Liquid-Polymer Contact Electrification: Modelling the Dependence with pH and Added-Salt Concentration of Surface Charges and Zeta Potential

SOSA, MARIANA D.; MARTÍNEZ RICCI, LUZ; D´ACCORSO, N.; NEGRI, RICARDO MARTÍN

LANGMUIR

AMER CHEMICAL SOC

Lugar: Washington; Año: 2022 vol. 38 p. 8817 - 8828

0743-7463

A mathematical model is presented, which accounts for the dependence of the surface electrical charge density (σ) with pH and concentration of added salts (Cs), generated when a water drop rolls or slides on the surface of a hydrophobic polymer, a process known as liquid-polymer contact electrification (LPCE). The same model was successfully applied to fit the isotherms of zeta potential (ξ) as a function of pH, reported in literature by other authors for water-polytetrafluoroethylene (PTFE) interfaces. Hence, the dependence of σ and ξ with pH was described using the same concept: acid-base equilibria at the water-polymer interface. Equilibrium constants were estimated by fitting experimental isotherms. The experimental results and the model are consistent with a number of 10-100 acid-base sites per m2. The model predicts the increase of |σ| and |ξ| with pH in the range 2-10 and the existence of a zero-charge point at pHzcp  3 for PTFE (independent of Cs). Excellent fits were obtained with Ka/Kb  9x107, where Ka and Kb are the respective acid and base equilibrium constants. On the other hand, the observed decrease of |σ| and |ξ| with Cs at fixed pH is quantitatively described by introducing an activity factor associated to the quenching of water activity by the salt ions at the polymer-water interface, with quenching constant Kq. Additionally, the quenching predicts a decrease of |σ| and |ξ| at extremes pH, where I > (1/Kq) (I : ionic strength), in agreement with literature reports.