Sosa MD, D'Accorso NB, Martínez Ricci ML, Negri RM. Liquid-Polymer Contact Electrification: Modeling the Dependence of Surface Charges and ξ-Potential on pH and Added-Salt Concentration.
LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022;
38:8817-8828. [PMID:
35834348 DOI:
10.1021/acs.langmuir.2c00813]
[Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Here, a mathematical model is presented, which accounts for the dependence of the surface electrical charge density (σ) on pH and the 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 ξ-potential as a function of pH, reported in the literature by other authors for water-poly(tetrafluoroethylene) (PTFE) interfaces. Hence, the dependence of σ and ξ on 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/μm2. The model predicts the increase of |σ| and |ξ| with pH in the range of 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 ∼ 9 × 107, where Ka and Kb are the respective acid and base equilibrium constants. On the other hand, the observed decrease in |σ| and |ξ| with Cs at fixed pH is quantitatively described by introducing an activity factor associated with the quenching of water activity by the salt ions at the polymer-water interface, with quenching constant Kq. Additionally, the quenching predicts a decrease in |σ| and |ξ| at extreme pH, where I > (1/Kq) (I: ionic strength), in agreement with literature reports.
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