Thin Polyelectrolyte Multilayers Made by Inkjet Printing and Their Characterization by Nanomechanical Cantilever Sensors

Abstract

Measurements with nanomechanical cantilever (NMC) sensors often reveal only qualitative results. Here we overcome this issue by inkjet printing well-defined polyelectrolyte multilayers (PEMs). We present a method that allows fabricating a 40 bilayer (BL) thick and 5 mm long line made of poly(allylamine hydrochloride) (PAH) and polystyrene sulfonate (PSS). NMC sensors were used to quantify the uptake of water in thin PEMs. We measured and analyzed the mass loading and the swelling response of the PEMs upon exposure to relative humidity between 5% and 80%. For a film made of 5 BLs we determined a Young’s module of ∼390 MPa for low humidity (<5%). Thicker PEM films made by 10 BLs exhibited a higher Young’s module of ∼560 MPa. The Young’s module decreased in both cases to 2–3 MPa at 80% relative humidity. Furthermore, the NMC measurements of mass and swelling upon exposure to humidity indicated a thickness-dependent swelling of the PEMs.