Surface tension and adsorption kinetics of amphiphiles in aqueous solutions: the role of carbon chain length and temperature.

The effects of carbon chain length and temperature were investigated on adsorption kinetics and surface tension of a group of slightly volatile, short carbon chain molecules: 1-octanol, 1-hexanol, and 1-butanol. Experiments were performed in a closed chamber where simultaneous adsorption from both sides of the vapor/liquid interface was considered. The dynamic (time dependent) and steady-state surface tensions were found to decrease with temperature ranging from 10 °C to 35 °C. It was shown that, at the final steady-state, the effect of adsorption from the vapor phase was much more important than that from the liquid phase especially for short carbon chain molecules (e.g., 1-butanol). The modified Langmuir equation of state and modified kinetic transfer equation, which account for adsorption from both sides of a vapor/liquid interface, were used to model the experimental data of the steady-state and dynamic surface tension, respectively. Modeling results showed that the equilibrium constants and adsorption rate constants were increased with temperature and carbon chain length. The maximum surface concentration showed a decrease with temperature and an increase with carbon chain length. Some variations in the fitting parameters were observed in the dynamic modeling. These variations may be due to the experimental errors or the limitations of the proposed model.