Water Microdrops Research Articles

Evaporative cooling of sessile water microdrops measured with atomic force microscope cantilevers

We monitored the evaporation kinetics of drops from solid surfaces and the resulting cooling of the surfaces. To do this we deposited water drops with diameters smaller than 100 µm onto atomic force microscope (AFM) cantilevers. Due to the surface tension of the liquid, the Laplace pressure inside the drop, the change of the interfacial stress at the solid–liquid boundary and evaporative cooling, the cantilevers are deflected by typically some hundred nanometers. We used pure silicon and gold-coated silicon cantilevers in order to be able to separate and quantify the cooling effect from that due to the surface tension. We measured the bending of the cantilevers along their longitudinal axis versus time with an AFM-like setup, and monitored the contact angle and radius of the evaporating drops with video microscopy. We developed a FEM model for the bending of a cantilever as a result of surface forces and evaporative cooling. Experimental results are reproduced by FEM simulations.

Nondestructive and noncontact method for determining the spring constant of rectangular cantilevers

We present here an experimental setup and suggest an extension to the long existing added-mass method for the calibration of the spring constant of atomic force microscope cantilevers. Instead of measuring the resonance frequency shift that results from attaching particles of known masses to the end of cantilevers, we load them with water microdrops generated by a commercial inkjet dispenser. Such a device is capable of generating drops, and thus masses, of extremely reproducible size. This makes it an ideal tool for calibration tasks. Moreover, the major advantage of water microdrops is that they allow for a nearly contactless calibration: no mechanical micromanipulation of particles on cantilevers is required, neither for their deposition nor for removal. After some seconds the water drop is completely evaporated, and no residues are left on the cantilever surface or tip. We present two variants: we vary the size of the drops and deposit them at the free end of the cantilever, or we keep the size of the drops constant and vary their position along the cantilever. For the second variant, we implemented also numerical simulations. Spring constants measured by this method are comparable to results obtained by the thermal noise method, as we demonstrate for six different cantilevers.

Mechanism of the appearance of a large-scale vortex in the troposphere above a nonuniformly heated surface

.This paper is dedicated to a numerical modeling study of the formation mechanisms of a large-scale vortex over a warm water band on the ocean surface. For this purpose, we developed a 3D model of the atmospheric circulation in a domain, which is a part of spherical layer over a limited region of the Earth’s surface (altitude 15 km, longitude and latitude 12 ° ). This model takes into account heating/cooling of the air due to absorption/emission of infrared radiation, as well as due to phase transitions of water vapor to microdrops of water and ice particles, which play an important role. Air transport in the troposphere over a warm region at the ocean surface was numerically simulated using the developed model under different physical conditions. The modeling results allowed us to distinguish the mechanism of cyclone formation over the ocean.

Laser ablation of silicon wafer with a water microdrop

We have developed a new laser ablation process using a water-microdrop with a diameter of 70 μm. The shapes of the debris were investigated at various delay times. A Q-switched Nd:yttrium-aluminium-garnet laser of 25 ns pulse width and 532 nm wavelength was used. The spattering of debris was remarkably reduced by using the water microdrop. The debris pattern was dependent on the shape of the microdrop on the wafer, which in turn was dependent on the surface condition of the wafer and the delay time. The use of a smaller microdrop would result in laser dicing with a small ridge at the rim of the ablation point and no debris. The flexural stress of 720 MPa was obtained near the blade dicing.

Lipase production by yeasts from extra virgin olive oil

Newly produced olive oil has an opalescent appearance due to the presence of solid particles and micro-drops of vegetation water from the fruits. Some of our recent microbiological research has shown that a rich micro-flora is present in the suspended fraction of the freshly produced olive oil capable of improving the quality of the oil through the hydrolysis of the oleuropein. Present research however has, for the first time, demonstrated the presence of lipase-positive yeasts in some samples of extra virgin olive oil which can lower the quality of the oil through the hydrolysis of the triglycerides. The tests performed with yeasts of our collection, previously isolated from olive oil, demonstrated that two lipase-producing yeast strains named Saccharomyces cerevisiae 1525 and Williopsis californica 1639 were able to hydrolyse different specific synthetic substrates represented by p-nitrophenyl stearate, 4-nitrophenyl palmitate, tripalmitin and triolein as well as olive oil triglycerides. The lipase activity in S. cerevisiae 1525 was confined to the whole cells, whereas in W. californica 1639 it was also detected in the extracellular fraction. The enzyme activity in both yeasts was influenced by the ratio of the aqueous to the organic phase reaching its maximum value in S. cerevisiae 1525 when the water added to the olive oil was present in a ratio of 0.25% (v/v), whereas in W. californica 1639 the optimal ratio was 1% (v/v). Furthermore, the free fatty acids of olive oil proved to be good inducers of lipase activity in both yeasts. The microbiological analysis carried out on commercial extra virgin olive oil, produced in four different geographic areas, demonstrated that the presence of lipase-producing yeast varied from zero to 56% of the total yeasts detected, according to the source of oil samples. The discovery of lipase-positive yeasts in some extra virgin olive oils leads us to believe that yeasts are able to contribute in a positive or negative way towards the organological quality of the olive oil.

Fast intracrystalline hydration of beta-chitin revealed by combined microdrop generation and on-line synchrotron radiation microdiffraction.

Water microdrops of about 50 microm in diameter, generated by an ink-jet system, have been used to hydrate fragments of Pogonophora tubes. In situ X-ray microdiffraction with a beam size of 10 microm was used to follow the structural transformations that affected the crystalline beta-chitin part of the specimens. Starting from anhydrous chitin, the formation of a full beta-chitin dihydrate was observed within about 90 s. A disordered intermediate phase with variable d-spacing that could be due to a mixture of anhydrous and hydrated beta-chitin layers was also detected.

Survival of micro-organisms in extra virgin olive oil during storage

When newly produced from the grinding of the olive fruits, olive oil contains solid particles and micro-drops of vegetation water which settle during the preservation of the product. The present research has demonstrated that, together with the suspended material in the extra-virgin olive oil, there are numerous micro-organisms, primarily yeasts. Fungi belonging to the genus Aspergillus, were occasionally observed, while bacteria were not found. When olive oil was artificially inoculated with Candida wickerhamii isolated from the same habitat, it was found that the yeasts were able to grow in the micro-drops of vegetation water or distilled water suspended in the olive oil. Furthermore, it was shown that the partial elimination of the sediments in the oil, carried out with cotton filtration by the bottling companies, allows an appreciable reduction of the number of micro-organisms present in the extra-virgin olive oil.

Non-contact methods of measuring moisture concentration in external layers of building partitions: II—Monitoring of the water vapour condensation on porous surfaces

This paper present the results of the investigation into a potential application of laser radiation for the detection of phase transition processes occurring on the surface layers of porous materials. An attempt was made to discuss in the approximation equations, the relationships between coefficients of the reflected light, the temperature and humidity of the surrounding environment. Laser light reflected from the porous surface carries information about the roughness of the structure. The presence of water microdrop on the surface of the porous material, as a result of condensation and thus a phase transition, leads to the phase displacement of individual rays, which is represented by different images. Therefore, a comprehensive analysis of the reflected light parameters allows a dynamic study of the phase transition phenomena without mechanical intervention.

Non-contact methods of measuring moisture concentration in external layers of building partitions: III—Water vapour condensation on the cementitious surfaces

This paper presents the results of the larger study into a potential application of laser radiation for the detection of phase transition processes in low temperatures occurring on the surface layers of cementitious materials. An attempt was made to identify relationships between the environmental conditions—temperature and air humidity, and the selected parameters of the reflected light. Onset of the condensation process and formation of water microdrops on the surface of the material leads to the phase displacement of individual laser rays, which are represented by different speckle images. Although the analysis of parameters of the reflected light are very difficult in the case of porous materials because of highly developed roughness of the surface structure it has been proved that a dynamic study of the phase transition phenomena can be successfully carried out without mechanical intervention.

疎水／親水マイクロ領域からなる不均一表面上の微小水滴

疎水／親水マイクロ領域からなる不均一表面上の微小水滴

Heterogeneous Surfaces of Structured Hairy-Rod Polymer Films: Preparation and Methods of Functionalization

We report a versatile technique for the formation of a biofunctionalized micrometer scale pattern on solids which is based on Langmuir−Blodgett multilayers of hairy-rod polymers stabilized by partial photochemical cross-linking. Three types of polymer patterns consisting of hydrophobic and hydrophilic domains are generated. These structured films are locally functionalized in two ways: (1) by activating the hairy-rod cushions with active esters and (2) by the deposition of a lipid monolayer onto the hydrophobic domains. For the latter procedure use is made of the fact that lipid monolayers are only assembled over domains with matched polarity. The fluidity and continuity of the monolayer domains was analyzed by lateral diffusion measurements on the basis of photobleaching techniques. The polarity of the domains is monitored by the interference contrast microscopic observation of water microdrops deposited on the structured hairy-rod films.

Collisions of microdrops of water

In this paper, collisions of microdrops of water were studied. Experimental studies of microdrops become very difficult as the drop dimensions become extremely small, particularly when the drops are so small that they contain only a few thousand molecules. To overcome these physical limitations, we produced a model for the H 2O molecule using molecular and atomic interaction forces. We then placed these molecules together to produce drops. Hence, using this new technique, we could study drops with no lower size limitations. To study the motions of these drops, large systems of second order nonlinear ordinary differential equations had to be solved numerically. The system of equations were solved using a CRAY Y-MP8/864 computer. To observe the motion of the drops, output data was transferred to a SGI IRIS 4D-70/GT graphics computer which drew three-dimensional pictures of the data.

Supercomputer simulation of the modes of colliding microdrops of water

Fluid microdrop collisions are important in both chemical and meteorological studies. A three-dimensional molecular model of colliding microdrops of water is developed and explored. Fundamental modes for coherent collisions are described and exhibited, as are results for noncoherent collisions.

Three-dimensional fluid microdrop interaction in the nucleation of raindrops

Computer modelling using classical molecular mechanics is used to simulate the nucleation of two microdrops of water. The process is a function of the relative velocities and separation distances of the drops. For relatively close drops, oscillating oblateness, elliptical and dumbbell modes are exhibited. For more widely separated drops, nucleation can proceed in stages which consist of relatively slow motion towards each other while maintaining sphericity, transition to oblateness, the development of arms, and a final cohesion with a loss of mass. Three-dimensional supercomputer simulations are described and discussed.

Supercomputer simulation of colliding microdrops of water

Microdrop collisions are important in fast kinetic, microwave, nucleation and rainstorm studies. In this paper a molecular model of colliding microdrops of water is simulated on a CRAY X-MP/24. A least squares fit of the force field allows relatively large time steps in the numerical procedure. Rotating “raindrop” modes, “dumbell” modes and oscillatory oblateness modes are demonstrated, as are nonadhesive soft and hard collisions.

Negentropy in microdrops of water

The negative sign of d P/d T which arises in microdrops of water was examined and it became clear that the microdrop has negative entropy (negentropy) for the increase in volume and that the microdrop can be a satisfactory engine for the biological cell.

The Formation and Fate of Tetrahymena patula Cryptostomes

ABSTRACTA reliable method for producing reproductive cysts in Tetrahymena patula is described. The procedure involves the isolation of macrostomes without cytopharyngeal pouches in microdrops of distilled water under oil. The study of silver‐impregnated specimens has shown that a complex pattern of oral resorption and reformation occurs within the cyst that leads to the formation of a group of small cells with recessed oral apparatuses. These cells, called “cryptostomes,” swim very rapidly on excystment and are incapable of either feeding or reproducing. They are presumably dispersal forms. Oral morphogenesis during the transformation of excysted cryptostomes into microstomes and macrostomes is also described.