The Adsorption of Nonionic Surfactants onto Stainless Steel Surfaces from Iso-Octane

Abstract

The synthesis of nine, nonionic, fuel-soluble poly(isobutylene)-based surfactants, and an assessment of their ability to remove and prevent carbonaceous deposit build up on light-duty vehicle engine valves, is described. Surfactants with varying surfactant head group polarity and structure, and tail length, were assessed for their potential fuel surfactant efficacy by establishing their adsorption kinetics and adsorption isotherms, from iso-octane, onto stainless steel surfaces, using both solution depletion and ellipsometry measurements. Increasing head group polarity from a simple phenol group, by the inclusion of an amine group, increased the adsorption affinity and the maximum adsorbed amount. Inclusion of additional amine groups also increased them maximum adsorbed amount, albeit only marginally. Replacing N-Me groups by N-H groups also increased the adsorbed amounts. Surfactant adsorption was found to be independent of tail length and the maximum adsorbed amount corresponded more-or-less to the surface concentration of strong acid groups on the steel surface, as determined by a Boehm titration. Additionally, all the surfactants studied appeared to adsorb onto the steel surface “irreversibly.”

Keywords:

• Fuel additives
• isooctane
• stainless steel
• surfactant adsorption
• synthetic fuel

The authors wish to thank Lubrizol (Belper, U.K.) for providing funding for this work, Katie Chapman (Lubrizol) for her assistance in synthesizing the surfactants, and Dr. John Clint (Hull University) for his assistance with the computer modeling program for ellipsometry analysis.

Notes

Part of the special issue, Surface and Colloid Chemistry Without Borders: An International Festschrift for Professor Per Stenius on the Occasion of His 70th Birthday.