Optical detection of pores in adipocyte membrane

Structures that can be interpreted as cytoplasm droplets leaking through the membrane are experimentally detected on the membranes of adipocytes using optical digital microscopy. The effect of an aqueous alcohol solution of brilliant green on the amount and sizes of structures is studied. It is demonstrated that the optical irradiation of the adipocytes that are sensitized with the aid of the brilliant green leads to an increase in the amount of structures (pores) after the irradiation. The experimental results confirm the existence of an earlier-proposed effect of photochemical action on the sensitized cells of adipose tissue that involves additional formation of pores in the membrane of the sensitized cell under selective optical irradiation. The proposed method for the detection of micropores in the membrane of adipose tissue based on the detection of the cytoplasm droplets leaking from the cell can be considered as a method for the optical detection of nanosized pores.     

Controlled Production of Emulsions Using a Crossflow Membrane

A method for manufacturing emulsions — crossflow membrane emulsification has been studied. This involves the formation of emulsions by breaking up the discontinuous phase into droplets in a controlled manner without the use of turbulent eddies. This is achieved by passing the discontinuous phase through a suitable microporous medium and injecting the droplets so formed directly into a moving continuous phase. This paper presents two examples of experimental data for droplet formation using a single pore (capillary tube) and a membrane tube. A high-speed video camera (up to 1000 frames per second) was used to record the formation of droplet from a single pore and thus measure droplet growth and the detachment processes as a function of process parameters such as transmembrane pressure drop, membrane pore size, continuous phase crossflow velocity etc. Real emulsions were prepared using a membrane tube.     

Droplet traffic at a simple junction at low capillary numbers

We report that, when a train of confined droplets flowing through a channel reaches a junction, the droplets either are alternately distributed between the different outlets or all collect into the shortest one. We argue that this behavior is due to the hydrodynamic feedback of droplets in the different outlets on the selection process occurring at the junction. A "mean field" model, yielding semiquantitative results, offers a first guide to predict droplet traffic in branched networks.     

Experiments on breakups of a magnetic fluid drop through a micro-orifice

We experimentally study the breakups of a ferrofluid drop passing through a narrow passage under the attraction of an external field. After passing through the orifice, the fluid thread starts to neck down significantly and eventually breaks to form new droplets. The dynamics of the ferrofluid breakup are analyzed parametrically, including the diameter of the orifice and the local field strength. The patterns of fluid breakups can be characterized by two measurements of the breaking droplets, such as their sizes and stretching lengths. These two characteristic measurements mainly depend on the diameter of the orifice. Breaking droplets with less stretching and smaller sizes are resulted from a narrower orifice. On the other hand, the number of total breaking droplets that represents the transport effectiveness of ferrofluids significantly depends on both the diameter of the orifice and the local field strength. While a stronger field generates more breaking droplets, a maximum number of breaking droplets occurs at an intermediate orifice's diameter.     

An investigation of the fluidity of concentration polarisation layers in crossflow membrane filtration of an oil-water emulsion using chemical shift selective flow imaging

A chemical shift selective NMR flow imaging sequence using stimulated echoes for data acquisition is presented. The sequence was tested using a 20% (vol/vol) oil-water emulsion formed from a soluble cutting oil, which was passed through a simple flow phantom to yield two-dimensional velocity distribution maps of the oil droplets and of the water separately. It was then used to investigate the fluidity of concentration polarisation layers formed from the oil droplets during crossflow membrane filtration of a 5% (vol/vol) emulsion of the same cutting oil. A simple membrane filtration module was used for this purpose, with the feedstock emulsion fed into the lumen of a single tubular membrane at a trans-membrane pressure difference P ∼ 70kPa and crossflow Reynolds number, Re, in the range 100–1000. The results confirm a net axial flow rate < 7.5 μm/s (half digital resolution in the velocity dimension) for the oil polarisation layer. Under these conditions, the upper limit for oil flow tangential to the membrane in the polarised layer is less than 15% of the convective flow of oil towards the membrane.     

Evaporation of two liquid droplets moving sequentially through high-temperature combustion products

We have performed an experimental study of the evaporation intensity for droplets in atomized-liquid flow moving through a flame of fixed height. Integral characteristics of the atomized-liquid evaporation process were evaluated. Evaporation of two water droplets moving sequentially one after the other through high-temperature combustion products is analyzed. A comparison of obtained data with available theoretical predictions is given.     

Persistent droplet motion in liquid-liquid dewetting

When a nonvolatile liquid film dewets from a partly compatible liquid substrate, the advancing dewetting front leaves behind droplets formed through a Rayleigh instability mechanism at its rim. We have found that these droplets continue to move in the direction of the dewetting front for extended periods (of order one day) with an initial droplet velocity varying linearly with the droplet size, and a displacement varying logarithmically with time. We attribute this persistent motion to a transient surface tension gradient on the substrate liquid surface trailing the dewetting front.     

Protein transfer to membranes upon shape deformation

Red blood cells, milk fat droplets, or liposomes all have interfaces consisting of lipid membranes. These particles show significant shape deformations as a result of flow. Here we show that these shape deformations can induce adsorption of proteins to the membrane. Red blood cell deformability is an important factor in several diseases involving obstructions of the microcirculatory system, and deformation induced protein adsorption will alter the rigidity of their membranes. Deformation induced protein transfer will also affect adsorption of cells onto implant surfaces, and the performance of liposome based controlled release systems. Quantitative models describing this phenomenon in biomaterials do not exist. Using a simple quantitative model, we provide new insight in this phenomenon. We present data that show convincingly that for cells or droplets with diameters upwards of a few micrometers, shape deformations induce adsorption of proteins at their interface even at moderate flow rates.     

Ag8 fluorescence in argon

The fluorescence of Ag8 in an argon matrix and in argon droplets is reported. This is the first unambiguous assignment of the fluorescence of a metal cluster larger than the tetramer, indicating that the excited state lifetime is longer than previously thought. It is discussed as a possible result of a matrix cage effect. The excitation spectrum is compared with two-photon-ionization measurements of Ag8 in helium droplets and to known absorption data. The agreement is excellent. We propose that the excited states relax rapidly through vibrational coupling to a long-lived state, from which the fluorescence occurs.     

液滴法制备空心玻璃微球的模拟计算

 通过对液滴法制备空心玻璃微球的成球过程进行分析,建立了成球过程数学模型,定量描述了液滴的形成、液滴的封装、凝胶球壳的形成与干燥,发泡剂的分解,球壳的预热与熔炼、冷却与收集等过程中,液滴/球壳的大小、速率、壁厚、气压等随操作条件的变化,计算了抽气速率、发泡剂浓度、玻璃溶液浓度和初始液滴大小等的改变对成球过程的影响,并进行了初步验证实验。     

Take off of small leidenfrost droplets

We put in evidence the unexpected behavior of Leidenfrost droplets at the later stage of their evaporation. We predict and observe that, below a critical size R_{l}, the droplets spontaneously take off due to the breakdown of the lubrication regime. We establish the theoretical relation between the droplet radius and its elevation. We predict that the vapor layer thickness increases when the droplets become smaller. A satisfactory agreement is found between the model and the experimental results performed on droplets of water and of ethanol.     

Jet formation in the laser forward transfer of liquids

The dynamics of the laser-induced forward transfer (LIFT) of an aqueous solution is investigated through time-resolved imaging. The experiment is carried out at conditions under which droplets are deposited on a receptor substrate. The obtained images reveal that after an initial balloon-like stage, a uniform jet with a very long length and high aspect ratio is formed, which advances at constant speed until it finally becomes unstable and breaks into several droplets. This dynamics demonstrates that the deposition process of well-defined droplets through LIFT results from the contact of the liquid jet with the receptor substrate, and not from a flying droplet.     

Liquid-liquid phase separation of a surfactant-solubilized membrane protein

Solubilization of membrane proteins requires surfactants, whose structural properties play a crucial role in determining the protein phase behavior. We show that ionization of a pH-sensitive surfactant, lauryldymethylamino-N-oxide, bound to the bacterial photosynthetic Reaction Center, induces protein phase segregation in micrometric "droplets." Liquid-liquid phase separation takes place in a narrow pH range, is promoted by increasing temperature, and vanishes by adding salt. After a fast initial droplet growth, the nearly arrested kinetics at a later stage leaves the system in a finely divided, long-lasting emulsified state.     

Determination of temperature and concentration of a vapor–gas mixture in a wake of water droplets moving through combustion products

Characteristic temperatures and concentrations of a vapor–gas mixture in a wake of water droplets moving through combustion products (initial temperature 1170 K) were determined using the Ansys Fluent mathematical modeling package. We investigated two variants of motion: motion of two droplets (with sizes from 1 mm to 3 mm), consecutive and parallel, and motion of five staggered droplets. The influence of the relative position of droplets and also of distances between them (varied from 0.01 mm to 5 mm) on temperatures and concentrations of water vapor was established. The distances determine the relation between the evaporation areas and the total volume occupied by a droplet aggregate in the gas medium. The results of modeling for conditions that take into account vaporization on the droplet surface at average constant values of evaporation rate and also with consideration of the change in the latter, depending on the droplet temperature field, are compared. We determined conditions under which the modeling results are comparable for the assumption of a constant vaporization rate and with regard to the dependence of the latter on temperature. The earlier hypothesis on formation of a buffer vapor layer (“thermal protection”) around a droplet, which decreases the thermal flow from the external gas medium, was validated.     

Coalescence of spreading droplets on a wettable substrate

We investigate experimentally and theoretically the coalescence dynamics of two spreading droplets on a highly wettable substrate. Upon contact, surface tension drives a rapid motion perpendicular to the line of centers that joins the drops and lowers the total surface area. We find that the width of the growing meniscus bridge between the two droplets exhibits power-law behavior, growing at early times as t1/2. Moreover, the growth rate is highly sensitive to both the radii and heights of the droplets at contact, scaling as ho3/2/Ro. This size dependence differs significantly from the behavior of freely suspended droplets, in which the coalescence growth rate depends only weakly on the droplet size. We demonstrate that the scaling behavior is consistent with a model in which the growth of the meniscus bridge is governed by the viscously hindered flux from the droplets.     

Different mechanisms of nucleation and self-organization of droplets in ferroelectric smectic membranes

New mechanisms of droplet nucleation and self-organization in ferroelectric membranes are described. The droplets may be accompanied by different number of topological defects (zero, one, two) whose location may be on the droplet boundary or in the membrane. Nucleation and self-organization of droplets with total topological charge S = 0 , S = + 1 and S = - 1 were investigated. We found that an S = - 1 topological defect may be the center of both droplet nucleation and chain formation. This mechanism of chaining drastically differs from the droplet self-organization described earlier which is realized by attraction of droplet-defect pairs. Our observations demonstrate new possibilities for manipulating the inclusions and their self-organization in smectic membranes.     

Coherent transmittance quenching effect in thin films of polymer-dispersed ferroelectric liquid crystals

The conditions for vanishing of the coherent component of radiation transmitted through a monolayer of polymer-dispersed ferroelectric liquid-crystal droplets are found. The influence of polydispersity and disorientation of axes of semispherical droplets on the conditions of interference quenching is studied. It is shown that these factors cause a change in the average size and concentration of droplets for which the quenching effect is realized. Data on the contrast ratio and the modulation depth of a monolayer, determined from the coherent component of transmitted radiation, are presented. It is shown that these characteristics can be considerably improved under quenching conditions for a film of polymer-dispersed ferroelectric liquid-crystal droplets.     

Coherent transmission and angular structure of light scattering by monolayer films of polymer dispersed liquid crystals with inhomogeneous boundary conditions

We consider monolayer polymer films with oriented droplets of a nematic liquid crystal (LC). Relations for the coherent transmission coefficients of a layer of oriented ellipsoidal droplets and for the intensity of light scattered by monolayers of spherical and spheroidal droplets have been obtained. The amplitude-phase screen model and the interference approximation of the theory of multiple wave scattering have been used. To describe light scattering by an individual ellipsoidal droplet with inhomogeneous surface binding, we have developed an anomalous diffraction approximation. For monolayers of spherical LC droplets, the coherent scattering coefficients and the angular scattering structure have been analyzed. The internal structure of nematic droplets have been calculated by the relaxation method based on the solution of the minimization problem of the free energy volume density. We have studied basic regular features of light scattering by a monolayer with homogeneous and inhomogeneous boundary conditions at the LC-polymer interface. We show that, for films that contain droplets with inhomogeneous boundary conditions of the tangentially normal type, the angular structure of the scattered light is asymmetric with respect to the polar scattering angle.     

A practical method for diameter,number density and material characterization of 40–90 µm size droplets by stimulated Raman scattering

We demonstrate that the technique of Stimulated Raman Scattering (SRS) is a practical method for the simultaneous characterization of diameter, number density and constituent material of microsize droplets. The method is applicable to all Raman active materials and to droplets with a diameter of at least 8 µm. Our experimental study was focused on water and ethanol monodisperse droplets in the diameter range of 40–90 µm. Results of a single laser pulse and multiple pulses are analyzed, indicating that the SRS method can diagnose droplets of mixed liquids and ensembles of polydisperse droplets.     

Enhancement of Raman scattering by deformation of microparticles

Raman scattering on deformed droplets levitated in an acoustic levitator and produced by a vibrating-orifice aerosol generator were investigated. Our samples experiments were diethyl hexyl sebecate (DEHS) droplets in the millimeter-size range and ethanol droplets in the size range 50-100 microm. The C-H stretching region from 2800 to 3100 cm(-1) was investigated. We found that the Raman intensity measured by a scattering angle of 90 degrees depended on the shape of the droplets. Raman scattering on spherical droplets was smaller than scattering on spheroidal droplets with the same volume. Similar results were observed for the fluorescence signal of Rhodamine 6G-doped DEHS droplets.