First experimental evidence of a giant permanent electric-dipole moment in cellulose nanocrystals

The existence of a permanent electric dipole in cellulose nanocrystals (CNCs) has been evidenced by designed rectangular reversing pulse experiments. Transient electric birefringence (TEB) was used to measure the orientation under electric fields of CNCs dispersed in an apolar solvent (toluene) at low volume fraction. We probed the static and the dynamic orientational behaviour of CNCs in order to evaluate both the permanent and induced electric-dipole contributions to the orientational order parameter S2. We demonstrated the presence of a permanent dipole of about Debye along the CNCs long axis. The existence of this permanent dipole can stem from the parallel arrangement of cellulose chains in a non-centrosymmetric crystallographic lattice within each CNC together with the dipole moment borne by each glucosyl monomer.