engleski

Temperature effects on the inert material/aqueous electrolyte solution interface

Hydrophobic materials, such as inert gases, hydrocarbon oils, ice, Teflon or diamond do not chemically react neither with water molecules neither with ions from aqueous electrolyte solution. Due to surface hydrophobicity water dipoles are repulsed from the surfaces and orientation of water molecules is less random than in the bulk of the solution. This ordering and distribution of the water molecules and ions in the vicinity of the surface causes the formation of the electrical interfacial layer [1]. It was found for all hydrophobic materials that the electrophoretic mobility, and thus the surface charge and surface potentials, are pH dependent [2]. The value of isoelectric point was found to be in the acidic region, between pH 2 and 4. The origin of electrical charge of the inert material/interface, and pH dependency, have been a subject of numerous debates in the recent years and is still not solved [3]. In this research we analyzed reactions and process within interfacial layer of inert (Teflon, diamond and graphite)/aqueous electrolyte solution. We defined hydronium (H+) and hydroxide (OH¬−) ion as potential – determining ions. The distribution of H+ and OH− ions between bulk and interface is described as separate accumulation of H+ and OH− ions at the interface. Total reaction is described as exchange of H+ and OH− ions between bulk of solution and the interface [ ] (Figure 1). The thermodynamic parameters of the above mentioned processes are obtained indirectly from the temperature dependency of equilibrium parameters. Determining temperature dependence of electroneutrality points (isoelectric point or point of zero charge) enables the evaluation of the difference in standard distribution enthalpies of H+ and OH−. This data enables us to better understand the behaviour of the electrical interfacial layer and creation of the suitable mathematical and physical models [4]. Electroneutrality points were obtained in the temperature range from 10 °C to 50 °C by using variety of methods: Streaming potential, Electrophoretic mobility and potentiometric mass titration. Differences in standard distribution enthalpy of H+ and OH− ions on the Teflon, diamond and graphite surfaces was calculated and compared.

PTFE, diamond, graphite, inert surfaces, electroneutrality point, temperature dependency, Streaming potential, Potentiometric mass titration, SCrE potential

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