Size and temperature effects on wetting in supercooled vacuum condensates

Abstract

The measured data of studying the temperature dependence of wetting angles of amorphous carbon films by island tin and indium Ž . condensates are presented in the broad temperature range 350-850 K encompassing the range of the supercooled state of metals together with the size dependence of wetting in the SnrC at 400 K. Considerable decrease of the wetting angle is observed with the liquid metal supercooling increasing, the fact being probably associated with the decrease of the interphase energy of the drop-substrate Ž . boundary. The size effect is observed for the supercooled tin microdrops DT s 105 K with the radii R -30 nm manifesting itself in the improvement of wetting with the decrease of the microdrop size. q 1998 Elsevier Science S.A. All rights reserved.

Surface Energy and Wetting in Island Films

“…Observed changes of the contact angle in the supercooled region, as noted in [42,43,72], is probably stipulated by abnormal behavior of either liquid metal surface energy or interface energy of the metal-carbon boundary. If σ ul is assumed to be constant or growing with decrease of temperature, then according to Young's equation experimental data for θ(T) is an evidence of sharp increase in liquid metal surface energy.…”

“…As long as condensation takes place on a substrate with temperature gradient, the relation θ(T) can be measured in single experiment on a wide range of temperatures with arbitrarily small temperature step. mm Hg at temperatures 400 K (a), 570 K (b), and 730 K (c) [72] The results of measurement of wetting angles in the Sn/C and In/C systems [72] are presented in Figure 14a, b. The obtained dependencies are characterized by the maximum at temperatures 550 and 500 K for tin and indium, respectively.…”

“…Contact pairs being island films of tin, indium, bismuth, and copper on amorphous carbon substrates and indium on aluminum substrate were investigated in [42,43,72]. The test samples were prepared by condensation in a vacuum of 5⋅10 -6 -2⋅10 -8 mm Hg on the circular substrate with temperature gradient (200-900 K) set along it.…”

“…The relations σ ul (T), calculated using linear extrapolation of the data for surface energy temperature dependence of liquid tin and indium [68] to the supercooling region, are presented in Figure 15. Among the reasons causing such a significant decrease in interfacial energy works [42,43,72] cite adsorption of gaseous impurities, which value increases with decrease of temperature or inversion of the surface energy of metal in supercooled state. However, considering the fact that for a number of analyzed metals (In, Sn, Bi) inversion of wetting temperature dependence occurs within approximately the same temperature range, while in the Cu/C system at high temperature it was not found at all, one should probably consider the adsorption of impurities from residual gases that grows at such temperatures crucial and causing decrease of interfacial energy on the carbon substrate boundary with increased supercooling, and hence, better wetting observed experimentally.…”

“…The samples were prepared using the technique described earlier [72] at the pressure of residual gases of 10 mm Hg. A mass spectrometer was employed to control residual atmosphere, and its content was changed by leaking gas into the unit pumped to a pressure of 10 -9 mm Hg.…”