Neutron Reflectivity of Linear−Dendritic Diblock Copolymer Monolayers

Abstract

Specular neutron reflectivity has been used to investigate the structure of monolayers formed from linear-dendritic diblock copolymers at an air-water interface. The dendritic block copolymers consist of a linear poly(ethylene oxide) (PEO) block of 2000 molecular weight linked to a third or fourth generation polyamidoamine (PAMAM) dendron. The dendritic end groups were functionalized with deuterated stearic acid to make the dendritic block hydrophobic, resulting in a macroamphiphile. Results indicate that stable monolayers are formed with PEO resting on the subphase and stearate groups extending into the air. In general, at low surface concentrations the PEO block intermixes with the PAMAM dendron, whereas at high surface concentrations the PAMAM forms a distinct layer above the PEO. The ordering of the stearate groups functionalized on the dendrimer was dependent on generation. Stearate groups form a distinct ordered layer which is separate from the third generation PAMAM dendron, whereas the stearate groups are intermixed with fourth generation PAMAM segments due to the curvature of the higher generation dendron. The PEO block becomes intermixed with the water subphase if the monolayer is held at constant area for at least 10 h. These finding are consistent with earlier published studies of pressure-area isotherms of these systems on the Langmuir-Blodgett trough.