Coupled chemical reactions in dynamic nanometric confinement: IV. Ion transmission spectrometric analysis of nanofluidic behavior and membrane formation during track etching in polymers

Abstract

In recent papers, it was shown that coupled chemical-topological reactions (CCRs) with both NaOH etchant and silver salts, performed in thin swift-heavy ion-irradiated polymers under the application of a test voltage across the polymer foils, eventually gave rise to characteristic current/voltage features and Bode plots that were tentatively attributed to the formation of Ag₂O membranes within the etched tracks. The same was also found when replacing the silver ions by lithium ions, and adding fluoride ions to the NaOH etchant, to promote LiF membrane formation. Ion Transmission Spectrometry (ITS) enabled us to reconfirm the existence of these membranes beyond doubt. The membrane thickness was determined to be ∼0.2–0.4 µm in the best cases.

ITS also revealed that hitherto membrane formation occurs only in ∼1% of all tracks, or even less. The reason for this poor abundance seems to be that the decisive factor for membrane formation, which is the firm anchoring of the emerging solid Ag₂O or LiF reaction products on the etched track walls, was hitherto rarely fulfilled. We attribute this tentatively to the too high test voltage applied for controlling the CCR process that might hinder the product anchoring on the walls by promoting nanofluidic electromigration. Indeed, voltage reduction seems to improve the situation.

Keywords:

• ions
• etching
• tracks

Acknowledgements

D.F. is grateful to the Universidad Autónoma Metropolitana-Cuajimalpa, Mexico City, for the guest professorship in the frame of the Cathedra “Roberto Quintero Ramírez” and to both the Ben Gurion University of the Negev, Beer Sheva, and the Nuclear Physics Institute, Rez, for providing travel support. We are further obliged to Dr P. Apel from JNRI Dubna, Russia, for providing us with the ion-irradiated polymer foils. L.A. would like to acknowledge the Edmond J. Safra Center for the Design and Engineering of Functional Biopolymers in BGU.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This project was supported by the Grant Agency of the Czech Republic [P108-12G-108].