Investigations of surfactant effects on gas hydrate formation via infrared spectroscopy

[Display omitted] ► Explain the full role of SDS in nucleation and extended growth phase using IR spectroscopy. ► Observe both ice- and water-like OH stretches of hydrate–water interface at or above 100ppm SDS. ► Detect both symmetric and asymmetric, free OH bands of the HB acceptor in the hydrate–water interface. ► Provide important insights to spatial positions of SDS molecules absorbed onto the interface from free/bonded OH bands. This infrared (IR) spectroscopic study addresses surfactant effects on cyclopentane (CP) hydrate–water interfaces by observing both ice-like (3100cm−1) and water-like (3400cm−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 (3100cm−1) features starting from 100ppm to 750ppm SDS, indicating favorable nucleation. At the same instance, water like (3400cm−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.