Moisture and solvent responsive cellulose/SiO2 nanocomposite materials

Water responsive SiO2/cellulose nanocomposite hydrogels and films were constructed, for the first time, by dispersing SiO2 nanoparticles into cellulose solution in LiOH/urea solvent, and then by crosslinking with epichlorohydrin or regeneration in coagulation bath, respectively. The cellulose nanocomposite materials were characterized by Field emission scanning electron microscopy, FTIR, dynamic rheology, wide angle X-ray diffraction and mechanical test. The SiO2/cellulose nanocomposites at wet state or in water displayed unique behaviors, showing higher light transmittance than those before contacting with water. The results revealed that strong hydrogen-bonding interaction among water, cellulose and SiO2 led the good dispersion of SiO2 nanoparticles in the cellulose matrix. The incorporation of SiO2 nanoparticles improved the transmittance and mechanical strength of the cellulose hydrogels, and also enhanced the mechanical strength of the films. Especially, the cellulose/SiO2 nanocomposite films were milky at dry state, and changed to transparent after being soaked in water, different from the cellulose film without the SiO2 nanoparticles. In our findings, SiO2 and cellulose with water could form strong hydrogen bonding to create a homogenous network structure. The cellulose/SiO2 composite as a smart material exhibited moisture and solvent responsiveness, showing potential applications in moisture detection.