Strain-Induced Anisotropic Alignments of Bacterial Nanocellulose Ionogels and Their Dynamic Mechanical Properties and Ionic Conductive Behaviors

Ionogels have attracted great attentions for various electrochemical applications due to their high physical and electrochemical properties. However, for practical usages, their mechanical properties and ionic conductivities still require improvements. Herein, we report anisotropically aligned bacterial nanocellulose (BC) ionogels and their dynamic mechanical properties and ionic conductive behaviors. Wet-stretching in water allows the BC nanofibers to be well-oriented throughout the films. After drying in the stretched state, the aligned BC films are obtained and the ionogels are prepared with swelling with ionic liquid of 1-ethyl-3-methylimidazolium. The aligned BC ionogels present superb mechanical properties of modulus about 5 GPa and ultimate strength of 300 MPa in the static tensile tests, majorly attributed to strengthening via anisotropic alignments of the nanofibers and molecular interactions between hydroxyl groups of glucose units. Additionally, the ionic conductivities of the ionogels are in the range of 0.12-0.45 mS cm^-1, even with such high values of the mechanical properties. It is possibly originated from the formation of Helmholtz-like electric double layers around the BC nanofibers that enables the fast ion transport of non-bound ions through the ionic channels. As a result, the combination of dynamic mechanical properties and ionic conductivities shows about 8.1 of E′σ values that surpass limit line value of E′σ = 5. These values were difficult to be achieved by previous ionogel materials. This approach provides the pathways to overcome the conflicts between mechanical properties and ionic conductivities for the ionogels and relevant systems.