Mix-and-match diols: adjusting self-assembly of micellar phases in choline chloride eutectics

DOI: 10.3390/cryst12111621

Authors: Oliver Hammond (University of Bath) , Adrian Sanchez-Fernandez (University of Bath) , Rachel Tyte (University of Bath) , Robert Dalgliesh (ISIS Neutron and Muon Source) , Andrew J. Smith (Diamond Light Source) , Karen Edler (University of Bath)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Crystals , VOL 12

State: Published (Approved)
Published: November 2022
Diamond Proposal Number(s): 15194

Abstract: The common Deep Eutectic Solvent (DES) ‘ethaline’ (1:2 choline chloride:ethylene glycol) was examined here as a basis for the self-assembly of the surfactant dodecyltrimethylammonium bromide (C12TAB). A phase diagram was constructed, showing evidence for a L1 (micellar) phase, confirmed by tensiometry to have a room temperature critical micelle concentration (CMC) of 1.2 wt.%. Small angle neutron scattering (SANS) measurements indicate formation of interacting globular micelles with slightly smaller apparent radii than in water. The apparent mesophase/multiphase region was studied using SWAXS, demonstrating rich mesoscopic lyotropic liquid crystalline phase behaviour, with evidence for lamellar Lα peaks, alongside potential co-crystalline phases. We attempted to tailor the self-assembly by studying binary DES containing longer diols including 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, and ternary DES where the HBD component was a 1:1 ethylene glycol:diol mixture. However, synchrotron SAXS showed that only ternary ‘propethaline’ mixtures displayed signs of self-assembly and micellization, perhaps due to the reduction in calculated Gordon parameter, which decreases linearly with increasing alkyl chain length. Systematic differences were thus observed in the ability of the solvents to modulate assembly, from globular micelles in ChCl:EG, to weaker assembly in long-tail DES, and complete solubilisation in butaline and pentaline.

Diamond Keywords: deep eutectic solvents; surfactants; self-assembly; liquid crystals; small-angle scattering

Subject Areas: Chemistry


Instruments: I22-Small angle scattering & Diffraction

Other Facilities: Larmor at ISIS

Added On: 17/11/2022 10:20

Documents:
crystals-12-01621.pdf

Discipline Tags:

Chemistry

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)