Interfacial and solution properties of binary mixtures containing partially fluorinated and hydrocarbon surfactants

Abstract

Use of fluorocarbon (FC) surfactants in industrial formulations is known to lead to environmental consequences, and as such these are often formulated as mixtures containing partially fluorinated and hydrocarbon (HC) surfactants. In this thesis, the solution, surface and bulk properties of three mixed surfactant systems each containing a partially fluorinated surfactant (anionic, non-ionic or zwitterionic) and a common anionic hydrocarbon (HC) surfactant (sodium dodecylsulfate) are investigated.

The surface and bulk properties of the individual FC surfactants were first of all characterised prior to studies of FC: HC surfactant mixtures. All FC surfactants were found to generate very low surface tensions (γ_CMC < 20.0 mN m^-1) at low critical micelle concentrations (< 2.00 mM).

Solution properties of the FC: HC surfactant mixtures were examined in terms of both critical aggregation concentrations (CACs) and dynamic surface tension decays (γ(t)). The γ(t) decay data were dominated by the presence of FC surfactants in all mixtures, so much so that mixtures containing high bulk HC surfactant compositions produced equilibrium surface tensions (γ_eq) values of ~ 18.7 mN m^-1. Contrast variation neutron reflectivity (NR) experiments allowed the composition of the air/ water interface to be determined, showing domination of the more surface active FC surfactants even at low concentrations, which was further enhanced through dilution of the bulk solution.

Small-angle neutron scattering (SANS) experiments showed formation of mixed FC: HC surfactant micelles in all investigated systems, with sizes tending towards those of the individual FC surfactant micelles at high FC bulk compositions and vice versa. The mixed micelle compositions were similar to bulk compositions, unlike surface compositions.

These results have shown mixed systems containing partially fluorinated and HC surfactants achieve the desired solution properties of FC surfactants (low γ_eq and CMC) even at both low FC compositions and concentrations, therefore providing important insight into the development of new low FC containing formulations.

Date of Award	25 Jun 2019
Original language	English
Awarding Institution	The University of Bristol
Sponsors	Angus Fire Ltd.
Supervisor	Julian Eastoe (Supervisor) & Paul Bartlett (Supervisor)