High tensile strength and high ionic conductivity bionanocomposite ionogels prepared by gelation of cellulose/ionic liquid solutions with nano-silica

Abstract

Novel bionanocomposite ionogels consisting of an ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate (EMIMAc), microcrystalline cellulose (MCC) and nano-silica (nano-SiO₂) particles with high tensile strength and high ionic conductivity have been successfully prepared. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements reveal a homogeneous dispersion of nano-SiO₂ in the MCC/nano-SiO₂/EMIMAc bionanocomposite ionogels. In order to clarify the influences of added nano-SiO₂ on the sol–gel transition process and liquid crystalline phase transition for the MCC/nano-SiO₂/EMIMAc systems, the complexes were investigated by dynamic rheological measurements, mechanical tensile property tests and polarized optical microscope (POM) observations. The rheological results indicate that the introduction of nano-SiO₂ can induce and accelerate the gelation for the MCC/nano-SiO₂/EMIMAc solutions. By adjusting the MCC and nano-SiO₂ concentrations, the gel-sol transition temperature and elastic modulus can be well controlled and the optimized values reach 125 °C and 7 × 10⁵ Pa, respectively. The POM results reveal that the addition of nano-SiO₂ significantly suppresses the liquid crystalline behavior of ionogels. A more significant result is that the bionanocomposite ionogels exhibit high ionic conductivity in the order of 10⁻³ S cm⁻¹ at 30 °C. The ionic conductivity of the ionogels increases with increasing temperature and decreasing MCC concentration. The above results demonstrate that the novel bionanocomposite ionogels with high tensile strength are promising for the application as gel polymer electrolytes (GPE) in electrochemical devices.