Adsorption of nonionic Brij and Tween surfactants at PTFE-water and air-water interfaces: Investigations on wetting, dispersion stability, foaming and drug solubilization

Abstract

Aqueous solutions of nonionic surfactants, namely Brij O10, Brij 35, Brij 98, Tween 20, Tween 60 and Tween 80 are investigated to understand their diffusion from the bulk solution to the surface and adsorption processes at PTFE-water interface using dynamic surface tension (DST), water penetration in packed PTFE powder and rate of sedimentation measurements. DST correlates well with the water penetration in packed PTFE powder (wettability) and the rate of sedimentation in aqueous dispersions for Brij surfactants. The results are described in terms of the structural features and HLB of respective surfactant and its ability to diffuse and adsorb at the interface. Brij O10 and Tween 60 showed maximum wettability and dispersion stability for respective series. We correlate the dynamic surface tension with interfacial phenomenon e.g. water penetration in the packed PTFE powder and the rate of sedimentation for aqueous dispersions. The diffusion towards air-water interface was essentially controlled by the molecular weight of the surfactant, while adsorption on the hydrophobic PTFE is controlled by the HLB of the respective surfactant molecule. We introduce a strategy to use PTFE particles as model for aqueous formulations involving hydrophobic drugs. The water penetration, wettability and stability of PTFE dispersions increase with lower DST values.