Surface tension

About: Surface tension is a research topic. Over the lifetime, 25410 publications have been published within this topic receiving 695471 citations.

Molecular interactions of cationic and anionic surfactants in mixed monolayers and aggregates.

Abstract: The properties of anionic-rich and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry and surface tension measurements and by determining the surfactant NMR self-diffusion coefficients. The critical aggregate concentration (CAC), surface tension reduction effectiveness(γCAC), surface excess(Γmax), and mean molecular surface area (Amin) were determined from plots of the surface tension (γ) as a function of the total surfactant concentration. The compositions of the adsorbed films (Z) and aggregates (χ) were estimated by using regular solution theory, and then the interaction parameters in the aggregates (β) and the adsorbed film phases (βσ) were calculated. The results showed that the synergism between the surfactants enhances the formation of mixed aggregates and reduces the surface tension. Further, the nature and strength of the interaction between the surfactants in the mixtures were obtained by calculating the values of...

Influence of hatch spacing on heat and mass transfer, thermodynamics and laser processability during additive manufacturing of Inconel 718 alloy

Abstract: A transient three-dimensional powder-scale model has been established for investigating the thermodynamics, heat and mass transfer and surface quality within the molten pool during selective laser melting (SLM) Inconel 718 alloy by finite volume method (FVM), considering the powder-solid transition, variation of thermo-physical properties, and surface tension. The influences of hatch spacing (H) on the thermodynamics, heat and mass transfer, and resultant surface quality of molten pool have been discussed in detail. The results revealed that the H had a significant influence on determining the terminally solidified surface quality of the SLM-processed components. As a relatively lower H of 40 μm was used, a considerable amount of molten liquid migrated towards the previous as-fabricated tracks with a higher velocity, resulting in a stacking of molten liquid and the attendant formation of a poor surface quality with a large average surface roughness of 12.72 μm. As an appropriate H of 60 μm was settled, a reasonable temperature gradient and the resultant surface tension tended to spread the molten liquid with a steady velocity, favoring the formation of a flat surface of the component and an attendant low average surface roughness of 2.23 μm. Both the surface morphologies and average surface roughness were experimentally obtained, which were in a full accordance with the results calculated by simulation.

Fluid-elastic instabilities of liquid-lined flexible tubes

Abstract: The dynamics of a thin film of Newtonian fluid coating the inner surface of an elastic circular tube is analysed. This problem is motivated by an interest in the closure of small airways of the lungs either by formation of a liquid bridge, the collapse of the airway wall or a combination of both processes. Liquid bridge formation is due to the destabilization of the liquid film that coats the inner surface of airways, while wall collapse can be due to either the high surface tension of the air–liquid interface or the flexibility of the wall.Nonlinear evolution equations for the film thickness and wall position are derived using lubrication theory, but an accurate representation of the curvatures of both the liquid and wall interfaces is employed which is valid for thick films. These approximations allow closure to be predicted. In addition, these approximations are justified by comparison with rigid-wall results obtained by solving the full Navier–Stokes equations and because fluid inertia only becomes important in the very late stages of closure. The linear stability of these equations is examined using normal-mode analysis for infinitesimal disturbances and the nonlinear stability is investigated by solving the governing equations numerically using the method of lines. Solutions show that there is a critical film thickness, strongly dependent on fluid and wall properties, above which unstable waves grow to form liquid bridges. The critical film thickness decreases with increasing surface tension or wall compliance since waves grow faster. Even for relatively stiff airways, the volume of fluid in the liquid lining required for closure can be approximately 70% of the volume for the rigid-tube case. Wall damping is an important effect only when the airway is sufficiently compliant. Airway closure occurs more rapidly with increasing unperturbed film thickness, surface tension and wall flexibility and decreasing wall damping.