Investigations of surfactant effects on gas hydrate formation via infrared spectroscopy

This infrared (IR) spectroscopic study addresses surfactant effects on cyclopentane (CP) hydrate-water interfaces by observing both ice-like (3100 cm(-1)) and water-like (3400 cm(-1)) bands in the bonded OH region together with free OH bands. IR spectroscopy of hydrates has not been actively employed due to the overwhelming signal saturation of the OH bonding. However, this work is able to utilize this large signal of the OH bonding to understand the water structure changes upon adding sodium dodecyl sulfate (SDS) to CP hydrate-water interfaces. The spectral data suggest a change to more ice like (3100 cm(-1)) features starting from 100 ppm to 750 ppm SDS, indicating favorable nucleation. At the same instance, water like (3400 cm(-1)) features are also shown in this range of SDS concentration, which suggests looser hydrogen bonding that is an indicator for facilitating hydrate growth. Additionally, this ATR-IR study firstly identifies both symmetric and anti-symmetric free OH bands of the hydrogen bond (HB) acceptors in the clathrate hydrate system. Relative area ratios of free and bonded OH bands provide important information about spatial arrangements of adsorbed SDS monomers.