Effect of the Interfacial Tension on the Stability of Silica Stabilized Pickering Emulsions near the Lower Critical Solution Temperature of 2,6-Lutidine - Water Mixtures.

In this paper, the kinetic stability of Pickering emulsions stabilized by spherical silica particles (100 nm in diameter) was examined in the water - 2,6-lutidine mixture. In the close vicinity of the lower critical solution temperature, Pickering emulsions were unstable due to the ultra-low liquid-liquid interfacial tension but increased their stability with increasing the temperature. In this system, the interfacial tension obeys universal scale law and can be tuned by temperature without adding any surface-active agents. Owing to this unique feature, we elucidated the relation between the interfacial tension and the stability of Pickering emulsions.

Demulsification of Silica Stabilized Pickering Emulsions Using Surface Freezing Transition of CTAC Adsorbed Films at the Tetradecane-Water Interface.

The adsorbed film of cetyltrimethylammonium chloride (CTAC) at the tetradecane (C14) - water interface undergoes a first-order surface transition from two-dimensional liquid to solid states upon cooling. In this paper, we utilized this surface freezing transition to realize a spontaneous demulsification of Pickering emulsions stabilized by silica particles. In the temperature range above the surface freezing transition, the interfacial tension of silica laden oil-water interface was lower than CTAC adsorbed film, hence, stable Pickering emulsion was obtained by vortex mixing. However, the interfacial tension of CTAC adsorbed film decreased rapidly below the surface freezing temperature and became lower than the silica laden interface. The reversal of the interfacial tensions between silica laden and CTAC adsorbed films gave rise to Pickering emulsion demulsification by the desorption of silica particles from the oil-water interface. The exchange of silica particles and CTAC at the surface of emulsion droplets was also confirmed experimentally by using phase modulation ellipsometry at the oil-water interface.

Oscillations in Dynamic Surface Tension of Cationic-nonionic Binary Surfactant Aqueous Solutions.

In this work, the adsorption dynamics of mixed aqueous solutions of tetraethyleneglycol monoocthyl ether (C8E4) - dodecyltrimethylammonium bromide (DTAB) were studied using sessile bubble surface tensiometry. When C8E4 was added to the DTAB solution, the dynamic surface tension exhibited a unique oscillation decay pattern. In contrast, the addition of DTAB to the C8E4 solution resulted in a simple monotonic decay of the surface tension. The same trend was observed for mixtures of tetradecyltrimethylammonium bromide (TTAB) and DTAB. The occurrence of two distinguishable dynamic surface tension behaviors showed reasonable similarity with the theory of the adsorption kinetics of polymer solutions, where the surface tension oscillation was caused by the delayed desorption of polymers due to the conformational change at the solution surface. We compared the dynamic surface tension of binary surfactant systems and the polymer solution theory, and discussed the origin of surface tension oscillations based on the difference in the surface activity of the surfactants.

Effect of Surface Freezing of a Cationic Surfactant and n-Alkane Mixed Adsorbed Film on Counterion Distribution and Surface Dilational Viscoelasticity Studied by Total Reflection XAFS and Surface Quasi-Elastic Light Scattering.

When liquid alkane droplets are placed on a surfactant solution surface having a proper surface density, alkane molecules penetrated into the surfactant-adsorbed film to form a mixed monolayer. Such a mixed monolayer undergoes a thermal phase transition from two-dimensional liquid to solid monolayers upon cooling when surfactant tail and alkane have similar chain lengths. We applied the total-reflection XAFS spectroscopy and surface quasi-elastic light scattering to the mixed adsorbed film of cetyltrimethylammonium bromide and hexadecane to elucidate the impact on the surface phase transition on the counterion distribution of the mixed monolayer. The EXAFS analysis verified that a higher percentage of counter Br- ions were localized in the Stern layer than in the diffuse double layer in the surface solid film compared to the surface liquid film, which resulted in a reduction in the surface elasticity measured by the SQELS. The finding that the surface phase transition accompanies the change in the counterion distribution will be important to consider the future applications of the colloidal systems, in which the coexistence of a surfactant and alkane molecules is essential, such as foams and emulsions.

One-dimensional harmonic chain model of vibration-mode matching in solid-liquid interfacial thermal transport.

Understanding the atomistic mechanism of interfacial thermal transport at solid-liquid interfaces is a key challenge in thermal management at the nanoscale. A recent molecular-dynamics study demonstrated that interfacial thermal resistance (ITR) at the interface between a solid and a surfactant solution can be minimized by adjusting the molecular mass of the surfactant. In the present study, we explain the mechanism of this ITR minimization in view of vibration-mode matching using a one-dimensional (1D) harmonic chain model of a solid-liquid interface having an interfacial adsorption layer of surfactant molecules. The equation of motion for the 1D chain is described by a classical Langevin equation and is analytically solved by the nonequilibrium Green's function (NEGF) method. The resultant ITR is expressed in a form of vibrational matching, and its relationship to the overlap of the vibrational density of states is also discussed. The analysis leads to a conclusion that the damping coefficient η in the Langevin equation should be a finite and sufficiently large value to represent the rapid damping of vibration modes at solid-liquid interfaces. This conclusion provides a clue to seamlessly extend the conventional NEGF-phonon transmission picture of solid-solid interfacial thermal transport, which assumes η to be infinitesimal, to solid-liquid interfaces.

Salicylaldehyde Suppresses IgE-Mediated Activation of Mast Cells and Ameliorates Anaphylaxis in Mice.

Mast cells (MCs) play key roles in IgE-mediated immunoresponses, including in the protection against parasitic infections and the onset and/or symptoms of allergic diseases. IgE-mediated activation induces MCs to release mediators, including histamine and leukotriene, as an early response, and to produce cytokines as a late phase response. Attempts have been made to identify novel antiallergic compounds from natural materials such as Chinese medicines and food ingredients. We herein screened approximately 60 compounds and identified salicylaldehyde, an aromatic aldehyde isolated from plant essential oils, as an inhibitor of the IgE-mediated activation of MCs. A degranulation assay, flow cytometric analyses, and enzyme-linked immunosorbent assays revealed that salicylaldehyde inhibited the IgE-mediated degranulation and cytokine expression of bone-marrow-derived MCs (BMMCs). The salicylaldehyde treatment reduced the surface expression level of FcεRI, the high affinity receptor for IgE, on BMMCs, and suppressed the IgE-induced phosphorylation of tyrosine residues in intercellular proteins, possibly Lyn, Syk, and Fyn, in BMMCs. We also examined the effects of salicylaldehyde in vivo using passive anaphylaxis mouse models and found that salicylaldehyde administration significantly enhanced the recovery of a reduced body temperature due to systemic anaphylaxis and markedly suppressed ear swelling, footpad swelling, and vascular permeability in cutaneous anaphylaxis.

Nucleation of Surfactant-Alkane Mixed Solid Monolayer and Bilayer Domains at the Air-Water Interface.

We investigated the wetting transitions of tetradecane and hexadecane droplets in dodecyltrimethylammonium bromide (C12TAB), tetradecyltrimethylammonium bromide (C14TAB), and hexadecyltrimethylammonium bromide (C16TAB) aqueous solutions. By varying the surfactant concentration, the formation of mixed monolayers of a surfactant and an alkane was observed at the air-water interface. Depending on the combination of surfactant and alkane, these wetting monolayers underwent another thermal phase transition upon cooling either to a frozen mixed monolayer (S1) or a bilayer structure composed of a solid monolayer of a pure alkane rested on a liquid-like mixed monolayer (S2). Based on the phase diagrams determined by phase modulation ellipsometry, the difference in the morphology of the nucleated S1 and S2 phase domains was also investigated using Brewster angle microscopy. Domains of the S1 phase were relatively small and highly branched, whereas those of the S2 phase were large and circular. The difference in domain morphology was explained by the competition of the domain line tension and electrostatic dipole interactions between surfactant molecules in the domains.

Structure-activity relationship study of hydroxyethylamine isostere and P1' site structure of peptide mimetic BACE1 inhibitors.

An aromatic substituent has been introduced into a known hydroxyethylamine (HEA)-type BACE1 inhibitor containing the superior substrate sequence to enhance inhibitory activity. The HEA-type isosteres bearing different hydroxyl group and methyl group configurations were prepared through a branched synthesis approach using intra- and inter-molecular epoxide opening reactions. The effect of their configuration was evaluated, showing that an R-configuration improved the inhibitory activity, while introduction of a methyl group on the isostere decreased the activity. Based on the non-substituted isostere with an R-configuration, 21 derivatives containing various substituents at the P1' site were synthesized. Our evaluation of the derivatives showed that the structure of the P1' site had a clear effect on activity, and highly potent inhibitor 40g, which showed sub-micromolar activity against recombinant BACE1 (rBACE1), was identified. The docking simulation of 40g with rBACE1 suggested that a carboxymethyl group at the para-position of the P1' benzene ring interacted with Lys285 in the S1' pocket.

Juxtaglomerular cell tumor diagnosed preoperatively by renal tumor biopsy.

INTRODUCTION: Diagnosis of small renal tumor from imaging analysis is limited. We report a case of juxtaglomerular cell tumor diagnosed preoperatively by renal tumor biopsy. CASE PRESENTATION: A 17-year-old male was urgently hospitalized for acute-onset congestive heart failure. Radiographic findings revealed a 2-cm mass lesion, and on renal biopsy, a juxtaglomerular cell tumor was suspected. The juxtaglomerular cell tumor was resected by laparoscopic partial nephrectomy, on suspicion of causing the heart failure. The patient's clinical symptoms improved drastically postoperatively. CONCLUSION: Biopsy may be a promising option for preoperative diagnosis of juxtaglomerular cell tumors.

Effect of the in-plane aspect ratio of a graphene filler on anisotropic heat conduction in paraffin/graphene composites.

Enhancement of polymer thermal conductivity using nanographene fillers and clarification of its molecular-scale mechanisms are of great concern in the development of advanced thermal management materials. In the present study, molecular dynamics simulation was employed to theoretically show that the in-plane aspect ratio of a graphene filler can have a significant impact on the effective thermal conductivity of paraffin/graphene composites. Our simulation included multiple graphene fillers aggregated in a paraffin matrix. The effective thermal conductivity of a paraffin/graphene composite, described as a second-rank tensor in the framework of equilibrium molecular dynamics simulation, was calculated for two types of graphene fillers with the same surface area but in-plane aspect ratios of 1 and 10. The filler with the higher aspect ratio was found to exhibit a much higher thermal conductivity enhancement than the one with the lower aspect ratio. This is because a high in-plane aspect ratio strongly restricts the orientation of fillers when they aggregate and, consequently, highly ordered agglomerates are formed. On decomposing the effective thermal conductivity tensor into various molecular-scale contributions, it was identified that the thermal conductivity enhancement is due to the increased amount of heat transfer inside the graphene filler, particularly along the longer in-plane axis. The present result indicates a possibility of designing the heat conduction characteristics of a nanocomposite by customizing the filler shapes so as to control the aggregation structure of the fillers.

Surface Freezing of Cetyltrimethylammonium Chloride-Hexadecanol Mixed Adsorbed Film at Dodecane-Water Interface.

The surface freezing transition of a mixed adsorbed film containing cetyltrimethylammonium chloride (CTAC) and n-hexadecanol (C16OH) was utilized at the dodecane-water interface to control the stability of oil-in-water (O/W) emulsions. The corresponding surface frozen and surface liquid mixed adsorbed films were characterized using interfacial tensiometry and X-ray reflectometry. The emulsion samples prepared in the temperature range of the surface frozen and surface liquid phases showed a clear difference in their stability: the emulsion volume decreased continuously right after the emulsification in the surface liquid region, while it remained constant or decreased at a much slower rate in the surface frozen region. Compared to the previously examined CTAC-tetradecane mixed adsorbed film, the surface freezing temperature increased from 9.5 to 25.0 °C due to the better chain matching between CTAC and C16OH and higher surface activity of C16OH. This then renders such systems much more attractive for practical applications.

Pickering Emulsion Transitions in 2,6-Lutidine Plus Water Critical Liquid Mixtures.

Silica particle (S) stabilized oil-in-water Pickering emulsions are observed in the two-phase region of the critical liquid mixture 2,6-lutidine (L) plus water (W). De-emulsification is found at temperatures below a particle wetting transition temperature Tw(R) where Tw(R) decreases toward the lower critical temperature Tc for smaller particle radii R. The presence of a Pickering emulsion transition and its dependence upon particle radius can be explained by a competition between destabilizing gravitational forces and stabilizing forces originating from the critical interfacial tension. As a corollary to these observations, the line tension τ at the three-phase SLW contact line is determined as a function of temperature.

Fabrication of Paper-based Microfluidic Devices Using a Laser Beam Scanning Technique.

This paper describes a novel method for fabricating paper-based microfluidic devices using a laser beam scanning technique. Cellulose chromatography papers were treated with octadecyltrichlorosilane (OTS) to make them entirely hydrophobic. A photoacid generator (CPI-410S) was soaked into the paper, and irradiated with a 405-nm laser beam to induce acid generating reactions. Since the silyl ether bond between cellulose and OTS was cleaved by the hydrolysis reaction, the photo-irradiated area changed to hydrophilic. By scanning the laser beam using a Galvo mirror system, arbitrary shaped hydrophilic patterns were successfully created on the paper in 50 µm resolution. To the best of our knowledge, this is the first report on the fabrication of hydrophilic channels on the OTS-treated paper using photo-induced acid generation processes coupled with the laser beam scanning technique. Quantification of nitrite was demonstrated with the paper device made by this method.

Cross-Plane and In-Plane Heat Conductions in Layer-by-Layer Membrane: Molecular Dynamics Study.

A material with anisotropic heat conduction characteristics, which is determined by molecular scale structure, provides a way of controlling heat flow in nanoscale spaces. As such, here, we consider layer-by-layer (LbL) membranes, which are an electrostatic assembly of polyelectrolyte multilayers and are expected to have different heat conduction characteristics between cross-plane and in-plane directions. We constructed models of a poly(acrylic acid)/polyethylenimine (PAA/PEI) LbL membrane sandwiched by charged solid walls and investigated their anisotropic heat conduction using molecular dynamics simulations. In the cross-plane direction, the thermal boundary resistance between the solid wall and the LbL membrane and that between the constituent PAA and PEI layers decrease with increasing degree of ionization (solid surface charge density and the number of electric charges per PAA/PEI molecule). When the degree of ionization is low, the cross-plane thermal conductivity of a constituent layer is higher than that of the bulk state. As the degree of ionization increases, however, the cross-plane thermal conductivity of PAA, a linear polymer, decreases because of the increase in the number of in-plane oriented polymer chains. In the in-plane direction, we investigated the heat conduction of each layer and found the enhancement of effective in-plane thermal conductivity again due to the in-plane oriented chain alignment. The heat conduction in the LbL membrane is three-dimensionally enhanced compared to those in the bulk states of the constituent polymers because of the electrostatic interactions in the cross-plane direction and the molecular alignment in the in-plane direction.

Application of atomic stress to compute heat flux via molecular dynamics for systems with many-body interactions.

Although the computation of heat flux and thermal conductivity either via Fourier's law or the Green-Kubo relation has become a common task in molecular dynamics simulation, contributions of three-body and larger many-body interactions have always proved problematic to compute. In recent years, due to the success when applying to pressure tensor computation, atomic stress approximation has been widely used to calculate heat flux, where the lammps molecular dynamics package is the most prominent propagator. We demonstrated that the atomic stress approximation, while adequate for obtaining pressure, produces erroneous results in the case of heat flux when applied to systems with many-body interactions, such as angle, torsion, or improper potentials. This also produces incorrect thermal conductivity values. To remedy this deficiency, by starting from a strict formulation of heat flux with many-body interactions, we reworked the atomic stress definition which resulted in only a simple modification. We modified the lammps package accordingly to demonstrate that the new atomic stress approximation produces excellent results close to that of a rigid formulation.

All- and one-particle distribution functions at nonequilibrium steady state under thermal gradient.

We provide a concrete expression for the phase-space distribution function at nonequilibrium steady state under a constant thermal gradient, which is a typical system of the nonequilibrium molecular dynamics simulation of heat conduction. First, the phase-space distribution function of all particles in a local volume is formulated. Our formulation explicitly takes into account the entropy production due to the change in equilibrium thermodynamic variables in addition to the traditional entropy production described by the spatial gradients and fluxes of equilibrium thermodynamic variables. This treatment is necessary to explain the nonequilibrium response of a quantity that has no equilibrium correlation with mass and heat fluxes and is essential to correctly deduce one-particle distribution functions from the all-particle one. From the all-particle distribution function, we derive the Green-Kubo relations that express the one-particle distribution functions of density and velocity in terms of equilibrium correlation functions and verify these expressions using the molecular dynamics simulation of a Lennard-Jones liquid. These nonequilibrium one-particle distribution functions are sufficiently tractable for practical use, such as for the analytical evaluation of the nonequilibrium average of physical quantities.

The membrane phospholipid cardiolipin plays a pivotal role in bile acid adaptation by Lactobacillus gasseri JCM1131T.

Bile acids exhibit strong antimicrobial activity as natural detergents, and are involved in lipid digestion and absorption. We investigated the mechanism of bile acid adaptation in Lactobacillus gasseri JCM1131T. Exposure to sublethal concentrations of cholic acid (CA), a major bile acid in humans, resulted in development of resistance to otherwise-lethal concentrations of CA by this intestinal lactic acid bacterium. As this adaptation was accompanied by decreased cell-membrane damage, we analyzed the membrane lipid composition of L. gasseri. Although there was no difference in the proportions of glycolipids (~70%) and phospholipids (~20%), adaptation resulted in an increased abundance of long-sugar-chain glycolipids and a 100% increase in cardiolipin (CL) content (to ~50% of phospholipids) at the expense of phosphatidylglycerol (PG). In model vesicles, the resistance of PG vesicles to solubilization by CA increased with increasing CL/PG ratio. Deletion of the two putative CL synthase genes, the products of which are responsible for CL synthesis from PG, decreased the CL content of the mutants, but did not affect their ability to adapt to CA. Exposure to CA restored the CL content of the two single-deletion mutants, likely due to the activities of the remaining CL synthase. In contrast, the CL content of the double-deletion mutant was not restored, and the lipid composition was modified such that PG predominated (~45% of total lipids) at the expense of glycolipids. Therefore, CL plays important roles in bile acid resistance and maintenance of the membrane lipid composition in L. gasseri.

Unique Interfacial Phenomena on Macroscopic and Colloidal Scales Induced by Two-Dimensional Phase Transitions.

This feature article addresses a variety of unique macroscopic-scale and colloidal-scale interfacial phenomena, such as wetting transitions of oil droplets into molecularly thin films, spontaneous merging and splitting of oil droplets at air-water interfaces, solid monolayer and bilayer formation in mixed cationic surfactant/alkane adsorbed films, switching of foam-film thickness, and oil-in-water emulsion stability. All of these phenomena can be observed using commercial cationic surfactants, liquid alkanes, and water.

Effect of Surface Freezing on Stability of Oil-in-Water Emulsions.

Penetration of alkane molecules into the adsorbed film of a cationic surfactant gives rise to a surface freezing transition at the alkane-water interface upon cooling. In this paper, we show that surface freezing of hexadecyltrimethylammonium chloride (CTAC) at the tetradecane-water interface stabilizes oil-in-water (OW) emulsions. For concentrations of CTAC near the critical micelle concentration, an OW emulsion coalesced readily above the surface freezing transition whereas the OW emulsion was stable in the surface frozen state. There was a discontinuous change in the stability of the OW emulsion at a temperature very close to the surface phase transition temperature as determined by interfacial tensiometry and ellipsometry on a planar oil-water interface. The mechanical elasticity of the surface frozen layer opposes film drainage and density fluctuations that could lead to rupture and is the most likely cause of the enhanced emulsion stability.

Myocardial motion analysis based on an optical flow method using tagged MR images.

We developed a method of velocimetry based on an optical flow method using quantitative analyses of tagged magnetic resonance (MR) images (tagged MR-optical flow velocimetry, tMR-O velocimetry). The purpose of our study was to examine the accuracy of measurement of the proposed tMR-O velocimetry. We performed retrospective pseudo-electrocardiogram (ECG) gating tagged cine MR imaging on a rotating phantom. We optimized imaging parameters for tagged MR imaging, and validated the accuracy of tMR-O velocimetry. Our results indicated that the difference between the reference velocities and the computed velocities measured using optimal imaging parameters was less than 1%. In addition, we performed tMR-O velocimetry and echocardiography on 10 healthy volunteers, for four sections of the heart (apical, midventricular, and basal sections aligned with the short-axis, and a four-chamber section aligned with the long-axis), and obtained radial and longitudinal myocardial velocities in these sections. We compared the myocardial velocities obtained using tMR-O velocimetry with those obtained using echocardiography. Our results showed good agreement between tMR-O velocimetry and echocardiography in the radial myocardial velocities in three short-axial sections and longitudinal myocardial velocities on the midventricular portion of the four-chamber section in the long-axis. In the study conducted on the rotating phantom, tMR-O velocimetry showed high accuracy; moreover, in the healthy volunteers, the myocardial velocities obtained using tMR-O velocimetry were relatively similar to those obtained using echocardiography. In conclusion, tMR-O velocimetry is a potentially feasible method for analyzing myocardial motion in the human heart.