Dynamics of caged microemulsion droplets: a neutron spin echo and dynamic light scattering study

We report a neutron spin echo (NSE) and dynamic light scattering (DLS) study of droplet dynamics in a microemulsion at high droplet packing fraction ( Φ droplet∼62%). NSE measurements in range qr⪢1 allow to investigate the short-range Brownian motion of droplets trapped within the cages formed by their nearest neighbors. For a particular scattering contrast, NSE also reveals, for q values around qr∼ π, the shape fluctuations of the caged droplets. In range qr⪡1, DLS correlation functions reveal two independent diffusive modes with well separated decay times. Comparing DLS results with NSE and pulsed-field gradient NMR measurements allows to associate both DLS modes with collective dynamics of ‘transient-trapped’ droplets, revealing strong similarity to the long-time and short-time diffusion modes observed by light scattering in concentrated colloidal suspensions below the glass transition.