2005 Volume 62 Issue 10 Pages 449-457
The nanostructures of strong and weak polyelectrolyte brushes in the ionic amphiphilic block copolymer monolayer at the air/water interface were investigated by in situ X-ray and neutron reflectometry. The hydrophilic layer under the water was found to be not a simple brush layer but a carpet/brush double layer structure when the hydrophilic chain is long enough and the brush density is high enough. The critical brush density and hydrophilic chain length for the transition between carpet only/carpet + brush structure transition were also found. The weak acid monolayer first expanded by addition of salt but was shrunk by further addition of salt. The strong acid monolayer was not affected by salt addition up to certain salt concentration around 10-1 M, but was shrunk by further addition of salt. These phenomena could be interpreted as due to the charged state of polyelectrolyte chains in the brush layer and the electrostatic repulsion between polymer brush chains in the brush layer.
