  Investigations of free-standing liquid films enjoy an increasing popularity
due to their relevance for many fundamental and applied scientific problems.
They constitute soap bubbles and foams, serve as membranes for gas transport or
as model membranes in biophysics. More generally, they provide a convenient
tool for the investigation of numerous fundamental questions related to
interface-and confinement-driven effects in soft matter science. Several
approaches and devices have been developed in the past to characterise reliably
the thinning and stability of such films, which were commonly created from
low-viscosity, aqueous solutions/dispersions. With an increasing interest in
the investigation of films made from strongly viscoelastic and complex fluids
that may also solidify, the development of a new generation of devices is
required to manage reliably the constraints imposed by these formulations. We
therefore propose here a microfluidic chip design which allows for the reliable
creation, control and characterisation of free-standing films of complex
fluids. We provide all technical details and we demonstrate the device
functioning for a larger range of systems via a selection of illustrative
examples, including films of polymer melts and gelling hydrogels.
