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2 Physicochemical Problems of Mineral Processing

2 2018

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Three-phase contact line expansion during air bubble attachment to hydrophobic solid surface – experiment and modeling

Basarova P., Soušková K., Zawala J.

Physicochemical Problems of Mineral Processing

2018

Vol. 54, iss. 4

1095--1106

Kinetics of spreading of the three-phase contact hole (dewetting) formed by an air bubble colliding with hydrophobic solid surface, after rupture of intervening liquid film, was studied both experimentally and numerically. During experiments it was found that evolution of the TPC line diameter with time occurs with characteristic S-shaped trend which, in consequence, causing rather unexpected maxima at the TPC line spreading velocity curves. It was determined that position of this maximum appears after 1-2 ms after TPC hole formation and its position (in respect to time) depends on the bubble diameter. In solution of surface-active substance this maximum was much smoother and longer. By means of complementary numerical calculations the source of maxima existence and differences in their position and shapes were explained. It was concluded that this effect has only hydrodynamic origin, caused by different course of bubble shape pulsations during TPC line formation and spreading, which depends on degree of liquid/gas interface immobilization (fluidity retardation).

Influence of dynamic adsorption layer formation on bubble attachment to quartz and mica surfaces in solutions of pure and mixed surface-active substances

Wiertel-Pochopień A., Zawala J.

Physicochemical Problems of Mineral Processing

2018

Vol. 54, iss. 4

1083--1094

The paper presents systematic studies on influence of state of dynamic adsorption layer (DAL) induced at the rising bubble interface on time-scale of the bubble attachment to quartz and mica surfaces immersed in pure n-cetyl-trimethylammonium bromide (CTAB) and mixed octanol/CTAB solutions of different concentrations. It was found that in the case of pure CTAB solutions, the influence of DAL on time of bubble attachment and the three-phase contact (TPC) formation (tTPC) strongly depends on solution concentration. Generally, two solution concentration regimes were distinguished – low and high - for which different degree of solid surfaces hydrophobization was observed. It was determined that for low concentration regime the solid surface is only slightly hydrophobized while for high regime, hydrophobicity of the solid surface is much higher. Consequently, wetting film rupture for low concentration regime is governed by electrostatic interactions while for high concentration regime significance of these interactions is much smaller. As a result, the DAL influenced the film rupture in these two regimes in a quite different manner. For mixed n-octanol/CTAB solutions it was found that CTAB molecules presence is necessary condition for wetting film destabilization. Moreover, thanks to the developed approach, allowing control of initial adsorption coverage over the bubble surface (independently on concentration), it was proved that constant adsorption degree of CTAB molecules at the bubble surface in the mixture, leads to identical times of the TPC formation.