Cation structure-dependence of the Pockels effect in aprotic ionic liquids

We report on the dependence of surface charge-induced birefringence (the Pockels effect) in room temperature ionic liquids (RTILs) with different cation constituents. The induced birefringence is related to the induced free charge density gradient (rho(f)) in the RTIL. The RTILs are confined in a lens-shaped cell and the surface charge density of the concave cell surface is controlled by the current passed through the surface ITO film. We find that, in all cases, the induced birefringence is proportional to the surface charge density and that the change in refractive index nearest the ITO surface can be on the order of 20%. Our findings indicate that the induced birefringence depends more sensitively on the cation aliphatic substituent length than on the identity of the charge-carrying headgroup.

Automated summary

This study reports on the relationship between surface charge-induced birefringence (the Pockels effect) and different cation constituents in room temperature ionic liquids (RTILs). The findings show that the induced birefringence is proportional to the surface charge density and can result in a refractive index change of up to 20% nearest the ITO surface. Additionally, the aliphatic substituent length of the cation has a greater impact on the induced birefringence than the identity of the charge-carrying headgroup.