Hierarchical Self-Assembly in Hydrogen-Bonding Rich Green Nonaqueous Solvents

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Understanding the self-assembly mechanism of surfactants in nonaqueous polar
solvents is important to many practical applications, industrial formulation, and biological processes. However, despite this importance, the mechanism of self-assembly in nonaqueous media is not well understood, and the applicability of concepts and models derived for selfassembly in aqueous media has not been well discussed in current literature. Improving our fundamental understanding of the self-assembly mechanism would allow us to link solvent properties, such as the solvent hydrogen-bonding, to the ability to support self-assembly, crucial for both industrial and biological applications.
This project investigates self-assembly behaviour of amphiphiles in a green hydrogen bonding rich nonaqueous solvent, glycerol, and to assess the validity of the models designed for aqueous self-assembly. The surfactant chosen, sodium dodecyl sulfate, is well-studied in aqueous media, allowing for direct comparisons with current literature. The differences in bulk self-assembly were probed using small-angle neutron scattering (SANS), rheology, and microscopy techniques.
The self-assembly structure in glycerol showed a striking difference compared to that in water, as a low molecular-weight gel formed upon addition of cSDS ~ 2 wt %. Through SANS and polarising light microscopy measurements, the structure was determined to be fibrillar on the microscale, with a diameter, D ~ 0.5 μm, and lamellar on the nanoscale. This contrasts with the behaviour observed in aqueous media, where globular ellipsoidal SDS micelles form. Furthermore, this gel phase was sensitive to many environmental conditions, e.g. temperature, water content, and the presence of electrolyte. Such unprecedented observations point to different driving forces for self-assembly in glycerol compared to in water, highlighting the role of a number of molecular parameters, in addition to hydrogen-bonding properties, of the solvent in mediating self-assembly.
Date of Award26 Nov 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SponsorsGlaxoSmithKline Consumer Healthcare, GlaxoSmithKline
SupervisorWuge H Briscoe (Supervisor), Paul Bartlett (Supervisor), Robert Sochon (Supervisor) & Andrew Johnson (Supervisor)

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