POLY(DIMETHYLSILOXANE) MOLECULAR LAYERS AT THE SURFACE OF WATER AND OF AQUEOUS SURFACTANT SOLUTIONS

We have studied poly(dimethylsiloxane) (PDMS) molecular layers spread on aqueous substrates by means of surface pressure, capillary wave, and ellipsometry experiments. We have observed different structural transitions of the PDMS layers when spread on different substrates. PDMS spreads more easily on a dense surfactant layer than on pure water: in the second case the polymer chains, with their polar Si-O groups, must accommodate themselves to the polar water surface; this new chain configuration favors multilayer formation at the water surface. Our observations show similarities with the spreading behavior of PDMS on hydrophobic and hydrophilic solid substrates. The spreading on dilute surfactant solutions appears to be even more difficult than on pure water, suggesting that the interpenetration of polymer and surfactant chains is a very slow process.