Direct influence of the interaction between the first layer and a hydrophilic substrate on the transition from Y- to Z-type transfer during deposition of phospholipid Langmuir-Blodgett films

In view of obtaining homogeneous LB films, monolayers of dipalmitoylphosphatidic acid (DPPA) and of mixed DPPA and dipalmitoylphosphatidylcholine (DPPC) (molar ratio, 2:1) were transferred onto hydrophilic (fluorine, glass, and silicon) or hydrophobic (silanized glass) substrates with conditions derived from the optimized procedure previously proposed in our group for the transfer of a fatty acid monolayer. Whatever the substrate used, the phospholipid multilayers obtained are homogeneous through Nomarski microscopic observations. The silicon substrate appears to be the most efficient to build up Y-type multilayers. Anew type referred to as ''YZ'' was defined to describe the structure of the LB film stacking. We demonstrate that the transition observed between the different Y-, YZ-, and Z-types depends directly on the strength of the interaction between the first layer and the hydrophilic substrate surfaces.