Controlling molecular interactions to define interfacial phenomena and structure

Polymers and surfactants are often employed together in a wide range of formulations, such as paints, foodstuffs, pharmaceuticals and in detergency. Using the polymers and the surfactants together in a formulation provides additional or modulated physicochemical properties required for certain applications. Therefore, a good knowledge of the properties of these components and the interactions between each in mixtures ensures that formulation is more of an engineered approach than a “black” art. In this thesis, the interactions between polymers and small molecules were probed in various states: solution, gel and foam. The main techniques used were tensiometry, diffusion NMR and small-angle neutron scattering (SANS). The experiments involved investigating the competitive interactions between Pluronic P123 and small molecule surfactants, SMS, (sodium dodecylsulfate, SDS or C12SO4Na, dodecyltrimethylammonium bromide, C12TAB and polyoxyethylene (23) lauryl ether, Brij 35) in the presence of alcohols (ethanol, hexanol and decanol). The composition of the mixed micelles formed was found to be sensitive to the nature of the alcohol present in the system. Gelation from Pluronic P123, F108 and their mixtures was also investigated. P123 showed very interesting changes in its phase behaviour as both temperature and polymer concentration were varied. Whilst for F108, the phase behaviour remained largely unchanged, insensitive to any variation in concentration and temperature. The phase behaviour of gels from mixtures of both Pluronics showed dependence on the Pluronic ratio in the mixture and the temperature. Finally, in-situ investigations of wet and dry foams stabilised by SMS (alkyl sulfates and alkyl bromides) and mixtures of polymers (P123, poly(vinylpyrrolidone), PVP) with the SMS were performed using SANS. SANS was deployed to probe the structure of the surfactant and/or polymer at the foam air/water interface. Data analysis and modelling suggested the presence of an interfacial structure comprising paracrystalline stacks (around five layers) of adsorbed surfactant and/or polymer layers interspersed with water layers. The thickness of these layers was found to be sensitive to the SMS architecture (hydrocarbon chain length) and to the strength of the interactions between the polymers and the SMS in the mixtures case.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Greenwich

Year dc:date.issued

2016

Author dc:creator

• Mansour, Omar

Advisors dc:contributor.advisor

• Griffiths, Peter
• Alexander, Bruce

• QD Chemistry

Language dc:language

en