Surface tension

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

Drying of Granular Ceramic Films: I, Effect of Processing Variables on Cracking Behavior

Abstract: Drying of binder-free granular ceramic films was studied to identify processing variables which affect their cracking behavior. Films were prepared from electrostatically stabilized suspensions of α-alumina in water. A critical cracking thickness (CCT) was determined, above which films would spontaneously crack during drying. The effects of particle size, liquid surface tension, drying rate, dispersion stability, and sedimentation time were evaluated by a statistical design methodology. The CCT for films prepared on glass substrates was used as a measure of the effect of each variable on cracking. The statistically significant variables were particle size, dispersion stability, and sedimentation time. The effect of substrate constraint was also studied by producing films on a Teflon substrate and a pool of liquid Hg. The observations were consistent with a capillary formed tensile stress acting on the entire film rather than differential stress generated by a moisture gradient over the film thickness.

Surface tension effects of humic-like substances in the aqueous extract of tropospheric fine aerosol

Abstract: Organic aerosol constituents can influence the surface tension of nucleating cloud droplets and thereby modify the critical supersaturation necessary to activate aerosol particles. Model calculations, based on experiments carried out with different surrogates, led to contradictory conclusions on the effect of organic components on activation, indicating that the results depend very much on the surrogate selected. In order to reduce this uncertainty surface tension measurements were performed on real atmospheric aerosol components. Humic-like substances (HULIS) that accounted for 60% of the water-soluble organic carbon present in rural aerosol were isolated from 32 samples covering different seasons. The isolated organic matter present in a concentration of about 1 g L−1, decreased the surface tension of the aqueous solutions by 25–42% as compared to pure water. This effect was further enhanced when humic-like substances were mixed with ammonium sulphate. In order to support model calculations Szyskowski functions were fitted to the data to formulate the surface tension effect as a function of concentration. Finally, natural humic substances (fulvic and humic acids) were investigated under the same conditions. The experiments revealed that the surface tension decreasing effect of atmospheric humic-like substances differed from that of the studied terrestrial and aquatic humic substances: the latter substances decreased the surface tension of the aqueous solution to a lesser extent (7–23%) than atmospheric HULIS. This deviation can be explained with the different composition (e.g. the ratio of aromatic to aliphatic moieties) of the substances investigated.

Indices for Characterizing Soil-Water Repellency Based upon Contact Angle-Surface Tension Relationships

Abstract: The relation between apparent liquid-solid contact angle and surface tension was established for 3 water- repellent materials using both a series of aqueous ethanol solutions and organic liquids. The media included 2 artifically treated sands and one naturally occurring soil. With one exception, there was an approximate linear relationship between the cosine of the contact angle and the surface tension. The relationship for the forest soil tended to be curvilinear when using ethanol solutions of high surface tension. The repellency of the materials was best differentiated by using their intercepts with cos phi = O. A simple drop test using the same materials and ethanol solutions placed the materials in the same order of repellency. The drop test was further developed to allow classification of porous media on the basis of (1) 90$ surface tension (gamma n), and (2) stability to water interaction. The tests can be readily performed both in the laboratory and the field. Two indices were then proposed to describe water-repellent characteristics of soils. These indices will be valuable in assessing erosion and runoff problems, and also the feasibility of surfactants to promote infiltration. (14 refs.)

Elucidating the mechanism of selective ion adsorption to the liquid water surface

Abstract: Adsorption of aqueous thiocyanate ions from bulk solution to the liquid/vapor interface was measured as a function of temperature by resonant UV second harmonic generation spectroscopy. The resulting adsorption enthalpy and entropy changes of this prototypical chaotrope were both determined to be negative. This surprising result is supported by molecular simulations, which clarify the microscopic origins of observed thermodynamic changes. Calculations reveal energetic influences of adsorbed ions on their surroundings to be remarkably local. Negative adsorption enthalpies thus reflect a simple repartitioning of solvent density among surface, bulk, and coordination regions. A different, and much less spatially local, mechanism underlies the concomitant loss of entropy. Simulations indicate that ions at the interface can significantly bias surface height fluctuations even several molecular diameters away, imposing restrictions consistent with the scale of measured and computed adsorption entropies. Based on these results, we expect an ion’s position in the Hofmeister lyotropic series to be determined by a combination of driving forces associated with the pinning of capillary waves and with a competition between ion hydration energy and the neat liquid’s surface tension.