Magnetic field effects on free surfactant-stabilised liquid films

Abstract

Adding nanomaterials to soap films provides opportunities to control the dynamics and stability of soap films using external stimuli, which could possibly lead to the development of new technologies, such as the use of soap bubbles as stimuli-responsive carriers. This work investigates the effects of electric/magnetic fields on soap films containing electrically/magnetically-responsive nanomaterial and also aims to provide solutions to general challenges in soap film research. First, carbon nanotubes (CNTs) are investigated for electric field control of soap films using molecular dynamics and experiments. The molecular dynamics trajectories highlight that the polarity of surrounding liquid molecules affects the orientation of CNTs in electric fields, and the experiments indicate that low-strength electric fields are insufficient to influence soap films containing CNTs. An experimental investigation of soap films containing magnetite nanoparticles is then conducted. The interference colours arising from white-light illumination reveal that an inhomogeneous magnetic field affects the drainage dynamics of these magnetic soap films, resulting in either a stabilising or destabilising effect, depending on the composition of the film. Next, an interference relation for soap films that accounts for coherence effects is derived and applied to analyse the method widely-used to calculate soap film interference colours. Three methods are then developed for the open problem of mapping interference colours to film thickness. The proposed flood-fill-type algorithm leads to the most accurate thickness mapping and is expected to outperform recently proposed methods in the literature. Finally, a thin film model for magnetic soap films is derived. With a capillary suction boundary condition, this model is able to predict effects in qualitative agreement with marginal regeneration, which is a first for thin film modelling. Ultimately, this work facilitates effective methods for investigating soap films and is a key step towards precisely controlling the behaviour of soap films.