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【摘要】

Langmuir monolayers of fatty amine (docosan-1-amine) on different pH solutions and electrolytes were investigated by sum-frequency vibrational spectroscopy. The surface charge density deduced from the sum frequency signal in OH region disagreed with those obtained from the classical Gouy-Chapman model incorporating the chemical equilibrium. A stern layer formation in between the monolayer and the diffuse layer (Guoy-Chapman-Stern model) was suggested to explain the discrepancy. Both neutral and charged amine groups had specific interaction with the anion (HCO3- and Cl-) in the solution. The specific interaction of the neutral amine (in comparison to the fatty aniline and the alcohol headgroup) and the anion was further investigated at high pH. The modified Poisson-Boltzmann equation incorporating Levin’s theory [1] was used to account for the specific interaction. The hydrogen bonding energy terms in Levin’s theory, between the OH- and the headgroup of the surfactants ranked as: amine > aniline > alcohol.

[1] Levin, Y. Polarizable Ions at Interfaces. Phys. Rev. Lett. 2009, 102 (14), 147803