Investigation of the aggregation behaviour of the anionic surfactant sodium dodecyl sulfate in ionic liquids 1-allyl-3-methylimidazolium chloride and 1-Ethyl-3-methylimidazolium diethyl phosphate

• Published in: Journal of molecular liquids 2021-12, Vol.343, p.117610, Article 117610
• Main Authors: Żywociński, Andrzej, Bernatowicz, Piotr, Pociecha, Damian, Górecka, Ewa, Gregorowicz, Jacek
• Format: Article
• Language: English
• Subjects: Anionic surfactant; Ionic liquids; Lamellar phase; Micelles
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2021.117610

[Display omitted] We investigated the aggregation behaviour of the anionic surfactant sodium dodecyl sulfate (SDS) in 1-allyl-3-methylimidazolium chloride (AMIMCl) ionic liquid at three temperatures 323 K, 333 K and 343 K using 1H Nuclear Magnetic Resonance (NMR) chemical shift and Pulsed-Field Gradient (PFG) spin-echo NMR self-diffusion measurements. Chemical shifts of SDS protons and diffusion coefficients of SDS as a function of the surfactant concentration have breakpoints, which indicate an onset of the surfactant micellisation. We estimated the critical micelle concentration (cmc) with high accuracy from SDS methyl protons' chemical shifts and the micelles' average aggregation number from diffusion coefficients. The formation of micelles does not influence the diffusion and chemical shifts of AMIMCl. We determined water concentration in the samples from the NMR spectra. We did not find evidence that water affects the aggregation process since water content practically does not influence the SDS protons' chemical shifts and diffusion coefficients. However, water appears to influence the diffusion and chemical shifts of AMIMCl. We also investigated the behaviour of SDS in 1-Ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) hydrophilic ionic liquid. The value of the Gordon parameter of EMIMDEP indicates that it does not possess the ability to support the self-assembly of amphiphiles. Within this work, we treat the system SDS/EMIMDEP as a reference one. SDS forms a lamellar phase in AMIMCl at high concentration, as revealed by Small Angle X-ray Scattering (SAXS) and Polarised Optical Microscopy (POM) investigations. At about 358 K, a transition from the lamellar phase to the isotropic liquid phase occurs. No other liquid-crystalline phase in this system was determined.