Tailoring the mechanical properties of starch-containing layer-by-layer films

The Youngʹs modulus of layer-by-layer (LbL) films containing starch was determined using the recently developed SIEBIMM (strain-induced elastic buckling instability for mechanical measurements) technique. By using cationic starch (CS) in combination with anionic starch (AS), silica nanoparticles (SNP), and nanofibrillated cellulose (NFC), the mechanical properties of these sub-micrometer starch-containing LbL films could be tailored. At 50% relative humidity (RH), the Youngʹs modulus of CS/AS, CS/SNP, and CS/NFC was 0.6 GPa, 0.9 GPa, and 1.8 GPa, respectively, in the 25–85-nm thickness range. As expected for these hygroscopic starch-containing LbL films, the mechanical properties depended on RH. At 0% RH, the Youngʹs modulus was 2–4.5 times higher than at 50% RH. The LbL buildup on polydimethylsiloxane (PDMS) was studied in situ using quartz crystal microgravimetry with dissipation (QCM-D), and atomic force microscopy (AFM) was used to characterize the surface morphology and thickness of the films.