Dynamic adsorption layer formation and time of bubble attachment to a mica surface in solutions of cationic surfactants (CnTABr)

The paper presents the influence of the dynamic adsorption layer (DAL) formation on time of the bubble attachment to mica surface in n-dodecyltrimethylammonium bromide (DDTABr) and n-hexadecyltrimethylammonium bromide (CTABr) solutions. Phenomena occurring during collisions of the single rising bubbles with mica plates, located at different distances (“close” and “far”) from the point of the bubble detachment, were monitored using high-speed camera. It was found that when the distance from the capillary to the mica plate was L = 3 mm (location “close”) then the time of the three-phase contact formation (tTPC), was significantly shorter than for the location “far” (L = 100 mm). The differences between the tTPC for the locations “close” and “far” were the largest at lowest concentration. For example in 1 × 10−6 M CTABr solution the tTPC was 162 ± 97 ms for L = 3 mm and was prolonged to 578 ± 121 ms for L = 100 mm. Similarly, in 1 × 10−6 M DDTABr solution the tTPC was 543 ± 79 and 1840 ± 440 ms for L = 3 and 100 mm, respectively. Longer the tTPC values at the mica location “far” were attributed to the formation of the dynamic adsorption layer (DAL), with the top pole of the rising bubble almost devoid of the adsorbed cationic surfactants. The bubble attachment to mica was due to the electric charge reversal by the cationic surfactant molecules adsorbed at the bubble surface, which led to the wetting film rupture due to electrostatic attractive interactions between oppositely charged interacting interfaces. Therefore, at the location “far” the time of the TPC formation (tTPC“far”) was longer because there was needed an additional time to restore such degree of cationic surfactant coverage at the bubble top pole, which caused the electric charge reversal from negative to positive. It was showed that the adsorption coverages needed for the electric charge reversal at the liquid gas interface can be restored during the ΔtTPC = tTPC“far” − tTPC“close” time intervals.