The aim of this study was to investigate possible interactions between a polymeric emulsifier and a non-ionic surfactant, with a view of achieving better understanding of emulsion stabilisation mechanisms. The polymeric emulsifier used was acrylates/C10-30 alkyl acrylate crosspolymer (Pemulen TR-2(R)), while Polyoxyethylene 20 sorbitan mono-oleate (Polysorbate 80) has been chosen as a model surfactant. Both materials were used within the concentration range relevant for their practical application. A 0.2%w/w aqueous dispersion of polymeric emulsifier, containing various amounts of surfactant (from 0.01 to 1.0% w/w) was used throughout the study. Interfacial aspects of the proposed polymer/surfactant interactions were analysed by means of surface tension measurements. Changes in the network structure of the test dispersions were quantified by continuous shear rheometry, supported by the texture analysis. To analyse the influence of hydrophobic alkyl groups present on the Pemulen TR-2(R) chains, an unmodified, hydrophilic polyacrylic acid polymer, Carbopol 934P(R), was assessed under the same conditions. The results obtained by both surface tension and rheological studies have revealed large differences in behaviour of the two polymers in the presence of the model surfactant. Pemulen TR-2(R) was shown to desorb the surfactant from the surface, within the whole concentration range studied. Furthermore, an increase in viscosity and texture profile parameters with increasing Polysorbate 80 concentration up to 0.3% w/w was evident in the case of Pemulen TR-2(R) dispersions. This was followed by a decrease in the gel network strength at higher surfactant concentrations. On the other hand, Carbopol 934P(R) has shown no signs of surfactant desorption and only small changes in the network structure with the increasing concentration of surfactant. It is shown in this study that an interaction between a polymeric emulsifier Pemulen TR-2(R) and a non-ionic surfactant Polysorbate 80 does occur in their aqueous dispersion, and that it is: (a) hydrophobic in nature; (b) concentration-dependent; and (c) has an impact on the rheological properties of dispersion.
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