Surface Analysis of PEDOTPSS Films

Jonsson et al. used synchrotron radiation to study the kinetic energy of photoelectrons from the S(2p) core level in PEDOTPSS films in electron spectroscopy for chemical analysis (ESCA). Photoelectrons from the S(2p) core level can be used as a quantitative measure of sulfur atoms in the aromatic thiophene ring of PEDOT and sulfur atoms in the sulfonic acid unit of PSS in the top layer of the film. By variation of the energy of the photons, the escape depth of photoelectrons from the polymer film can be tuned and a depth profile of the film can be obtained. Using this technique the authors demonstrated that pristine PEDOTPSS films have a PSS rich surface. With a photon energy of 270 eV, 95% of the signal stems from the outmost 15 A and a clear dominance of PSS is observed (see Table 9.4). When NMP and sorbitol are used as additives and the film is dried at room temperature, no PSS rich 

PEDOT-to-PSS Ratios for PEDOT PSS Films Based on S(2p) Core Level Spectra Recorded by Electron Spectroscopy for Chemical Analysis Based Photon Energy Depth Profiling at Photon Energies of 270 and 1486.6 eV 

Contact angle measurements show that the surface becomes more hydro-phobic upon the addition of ethylene glycol. The contact angle of a pristine film is 10° to 12° whereas that of an ethylene glycol treated film is 20° to 22°.  

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