Journal
SOFT MATTER
Volume 16, Issue 30, Pages 7040-7051Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d0sm00738b
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Funding
- CONICET
- UBA (UBACyT) [20020150100079BA, 20020170200298BA]
- Ministry of Science, Technology and Innovation (MINCYT-FONCYT, Argentina) (Swiss National Science Foundation, Switzerland) [PICT 2011-0377, CONICET 1084/17]
- Ministry of Science, Technology and Innovation (Bilateral Project CONICET-SNSF) (Swiss National Science Foundation, Switzerland) [CONICET 1084/17]
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Liquid-polymer contact electrification between sliding water drops and the surface of polytetrafluoroethylene (PTFE) was studied as a function of the pH and ionic strength of the drop as well as ambient relative humidity (RH). The PTFE surface was characterized by using SEM, water-contact-angle measurements, FTIR spectroscopy, XPS, and Raman spectroscopy. The charge acquired by the drops was calculated by detecting the transient voltage induced on a specifically designed capacitive sensor. It is shown that water drops become positively charged at pH > pH(zch)(pH(zch)being the zero charge point of the polymer) while they become negatively charged for pH < pH(zch). The addition of non-hydrolysable salts (NaCl or CaCl2) to water decreases the electrical charge induced in the drop. The charge also decreases with increasing RH. These results suggest proton or hydroxyl transfer from the liquid to the hydrophobic polymer surface. A proposed thermodynamic model for the ion transfer process allows explaining the observed effects of RH, pH and ionic strength.
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