Difference In Surface Tension Research Articles

Improving the wettability of aluminum on carbon nanotubes

The wetting of a metal on carbon nanotubes is fundamentally difficult due to the unusually large difference between their surface tensions and is a bottleneck for making metal–carbon nanotube (CNT) composites. Here, we report a simple method to enhance the wettability of metal particles on the CNT surface by applying aluminum, which is the material with the largest surface tension. This method involves two steps: (i) Al nanoparticles are decorated on multiwalled carbon nanotubes by electroplating and (ii) Al powder is further spread on Al-electroplated CNTs, followed by high-temperature annealing to accommodate complete wetting of the aluminum. The large surface tension difference is overcome by forming strong Al C covalent bonds initiated by defects of the CNTs. The decrease in the D-band intensity, the G-band shift in the Raman spectroscopy and the formation of Al C covalent bonds, as confirmed by X-ray photoelectron spectroscopy, were in agreement with our structural model of CNT vacancy O Al determined by density functional calculations.

Threshold onset of Marangoni convection in narrow channels

There are several experimental studies where the Marangoni convection begins only at a certain difference in the surface tension, i.e. in a threshold way. This effect contradicts a traditional point of view according to which the surface flow in Newtonian fluids should begin at an arbitrary small difference in surface tension. To explore this phenomenon in detail we investigated the initiation of the Marangoni convection at a free liquid surface caused by injection of a droplet of surfactant. It was found that the surface motion occurs in a threshold manner, i.e. when a surfactant concentration in the droplet approaches a certain critical value. The described phenomenon is more important in narrow channels and essentially depends both on the purity of the basic liquid and on the surfactant used. Based on the experimental results, a hypothesis about an important role of residual impurities contained in basic liquids which can thoroughly change a surface rheology was suggested. The theoretical model taking into account special rheological properties in the free surface is considered. The results of the numerical simulation are in a good agreement with the experimental observations.

Tensile Forces Stabilize Observed Crista Structure in Mitochondria

Electron tomograms have revealed that, in normal mitochondria, crista membrane self-assembles into a complex structure that contains both flat lamellar and tubular components connected to the inner boundary membrane through crista junctions. This structure with one single matrix compartment is believed to be essential to the proper functioning of mitochondria. We present a model from which the observed morphology of the inner mitochondrial membrane can be inferred as minimizing the system's free energy. Using the observed geometrical features, we then predict thermodynamic properties of the system; such properties include surface tension, pressure difference and stabilizing tensile forces which have not been directly observed. Free energy of the membrane has contributions from resistance of the membrane to bending, surface tension and osmotic pressure difference across the membrane and assumes mechanical forces acting on the membrane that we believe to be exerted by mechano-enzyme protein scaffolds such as dynamin-like OPA1. To that end, a set of geometric measurements from the structural features of mitochondria in Hela cells and mouse embryonic fibroblasts were obtained. Structural features were measured from full 3D electron tomograms of mitochondria, obtained by joining the reconstructions of up to four serial 300nm sections. The free energy model combined with the geometric measurements predicts that a stress-induced coexistence of tubular and flat lamellar phases are stabilized by tensile forces of the order of 20pN (1), comparable to those measured for dynamin protein scaffolds.(2) It also predicts the pressure differences of −0.037 +/- 0.008atm (pressure higher in the matrix) and surface tension equal to 0.077 +/- 0.02pN/nm.(1)1 M. Ghochani, J. D. Nulton, P. Salamon, T. G. Frey, A. Rabinovitch, and A. R. C. Baljon, Biophysical Journal (2010)-Accepted.2 A. Roux et al., Proceedings of the National Academy of Sciences107, 4141-4146 (2010).

The structure of mixed methanol/chloroform clusters from core-level photoelectron spectroscopy and modeling

Mixed neutral molecular clusters have been produced by co-expansion of chloroform and methanol and characterized by carbon 1s photoelectron spectroscopy and theoretical modeling. The produced clusters are in the range 50–150 molecules and the clusters are not homogeneously mixed: chloroform is enriched in the bulk and methanol is found on or close to the surface. This is based on evidence from photoelectron depth profiling and molecular dynamics simulations of mixed clusters. The simulations suggest that methanol forms cyclic or linear oligomers in the surface layers of the mixed clusters. From thermodynamic models, the enrichment of methanol on the cluster surface can be rationalized from the difference in surface tension between the two pure components, which is connected to the qualitative differences in the respective bonding patterns.

Quantitative Experimental Study on the Transition between Fast and Delayed Coalescence of Sessile Droplets with Different but Completely Miscible Liquids

Quantitative experimental data on the coalescence behavior of sessile droplets with different but completely miscible liquids are presented. The liquids consist of various aqueous mixtures of different nonvolatile diols and carbon acids with surface tensions ranging from 33 to 68 mN/m, contact angles between 9 degrees and 20 degrees, and viscosities from 1 to 12 cP. Two distinctly different coalescence behaviors, a delayed and a fast regime, are found. The transition between the two behaviors is remarkably sharp. It is found that the coalescence mode depends predominantly on the differences in the surface tensions of the two droplets. If the surface tension difference exceeds approximately 3 mN/m, the coalescence is delayed. If it is less, droplet fusion occurs fast. Within the investigated parameter space, the transition seems independent from droplet size, absolute values of the surface tensions, and viscosity. Certain aspects of the experimental findings are explained with the simple hydrodynamic model presented in a recent publication.

Dramatic squat and trim phenomena of mm-scaled SU-8 boats induced by Marangoni effect

Surface tension gradients may induce the motions of a floating solid fragment. This mechanism has been employed to drive miniaturized objects on a water surface, which could potentially serve as rotators, mixers, locomotives, and so on. To properly apply these objects, it is important to understand their motions. The previous consideration mainly focused on the horizontal motions of these small objects. In this work, we considered translational and rotational motions of a mm-scaled SU-8 boat in the vertical plane, which were so-called squat and trim phenomena, respectively, in the case of a macroboat. Through two types of tests, we demonstrated that dramatic squat and trim phenomena observed in the motions of the SU-8 boat were mainly induced by the surface tension difference between water and isopropyl alcohol (boat propellant), instead of horizontal movements of the miniaturized boat. This difference created a hollow spot behind the stern and made the boat sink and tilt along the sidewall of the hollow spot. In addition, we found that the motion of a SU-8 boat in a channel included two stages. In the first stage, it was propelled due to the difference between fore-and-aft surface tensions. In addition to moving forward, it also had dramatic squat and trim movements. However, in the second stage, in which no more isopropyl alcohol exited the boat, it was driven by a water wave generated in the first stage and did not show any visible squat and trim phenomena. The results of this work provided a better understanding of motions of the SU-8 boats. These results might also apply to surface tension-driven motions of other miniaturized objects.

The surface tension of TIP4P/2005 water model using the Ewald sums for the dispersion interactions

The liquid-vapor phase equilibria and surface tension of the TIP4P/2005 water model is obtained by using the Ewald summation method to determine the long range Lennard-Jones and electrostatic interactions. The method is implemented in a straightforward manner into standard simulation programs. The computational cost of using Ewald sums in dispersion interactions of water is estimated in direct simulation of interfaces. The results of this work at 300 K show a dramatic change in surface tension with an oscillatory behavior for surface areas smaller than 5x5sigma(2), where sigma is the Lennard-Jones oxygen diameter. The amplitude of such oscillations substantially decreases with temperature. Finite size effects are less important on coexisting densities. Phase equilibria and interfacial properties can be determined using a small number of water molecules; their fluctuations are around the same size of simulation error at all temperatures, even in systems where the interfaces are separated a few molecular diameters only. The difference in surface tension of this work compared to the results of other authors is not significant (on the contrary, there is a good agreement). What should be stressed is the different and more consistent approach to obtain the surface tension using the Ewald sums for dispersion interactions. There are two relevant aspects at the interface: An adsorption of water molecules is observed at small surface areas and its thickness systematically increases with system size.

Solutocapillary convection in germanium‐silicon melts

AbstractSurface tension gradients in free crystal growth melts give rise to convective flow. If these gradients are due to thermal gradients, the well known thermocapillary (Marangoni) convection ensues. Concentration gradients due to segregation at the interface during growth can lead to additional solutocapillary convection. A system with large solutocapillary convection is Ge‐Si due to the pronounced segregation and the strong difference in surface tension; solutal buoyancy convection is also present due to the large density difference between Ge and Si. Solutocapillary convection will oppose thermocapillary convection in the Ge‐Si system since Si, having the higher surface tension, is preferentially incorporated into the crystal. A set of experiments directly proving and partially quantifying the effect has been conducted under microgravity during a parabolic flight campaign by recrystallizing Ge‐Si mixtures of different compositions, between 3% and 9% Si, in a crucible with tracers to visualize the movement. Solutocapillary flow with initial flow rates in excess of 5.5 cm/s at the onset of crystallization was measured. A slight dependence of the flow velocity on the initial Si content has been found. Experiments on the ground showed the same effect but with overall smaller speeds; this difference can be explained by the additional action of solutal buoyancy convection. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface structure of the liquidAu72Ge28eutectic phase: X-ray reflectivity

The surface structure of the liquid phase of the Au{sub 72}Ge{sub 28} eutectic alloy has been measured using resonant and nonresonant x-ray reflectivity and grazing incidence x-ray diffraction. In spite of the significant differences in the surface tension of liquid Ge and Au the Gibbs adsorption enhancement of Ge concentration at the surface is minimal. This is in striking contrast to all the other binary alloys with large differences in the respective surface tensions measured up to date. In addition there is no evidence of the anomalous strong surface layering or in-plane crystalline order that has been reported for the otherwise quite similar liquid Au{sub 82}Si{sub 18} eutectic. Instead, the surface of eutectic Au{sub 72}Ge{sub 28} is liquidlike and the layering can be explained by the distorted crystal model with only slight modifications to the first layer.

Diffusion measurements using the shear cell technique: Investigation of the role of Marangoni convection by pre-flight experiments on the ground and during the Foton M2 mission

An experimental investigation on the disturbing influence of the solutal Marangoni convection during diffusion measurements is presented. We used the systems Sn–Bi, Pb–Ag and Sn–In with decreasing differences in surface tension. For all systems we measured surface tension and – under varying free surface conditions – diffusion coefficients. We succeeded in measuring diffusion coefficients on the ground under nearly non-free surface conditions. The results are compared with the results of the FOTON M2-satellite mission with similar μg-experiments. We show that temperatures from around 400 °C to about 800 °C and the degree of free surfaces influences strongly the measured value for the diffusion coefficient.

The influence of surface tension gradients on drop coalescence

We present the results of a combined experimental and numerical investigation of the coalescence of a drop with a liquid reservoir of a miscible but distinct fluid. Particular attention is given to elucidating the influence on the coalescence process of a surface tension difference between drop and reservoir. Drops are gently deposited on the surface of the reservoir, and so coalesce with negligible initial vertical velocity. Depending on the drop size and reservoir composition, partial or total coalescence may occur. Three distinct regimes, depending on the reservoir to drop surface tension ratio, Rσ, are identified and delineated through both experiments and numerics. If Rσ<0.42, droplets are ejected from the top of the drop, while satellite droplets are left in its wake. For 0.42≤Rσ<0.93, only total coalescence is observed. When Rσ≥0.93, partial coalescence is increasingly favored as the reservoir’s surface tension increases.

Polyamine-Guided Synthesis of Anisotropic, Multicompartment Microparticles

Colloidal particles that have nonuniform bulk or surface compositions are of emerging interest because of their potential applications involving advanced chemical storage and delivery and the self-assembly of novel functional materials. Experimental realization of anisotropic particles is much more difficult than that for particles with uniform bulk and surface composition, however. A new wet-chemical synthesis method to anisotropic microparticles is presented. This approach makes convenient use of the unusual observation of a salt-triggered separation of two water-solubilized polyamines into colloidal aggregates with nonuniform polymer composition. The anisotropic structure of these ionically cross-linked aggregates is explained by the difference in surface tensions of the contained single-polymer domains. Contacting the polymer aggregates with silicic acid or 13-nm silica nanoparticles leads to the charge-driven formation of solid or hollow microspheres, respectively. Depending on the poly(lysine)/poly(allylamine) ratio, the nonuniformity of the polymer aggregates translates to surface patches or internal compartments found in the resultant silica/polymer microparticles. Such hybrid materials with their unique structure could serve as a new basis for targeted chemical delivery and controlled release for potential applications in medicine, food, and cosmetics.

Surface tension of molten Ni-(Cr, Co, W) alloys and segregation of elements

Surface tension of molten Ni-(Cr, Co, W) alloys was measured at the temperature of 1 773–1 873 K in an Ar+3%H 2 atmosphere using an improved sessile drop method. The segregation of Cr, Co and W in alloy was calculated and analyzed using Butler's equation. The results show a good agreement between measured and calculated data. The surface tension of molten Ni-(Cr, Co, W) alloys decreases with increasing temperature. In Ni-(Cr, Co, W) alloys, the element with lower surface tension tends to segregate on the surface of molten alloy while that with higher surface tension tends to segregate inside of the molten alloy. The larger the differences in surface tension, atom radius and electron configuration between solvent and solute are, the more significant the segregation is. As a result, Ni segregates onto the surface and Co and W segregate inside the alloys.

Adsorption layer characteristics of Triton surfactants: 1. Surface tension and adsorption isotherms

The adsorption of the non-ionic surfactants Triton X-45, Triton X-100, Triton X-165, and Triton X-405 can be described by a reorientation model, assuming that molar area required by adsorbed molecules depends on the surface coverage. The surface tension isotherms we measured by drop and bubble profile tensiometry, where it was shown that at low surfactant bulk concentrations, significant differences in the measured equilibrium tensions are due to depletion effects from the volume of a single drop. This difference in equilibrium surface tensions, observed between data from drop and bubble experiments, is a good tool to determine the adsorbed amount from the total mass balance. An intersection point of all surface tension isotherms at about 1 μmol/l is explained by a respective displacement of the ethylene oxide chain from the interface by the hydrocarbon chain.

Deformation and rupture of a horizontal liquid layer by thermal and solutal Marangoni flows

The evolution of strong surface deformation of a thin viscous fluid layer on a horizontal solid wettable substrate was studied experimentally. Layer deformation is caused by the concentration gradient of surface tension generated by a drop of soluble surfactant placed on the free layer surface. The conditions leading to the layer rupture and drying of the bottom section under the spreading drop were studied. The dependence of the dry spot radius on time, horizontal dimension and thickness of the layer, volume of the introduced droplet and fluids properties, were obtained for various fluid pairs. It was found that the critical initial thickness of the layer, at which its deformation reaches the layer bottom, is practically insensitive to the quantity of the applied surfactant and is defined by the difference in surface tension between the drop and the layer. Comparison of the data with the results of the study of the thermocapillary rupture of a cylindrical layer heated at the center and cooled along the periphery showed good agreement between the dependences of the critical layer thickness on the thermal and the solutal surface tension difference.

Delayed Coalescence Behavior of Droplets with Completely Miscible Liquids

Because of capillary forces, sessile droplets usually fuse instantaneously after contact. We find however a delay of the droplet fusion by many seconds if the droplets consist of different but completely miscible liquids. After the initial contact, the main bodies of the droplets remain separated, connected only through a shallow conduit with a flow from the low to the high surface tension liquid. Sporadically, this connecting film can thicken with turbulent or pulsating flows. The droplets will finally fuse when the flow has sufficiently reduced the difference in composition and surface tension. We present calculations which explain this delayed droplet fusion with the compensation of the fusion-promoting capillary pressure by a droplet-separating dynamic pressure caused by the flow between the droplets. Droplets with high contact angles fuse instantaneously. In this case, no separation-stabilizing dynamic pressure can build up because the interdroplet flow becomes turbulent.

Self-motion of a phenanthroline disk on divalent metal ion aqueous solutions coupled with complex formation

The self-motion of a 1,10-phenanthroline disk on divalent metal ion aqueous solutions was investigated as a simple autonomous motor coupled with complex formation. The characteristic features of motion (continuous and oscillatory motion) and their concentration regions differed among metal ions, and the frequency of oscillatory motion depended on the temperature of the aqueous solution. The nature of the characteristic motion is discussed in relation to the stability constant of complex formation between phenanthroline and a metal ion, and the difference in surface tension between phenanthroline and its metal complex as the driving force.

Factors influencing the capillary separation of leukocytes from whole blood in a plastic-based microfluidic chip

Abstract This study describes some of the influencing factors, such as capillary action, static electricity and magnetic force, on the ability to separate living leukocytes from a single droplet of blood ( The chip was constructed from two substrate materials sandwiched together to form a micron-order gap (40 μm) with an upper hydrophilic (glass) surface and a lower hydrophobic (acrylic resin) surface. A blood sample flowed into the gap between the two substrates driven by the difference in surface tension between the two materials. Leukocytes adhered to the lower hydrophobic surface, whereas red corpuscles flowed toward the exit of the microfluidic device (this phenomenon is referred to as micro-flow). The separation rate of the red corpuscles was 91 ± 9% in a unit area of 0.1 mm2. Furthermore, we analyzed the change in the numbers of living leukocytes that could be collected after separation in the chip under different conditions. When SiO2 and iron composite particles, 10 μm in size, were added to the blood sample, leukocytes formed colonies containing two or three cells. The colonies could be moved freely on the x–y plane using a Nd magnet. When the upper board was charged by static electricity, the colonies adhered to the underneath of the upper board. Five or more colonies, as well as 10 or more individual leukocytes, were able to collect in a 0.1 mm2 area of the chip after micro-flow operation. Thus, the separation efficiency of a living cell colony containing Fe particles in a capillary chip is markedly influenced by magnetic and electrostatic forces.

Interfacial and stability study of microbubbles coated with a monostearin/monopalmitin-rich food emulsifier and PEG40 stearate

The stability and presence of micron-scale bubbles (microbubbles) is of considerable interest in environmental, biomedical, and food sciences. Here we show that microbubbles can be formed and stabilized in a solution of low cost food-grade emulsifier (a mixture of saturated long-chain monoglycerides, diglycerides and sodium stearoyl-2-lactylate) in combination with polyethylene glycol (PEG)-40 stearate. Langmuir trough methods and fluorescence microscopy were combined to investigate the surface tension, interfacial elastic modulus, phase behavior and microstructure of monolayer shells coating these microbubbles. Our results strongly suggest that although the PEG40S is necessary to form microbubbles this component, as well as sodium stearoyl-2-lactylate, are “squeezed out” in the form of collapse aggregates. This process leaves a microbubble shell, composed of a condensed-phase low surface tension mono- and diglycerides mixure with some of the PEG40S and SSL2 remaining trapped between the condensed-phase domains. We find that other commercially available emulsifiers, containing unsaturated or bulky components unable to form condensed phases, do not to form or stabilize a microbubble layer, although they may form a foam, a finding that we relate to differences in surface tension.

Quantitative differences in tissue surface tension influence zebrafish germ layer positioning.

This study provides direct functional evidence that differential adhesion, measurable as quantitative differences in tissue surface tension, influences spatial positioning between zebrafish germ layer tissues. We show that embryonic ectodermal and mesendodermal tissues generated by mRNA-overexpression behave on long-time scales like immiscible fluids. When mixed in hanging drop culture, their cells segregate into discrete phases with ectoderm adopting an internal position relative to the mesendoderm. The position adopted directly correlates with differences in tissue surface tension. We also show that germ layer tissues from untreated embryos, when extirpated and placed in culture, adopt a configuration similar to those of their mRNA-overexpressing counterparts. Down-regulating E-cadherin expression in the ectoderm leads to reduced surface tension and results in phase reversal with E-cadherin-depleted ectoderm cells now adopting an external position relative to the mesendoderm. These results show that in vitro cell sorting of zebrafish mesendoderm and ectoderm tissues is specified by tissue interfacial tensions. We perform a mathematical analysis indicating that tissue interfacial tension between actively motile cells contributes to the spatial organization and dynamics of these zebrafish germ layers in vivo.