We have designed a family of peptide surfactants (Pepfactants®) that undergo self-assembly at the air-water or oil-water interface to create a nano-structured interfacial film. These peptide surfactants have been designed such that the architecture of the interfacial film changes in response to environmental stimuli, resulting in significant shifts in mechanical properties.

The Cambridge Interfacial Tensiometer was used to characterise the mechanical properties of interfacial peptide films. Under defined solution conditions the adsorbed Pepfactants® form a cohesive ‘film state' with mechanical properties similar to adsorbed proteins. Under alternate solution conditions the adsorbed Pepfactants® adopt a mobile ‘detergent state' incapable of transmitting force in the plane of the interface, analogous to low molecular weight detergents. Switching between film and detergent states is readily and reversibly achieved by a change in the bulk solution composition, such as a change in pH, or the addition or sequestering of metal ions.

Pepfactants® are capable of stabilizing foams and emulsions in a stimuli-responsive manner, where emulsion and foam stability is switched by the transition of the adsorbed peptide from the mechanically strong film state to the mobile detergent state. Control of the bulk emulsion and foam stability is achieved through the rational design of surfactant molecules that can reversibly switch interfacial properties on demand.