Filler size effect in an attractive fibrillated network: a structural and rheological perspective

The effect of the filler size on the structural and mechanical properties of an attractive fibrillated network composed of oxidised cellulose nanofibrils (OCNF) in water was investigated. Silica nanoparticles, SiNp5 and SiNp158 which were ≈ 5 and ≈ 158 nm diameter, respectively, were chosen to be of a similar and a greater dimension of the network mesh size. Contrast matched Small Angle Neutron Scattering (SANS) experiments revealed that the presence of the fillers (SiNp5 and SiNp158) did not perturb the structural properties of the OCNF network at the nm- length scale. However, the filler size difference strongly affected the mechanical properties of the hydrogel upon large amplitude oscillatory shear. The presence of the smaller filler, SiNp5, preserved the mechanical properties of the hydrogels while the larger filler, SiNp158, allowed a smoother breakage of the network and low network recoverability after breakage. This study, show that the filler-to-mesh size ratio, for non-interacting fillers, is pivotal for tailoring the non- linear mechanical properties of the gel such as yielding and flow.