Investigating the surface structure of liquids containing ionic species
1 pm in Physical Sciences room 2105, Tuesday 5th August 2014.
School of Chemical and Physical Sciences
Understanding the behaviour of ionic species at liquid surfaces is vital to understanding the forces that govern the surface structure of liquids. The structure of ions at liquid surfaces, or charge distribution, is especially important in foam films (such as soap bubbles) where the electrostatic forces generated from the separation of charges at the liquid/air interfaces play a pivotal role in stopping the film from collapsing. These stabilising forces are typically described using DLVO theory and the electrical double layer model. These models work well for simple systems at low electrolyte concentration, but use a number of assumptions that cause them to fail at describing more complicated systems. Some of these assumptions, such as neglecting the chemical nature of the ionic species, can be accounted for once the surface structure of the system is known.
Many powerful techniques for investigating surfaces require the samples to be measured under ultra-high vacuum. The volatile nature of liquids makes their use in these instruments difficult, especially so in the case of foam films which are already in a fragile, metastable state. In this work, specialised equipment and experimental techniques are developed for the investigation of foam films under vacuum which have not previously been possible. This has led to the first experimentally determined charge distributions at foam film surfaces being measured for both ionic surfactants, and non-ionic surfactants containing electrolyte.