Lateral Phase Research Articles

The characteristics of interactions of pharmaceuticals and their active ingredients with lipid membranes

A comparative study of the effects of the active pharmaceutical ingredients of amixin, aspirin, metronidazole, phenibut, and fenspiride, as well as corresponding pharmaceuticals on lipid membranes was carried out. Lipid membranes of L-α-dipalmitoylphosphatidylcholine and native carp spermatozoa were used as models. A decrease in the melting temperature of L-α-dipalmitoylphosphatidylcholine membranes in the presence of all active ingredients and pharmaceuticals was found using differential scanning calorimetry. The only exception was the group of phenibut, where a splitting of the melting peak was observed. It was found that in the pharmaceuticals studied the active pharmaceutical ingredients exhibit a determinative membranotropic effect, whereas excipients play a modulating role. Changes in the parameters of water νОН bands in the L-α-dipalmitoylphosphatidylcholine membranes containing active pharmaceutical ingredients were quantitatively characterized by Fourier transform infrared spectroscopy. According to these parameters, the effect of the phenibut group differed in these parameters from that of the other ingredients. The changes of νОН bands caused by excipients were elucidated. An increase in the permeability of carp sperm cell membranes to water was observed in vitro for pharmaceuticals that induced a decrease in the phase transition temperature of a model membrane (amixin) and lipid lateral phase separation (phenibut).

Manipulation of vector beam polarization with geometric metasurfaces.

Describing a class of beams with space-variant polarization, vector beams find many applications in both classical and quantum optics. However, simultaneous manipulation of its space-dependent polarization states is still a challenge with a single optical element. Here we demonstrate polarization modulation of a vector field by employing a plasmonic metasurface exhibiting strong and controllable optical activity. By changing the lateral phase shift between two reflective metasurface supercells, the rotation angle of a linear polarized light can be continuously tuned from zero to π with a high efficiency. As the optical activity of our metasurface devices only depends on geometrical phase, the metasurfaces can simultaneously modulate the rotation angle of a vector beam regardless of its space-variant polarization distribution. Our work provides a high efficient method in manipulating the polarization state of vector beams, especially with metasurface in a compact space, which presents great potential in research fields involving vector beams.

Optical and structural approaches for improved luminance distribution and enhanced efficiency of organic light emitting diodes

We combined cavity based optical method and polymer based structural approach to achieve efficiency enhancement and widened luminance distribution of organic light emitting diodes. Cavity method was implemented by adjusting the thickness of the hole transport layer and using a ITO-Metal-ITO transparent electrode. Utilizing the lateral phase separation of immiscible polystyrene/ polyethylene glycol binary system, we have fabricated an aperiodic protruding structure. The application of the two methods yielded two fold efficiency enhancement and widened luminance distribution. To be specific the external quantum efficiency increased from 8.9% to 17.9%.

Vertical vs Lateral Macrophase Separation in Thin Films of Block Copolymer Mixtures: Computer Simulations and GISAXS Experiments.

Mixtures of two diblock copolymers of very different lengths may feature both macro- and microphase separation; however, not much is known about the mechanisms of separation in diblock copolymer thin films. In the present work, we study thin films of mixtures of two compositionally symmetric block copolymers, both in the one-phase and in the two-phase state, combining coarse-grained molecular simulations (dissipative particle dynamics, DPD) with scattering experiments (grazing-incidence small-angle X-ray scattering, GISAXS). We reveal that the film thickness and selective adsorption of different blocks to the substrate control the distribution of macrophases within the film as well as the orientation of the lamellae therein. In thick films, the mixtures separate in the vertical direction into three layers: Two layers being rich in short copolymers are formed near the film interfaces, whereas a layer being rich in long copolymers is located in the film core. The lamellar orientation in the layers rich in short copolymers is dictated by the surface selectivity, and this orientation only weakly affects the vertical orientation of lamellae in the film core. This provides the opportunity to control the domain orientation in the copolymer films by mixing block copolymers with low-molecular additives instead of relying on a more complicated chemical modification of the substrate. In thinner films, a lateral phase separation appears.

Low-Cost 3-D Flow Estimation of Blood With Clutter.

Volumetric flow rate estimation is an important ultrasound medical imaging modality that is used for diagnosing cardiovascular diseases. Flow rates are obtained by integrating velocity estimates over a cross-sectional plane. Speckle tracking is a promising approach that overcomes the angle dependency of traditional Doppler methods, but suffers from poor lateral resolution. Recent work improves lateral velocity estimation accuracy by reconstructing a synthetic lateral phase (SLP) signal. However, the estimation accuracy of such approaches is compromised by the presence of clutter. Eigen-based clutter filtering has been shown to be effective in removing the clutter signal; but it is computationally expensive, precluding its use at high volume rates. In this paper, we propose low-complexity schemes for both velocity estimation and clutter filtering. We use a two-tiered motion estimation scheme to combine the low complexity sum-of-absolute-difference and SLP methods to achieve subpixel lateral accuracy. We reduce the complexity of eigen-based clutter filtering by processing in subgroups and replacing singular value decomposition with less compute-intensive power iteration and subspace iteration methods. Finally, to improve flow rate estimation accuracy, we use kernel power weighting when integrating the velocity estimates. We evaluate our method for fast- and slow-moving clutter for beam-to-flow angles of 90° and 60° using Field II simulations, demonstrating high estimation accuracy across scenarios. For instance, for a beam-to-flow angle of 90° and fast-moving clutter, our estimation method provides a bias of -8.8% and standard deviation of 3.1% relative to the actual flow rate.

Low-Enthalpy Phase Transitions Yield Entropy-Driven Lateral Reorganization and Phase Separation in Synthetic and Natural Multi-Component DIB Membranes

Low-Enthalpy Phase Transitions Yield Entropy-Driven Lateral Reorganization and Phase Separation in Synthetic and Natural Multi-Component DIB Membranes

Hallmarks of Reversible Phase Separation in Living, Unperturbed Cell Membranes

Controversy has long surrounded the question of whether micron-scale lateral phase separation can organize proteins and lipids within the membranes of unperturbed living cells. A clear answer hinges on observation of hallmarks of a reversible phase transition. Here, by directly imaging micron-scale membrane domains of yeast vacuoles in vivo, we demonstrate that the domains arise through a phase separation mechanism. The domains disappear above a distinct miscibility transition temperature, Tmix, and reappear below Tmix over multiple heating and cooling cycles. The domains are large, have smooth boundaries, and can merge, consistent with fluid phases. Hence, large-scale membrane organization in living cells under physiologically relevant conditions can be controlled by tuning a single thermodynamic parameter.

Size-dependent kinetics of reactive diffusion in nano-grained Ag-Sn thin films

The kinetics of lateral Ag3Sn intermetallic phase propagation during Sn diffusion into nano-grained Ag films has been studied by optical microscopy, SEM and electron microprobe in a temperature range 140 – –200°C. The Sn and Ag films of various thicknesses were deposited onto glass substrate with small overlap (5–10μm). It was detected that the rates of Ag3Sn propagation in thin film couples exceed more than two orders of magnitude the propagation rate in a bulk of massive Ag-Sn samples. Kinetics of the phase propagation depends on the grain size in Ag-film: the smaller grain size, the faster is the propagation rate. The mechanism of phase propagation is proposed in assumption that the kinetics is controlled by grain boundary (GB) diffusion through the intermetallic layer with subsequent chemical reaction between Ag and Sn atoms at the Ag3Sn -Ag interface. By comparison of experimental data on Ag3Sn propagation with the proposed theory the Arrhenius equation Diδ=8.1×10-14exp-55.4kJ/molRTm3/s was obtained for products Di δ (Di is the GB diffusion coefficient of Sn in the Ag3Sn phase, δ is the GB width).

Solvent-Morphology-Property Relationship of PTB7:PC71BM Polymer Solar Cells.

The influence of three different solvents and a solvent additive on the morphology and photovoltaic performance of bulk heterojunction films made of the copolymer based on thieno[3,4-b]thiophene-alt-benzodithiophene unit PTB7-F40 blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is investigated. Optical microscopy and atomic force microscopy are combined with X-ray reflectivity and grazing incidence small and wide-angle X-ray scattering (GISAXS and GIWAXS, respectively), enabling the characterization of the morphology of the whole photoactive film. The detailed study reveals that different length scales of PCBM clusters are observed using different solvents, while adding a solvent additive results in the PCBM clusters being selectively dissolved. Vertical and lateral phase separation occurs during spin coating and depends on the solvent used. A hierarchical morphology is detected within the bulk film through GISAXS measurements. Furthermore, GIWAXS shows that a rather amorphous film with low crystallinity was probed, which substantiates that high crystallinity is not necessarily required for high performance organic solar cells. Different models for the morphology are proposed through the combination of all the findings and correlated with the corresponding device properties. Consequently, the solvent-induced different device performance is mainly ascribed to the varied lateral structure sizes, whereas the highest device performance is a result of the smallest average multilength scale lateral structure sizes with the smallest length scale matching the exciton diffusion length.

Lateral phase separation in Cu-In-Ga precursor and Cu(In,Ga)Se2 absorber thin films

Sequential Cu(In,Ga)Se2 fabrication with a thermally activated reaction of Cu-In-Ga metal precursor layers in chalcogen atmosphere is an industrially attractive route for preparation of Cu(In,Ga)Se2 absorber based thin film solar cells. Recent results show that controlling the selenium supply during rapid thermal processing has a huge impact on absorber growth. Especially a two stage process applying a first annealing step with or without Se at temperatures up to 400°C was shown to have a positive effect on the elemental in-depth distribution. However, during this annealing, lateral phase separation, dewetting and coarsening may occur in the metal phase, leading to lateral non-uniformity of the absorber. In this study we show how the dewetting can be strongly decreased by adjusting the precursor architecture, applying faster heating rates and NaF addition on top of a precursor. In contrast, NaF deposited underneath the precursor increases the dewetting effect. Further we show that lateral phase separation during annealing increases with temperature and leads to phase domain sizes of several micrometers at 580°C.

Dynamic characteristic analysis of cracked cantilever beams under different crack types

Abstract In order to simulate the complicated dynamic phenomena of cantilever beam structures with different crack types and levels in the engineering machinery, three types of cracks are assumed, i.e., non-penetrating parabolic crack (NPPC), penetrating trapezoid crack (PTC) and uniform-penetrating crack (UPC). Based on ANSYS software, mixed elements combining beam elements and solid elements are adopted to establish the finite element (FE) models of cracked cantilever beams where the crack levels are evaluated by introducing the area damage factor, i.e., the ratio of the damage area to the cross-sectional area. Then vibration responses and crack level identification of the system under three cases of crack severity are discussed by the spectrum cascades, acceleration-velocity and velocity-displacement phase portraits, and contact pressure nephograms. The results show that the magnitudes of constant components in the spectra increase with the increase of crack severity. Lateral velocity-displacement phase portraits, perpendicular to the excitation direction, are more sensitive to the appearance of the small crack than acceleration-velocity phase portraits in the excitation direction, and the combination of the two phase portraits can be used to identify the crack severity. The crack breathing effects can be evaluated using contact pressures distributions, and local contact phenomenon can be observed during the positive half circle of the excitation period under the larger crack conditions.

Thermodynamic Consideration on Cholesterol-Induced Lateral Phase Separation within Lipid Bilayer Membranes

Thermodynamic Consideration on Cholesterol-Induced Lateral Phase Separation within Lipid Bilayer Membranes

Anisotropic Self-Assembly of Hairy Inorganic Nanoparticles.

Current interest in functional assemblies of inorganic nanoparticles (NPs) stems from their collective properties and diverse applications ranging from nanomedicines to optically active metamaterials. Coating the surface of NPs with polymers allows for tailoring of the interactions between NPs to assemble them into hybrid nanocomposites with targeted architectures. This class of building blocks is termed "hairy" inorganic NPs (HINPs). Regiospecific attachment of polymers has been used to achieve directional interactions for HINP assembly. However, to date anisotropic surface functionalization of NPs still remains a challenge. This Account provides a review of the recent progress in the self-assembly of isotropically functionalized HINPs in both the condensed state and aqueous solution as well as the applications of assembled structures in such areas as biomedical imaging and therapy. It aims to provide fundamental mechanistic insights into the correlation between structural characteristics and self-assembly behaviors of HINPs, with an emphasis on HINPs made from NPs grafted with linear block copolymer (BCP) brushes. The key to the anisotropic self-assembly of these HINPs is the generation of directional interactions between HINPs by designing the surrounding medium (e.g., polymer matrix) or engineering the surface chemistry of the HINPs. First, HINPs can self-assemble into a variety of 1D, 2D, or 3D nanostructures with a nonisotropic local arrangement of NPs in films. Although a template is not always required, a polymer matrix (BCPs or supramolecules) can be used to assist the assembly of HINPs to form hybrid architectures. The interactions between brushes of neighboring HINPs or between HINPs and the polymer matrix can be modulated by varying the grafting density and length of one or multiple types of polymers on the surface of the NPs. Second, the rational design of deformable brushes of BCP or mixed homopolymer tethers on HINPs enables the anisotropic assembly of HINPs (in analogy to molecular self-assembly) into complex functional structures in selective solvents. It is evidenced that the directional interactions between BCP-grafted NPs arise from the redistribution and conformation change of the long, flexible polymer tethers, while the lateral phase separation of brushes on NP surfaces is responsible for the assembly of HINPs carrying binary immiscible homopolymers. For HINPs decorated with amphiphilic BCP brushes, their self-assembly can produce a variety of hybrid structures, such as vesicles with a monolayer of densely packed NPs in the membranes and with controlled sizes, shapes (e.g., spherical, hemispherical, disklike), and morphologies (e.g., patchy, Janus-like). This strategy allows fine-tuning of the NP organization and collective properties of HINP assemblies, thus facilitating their application in effective cancer imaging, therapy, and drug delivery. We expect that the design and assembly of such HINPs with isotropic functionalization is likely to open up new avenues for the fabrication of new functional nanocomposites and devices because of its simplicity, low cost, and ease of scale-up.

Solid phase crystallization of germanium films on crystalline silicon

We have investigated the lateral solid phase crystallization (SPC) of amorphous germanium (a-Ge) precursors on single crystalline silicon (c-Si) substrates with a silicon dioxide (SiO2) stripe structure. The a-Ge layers were deposited on c-Si with SiO2 stripes at 100°C and SPC was carried out at 375–385°C. The crystallization in a-Ge layers is only nucleated on c-Si substrates and thus, the preferential crystalline growth occurred along the normal orientation of the c-Si substrates, with no crystallization of the Ge layers nucleated on a-Ge layers over SiO2 layers, except near the c-Si/SiO2 boundary. As a result we have obtained lateral preferential crystalline growth of c-Ge of large grain size by SPC from a-Ge films on c-Si over SiO2 stripes, where the preferential crystalline growth distance in a-Ge on SiO2 increased from 3 to 5μm, when the annealing temperature increased from 375 to 385°C.

Photonic Multitasking Interleaved Si Nanoantenna Phased Array.

Metasurfaces provide unprecedented control over light propagation by imparting local, space-variant phase changes on an incident electromagnetic wave. They can improve the performance of conventional optical elements and facilitate the creation of optical components with new functionalities and form factors. Here, we build on knowledge from shared aperture phased array antennas and Si-based gradient metasurfaces to realize various multifunctional metasurfaces capable of achieving multiple distinct functions within a single surface region. As a key point, we demonstrate that interleaving multiple optical elements can be accomplished without reducing the aperture of each subelement. Multifunctional optical elements constructed from Si-based gradient metasurface are realized, including axial and lateral multifocus geometric phase metasurface lenses. We further demonstrate multiwavelength color imaging with a high spatial resolution. Finally, optical imaging functionality with simultaneous color separation has been obtained by using multifunctional metasurfaces, which opens up new opportunities for the field of advanced imaging and display.

Coarse-grained molecular dynamics simulation of binary charged lipid membranes: Phase separation and morphological dynamics.

Biomembranes, which are mainly composed of neutral and charged lipids, exhibit a large variety of functional structures and dynamics. Here, we report a coarse-grained molecular dynamics (MD) simulation of the phase separation and morphological dynamics in charged lipid bilayer vesicles. The screened long-range electrostatic repulsion among charged head groups delays or inhibits the lateral phase separation in charged vesicles compared with neutral vesicles, suggesting the transition of the phase-separation mechanism from spinodal decomposition to nucleation or homogeneous dispersion. Moreover, the electrostatic repulsion causes morphological changes, such as pore formation, and further transformations into disk, string, and bicelle structures, which are spatiotemporally coupled to the lateral segregation of charged lipids. Based on our coarse-grained MD simulation, we propose a plausible mechanism of pore formation at the molecular level. The pore formation in a charged-lipid-rich domain is initiated by the prior disturbance of the local molecular orientation in the domain.

Strip-loaded waveguide-based optical phase shifter for high-efficiency silicon optical modulators

We propose a novel silicon optical phase shifter structure based on heterogeneous strip-loaded waveguides on a photonic silicon on insulator (SOI) platform. The features of an etchless SOI layer and loaded strip would enhance the performance and uniformity of silicon optical modulators on a large-scale wafer. We implemented the phase shifter by loading an amorphous silicon strip onto an SOI layer with a vertical PN diode structure. Compared to the conventional lateral PN phase shifter based on half-etched rib waveguides, this phase shifter shows a >1.5 times enhancement of modulation efficiency and provides >20 GHz high-speed operation.

Modeling of θ → α alumina lateral phase transformation with applications to oxidation kinetics of NiAl-based alloys

In the present work, a physical model has been developed to predict the growth of Al2O3 scale, which involves the thickening of metastable transient θ-Al2O3 phase and finally thermodynamically stable α-Al2O3 phase, accompanied by the concurrent θ→α-Al2O3 phase transformation. Based on nucleation and growth theory, the phase transition kinetics and alumina growth were modeled for both isothermal and continuous heating paths. Using this model, the phase transformation kinetics, evolution of grain size and Al2O3 scale thickness can be predicted for a given thermal path. A new scaling parameter has been proposed that quantitatively reveals the relative significance of nucleation and grain growth to the overall phase transformation kinetics. Predictions based on the model are in good agreement with the experimental observations. Limitations of the model are also presented and discussed.

Budding transition of asymmetric two-component lipid domains.

We propose a model that accounts for the budding transition of asymmetric two-component lipid domains, where the two monolayers (leaflets) have different average compositions controlled by independent chemical potentials. Assuming a coupling between the local curvature and local lipid composition in each of the leaflets, we discuss the morphology and thermodynamic behavior of asymmetric lipid domains. 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 containing fully budded, dimpled, and flat states as a function of the two leaflet compositions. The global phase behavior is analyzed, and depending on system parameters, the phase diagrams include one-phase, two-phase, and three-phase regions. In particular, we predict various phase coexistence regions between different morphologies of domains, which may be observed in multicomponent membranes or vesicles.

Tuning Surface Properties of Poly(methyl methacrylate) Film Using Poly(perfluoromethyl methacrylate)s with Short Perfluorinated Side Chains.

To control the surface properties of a commonly used polymer, poly(methyl methacrylate) (PMMA), poly(perfluoromethyl methacrylate)s (PFMMAs) with short perfluorinated side groups (i.e., -CF3, -CF2CF3, -(CF3)2, -CF2CF2CF3) were used as blend components because of their good solubility in organic solvents, low surface energies, and high optical transmittance. The surface energies of the blend films of PFMMA with the -CF3 group and PMMA increased continuously with increasing PMMA contents from 17.6 to 26.0 mN/m, whereas those of the other polymer blend films remained at very low levels (10.2-12.6 mN/m), similar to those of pure PFMMAs, even when the blends contained 90 wt %PMMA. Surface morphology and composition measurements revealed that this result originated from the different blend structures, such as lateral and vertical phase separations. We expect that these PFMMAs will be useful in widening the applicable window of PMMA.