Temperature-induced changes in polyelectrolyte films at the solid-liquid interface

Polyelectrolyte multilayers (film thickness 30-60 nm) were built on top of silicon substrates by layer-bylayer deposition of oppositely charged polyelectrolytes from aqueous solutions. Three kinds of films were investigated: (A) films of a homo-polyelectrolyte and a diblock copolymer with a thermosensitive poly(N-isopropyl-acrylamide) block and (B) and (C) two reference systems built solely from homo-polyelectrolytes of opposite charges. Thermal behavior and subsequent structural changes of the functionalized films against D2O were investigated by neutron reflectometry. All films showed irreversible annealing effects upon heating. In addition, the thermosensitive films showed a decrease in thickness at elevated temperature (> 30 degreesC while the reference samples, composed of thermo-insensitive polyelectrolytes only, did not.