Dynamical shapes of droplets of cyclodextrin-surfactant solutions

Abstract

We present a series of experiments with droplets of aqueous cyclodextrin-surfactant solutions, in which the volume is reduced after the equilibrium spherical shape is reached. The final shape of the drop after this perturbation is found to be dependent on the concentration of inclusion complexes in the bulk of the solution. These inclusion complexes are formed by two cyclodextrin molecules and one surfactat molecule. We propose a model to describe these dynamical processes. Dipole–dipole interactions on the surface of the drop trigger a competition between water surface tension and dipole–dipole interaction energies. The results of the model reproduce the spherical and rod-like shapes found in the experiments.

High Interfacial Viscoelasticity of Aqueous Mixed Dodecyltrimethylammonium Bromide–Sodium Dodecyl Sulfate Surfactants Forming Inclusion Complexes with α-Cyclodextrin

“…Modeling the present two-surfactant systems would be a difficult task, but a starter point could be the work previously reported for the one-surfactant systems, where electrostatic interactions at the surface were considered. 21,39 It is important to mention that the surface tension values and drop pendant volumes during an oscillatory measurement can be interpreted in microscopic terms, i.e., in terms of the 2:1 ICs forming the film. This is done in detail in the Supporting Information, with one of the main conclusions being that the two-surfactant film is reversible, as was the case in the one-surfactant systems using the temperature as the experimental variable.…”

“…We can conclude that the film is formed by a viscoelastic structure formed by 2:1 ICs, interacting by forming hydrogen bonds between adjacent αCD and by attractive electrostatic interactions between the surfactant polar heads. Modeling the present two-surfactant systems would be a difficult task, but a starter point could be the work previously reported for the one-surfactant systems, where electrostatic interactions at the surface were considered. , …”