Microcontact printing of polyelectrolyte multilayer thin films: Glass-viscous flow transition based effects and hydration methods

Micro and nano-patterned surfaces are important for many applications ranging from antibiofouling over tissue engineering to electronics. Often the incorporation of functional entities is of interest. Polymer coatings especially polyelectrolyte multilayer (PEM) films and patterns are materials offering a large variety of tuning and engineering. The PEM pattern printing quality bases not only on the surface force balance but also in the way the PEM is softened, which can be done by printing the PEM in water, using an ultrasound humidifier or by exposing the film to (hot) water vapor. In this publication it is shown, that cold water vapor from an ultrasound humidifier or direct printing in water is superior to steam evaporation onto PEM thin films as humidification method. In addition the capillary pressure of the patterns within the stamp and the glass-viscous flow transition point of the PEM thin film are the significant parameters for PEM printing. This is because the PEM can surpass the glass-viscous flow transition point due to the shear forces and be sucked into the stamp microwells (or holes) preventing a structure replication. Under high temperatures and in aqueous conditions, the PEM can be expelled from the microwells due to the osmotic pressure produced by the counter ions of PEM in glass-viscous flow state and dissolving polyelectrolyte if a PEM with counter ion based charge balance is used.