Difference In Surface Tension Research Articles

Molecular features of the air/carbonate solution interface

The nature of the air/carbonate solution interface is considered with respect to water structure by sum-frequency vibrational spectroscopy (SFVS) and molecular dynamics simulations (MDS). Results from this study provide further understating regarding previous observations that the surface tensions of structure making sodium carbonate solutions have been shown to be significantly greater than the surface tensions of structure breaking bicarbonate solutions at equivalent concentrations. This difference in surface tension and its variation with salt concentration is related to the organization of water and ions at the air/solution interface. Spectral results from SFVS show at equivalent concentrations that, for the carbonate solution, the strong water structure signal of 3200 cm −1 at the air/carbonate solution interface is increased by a factor of 4 when compared to the same signal for the air/bicarbonate solution interface, which spectrum is weaker than the spectrum for the air/water interface in the absence of salt. These results from SFVS are explained by the results from MDS which show that in the case of carbonate solutions the structure making carbonate ions are excluded from the interfacial water region which region is extended in depth. On the other hand, in the case of bicarbonate solutions, the bicarbonate ions are accommodated in the interfacial water region and there is no evidence of an increase in the extent of water structure. These SFVS experimental and MD simulation results provide further information to understand interfacial phenomena of soluble salts at the molecular level.

ESTIMATING THE SEGREGATION ENERGIES IN Cu BINARY SYSTEMS

The segregation energy of diluted species in a matrix can be calculated by first principles. These calculations are generally very computational demanding. The existing empirical models which use the difference in surface tensions to predict the segregation energy are limited, because they do not take the surface orientation of the matrix into account. In this investigation a model was developed which can estimate the segregation energies of segregating species in a binary system. The model makes use of the sublimation energies and takes the orientation of the surface into account. The model shows that the driving force for segregation is not the difference in surface tensions (between the surface tension of the pure element and the surface tension of the element in the alloy) but the difference in surface energies. The results of the calculations were used to simulate the Ag and Sb segregation to the (111) surface of copper.

Effect of temperature on surface properties of cervical tissue homogenate and organic phase monolayers

The temperature dependence of Langmuir monolayers of normal and cancerous human cervical tissues and their organic phases between temperatures of 37 and 45 °C was evaluated. Analysis of the surface pressure–area isotherms revealed significantly different increase in fluidity of the cancerous cervical tissue monolayer at 42 °C as opposed to the normal cervical tissue monolayers ( p < 0.05). Similarly, in the case of cervical cancerous organic phase monolayers significant increase of fluidity was observed at 40 °C whereas no such change was observed in the normal cervical organic phase monolayers. The effect of temperature was found to be different in cancerous and normal cervical tissues and this may be due to the different lipid profiles in them. Cancerous cervical tissues had 1.8-fold higher total lipids as compared to the normals. Similarly, the PC, PE, PI, PG, SM and PS levels in cancerous cervical tissues were 3.6, 2.0, 2.3, 4.7, 1.7 and 2.2 times higher than those of normal cervical tissues, respectively. Significant cancer–normal difference in minimum surface tension and hysteresis area was found at all temperatures studied for both tissue homogenates and organic phases. For example, cancerous tissue homogenates showed minimum surface tensions of 51.9 ± 4.6, 54.4 ± 5.9, 57.6 ± 6.0 and 51.9 ± 5.6 mN/m at temperatures 37, 40, 42 and 45 °C whereas the corresponding values for normal cervical tissue homogenates were 39.3 ± 3.6, 39.2 ± 3.7, 39.2 ± 3.8 and 39.1 ± 3.6, respectively. The fluidity change at hyperthermic range of temperature can be correlated to the increased efficiency of drug on combination therapy with hyperthermia. These results may have implications in manipulating the fluidity of cervical cancer tissue membranes for better permeability thereby leading to better therapeutic strategies for cervical cancer.

Turbo-Mixing in Microplates

How to effectively mix small volumes of liquids within microplate wells is a still underestimated and often neglected challenge. The method the authors introduce here relies on violent turbulent motion within a liquid caused by spotting an organic solvent drop onto its surface. The amount needed, less than 1 to 3 microL, is generally small enough not to alter bioactive molecules. Moreover, a solvent may be selected for its compatibility with assay components. The method was tested with layers of aqueous liquids that differ in pH and concentration of a pH-dependent dye, allowing mixing to be monitored optically. Rapid mixing was caused by spotting drops of alcohols, acetone, acetonitrile, and aqueous solutions of these, as long as the difference of surface tension between the drop and the uppermost layer of the bulk liquid surpassed 30 dynes/cm. Along with this difference, position and velocity of spotting, as well as viscosity and geometry of the bulk liquid volume, may influence the turbulence evoked. No significant difference was found for the activity of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase when measured after mixing by shaking and after mixing by spotting 1 microL of methanol onto assays within 96-well microplates.

Hydroxyapatite Morphology Control by Using Hydrothermal Treatment

After hydrothermal treatment of tricalcium phosphate (TCP), calcium deficient hydroxyapatite (HA) with much amount of a-surface (h00) was obtained. It was considered that c-surface of HA had larger surface tension than that of a-surface, therefore HA crystals elongated along c-axis of &lt;001&gt; directions. By using hydrothermal treatment, difference of surface tension was affected crystal growth of HA. The adsorption property of HA will be controlled by designing of HA morphology, because different crystal surfaces have different properties.

A direct methanol fuel cell system with passive fuel delivery based on liquid surface tension

The existing direct methanol fuel cell (DMFC) systems are fed with a fixed concentration of fuel, which are either a diluted methanol solution or an active fuel delivery driven by an attached active pump. Both approaches limit the power conversion density or degrade the overall efficiency of the DMFC system significantly. Such disadvantages become more severe in small-scale DMFCs, which require a high conversion efficiency and a small physical space suitable for portable electronics. In this paper, passive fuel delivery based on a surface tension driving mechanism was designed and integrated in a laboratory-made prototype to achieve consumption depending on fuel concentration and power-free fuel delivery. Unidirectional methanol-to-water smooth flow is achieved through the capillaries of a Teflon PTFE (polytetrafluoroethylene) membrane based on the difference in liquid surface tension. The prototype was demonstrated to exhibit a better polarization performance and to last for an extended operating time compared to conventional DMFCs. Its high efficiency and load regulation performance were also demonstrated in contrast to an active DMFC supplied with a constant concentration fuel. The fuel delivery driven by the liquid surface tension effect demonstrated here is believed to be more applicable for future small-scale DMFCs for portable electronics.

A Non-Wetting Packed Bed Gas Scrubber

The operation of a small-scale packed column working under non-wetting condition was investigated to provide insight and design data for the subsequent development of a liquid metal irrigated packed bed gas scrubber. An 8 cm internal diameter Perspex column was used, packed with 9.5 mm polyethylene spheres and 10.0 mm glass spheres coated with paraffin wax. A counter-current air–water system was used. The packings well all essentially hydrophobic promoting a non-wetting water flow condition, simulating liquid metal flow on solid packings. Results on flow visualization, flooding capacity and liquid holdup trends, as well as the particulate removal performance of the non-wetting packed bed scrubber are presented in this paper. The maximum water droplet size on the non-wettable spherical packing surface could be estimated from the static equilibrium of a pendent droplet, governed by surface tension and gravitational force. The flooding capacity and liquid holdup trends of the water-irrigated packed column operating under non-wetting condition were found to be similar to those reported for liquid metal systems despite the pronounced differences in liquid density and surface tension. This suggests that the hydrodynamics of a packed column in non-wetting operation are largely influenced by the liquid–solid contact angle which overrides the dissimilarities in liquid physical properties. Good particulate removal performance was demonstrated by the non-wetting packed bed scrubber.

Fluorescence imaging of multi-component wetting

Fluorescence imaging methods are explored as tools to study multi-component wetting of liquids. A novel approach was employed using polymer labeled with contrasting fluorescent dyes, which allow optical recognition and also caused differences in surface tension between blend components. Total internal reflection-fluorescence microscopy probes a thin surface layer to the order of 100 nm to investigate the structure of the spreading drop next to the substrate. Dye segregation out of solution and phase separation of polymer blends were observed. Confocal microscopy can visualize the larger three-dimensional structure of sessile drops. Component segregation was observed and quantified using relative fluorescence intensities.

Inside Front Cover: Hexagonal Network Organization of Dye-Loaded Zeolite L Crystals by Surface-Tension Driven Autoassembly (Adv. Funct. Mater. 17/2006)

The two-dimensional (2D) ordering of zeolite L crystals on polydimethylsiloxane is reported in the Full Paper by Yunus et al. on p. 2213. The highly fluorescent dye-loaded zeolite L crystals are organized into a 2D hexagonal network by surface-tension-driven autoassembly. The resulting film displays a hexagonal pattern of polarized fluorescence, reflecting the properties of the dye molecules in the parallel nanochannels of the zeolite crystals. Highly fluorescent dye-loaded zeolite L crystals, approximately 1.4 μm long and 650 nm in diameter, are organized in a hexagonal network by a surface-tension-driven autoassembly process. A polydimethylsiloxane (PDMS) film presenting a trigonal ordering of spherical protuberances, including a polystyrene (PS) hexagonal network occupying their interstices, is chosen as the platform for the assembly. The overall wettability and the difference in surface tension between PDMS and PS surfaces are found to offer good conditions for ordering micrometric dye-loaded zeolite L crystals in a 2D hexagonal network. The resulting film displays a regular hexagonal pattern of polarized fluorescence, reflecting the polarization properties of the dye molecules inserted in the parallel nanochannels of the zeolites.

Hexagonal Network Organization of Dye-Loaded Zeolite L Crystals by Surface-Tension Driven Autoassembly

Highly fluorescent dye-loaded zeolite L crystals, approximately 1.4 μm long and 650 nm in diameter, are organized in a hexagonal network by a surface-tension-driven autoassembly process. A polydimethylsiloxane (PDMS) film presenting a trigonal ordering of spherical protuberances, including a polystyrene (PS) hexagonal network occupying their interstices, is chosen as the platform for the assembly. The overall wettability and the difference in surface tension between PDMS and PS surfaces are found to offer good conditions for ordering micrometric dye-loaded zeolite L crystals in a 2D hexagonal network. The resulting film displays a regular hexagonal pattern of polarized fluorescence, reflecting the polarization properties of the dye molecules inserted in the parallel nanochannels of the zeolites.

Diesel–diesel and diesel–ethanol drop collisions

In view of the possible occurrence of unlike drop collisions in a diesel spray due to the increasing application of alcoholic fuels as supplementary fuels in diesel engines, collisions of a diesel drop with either a diesel drop or an ethanol drop were studied. Diesel drop collision results do not display appreciable difference, within experimental errors, from those of tetradecane drops except for very small Weber numbers. The collision of an ethanol drop with a diesel drop, when compared to binary diesel drop collisions, exhibits higher tendency towards reflex separation for near head-on collisions and lower tendency towards stretching separation for medium to high impact parameter collisions. These distinctions come from the spreading of ethanol over the diesel drop due to their difference in surface tension.

Collision between immiscible drops with large surface tension difference: diesel oil and water

The collision outcomes of immiscible drops with large surface tension difference, namely, a water drop and a diesel oil drop, were observed experimentally. In a near head-on collision between immiscible drops with large surface tension difference, an “overlaying” action for the drop of the smaller surface tension, i.e., the diesel oil drop, to go around the surface of the drop of the larger surface tension, i.e., the water drop, occurs during the collision. This overlaying action reduces the reflex energy for head-on collisions, making reflex separation more difficult to occur. At the same time, due to the immiscibility, the liquid bridge during stretching separation becomes narrower, which makes stretching separation easier to happen. No coalescence could be observed for a collision of Weber number greater than 60. In addition, compound drops are produced frequently.

Self-Assembly in Two-Dimensions of Colloidal Particles at Liquid Mixtures

The aim of this work is to simulate the formation of colloidal rings, circular clusters, and voids induced by oily lenses at the air-water interface. The presence of two liquids with different surface tension leads to the formation of a nonhomogeneous interface. In this case, the total interaction potential is assumed to be composed of only two terms; the first one is due to the (repulsive) pairwise dipolar force between partly immersed charged microspheres, whereas the second depends on the position of the particle at the interface and is connected to the interfacial stress caused by the difference of surface tension between both liquids. This simple potential is able to reproduce the experimental rings, circular clusters and voids found by different authors.

Reciprocating thermocapillary plug motion in an externally heated capillary

This paper reports the concept and experimental results of reciprocating thermocapillary motion of a liquid plug in microchannels. This paper first describes a one-dimensional analytical model for the transport of microplugs in a capillary. The model considers the coupling effect between heat transfer in the capillary wall and the surface tension driven movement of the plug. Because surface tension depends on temperature, the transient temperature distribution determines the surface tension difference across a plug and thus its movement. In the experiments, we used two heaters, which were activated alternatively. The liquid plug was positioned between the two heaters. The periodic temperature gradients generated by the two heaters made the liquid plug to move back and forth. The position of the plugs was captured and evaluated using a CCD camera. This paper presents the results of this motion with different switching frequencies, viscosities and plug sizes. This actuation concept has potential applications in postprocessing stages for droplet-based microfluidics.

ANALYSIS OF EFFECT OF GAS–LIQUID INTERFACIAL DISTURBANCE ON MASS TRANSFER PERFORMANCE

In order to study the mass transfer phenomena for water vapor absorbed by triethylene glycol (TEG) solution and to elucidate effect of interfacial disturbance on absorption performance, the interfacial phenomena for water drop instilling on the surface of TEG solution and mass transfer process were observed and operated in this study. Besides liquid and gas flow rates, the interfacial disturbance can also affect the mass transfer performance in the absorption system with continuous liquid phase, and the advanced mass transfer phenomena must be discussed from the interface of matter. Therefore, the surface tensions of desiccant solutions were measured to analyze the disturbed phenomena of water drop instilling on the surface of TEG solution. Since the Marangoni-Index (MI) means the maximum surface tension difference on the surface of liquid layer, the values of MI were calculated and compared with the mass transfer performance of packed-bed absorber. Generally speaking, the interfacial disturbance, resulted from the surface tension difference, would promote the contacting area of gas and liquid phases. The observation of water drop instilling on surface of TEG solution found that the interfacial disturbance existed between water drop and TEG solution, and the interfacial instability was found in the peripheral region of the water drop. On the other hand, the values of MI were increased by the increased TEG concentrations, and it can be deduced that the surface tension effect should be significant in the higher concentration of TEG solution and the interfacial disturbance would be heavier above 95 wt.% TEG solutions. Finally, the absorption performance for 95 and 96 wt.% TEG solutions were much larger than that of 90 and 88.6 wt.% TEG solutions in the operation of packed-bed absorber.

Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions

The metastable liquid phase separation and rapid solidification behaviours of Co61.8Cu38.2 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing, electromagnetic levitation (EML) and drop tube techniques. It is found that the liquid phase separation process and the solidification microstructures intensively depend on the experimental processing parameters, such as undercooling level, cooling rate, gravity level, liquid surface tension and the wetting state of crucible. Large undercooling and surface tension difference of the two liquids tend to facilitate further separation and cause severe macrosegregation. On the other hand, rapid cooling and low gravity effectively suppress the coalescence of the minority phase. Severe macrosegregation patterns are formed in the bulk samples processed by both DTA and EML. In contrast, disperse structures with fine spherical Cu-rich spheres homogeneously distributed in the matrix of Co-rich phase have been obtained in drop tube.

Effect of mass transfer on the film drainage between colliding drops

The influence of mass transfer on the drainage behaviour of the thin liquid film between two drops immersed in another liquid colliding at constant approach velocity has been studied experimentally. The liquid–liquid system used is glycerol in silicone oil. The transferred solute is acetone and the volume concentration difference across the interface ranges from 1 to 5%. The film thickness evolution has been measured using a laser interferometry technique. The direction of mass transfer (from the drops towards the film phase and inversely) has been investigated and the results compared to the case with no mass transfer [E. Klaseboer, J.P. Chevaillier, C. Gourdon, O. Masbernat, J. Colloid Interface Sci. 229 (2000) 274–285]. When the solute transfers from the drops towards the continuous phase, the drainage rate is significantly higher than in the case with no mass transfer. This result is interpreted as a consequence of the mass transfer induced surface mobility in the film region (the so-called Marangoni effect) due to localized surface tension differences. This effect has been demonstrated by the visualization of the flow patterns in the drops and in the film phase (using a particle tracer technique). In this case, the slope of the film height as a function of time seems to be independent of the approach velocity condition imposed on the drop and appears to be controlled by the interfacial tension gradient. In the opposite case, when the solute transfers from the continuous phase towards the drops, the film drainage rate is lowered with respect to the case of no mass transfer, goes to zero or even changes its sign depending on the mass transfer intensity. The results also show that in the range of solute concentration studied, the effect of mass transfer on the film drainage process takes place at large distances compared to the scales at which lubrication theory is valid.

Characterization of the Human Upper Gastrointestinal Contents Under Conditions Simulating Bioavailability/Bioequivalence Studies

This study was conducted to compare the luminal composition of the upper gastrointestinal tract in the fasted and fed states in humans, with a view toward designing in vitro studies to explain/predict food effects on dosage form performance. Twenty healthy human subjects received 250 mL water or 500 mL Ensure plus (a complete nutrient drink) through a nasogastric tube and samples were aspirated from the gastric antrum or duodenum for a period up to 3.5 h, depending on location/fluid combination. Samples were analyzed for polyethylene glycol, pH, buffer capacity, osmolality, surface tension, pepsin, total carbohydrates, total protein content, and bile salts. Following Ensure plus administration, gastric pH was elevated, buffer capacity ranged from 14 to 28 mmoL L-1 DeltapH-1 (vs. 7-18 mmol L-1 DeltapH-1), contents were hyperosmolar, gastric pepsin levels doubled, and surface tension was 30% lower than after administration of water. Post- and preprandial duodenal pH values were initially similar, but slowly decreased to 5.2 postprandially, whereas buffer capacity increased from 5.6 mmol L-1 DeltapH-1 (fasted) to 18-30 mmol L-1 DeltapH-1 (p<0.05). Postprandial surface tension in the duodenum decreased by >30%, bile salt levels were two to four times higher, luminal contents were hyperosmotic, and the presence of peptides and sugars was confirmed. This work shows that, in addition to already well characterized parameters (e.g., pH, and bile salt levels), significant differences in buffer capacity, surface tension, osmolality, and food components are observed pre-/postprandially. These differences should be reflected in test media to predict food effects on intralumenal performance of dosage forms.

Conformal AZ5214-E resist deposition on patterned (1 0 0) InP substrates

A draping technique was studied to deposit thin, visco-elastic AZ5214-E resist layers from a water surface over planar and patterned substrates. A visco-elastic AZ5214-E layer forms on the water surface when a drop of AZ5214-E makes contact with it. The drop spreads out within a fraction of a second because of a large positive difference in surface tension between water and AZ5214-E. The spreading mechanism lies in the ability of PGMEA (AZ5214-E liquid constituent) to form hydrogen bonds with water. We brought AZ5214-E drops to make contact with water at 20 ± 0.1 °C via adhesive forces to form AZ5214-E layers on the water surface of (1) circular and (2) square shapes. In case (1), the layers, formed from drops of V = 3 µl, had thickness t ≈ c ⋅ 4V/πΦ−2 for Φ < 32 mm, and t > c ⋅ 4V/πΦ−2 for larger Φ. In case (2), the layers had t ≈ a + bV for V between 7 and 12 µl on square-shaped water surfaces of constant area A = 34.5 mm × 34.5 mm. All layers exhibited microscopic waviness with an average thickness uniformity u ∼ 91%, and submicron waviness with a root-mean-square roughness σ ∼ 12 nm and a lateral correlation length ξ ∼ 32 µm. AZ5214-E sheets coated conformally high mesa objects with sharp convex and concave edges: 61 µm high ridges confined to ∼35°-inclined facets and 9 µm high ridges confined to negatively sloped facets. The draping technique can be used to deposit conformal AZ5214-E layers over non-planar substrates for non-planar device processing.

A Molecular Dynamics Study of the Response of Lipid Bilayers and Monolayers to Trehalose

Surface tensions evaluated from molecular dynamics simulations of fully hydrated dipalmitoylphosphatidylcholine bilayers and monolayers at surface areas/lipid of 54, 64, and 80 Å 2 are uniformly lowered 4–8 dyn/cm upon addition of trehalose in a 1:2 trehalose/lipid ratio. Constant surface tension simulations of bilayers yield the complementary result: an increase in surface area consistent with the surface pressure-surface area ( π-A) isotherms. Hydrogen bonding by trehalose, replacement of waters in the headgroup region, and modulation of the dipole potential are all similar in bilayers and monolayers at the same surface area. These results strongly support the assumption that experimental measurements on the interactions of surface active components such as trehalose with monolayers can yield quantitative insight to their effects on bilayers. The simulations also indicate that the 20–30 dyn/cm difference in surface tension of the bilayer leaflet and monolayer arises from differences in the chain regions, not the headgroup/water interfaces.