Surface charge density on silica in alkali and alkaline earth chloride electrolyte solutions

摘要

The surface charge density of colloidal SiO2 (Aerosil 380) was measured in alkali chloride (0.067 and 0.20 M LiCl, NaCl, and KCl) and alkaline earth chloride (0.067 M MgCl2, CaCl2, SrCl2, BaCl2) solutions. Measurements were conducted at 25 degrees C by potentiometric titrations using the constant ionic medium method in a CO2-free system. The experimental design measured surface charge for solutions with constant ionic strength as well as constant cation concentration. Alkali chloride solutions promote negative surface charge density in the order LiCl < NaCl < KCl to give the "regular" lyotropic behavior previously reported. In contrast, the alkaline earth chloride solutions exhibit a reversed lyotropic trend with increasing crystallographic radius where increasing negative charge is promoted in the order BaCl2 < SrCl2 < CaCl2 < MgCl2.