(464h) Modulation of Phase Morphology of Surfactant Monolayer with Interfacial Curvature

Sachan, A. K., University of Minnesota
Zasadzinski, J. A., University of Minnesota
For the past 100 years, surfactant monolayers have been studied on planar interface of the Langmuir trough while most physiological, such as, alveolar interface in mammals, and technological interfaces are curved at the micron to millimeter scale. We present the design and engineering of a unique instrument assembly and methodology for creating curved monolayer on air-aqueous interfaces of different background curvatures (25-500 µm radius). Our unique approach combines 3-D imaging capabilities of confocal fluorescence microscopy with this setup to investigate curvature-dependent changes in the phase morphology of monolayer on interface. Using a biologically relevant multi-component surfactant system that forms coexisting ordered, ‘solid-like’ domains in the disordered, ‘liquid-like’ phase on a planar interface, we show that as the background curvature of interface approaches a critical range the monolayer yields a contrasting equilibrium phase-coexistence pattern where size, shape and connectivity of the domains dramatically change. Time-lapsed investigation of early events at interfaces reveals curvature sensitive conversion of adsorbed surfactant MLVs into monolayer and subsequent evolution of phase pattern. Surprisingly, the background curvature-mediated dramatic shift in phase-coexistence pattern impacts the dynamic properties of monolayer as well, in particular the complex dilatational modulus. Modulation of local phase structure and dynamics with the background curvature is found reversible up to certain extent. We present a theoretical model to explain how electrostatic (dipole:dipole) interaction energy between phases and within domains compete with the line tension energy on a curved interface and yield distinct phase morphology in the monolayers.