Strong Dipolar Intermolecular Correlations and High Performance Zwitterionic Dielectric Materials

We have developed zwitterionic molecules based on ionic liquids for use in flexible and printed electronics. When blended with poly(methyl methacrylate) (PMMA), the materials exhibit a thickness-independent capacitance nearly equivalent to what is typical at an electrochemical interface. To understand these properties, we have used grazing incidence wide angle x-ray scattering to examine film nanostructure. We find that the extremely large dipole moment of these molecules causes strong correlations between them. Below the melting temperature of the zwitterions, they tend to orient in an antiparallel fashion, resulting in low capacitance. However, when melted, the are free to rotate, cancelling fields in the bulk of the material and behaving as an electrolyte dielectric. One of the key advantages of zwitterions is their ability to gate organic transistors in field-effect mode for both n-type and p-type devices. When blended with poly(vinyl alcohol) (PVA), zwitterions containing films benefit from elevated humidity, increasing their capacitance properties by several orders of magnitude as compared to devices prepared in an inert atmosphere glove box. Transistors based on these materials operate at < 2 volts. Infrared spectroscopy suggests that the humidity sensing properties of our materials is the result of intermolecular interactions between the anionic segment of the zwitterion and the PVA matrix. These results demonstrate the unique and largely untapped potential of this class of materials as insulators in printed electronics applications.

Kaur, S.; D’Souza, R. M.; Kelly, T. L.; Williams, V. E.; Kaake, L. G., Electrostatic Correlations Lead to High Capacitance in Zwitterion-Containing Thin Films. ACS Appl. Mater. Interfaces 2024, 16 (29), 38290-38299.

Kaur, J.; Kaur, H.; Kaake, L. G., N and P-type zwitterion gated organic field effect transistors. RSC Applied Polymers 2024, 2 (5), 926-935.