Investigation of Different Growth Steps in the Preparation of Layer-by-Layer Self-Assembled Films by Second Harmonic Generation
M Breit, M Gao, G von Plessen, J Lemmer, J Feldman, Steven T. Cundiff
Second harmonic generation (SHG) is used to investigate various growth steps in the preparation of layer-by-layer self-assembled films of oppositely charged polyelectrolytes. Two very important steps in the film preparation, namely the adsorption and drying process, as well as dry films are studied. It is found that the second harmonic (SH) signal from multilayer self-assembled films is strongly related to the polyelectrolyte forming the surface layer. Since the SH signals from different surface layers are clearly distinguishable, the adsorption kinetics of each monolayer can be monitored during the film formation. The SH signal also reflects the drying kinetics. During the drying process the intensities of the SH signals from polycation- and polyanion-ending films show different time behaviours. As a result, the signal intensities from dried polycation- and polyanion-ending films are strongly different and their relative strengths inverted. For the dry films, the difference in SH signal intensity between the polyanion- and the polycation-ending films is much smaller than in the wet state. It is also found from the measurements of the dry films that in addition to the surface layer, the three monolayers closest to the surface layer have a measurable influence on the SH signal. This indicates that layers embedded in the film structure can have an effect on the surface structure of the film. We refer to this 'Memory Effect.'
polymers, second harmonic
, Gao, M.
, von Plessen, G.
, Lemmer, J.
, Feldman, J.
and Cundiff, S.
Investigation of Different Growth Steps in the Preparation of Layer-by-Layer Self-Assembled Films by Second Harmonic Generation, Langmuir
(Accessed December 11, 2023)