Spontaneous multilayer formation at interfaces from self-assembly of mixed surfactant and polymer/surfactant mixtures

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Until relatively recently the formation of multilayer structures at surfaces and interfaces from self-assembling systems was rarely observed. This was in part due to a lack of suitable experimental tools to probe such surface structures. They are being increasingly recognised as an important structural signature associated with a wide range of technological applications and biological functions. There is now some preliminary experimental evidence that an increasing range of different systems can be manipulated to form or will spontaneously form multilayer structures at interfaces; including lipids, surfactants, mixed surfactants, polyelectrolytes, and polyelectrolyte / surfactant mixtures. Such structures have important implications in many aspects of lubrication, such as in fabric and hair conditioners, and in bio-lubrication in general. Although the criteria for the formation of lamellar type structures in bulk solution are well-established, the major factors controlling their formation at surfaces and interfaces are not understood and have not been extensively investigated. We propose here to use primarily neutron scattering techniques (specular and off-specular reflectivity, in combination with H/D isotopic substitution) to investigate the nature of the multilayer structures at the air-solution, solid-liquid and liquid-liquid interfaces, in surfactants and surfactant mixtures and in polymer / surfactant mixtures, in order to establish the key factors that determine multilayer formation, and to provide a theoretical link to the associated surface tension and wetting properties, and the kinetics of formation / dissolution. It is expected that this research programme will provide new understandings relating to biological function and to developments of new products associated with soft lubrication and efficient controlled delivery of benefit agents to interfaces.