Schürer, B.; Hoffmann, M.; Wunderlich, S.; Harnau, L.; Peschel, U.; Ballauff, M.; Peukert, W.: Second Harmonic Light Scattering from Spherical Polyelectrolyte Brushes. The Journal of Physical Chemistry C 115 (2011), p. 18302-18309
Optical second harmonic generation (SHG) was applied to study the shell layer of spherical polyelectrolyte brushes as a function of ionic strength. The particles consist of a polystyrene core from which linear chains of a quenched polyelectrolyte are grafted. Compared to all systems studied by SHG previously, the shell layer in this study has a remarkable thickness of ca. 100 nm. Angle-resolved second harmonic (SH) scattering profiles were recorded and compared to simulations with different model geometries using a nonlinear Mie scattering model. The analysis reveals that the second harmonic signal is not generated by the polyelectrolyte molecules, but rather by oriented and polarized water molecules at the inner (polystyrene/polyelectrolyte) and at the outer (polyelectrolyte/solvent) interface of the polyelectrolyte shell. The results demonstrate that angle-resolved SH light scattering provides direct access to the structure of water and the screening of charges at the inner and outer interface of the polyelectrolyte shell. Correspondingly, this work sets the experimental and theoretical basis for the study of the extended interfacial layer of electrosterically stabilized particles by SH light scattering.