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

Area of Science:

• Materials Science
• Electro-optics
• Physical Chemistry

Background:

• Birefringence, the Pockels effect, is a phenomenon where refractive index changes with electric field.
• Room temperature ionic liquids (RTILs) are salts that are liquid at ambient temperatures, exhibiting unique electrochemical properties.

Purpose of the Study:

• To investigate the relationship between surface charge and induced birefringence in RTILs.
• To understand how different cation structures affect the Pockels effect in RTILs.

Main Methods:

• RTILs were confined in a lens-shaped cell with an Indium Tin Oxide (ITO) coated surface.
• Surface charge density was controlled by applying current to the ITO film.
• Induced birefringence was measured as a function of surface charge density.

Main Results:

• Induced birefringence was found to be directly proportional to the surface charge density in all tested RTILs.
• A significant change in refractive index, up to 20%, was observed near the ITO surface.
• The magnitude of induced birefringence showed a stronger dependence on the length of the cation's aliphatic substituent than on the headgroup identity.

Conclusions:

• Surface charge density is a key factor in inducing birefringence in RTILs.
• The cation's aliphatic chain length plays a critical role in tuning the electro-optic response of RTILs.
• These findings contribute to the understanding of charge-induced optical phenomena in ionic liquids for potential device applications.