“The ability to detect surface chemistry alterations of PEDOT-coated electrodes has thus been found to be sufficiently possible through O-PTIR characterization, as shown through the detection of carbonyl bonds present in maleimide subgroups being found in PEDOT-MA-coated electrodes, but not PEDOT-coated ones.”
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Reporting in MRS Communications, researchers at The University of Delaware demonstrated the application of optical photothermal infrared spectroscopy (O-PTIR) for characterizing surface chemical modifications in electrochemically deposited conducting polymer films. PEDOT (poly(3,4-ethylenedioxythiophene)) is widely used in bioelectronic applications for its excellent electrical properties and chemical stability, but this stability makes post-deposition chemical modification challenging. PEDOT-MA, a maleimide-functionalized variant, enables surface modification through maleimide coupling reactions, but characterizing these interfacial modifications requires non-destructive surface-sensitive analytical methods. The team used O-PTIR to differentiate PEDOT and PEDOT-MA thin films deposited on interdigitated electrodes and to verify the presence of maleimide functional groups.
The researchers first characterized EDOT and EDOT-MA monomers using O-PTIR, identifying key spectral differences including a prominent peak at 1718 cm⁻¹ corresponding to the maleimide carbonyl group in EDOT-MA that was absent in base EDOT. Following electrochemical polymerization on interdigitated gold electrodes, both PEDOT and PEDOT-MA films showed approximately two orders of magnitude reduction in low-frequency impedance, confirming successful coating. The films were estimated at 24 nm thickness for PEDOT and 120 nm for PEDOT-MA based on charge density measurements.
O-PTIR surface mapping at 1718 cm⁻¹ across a 60 μm × 10 μm area clearly distinguished PEDOT from PEDOT-MA coated electrode digits. Interestingly, complementary Raman spectroscopy showed the maleimide carbonyl peak at 1773 cm⁻¹ in EDOT-MA monomer but not in the PEDOT-MA polymer film. This discrepancy was attributed to the highly optically absorbing nature of PEDOT which limits the penetration of visible probe.
O-PTIR spectroscopy proved to be a powerful non-destructive analytical tool for detecting surface chemical alterations in conducting polymer coatings. The technique successfully identified carbonyl bonds in maleimide subgroups in PEDOT-MA-coated electrodes while distinguishing them from unmodified PEDOT-coated electrodes, with submicron spatial resolution. The ability to perform chemical mapping without sample destruction makes O-PTIR particularly valuable for characterizing interfacial modifications in functional polymer films intended for bioelectronic and other surface-sensitive applications.
Authors:
Quintin Baugh, Junghyun Lee, Yuhang Wu, Nurdan Cocuk, David C. Martin
Department of Materials Science and Engineering, The University of Delaware
