Charge regulation in polyelectrolyte brushes studied by FTIR spectroscopy

Brush layers of a polyelectrolyte, ionized poly(glutamic acid) (polymerizat ion degree n = 48), were studied using FTIR spectroscopy as a function of t he polyelectrolyte chain density. The Langmuir-Blodgett (LB) deposition of the mixed monolayers of a poly (glutamic acid) functionalized amphiphile an d dioctadecylphospholic acid afforded the preparation of polyelectrolyte br ushes at the desired density on various substrates. FTIR spectroscopy on th e LB films demonstrated that the ionization degree of the carboxylic acid g roups decreased with increasing polyelectrolyte density in order to maintai n the charge density below the critical value of 0.8 similar to 1 charge nm (-3). The average distance between the charges at the maximum density was c a. 1.1 +/- 0.1 nm which is close to twice the Bjerrum length, the distance at which the Coulomb interaction between elementary charges is equal to the thermal energy. (C) 2000 Elsevier Science B.V. All rights reserved.