Papers by Keyword: Surface Tension

Abstract: This paper focuses on the mathematical modelling and the numerical approximation of the flow of two immiscible incompressible fluids,which is influenced by the surface tension and the contact angle effects. The weak formulation is introduced, discretized in time, and the finite element method is applied. The surface tension effects are taken into account using the variational reformulation. The stability of the discrete problem is increased using the implicit formulation of the surface tension. The free surface motion is treated with the aid of the level set method. The numerical results are shown.

Abstract: The objective of the present work was to assess the surface properties of silica-cell complexes formed by Bacillus pumilus strain SKC-2 for bioflotation purposes. This bacterial strain was employed in this study because it is a Gram-positive, mixotrophic bacterium whose metal binding capacity extends to many different metals and circumstances as well as a biosurfactant producer. The strain was found to promote the formation of silica-cell complexes due to the generation of surface-active agents (i.e., extracellular polymeric substrances (EPS)) as represented by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS) observation. Surface properties of the complexes was assessed by water contact angle and surface tension measurements, demonstrating that bacterial cells reduced the surface tension of the solutions and increased the contact angle of the silica surfaces, representing a larger hydrophobic property. Therefore, the findings of this study provide clear evidence for the potential application of the bacterium Bacillus pumilus strain SKC-2 for silicate bioflotation processes (i.e., as frother and collector).

Abstract: A novel class of cationic gemini fluorosurfactants with different spacer and same hydrophobic chain were synthesized. They were structurally characterized by NMR (1H and 19F), FT-IR, ESI-MS and elemental analysis. The equilibrium surface tensions were studied. The results showed that the gemini fluorosurfactants with the shorter spacer displayed higher surface activity, lower surface tension (21.48 mN/m) can be reached. Besides, the synergistic properties of these synthesized gemini fluorosurfactants with sodium dodecyl benzene sulfonate (SDBS) were investigated.

Abstract: This paper describes the analysis on the characteristics of semi-permeable membrane sound absorber. The effects of membrane surface tension on the sound absorption characteristics were investigated. The characteristics of the membrane absorber was measured experimentally in terms of Sound Absorption Coefficient, α and Noise Reduction Coefficient, NRC. The membrane is made of thin, flexible, semi-permeable latex material and the tests were carried out by using impedance tube method according to ISO 10534-2 standard. The results showed that the surface tension has significant influence on the sound absorption characteristics. For the parameters used in the laboratory work, specimen with unstretched surface tension has the best absorption performance.

Abstract: The wave characteristics of horizontal annular two-phase flow in 16 mm diameter pipe were experimentally investigated using flush-mounted constant electric current method (CECM) sensors and visual observations. To examine the effect of surface tension on the wave velocity and frequency, air and three kinds of liquids with different surface tension were used, i.e., water, 2%-butanol solution, and 5%-butanol solution. The gas and liquid superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The liquid holdup was measured directly using CECM, while the wave velocity and frequency were determined using cross correlation and power spectral density functions of liquid holdup signals. Generally, combination of air and liquid with the highest surface tension gives the highest liquid holdup and wave frequency. Simple correlations for wave velocity and wave frequency were also developed.

Abstract: The wettability of the carbon composite electrode on paper substrate was studied using contact angle measurement. Y-Shield HSF54 carbon composite material were coated on paper substrates with a mask using squeegee coating technique. Contact angles of the ten polar probe liquids with the HSF54 electrodes were measured using a customed-built image acquisition system. With the contact angles obtained for each probe liquid placed on the electrodes, the surface tension of the electrodes was determined using Fox-Zisman theory. The result showed that the critical surface tension of HSF54 carbon composite electrodes was 37.2 mN/m which is considered to be moderately hydrophobic.

Abstract: The surfactivity of nonionic fluorocarbon surfactants, polyethylene glycol perfluoro-nonyl monoether (C₉F₁₇-PEG-n) and diether (C₉F₁₇-PEG-n-C₉F₁₇), was systematically investigated, including the surface tensions (γ), critical micelle concentration (CMC), cloud point, foaming property and emulsifiability. The relation between their surface performance and their chemical structure of C₉F₁₇-PEG-n and C₉F₁₇-PEG-n-C₉F₁₇ were studied. The result showed that this series of fluorocarbon surfactant possessed high surface activity, the CMC < 2.8 × 10^-4 mol/L and the γ_CMC < 25 mN/m. Compared to C₉F₁₇–PEG-n, C₉F₁₇-PEG-n-C₉F₁₇ have smaller minimum molecular area (A_min), greater saturated adsorption quantity (Γ_m), lower cloud point, poorer emulsifiability in toluene and greater foaming volume for their aqueous solutions. For either C₉F₁₇-PEG-n or C₉F₁₇-PEG-n-C₉F₁₇, with the increase of the PEG molecular weight (PEG-n), Γ_m declines, A_min increases and the emulsifiability in toluene becomes better, the CMC, γ_CMC and cloud point of their aqueous solutions increases, and their foaming volumes increase first and then decline, getting the maximum value at n=1000.

Abstract: The surface tension of the liquid ternary Cu-Pb-Fe alloys at the constant content of copper (X_Cu=0.9)-refractory material Al₂O₃-gaseous phase was determined. The experiments were performed in the range of temperature between 1100 and 1350 °C at the different content of lead and iron (X_Fe/X_Pb+X_Fe). The surface tension was determined by sessile drop method. The composition of the investigated alloys corresponds to the composition of the Cu-Pb-Fe alloys obtained via the reduction of the slag obtained during the direct-to-blister flash smelting process in an electric furnace. Images of the liquid drops were made using the X-ray technique and the surface tension values were calculated using the corresponding software programs.

Abstract: The gold-catalyzed vapor-liquid-solid (VLS) method is widely used for silicon nanowire (Si NW) fabrication. As the VLS process is influenced by the physical properties of the catalytic silicon-gold (Si-Au) droplet, quantifying the surface tension of the liquid alloy is important to achieve better control of the wire growth. Because the experimental measurement of the surface tension is difficult, it is necessary to obtain reasonable estimates from computational models. In this work, we conducted molecular dynamics simulations with a modified embedded-atom potential developed for the Si-Au binary system, and evaluated the surface tension γ based on the Virial stress expression. The dependence of surface tension γ on the Si fraction χ and temperature T is predicted. The entropy of the liquid-vapor interface was extracted from the slope of the γ-T curve. The Si concentration and stress distributions near the surface are also predicted. Our surface tension evaluation enables theoretical predictions of droplet and nanowire shape, and provides physical inputs for continuum phase field models of VLS growth.

Abstract: The present paper describes the results of the physicochemical and rheological characterisation of the selected self-made solutions of synthetic saliva. The substitutes of the used saliva were prepared on the basis of gums (xanthan, guar, arabic and carob bean) dissolved in saline buffer. Additionally, one of preparations were composed of xanthan gum and sodium dodecyl sulphate (SDS). The analysis of the viscosity, pH, surface tension and conductivity of the tested solutions was performed. The tests were carried out following one, three and seven days. The obtained results of the conducted studies showed differences between the tested preparations in the scope of the above evaluated quantities. The preparations based on the tested gums have similar properties in terms of pH, surface tension and conductivity. Only the substitute with the addition of xanthan gum and SDS exhibited different characteristics: the highest value of pH and the lowest values of conductivity and surface tension. In the case of viscosity, some preparations exhibited Newtonian rheological characteristics while others exhibited non-Newtonian characteristics.