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Frothing in liquid mixtures
We explain for the first time a long-known effect : the formation of
froths, i.e. foams with lifetimes of a few seconds, in mixtures of
liquids. In everyday life, this effect is generally observed in oil
mixtures, such as gasoline. In contrast, pure oils do not foam because the
liquid films between bubbles thin down and break up so quickly that
bubbles cannot be seen with the naked eye. In some liquid mixtures, film
drainage is greatly slowed down, allowing the observation of froths. We
have measured this effect and we provide a quantitative explanation for
it, based on the simple fact that that bulk and surface concentrations in
each species slightly differ in the liquid films. These results open new
perspectives for the understanding of pro and anti-foaming mechanisms in
oils.