Programmable Interactions of Cellulose Acetate with Octadecyltrichlorosilane-Functionalized SiO₂ Nanoparticles

It is significant to understand the interfacial interactions involved between the cellulose acetate (CA) and dispersed nanomaterials, in which the enhanced interaction improves the mechanical behavior of CA. In this work, the amendments of CA with SiO₂ nanoparticles have been found to be endowed by grafting varying concentrations (0, 3, 5, and 6%) of octadecyltrichlorosilane (OTS). Aided by SiO₂ colloid probe atomic force microscopy (AFM with a probe diameter of 20 μm), the adhesion force between CA and SiO₂ is found to be programmable by tuning OTS concentrations functionalized onto SiO₂ surfaces. The adhesion forces of 5% OTS-functionalized SiO₂ with CA are the strongest, followed by the ones of 0, 3, and 6% OTS, resulting in a smoother and denser morphology on the film with 5% OTS. The AFM-measured approaching force–distance curves have been further compared to predictions by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory, in which the XDLVO force is summed as the Liftshitz–van der Waals force (F^LW), the electrostatic double-layer force (F^EL), and the acid–base interaction force (F^AB). F^LW and F^EL do not change significantly with OTS concentrations functionalized onto SiO₂. However, F^AB is sensitive to the functionalized OTS concentration onto SiO₂ and significantly contributes to the interaction force of the composite films with 5% OTS, promoting the formation of a smooth and dense surface feature with a considerable mechanical performance demonstrated by load–displacement curves from a nanoindenter. This is highly encouraging and suggests that nanomaterials can be incorporated into CA to effectively improve their mechanical compatibility by programming the interaction between the CA matrix and nanomaterials.