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Adsorption kinetics of heptadecafluoro-1-nonanol: Phase transition and mixed control.

Research paper by Alvin A Casandra, Boris A BA Noskov, Min-Yu MY Hu, Shi-Yow SY Lin

Indexed on: 20 May '18Published on: 20 May '18Published in: Journal of Colloid and Interface Science



Abstract

The adsorption kinetics of heptadecafluoro-1-nonanol (CHFOH) onto a clean air-water interface at low surfactant concentrations (equilibrium surface tension, γ(C) > 65 mN/m) has been reported, and the controlling mechanism was found to be mixed diffusive-kinetic controlled (Kuo et al., JCIS 402 (2013) 131). However, it remains to be determined what the adsorption kinetics are at higher concentrations. Hence, the dynamic surface tension, γ(t) of CHFOH was measured and compared with the theoretical γ(t) curves predicted from phase transition model. A video-enhanced pendant bubble tensiometer was used to measure the γ(t) data of aqueous CHFOH solutions at higher concentrations (C > 7.7 × 10 mol/cm). A new generalized Frumkin-Langmuir phase transition model was built up to simulate the γ(C) and γ(t) data. At higher surfactant concentrations, a constant-γ region at 64.8 mN/m was observed for one hundred to a few thousand seconds during the γ(t) relaxation. This constant-γ region implies the existence of a phase transition of the adsorbed surfactant monolayer at air-water interface. The γ(t) data of CHFOH can be simulated perfectly using this mixed-controlled phase transition model with the adsorption rate constants β = 1.0 ± 0.5 and β = 13 ± 4 (10 cm/mol·s). It is therefore concluded that the adsorption process of CHFOH onto a clean air-water interface is of mixed-control. Copyright © 2018 Elsevier Inc. All rights reserved.