"Complex fluids are binary mixtures that have a coexistence between two phases: solid\u2013liquid (suspensions or solutions of macromolecules such as polymers), solid\u2013gas (granular), liquid\u2013gas (foams) or liquid\u2013liquid (emulsions). They exhibit unusual mechanical responses to applied stress or strain due to the geometrical constraints that the phase coexistence imposes. The mechanical response includes transitions between solid-like and fluid-like behavior as well as fluctuations."@en .