Abstract
Cationic amphiphilic diblock copolymers were synthesized by RAFT polymerization and the nanostructure of their monolayers was investigated by π-A isotherm and X-ray reflectivity. Carpet layer (dense hydrophilic block layer) formation under the hydrophobic layer was confirmed and a “brush” layer was found beneath the carpet layer. However, the thickness of brush layer was much thinner than that of the fully-stretched chain length. The critical salt concentration was found to be 0.01 M NaCl, which is much lower than that of the previous strongly anionic brush. These differences were probably caused by the low effective charge on the brush chains due to the hydrophobic nature of the quarternized ammonium cation.
Highlights
Cationic amphiphilic diblock copolymers were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and the nanostructure of their monolayers was investigated by π-A isotherm and X-ray reflectivity
There was a different critical salt concentration for PSS brush for different kinds of added salt, e.g., NaCl, KCl, and LiCl, which follows the Hofmeister series, which reminds us of the special situation of water structure in the polyelectrolyte brush layer which has a high ion concentration.[14]
We investigated cationic brush systems using the cationic amphiphilic diblock copolymer (P(QBm)-b-P(nBA), and P(QBm)-b-P(EHA) monolayer on the water surface
Summary
Polyelectrolyte brushes have been attracting much attention as a novel surface modification technique for improvement of friction, biocompatibility etc.[1,2,3,4,5,6,7] We have been investigating the nanostructure and the transition of the polyelectrolyte brush in the ionic amphiphilic diblock copolymer monolayer at the air/water interface by utilizing surface pressure – area (πA) isotherm and X-ray and neutron reflectivity techniques.[8,9,10,11,12,13] The primary advantage of monolayer systems for brush study is easy control/change of brush density (number of brush chains in unit area) and precise control of molecular weight and the distribution of brush chains. A systematic study was conducted using π-A isotherm and X-ray reflectivity (XR)
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