X-RAY REFLECTIVITY OF DIBLOCK COPOLYMER MONOLAYERS AT THE AIR WATER INTERFACE/

AB diblock copolymers PS260-b-PVP-C(n)X(240)(-) (PS = polystyrene; PVP -C-n = alkylated poly(vinylpyridine); X(-) = I-, Br-; n = 1, 4, 8, 10) have recently been found to self-assemble at the air/water interface to form circular structures referred to as surface micelles. These sur face micelles are ordered into a quasi-two-dimensional array in the co rresponding Langmuir-Blodgett (LB) films. Many questions arise in thes e systems, including the structure relationships between the air/water Langmuir films and the LB films deposited onto carbon or silicon surf aces. A detailed in situ synchrotron X-ray reflectivity study was perf ormed to address these issues of the polymer film structure. Specular reflectance of all samples (n 1, 4, 8, 10) reveals that the thickness of the polyelectrolyte layer only increases by a factor of 2 as polyme r surface density increases 4-fold. No significant hydration of the la yer is observed. The off-specular scattering data are well fit by an e xact expression for the scattering intensity from a two-dimensional-or dered hexagonal lattice with a capillary wave contribution. The micell e-micelle distances obtained are in excellent agreement with atomic fo rce microscopy images of the LB films, confirming that no change in st ructure occurs in the film liftoff process. The change in micelle-mice lle distance or in film thickness does not correlate in the pressure-a rea isotherm for n greater than or equal to 6. A correlation was obser ved only for the degree of surface ordering and the him stiffness.