LIQUID FILM INVESTIGATIONS UNDER MICROGRAVITY CONDITIONS BY THE LIFT TENSIOMETER

Most features of foams and emulsions are defined by the behaviour and the chemico-physical properties of the corresponding liquid films (LF). Investigating these properties is particularly important to boost the comprehension of the behaviour of emulsions and foams in relation to complex blends of stabilising/destabilising agents, such as those composed by associations of surface active molecules and particles. LF features cannot be straightforwardly extrapolated by the properties of the single interfaces composing it, due to the involved volume finiteness and the small thickness, which limits the exchange of molecules with the bulk and makes the adsorption layers at the two sides of the films to interact. Among the various approaches proposed to study different aspects of the chemico-physical properties of LF, particularly attracting is the possibility to investigate the dynamic film tension and dilational film rheology of spherical films on the basis of the Capillary Pressure tensiometry. Such technique has been in fact successfully utilised for studies on single interfaces, offering evident advantages in terms of accessible time scales for the interfacial tension and perturbation frequency and flexibility for the dilational rheology. Based on such concept we have started the development of a Liquid Film Tensiometer (LIFT), proposing it as a new device for LF investigations under weightlessness conditions on board the International Space Station with the support of the Italian Space Agency. These conditions are in fact useful to study the properties of the film only subject to capillary drainage and will also allow investigating these properties in the wet film regime, which is the most difficult to access under gravity. Such instrument will also include enhanced optical techniques for the simultaneous measurement of the film thickness. References 1. Y.H. Kim, et al., J. Colloid Interface Sci.,187 (1997) 29 2. V.I. Kovalchuk et al., J. Colloid Interface Sci., 280 (2004) 498. 3. A. Georgieva et al., Soft Matter, 5 (2009) pp 2063-2071