Like polymers, wormlike micelles (WLM) form viscoelastic solutions, but their structure is maintained by a delicate balance of transient molecular interactions, in which they are continuously breaking and reforming within a finite timescale. Another interesting feature of WLM involves the possibility to modulate their rheology. For example, in the case of cationic surfactant, by changing the aromatic co-solute used in the aqueous formulation. WLM are favourable formed by combination of cetyltrimethylammonium bromide (CTAB) with salicylate. However, it is well known that salicylate also form complex with Fe (III), giving to the solution the characteristic purple colouring. Therefore, it is expected that in presence of the three components, CTAB, salicylate and Fe (III) a competition by salicylate can be stablished. The hydrolysis of Fe(III) naturally conditioned the system to lower pH, and Fe(III) hydroxide are prompt formed by the adjustment of the pH to 7. By combination of the three components, followed by the adjustment of the pH to 7, spherical nanoparticles of iron (III) oxy-hydroxide with diameter around 3-5 nm were generated and maintained dispersed in aqueous solutions due to the presence of WLM. It was observed that the colloidal dispersion was stable for more than six months and the great stability is explained by the adsorption of the nanoparticles onto the surface of the wormlike micelles, forming a supramolecular pearl-necklace-like structure. Such structure was confirmed by DLS and SAXS experiments, in which the structural parameters of the complex formed by WLM and particle were obtained. Finally, TEM and Cryo-TEM were used to obtain a final characterization of the system.<br/>

Stabilization of spherical nanoparticles of iron (III) oxy-hydroxides by wormlike micelles

254th National Meeting (2017)

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