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Fracto-eutectogels: SDS dendritic fractals via counterion condensation in a deep eutectic solvent

DOI: 10.1039/D1CP01370J DOI Help

Authors: Lauren Matthews (University of Bristol) , Silvia Ruscigno (University of Bristol) , Sarah E. Rogers (University of Bristol) , Paul Bartlett (University of Bristol) , Andrew J. Johnson (ISIS Muon and Neutron Source) , Robert Sochon (ISIS Muon and Neutron Source) , Wuge H. Briscoe (University of Bristol)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Chemistry Chemical Physics

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 20171

Open Access Open Access

Abstract: Glyceline, a deep eutectic solvent comprising glycerol and choline chloride, is a green nonaqueous solvent with potential industrial applications. Molecular mechanisms of surfactant self-assembly in deep eutectic solvents are expected to differ from those in their constituent polar components and are not well understood. Here we report the observation of self-assembled SDS fractal dendrites with dimensions up to ~ mm in glyceline at SDS concentrations as low as cSDS ~ 0.1 wt%. The prevalence of these dendritic fractal aggregates led to the formation of a gel phase at SDS concentrations above ≥ 1.9 wt% (the critical gelation concentration cCGC). The gel microscopic structure was visualised using polarised light microscopy (PLM); rheology measurements confirmed the formation of a colloidal gel, where the first normal stress difference was negative and the elastic modulus was dominant. Detailed nano-structural characterisation by small-angle neutron scattering (SANS) further confirmed the presence of fractal aggregates. Such SDS aggregation or gelation has not been observed in water at such low surfactant concentrations, whereas SDS has been reported to form lamellar aggregates in glycerol (a component of glyceline). We attribute the formation of the SDS fractal dendrites to the condensation of counterions (i.e. the choline ions) around the SDS aggregates - a diffusion-controlled process, leading to the aggregate morphology observed. These unprecedented results shed light on the molecular mechanisms of surfactant self-assembly in deep eutectic solvents, important to their application in industrial formulation.

Subject Areas: Chemistry, Physics

Instruments: I07-Surface & interface diffraction

Other Facilities: ISIS

Added On: 10/05/2021 13:54


Discipline Tags:

Surfaces Physics Physical Chemistry Chemistry

Technical Tags:

Diffraction X-ray Reflectivity (XRR)