Tailored\nInteraction between Cellulose Nanowhiskers\nand Core–Shell Particles Determines the Optical and Mechanical\nProperties in Hybrid Films

Hybrid materials\nof core–shell particles and cellulose nanowhiskers\n(CNWs) were synthesized to produce opal films with increasing tensile\nstrength. After the incorporation of CNWs into the processed particle\nfilms, differences in the mechanical and optical properties were noticeable,\nwhich stemmed from the adhesion forces between the cellulose and the\nparticles’ shell material. Two different particle compositions\nwere compared, using polystyrene as cores, and either poly(ethyl acrylate)\n(PEA) or a copolymer of ethyl acrylate and 3 wt % of 2-hydroxyethyl\nmethacrylate (HEMA) as the shell material. Stronger interactions between\nthe particles containing HEMA and the CNWs were displayed via atomic\nforce microscopy particle manipulation experiments, where higher forces\nwere required to deliberately move P(EA-<i>co</i>-HEMA)\nparticles on a CNW substrate compared to PEA particles. The stronger\ninteraction behaviors increased the disorder of the particles within\nthe opal films toward photonic glasses with angle-independent structural\ncolors. Also, the increase in tensile strength from <1 MPa at a\ncellulose content of 0 wt % to 6 MPa at the optimal CNW content of\n15 wt % was more pronounced compared to the particle-cellulose mixture\nwith only PEA in the particle shell. Thus, the presence of the hydroxy\ngroups in the particles’ shell material on the molecular level\nsignificantly influenced the optical and mechanical properties on\nthe macroscopic level.