Oscillatory wetting instability induced by liquid–liquid decomposition in a Ga–Pb alloy

Abstract

We present the first experimental investigation and pertinent theoretical modeling of an interfacial oscillatory instability in a binary fluid alloy, the Ga-Pb system. It is characterized by spinodal decomposition at elevated temperatures and by a complete wetting transition at liquid-liquid coexistence. For the alloy Ga(0.95)Pb(0.05) the fluid interface has been probed by second harmonic generation (SHG) under UHV conditions at temperatures between 740 and 550 K. At conditions inside the miscibility gap clear oscillations of the SHG-intensity with a period of approximately 30 min are found for different cooling cycles and also at constant temperatures. These interfacial oscillatory instabilities simultaneously induce temperature oscillations in the bulk fluid with the same period. This phenomenon can be explained by a periodic variation of the fluid interfacial emissivity. A model has been developed which describes the wetting-dewetting dynamics by hydrodynamic equations within the Reynolds approximation. It is found that the interfacial oscillatory instability is determined by capillary-gravitation instability. The model quantitatively describes the time evolution of the interfacial and temperature oscillations and gives the correct value of the oscillation period. A detailed comparison of the experimental and model results is given.

Surface freezing and wetting in Ga–Pb alloy: Second harmonic and plasma generation study

“…This is described in more detail in a forthcoming paper. 29 As is generally known, the thermal emissivity data are very difficult to get. However, existing literature data indicate a difference of the integral thermal emissivity coefficients of $0.04 between liquid Pb 27 and Ga 28 which can explain the kinks in the cooling curves.…”

Asymmetric oscillations during phase separation under continuous cooling: A simple model

“…In the latter case, qualitatively new features can arise, like oscillations of the turbidity and apparent heat capacity. [3][4][5][6][7][8] Oscillatory phase separation in volume-dominated systems has been observed in several systems as different as microemulsions, 3 polymer solutions 4 and even mixtures of olive oil and methanol. 5 It is a universal phenomenon that can be found, both in low molecular weight and polymer mixtures.…”

Oscillatory instabilities in phase separation of binary mixtures: Fixing the thermodynamic driving

“…25,28,30,32 We studied two different binary mixtures that phase separate as a function of temperature. Since the time scale of the temperature ramp is in the same range as time scales involved in the various mechanisms of phase separation, a complex interplay between them is observed.…”

“…They separate into two liquid phases. 19,20,[24][25][26][27][28][29][30][31][32] Irrespective of the ramp rate only a small number of oscillations is observed when linearly cooling a sample. Phase separation leads to a polymer-poor liquid phase and a polymerrich gel phase.…”