THE STRUCTURE OF BLOCK-COPOLYMERS AT THE FLUID FLUID INTERFACE/

We have developed a method of measuring the distribution of polymer se gments at a liquid/liquid interface using neutron reflection. The meth od consists of forming a stable (1-4 mu m) hexane layer on top of an a queous sub-phase so that two interfaces contribute to the measured ref lectivity. This has been done by condensing vapour onto the surface in an accurately temperature-controlled environment. The neutron reflect ivity was measured at four angles of incidence on the SURF reflectomet er. The attenuation of the reflectivity from the lowest angle is used to determine the thickness of the hexane layer. A series of poly(ethyl ene oxide) poly(propylene oxide) ABA block copolymers adsorbed at the hexane/water interface have been investigated. Since the polymers were hydrogenous, measurements were made with D2O as the aqueous phase and with either null reflecting hexane or 60% D-hexane as the oil phase i n order to obtain adequate contrast. The polymer volume fraction profi le has been determined by simultaneous fits to the data from these com binations of solvent contrasts. It was found that there was a good cor relation between the molar mass of the poly(ethylene oxide) block and the thickness of the polymer layer in the aqueous phase and that the c hains were stretched beyond their radii of gyration expected for bulk solution. (C) 1998 Elsevier Science B.V. All rights reserved.