Polymer/surfactant Interactions at the Air-water Interface
: From Synergy to Competition

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Understanding the adsorption behaviour of polymer/surfactant mixtures at the air-water interface is of fundamental importance and has direct relevance to a variety of practical applications. Polymer/surfactant systems comprising neutral amphiphilic PEG-g-PVAc co-polymer (consisting of a hydrophilic polyethylene glycol backbone with hydrophobic polyvinyl acetate grafts) with anionic sodium dodecylsulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and non-ionic dodecylpentaethyleneglycol ether (C12E5) were investigated at the air-water interface by a combination of dynamic and equilibrium surface tension, neutron and X-ray reflectivity (NR and XRR), and preliminary foam behaviour tests.
Surface tension data analysis revealed a transition from synergistic adsorption at low surfactant concentrations to a competitive adsorption behaviour with increasing surfactant concentration. The effect of surfactant headgroup characteristics (charge and size), and the effect of polymer architecture (PVAc graft length, number and ratio) was linked to the polymer/surfactant adsorption behaviour. Complementary NR and XRR measurements allowed elucidation of the interfacial composition and structure, revealing ~ 2 nm thick layer at the air-water interface (depending on the polymer/surfactant concentrations). The polymer was depleted from the interface with increasing surfactant concentration and formed a weakly associated layer “hanging” proximally to the interface. The thickness of this polymer layer, as well as the overall composition of the interfacial layer, played an important role in enhancing foam stability, and strongly depended on the surfactant and polymer characteristics.
Furthermore, the adsorption and complexation behaviour of anionic SDS and cationic surfactant vesicles, formed from double-tailed diethyloxyester dimethylammonium chloride (DEEDMAC), were investigated in bulk and at interfaces. Dynamic light scattering and ζ-potential studies, as well as imaging techniques, indicated strong complexation of SDS/DEEDMAC in bulk. Finally, DEEDMAC bilayers were formed on mica via vesicle rupture, and the interactions with SDS were studied using XRR and surface force apparatus (SFA) at the solid-liquid interface, where a pronounced increase in layer thickness was observed assigned to a formation of alternating DEEDMAC/SDS strongly-interacting layers at the interface.
Date of Award24 Mar 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SponsorsProcter & Gamble Newcastle Innovation Centre & Procter & Gamble Bejing Innovation Centre, China
SupervisorWuge H Briscoe (Supervisor)

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