盐溶液条件对边界润滑添加剂在带电表面吸附行为的影响

To reveal the effect of salt solution condition on adsorption behaviors of boundary lubrication additive poly(carboxylate ether) (PCE), normal interaction forces are directly measured between charged mica surfaces in multiple aqueous solutions of a commercial PCE by a surface forces apparatus. Force-distance measurements indicate that the PCE weakly adsorbs onto mica from 0.1 mol/L K₂SO₄ and its boundary adsorption layers (about 50 Å thick) are totally squeezed out from the surface gap under an equivalent load level of three to four atmosphere pressures. The PCE is able to immediately accomplish the same adsorption after desorption. In the same ionic strength condition of 0.1 mol/L Ca(NO₃)₂, the PCE does not adsorb onto mica. However, the PCE builds up a 40-angstrom-thick robust adsorption layer on mica in the low calcium solution of 5 mmol/L Ca(NO₃)₂. Divalent Ca²⁺ ions are able to bridge adsorbed PCE layers while monovalent K⁺ ions unable. The divalent cation bridging adsorption mechanism only functions in a finite ion concentration range.