Liquid-Polymer Triboelectricity: Chemical Mechanisms in the Contact Electrification Process

SOSA, M.D.; MARTÍNEZ RICCI, M.L.; MISSONI, L.L.; MURGIDA, D.H.; CÁNNEVA, A.; DÁCCORSO, M.B.; NEGRI, R.M.

SOFT MATTER

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2020

1744-683X

The liquid-polymer contact electrification between sliding water drops and the surface ofpolytetrafluoroethylene (PTFE) was studied as function of pH and ionic strength of the drop as wellas ambient relative humidity (RH). The PTFE surface was characterized by SEM, water-contactanglemeasurements, FTIR, XPS, and Raman spectroscopy. The charge acquired by the drops wascalculated by detecting the transient voltage induced on a specifically designed capacitive sensor. It is shown that water drops become positively charged at pH> pHzch (being pHzch the zero charge point of the polymer), while negatively charged for pH< pHzch. The addition to the water of nonhydrolysable salts (NaCl, CaCl2) decreases the electrical charge induced in the drop. The charge alsodecreases 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.