From convective assembly to Landau-Levich deposition of multilayered phospholipid films of controlled thickness.

In this letter, we describe a method to control the organization and thickness of multilayered phospholipid films. The meniscus of an organic solution of phospholipid molecules was dragged at a speed v on a solid substrate under controlled temperature and forced convection, leading to the deposition of a dried multilayered phospholipid film with a thickness h in the range of 20-200 nm. We found two distinct regimes dominating the film deposition. At low speeds, phospholipid molecules accumulate near the contact line and form a dry film behind the meniscus (evaporation regime). At high speed, viscous forces become predominant and pull out a liquid film that will dry afterward (Landau-Levich regime). Both regimes show robust scaling h infinity v(alpha) with alpha = -1.1 and 0.76, respectively. Although these regimes have been observed separately in the past, they have not been demonstrated in the same material system. Moreover, we present models whose scalings (alpha = -1 and 2/3) are in close agreement with the observed values. The microscale organization of the resulting film is independent of v for a given regime but differs from one regime to another. In the Landau-Levich regime, h is very homogeneous on the microscale with discrete variations of +/- 5 nm, that is, the thickness of one bilayer.