Author: Md Rubel Khan

Publisher:

Published: 2021

Total Pages: 192

ISBN-13:

Surfactants are extensively used as corrosion inhibitors to mitigate the internal corrosion of oil and gas pipelines. Surfactants are amphiphilic, consisting of both polar headgroup and nonpolar tail group. The arrangement of headgroup and tail group governs the adsorption as well as the inhibition process. In this dissertation, we explore the conformation of the short alkyl chain length and the nature of the headgroup of surfactants that affects on the ordering of interfacial water molecules. Quaternary ammonium compound (Quat) with five different chain lengths were synthesized via Quaternization of primary amine with Bromo alkane. Imidazolines with five different chain lengths were synthesized from fatty acid or aldehyde and amine. Aqueous solutions of Quat at different ionic strengths were studied by surface and interface selective sum frequency generation spectroscopy technique at the air-liquid interface. We found that Quat solutions containing 0%, 1%, and 10% NaCl salt showed no clear trend for the number of gauche defect as a function of ionic strength. In general, the longer chain surfactants were found to have more ordered interfacial water molecules compared to the shorter ones at the air-liquid interface. The SFG results were correlated with the surface tension measurements and pH values. As a continuation, the self-assembly of surfactant was also studied in-situ at the liquid-metal interface by SFG spectroscopy. A self-assembled monolayer at liquid-metal interface is vital for corrosion, catalysis, and electrochemical reactions. We probed the adsorption and self-assembly of Quats at the liquid-metal interface by SFG spectroscopy without applying any external potential. This provides direct evidence of the effect of alkyl chain length of surfactants in the conformational changes of an adsorbed monolayer on the liquid-metal interface. We found that longer chain surfactant forms highly ordered monolayer due to the strong tail-tail interaction. On the other hand, shorter chain surfactant forms less ordered monolayer due to weak tail-tail interaction.