POLYMER SURFACTANT STRUCTURE AT THE AIR-WATER-INTERFACE

We report the first study of the structure of a monofunctional polymeric surfactant, hydroxyl terminated 1,4-polyisoprene, MW 3200, spread at the air-water interface from hexane solution. The system shows a highly reversible pi-A isotherm and remarkable constancy in the film thickness determined by neutron reflectivity at surface pressures above and below the classical ''collapse transition''. The thickness is approximately 30 angstrom with head group penetration into the water layer of about 10 angstrom and is consistent with a rigid chain conformation for the polymer. As the film is compressed, it thickens slightly indicating that the tilt of the chains increases from ca. 10-degrees to ca. 15-degrees, but even at relatively low pressures up to 50% of the polymer present does not contribute to the reflectivity and is probably present as multilayers. Ellipsometry measurements indicate that the same film can be transferred to a silicon substrate by Langmuir-Blodgett methods.