Influence of non-ionic and ionic surfactants on kinetics of the bubble attachment to hydrophilic and hydrophobic solids

• At hydrophobic solid the TPC is formed independently on the solution composition.
• Time of the TPC formation is prolonged at higher surfactants concentrations.
• The TPC formation at hydrophobic solid surface is air-induced.
• At hydrophilic solid the TPC formation depends on the surfactant polar group type.
• For hydrophilic solid surface the TPC formation is electrostatically driven.

The paper is devoted to kinetics and mechanism of the three-phase contact (TPC) formation by the colliding bubble at model hydrophobic (polytetrafluoroethylene – Teflon) and hydrophilic (muscovite mica) solid surfaces. To determine influence of type of the surfactant polar group the experiments were carried out in solutions of non-ionic (n-hexanol and n-octanol), cationic (n-octyl-(OTABr), n-dodecyl-(DDTABr) and n-hexadecyl-trimethylammonium (CTABr) bromides, and anionic (sodium hexadecyl sulfate (SHS)) surface active substances (SAS). The time of the TPC formation (tTPC) and timescale of rupture of the thin liquid film separating the colliding bubble and a solid surface was determined using high-speed video registrations. The tTPC was defined as the time span from the moment of the bubble first collision up to the liquid film rupture and formation of the TPC (dewetted) hole. It was shown that the influence of SAS on the kinetics of the TPC formation could be completely different depending on the hydrophilic/hydrophobic properties of the solid surface. At the Teflon surface the TPC was formed always, both in distilled water and in SAS solutions of various composition and concentration. Moreover, the tTPC was significantly prolonged at higher SAS concentrations, independently on the SAS type (ionic, non-ionic). At the mica surface the wetting film was stable and the TPC was never registered in distilled water as well as in solutions of non-ionic and anionic surfactants. However, the TPC was formed at the mica surface in solutions of cationic surfactants, but the tTPC values were decreasing with increasing cationic surfactants concentration. Mechanism of the TPC formation is presented and reasons of the completely different influence of SAS on kinetics of the TPC formation at the hydrophilic and hydrophobic solid surfaces are explained.

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