Small-angle neutron scattering has been used to probe the interfacial structure of nitrogen-in-water foams created using a series of small molecule surfactants, triblock polymeric surfactants of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(EOx-POy-EOx) range, their blends and partially hydrophobic particles. Universally, the data follow a pronounced Q<sup>-4 </sup>decay, along with a number of inflexions and weak but well defined peaks. For the surfactants, these characteristics were well described by a model embodying paracrystalline stacks of adsorbed surfactant layers, whose formation is induced by the presence of the air-water interface, adsorbed at the flat air-water (film lamellae) interface. Typically, a minimum of five paracrystalline surfactant layers of thickness of the order 85-160 Å, interspersed with somewhat thicker (400 Å) films of continuous aqueous phase were found to best fit the data. For the triblock copolymer data, the thickness of the layer (L) was shown to follow a simple empirical relationship with the EO and the PO block sizes. Similar features were observed in the particle foams data, but it is less obvious how to interpret these data. A selection of data will be discussed and set into the wider context of how surface actives species assemble at air/water interfaces.

Interfacial structure of small molecule surfactant, polymeric surfactant and particle stabilised air-in-water foams</b>

251st National Meeting (2016)

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