X-ray reflectivity study of polymer assembly at air-water interface

X-ray reflectivity (XR) measurements were carried out for amphiphilic diblock copolymer monolayers on water surface. From XR data, the layer thickness, and surface and interface roughnesses could be determined as a function of surface pressure. The XR experiments were performed using an ‘Air–Water Interface X-ray Reflectometer’ with conventional X-ray source (Cu target) in our laboratory. LB trough was equipped to the reflectometer, so the in situ measurements could be carried out for spread monolayers on water surface at different surface pressures. Kiessig fringes were observed for specular measurement for amphiphilic diblock copolymer, poly(α-methylstyrene)-poly(decyl 4-vinylpyridine) (P(α MSt)-b-P(4VP-C₁₀H₂₁I)) monolayers on water surface. It was observed that the thickness of the monolayer became thicker with increasing surface pressure. By curve fitting for the data obtained for the monolayer at surface pressure of 37 mN m^-1, the thicknesses of P(αMSt)₅₀ and P(4VP-C₁₀H₂₁I)₅₀ layers was determined to be 21 and 22 Å, respectively. Because the chain length of P(αMSt)₅₀ is calculated to be 126 Å in all-trans conformation, it was indicated that the molecules did not get aligned even when they were pressedto become such a dense state.