Adsorption of Gemini surfactants onto clathrate hydrates

•Understand the adsorption behavior of anionic Gemini surfactants onto clathrate hydrates.•Multi-layer adsorption isotherms for two Gemini surfactants, Dowfax 2AI and Dowfax C6L.•Observe a clear second layer of Dowfax 2AI having an aggregation number of 3.•Elucidate one head group of the Gemini surfactants adsorbed at the hydrate–water interface.

This work addresses the adsorption of two Gemini surfactants at the cyclopentane (CP) hydrate–water interface. The Gemini surfactants investigated here are Dowfax C6L and Dowfax 2A1 that have two anionic head groups and one hydrophobic tail group. The adsorption of these surfactants was quantified using adsorption isotherms and the adsorption isotherms were determined using liquid–liquid titrations. Even if the Gemini surfactant adsorption isotherms show multi-layer adsorption, they possess the first Langmuir layer with the second adsorption layer only evident in the 2A1 adsorption isotherm. Zeta potentials of CP hydrate particles in the surfactant solution of various concentrations of Dowfax C6L and Dowfax 2A1 were measured to further explain their adsorption behavior at the CP hydrate–water interface. Zeta potentials of alumina particles as a model particle system in different concentrations of sodium dodecyl sulfate (SDS), Dowfax C6L and Dowfax 2A1 were also measured to confirm the configuration of all the surfactants at the interface. The determination of the isotherms and zeta-potentials provides an understanding framework for the adsorption behavior of the two Gemini surfactants at the hydrate–water interface.

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