Layer Structures Formed by Silica Nanoparticles and Cellulose Nanofibrils with Cationic Polyacrylamide (c-pam) on Cellulose Surface and Their Influence on Interactions

A quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study the adsorption of the layer formed by silica nanoparticles (SNP) and cellulose nanofibrils (NFC) together with cationic polyacrylamide (C-PAM) on cellulose surface, accompanied by use of atomic force microscope (AFM) to study the interactions between cellulose surfaces. The purpose was to understand the multilayer buildup compared to complex structure adsorption. The layer thickness and consequently also the repulsion between surfaces increased with each addition step during layer formation in the SNP-C-PAM systems, whereas the second addition of C-PAM decreased the repulsion in the case of NFC-C-PAM multilayer formation. An exceptionally high repulsion between surfaces was observed when nanofibrillar cellulose was added. This together with the extremely high dissipation values recorded with QCM-D indicated that nanofibrillar cellulose formed a loose and thick layer containing a lot of water. The multilayer systems formed fully and uniformly covered the surfaces. Silica nanoparticles were able to penetrate inside the loose C-PAM structure due to their small size. In contrast, NFC formed individual layers between C-PAM layers. The complex of C-PAM and SNP formed only a partly covered surface, leading to long-ranged pull-off force. This might explain the good flocculation properties reported for polyelectrolyte-nanoparticle systems.