilibrium with supported bilayers at the contacting solid surface. By using the standard cholesterol depletion by methyl-β-cyclodextrin treatment, a quartz crystal microbalance with dissipation monitoring assay confirms that the cholesterol concentration in the supported membranes is comparable to that in the surrounding bulk phase. A quantitative characterization of the biophysical properties of the resultant bilayer, including lateral diffusion constants and phase separation, using epifluorescence microscopy and atomic force microscopy establishes the formation of laterally contiguous supported lipid bilayers, which break into a characteristic domain-pattern of coexisting phases in a cholesterol concentration-dependent manner. With increasing cholesterol fraction in the supported bilayer, the size of the domains increases, ultimately yielding two-dimensional cholesterol bilayer domains near the solubility limit. A unique feature of the approach is that it enables preparation of supported membranes containing limiting concentrations of cholesterol near the solubility limit under equilibrium conditions, which cannot be obtained using conventional techniques (i.e., vesicle fusion).

P(VDF-TrFE) nanorod assemblies with anisotropic piezoelectric properties investigated by piezoelectric response microscopy

Highly ordered assemblies of the copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) nanorods with anisotropic piezoelectric response were fabricated on different substrates by using a template-free self-organization method. The significant difference in vertical and lateral piezoelectric responses of the nanorods in piezoresponse force microscopy (PFM) revealed that their molecular dipoles were preferentially oriented parallel to the substrate plane. In addition, dipole orientation distribution map in the nanorods was derived by analyzing the vertical and lateral PFM amplitude and phase images. Infrared reflection spectra further showed that the macromolecular backbones were oriented perpendicularly relative to the substrate. A flat-on lamellar structure and a confined crystallization of dewetted melt phase nanorod formation mechanism were proposed. The highly anisotropic piezoelectric response of the assemblies of nanorods may be promising for nanoscale devices for application in energy harvesting, etc. More importantly, the results demonstrated that self organization could be used for fabricating P(VDF-TrFE) nanostructures by controlling the surface energy of the substrates.

Lateral phase separation in polymer-blend thin films: surface bifurcation.

We use simulations of a binary polymer blend confined between selectively attracting walls to identify and explain the mechanism of lateral phase separation via a transient wetting layer. We first show that equilibrium phases in the film are described by one-dimensional phase equilibria in the vertical (depth) dimension, and demonstrate that effective boundary conditions imposed by the film walls pin the film profile at the walls. We then show that, prior to lateral phase separation, distortion of the interface in a transient wetting layer is coupled to lateral phase separation at the walls. Using Hamiltonian phase portraits, we explain a "surface bifurcation mechanism" whereby the volume fraction at the walls evolves and controls the dynamics of the phase separation. We suggest how solvent evaporation may assist our mechanism.

Quantitative phase imaging unit.

A simple and cost-effective method is presented for quantitative phase imaging. A common-path lateral phase shifting interferometer is realized through attaching a compact filter set to the output port of an existing microscope. The working principles, design criteria, and limitations are also derived and explained. In order to demonstrate the capability and applicability of the method, the optical phase images of a microsphere and individual human red blood cells are measured with high stability.

Vibration of the organ of Corti within the cochlear apex in mice

The tonotopic map of the mammalian cochlea is commonly thought to be determined by the passive mechanical properties of the basilar membrane. The other tissues and cells that make up the organ of Corti also have passive mechanical properties; however, their roles are less well understood. In addition, active forces produced by outer hair cells (OHCs) enhance the vibration of the basilar membrane, termed cochlear amplification. Here, we studied how these biomechanical components interact using optical coherence tomography, which permits vibratory measurements within tissue. We measured not only classical basilar membrane tuning curves, but also vibratory responses from the rest of the organ of Corti within the mouse cochlear apex in vivo. As expected, basilar membrane tuning was sharp in live mice and broad in dead mice. Interestingly, the vibratory response of the region lateral to the OHCs, the "lateral compartment," demonstrated frequency-dependent phase differences relative to the basilar membrane. This was sharply tuned in both live and dead mice. We then measured basilar membrane and lateral compartment vibration in transgenic mice with targeted alterations in cochlear mechanics. Prestin(499/499), Prestin(-/-), and Tecta(C1509G/C1509G) mice demonstrated no cochlear amplification but maintained the lateral compartment phase difference. In contrast, Sfswap(Tg/Tg) mice maintained cochlear amplification but did not demonstrate the lateral compartment phase difference. These data indicate that the organ of Corti has complex micromechanical vibratory characteristics, with passive, yet sharply tuned, vibratory characteristics associated with the supporting cells. These characteristics may tune OHC force generation to produce the sharp frequency selectivity of mammalian hearing.

Ultra-Multilevel-Storage Phase Change Memory

In this study, we investigated ultra-multilevel-storage (UMLS) in lateral phase change memory (PCM) on the basis of device structure, reliability and programming method. We found that the number of resistance levels was limited strictly by the number of PC layers in multilayer multilevel cell (ML-MLC). A number of distinct levels up to 16 were obtained using a simple single-layer multilevel cell (SL-MLC). And material engineering is expected to greatly improve the reliability of MLS. We believe that fast-freely-achievable (FFA)-MLC by stair-like-pulse programming is a very promising method for futures application.