Showing papers on "Sessile drop technique published in 1975"

Wettability of hydrogels. I. Poly (2-hydroxyethyl methacrylate).

Abstract: The wettability characteristics of the contact lens material, PHEMA, with respect to water have been determined by using the sessile drop, and the captive air bubble techniques of contact angle goniometry. It is concluded that on PHEMA gels water does not spread spontaneously. Large hysteresis has been observed in the advancing and receding contact angles. This suggests that this hydrogel surface is capable of changing its free energy through reorientation of the polymer side chains and chain segments depending on the nature of the adjacent phase. The water content of the gels does not appear to have an effect on water wettability in the hydration range investigated. The minor wettability differences among the various gels studied were most likely due to differences in surface structure and segmental mobility due to inherent variations in the method of preparation. Small but consistent differences were found between the contact angles measured by the captive bubble method and those obtained by the sessile drop method, the former values being higher. These differences may not be method-related artifacts and cannot be explained at the present time.

High-confidence measurement of solid/liquid surface energy in a pure material

Abstract: A new method for measuring solid/liquid surface energies, with a total systematic and random error of well under 10%, is described. The surface energies are derived from measurements of grain-boundary grooves in solid/liquid interfaces which are maintained in shallow temperature gradients. The gradients are established by an axial heater wire in a cylindrical specimen chamber. Applying the method to highly-purified succinonitrile, a solid/liquid surface energy of 8·94±0·5 erg/cm2 was determined. This corresponds to 37% of the heat of fusion per surface molecule.

Wetting of SiC, Si3N4, and Carbon by Si and Binary Si Alloys

Abstract: The wetting of several new materials for gas turbine engines, e.g. SiC, Si3N4, and C, by liquid Si and binary Si alloys containing Cu, Fe, and B was determined by the sessile drop method. All contact angles measured were < 90°. Hot-pressed SiC, Si3N4, and Refel SiC are easily wet by Si; wetting is controlled by the balance of interfacial energies. Carbon is wet well by Si, but wetting is controlled by reaction and, in some carbons, by infiltration of Si into C. Additives to Si such as B and Fe can form compounds in reaction zones during wetting at interfacial areas.

The wetting and bonding of diamonds by copper-base binary alloys

Abstract: The wetting and bonding behaviour between diamond plaques and copper alloyed with chromium, titanium or vanadium has been studied using the sessile drop technique. Wetting was induced at 1150° C by additions of more than 0.1 at. % of titanium, but additions of vanadium up to and beyond the solubility limit did not cause wetting to occur. The room temperature strengths of the interfaces between the diamond plaques and the solidified sessile drops increased with increasing alloying element concentration, reached a maximum value at a concentration less than that needed to induce wetting, and thereafter decreased. The maximum strengths achieved by alloying with chromium, titanium or vanadium were 35.5, 42.0 and 69.8 kg mm−2 respectively. The reactivity of the alloyed sessile drops was assessed using metallography, EPMA and a surface contour device. A tentative picture of the effects of diamond-metal interactions on wetting and bonding behaviour was developed.

Apparatus for measuring the contact angles at crystal-solution-vapor interfaces

Abstract: This paper describes an apparatus for measuring the contact angle between an air bubble and the underside of a solid surface to which the bubble adheres. This general method of measurement of contact angles replaces the usual sessile drop method. The purpose of submerging a bubble in the liquid is to assure an equilibrium vapor pressure, so that, in case of solutions, the surface concentration does not change during measurement. The apparatus was especially designed to study the interfacial energies between saturated solutions and the various faces of a chosen crystal.