Forças hidrofóbicas e eletrostáticas na formação de micelas gigantes de surfactantes quaternários de amônio e cossolutos aromáticos

Abstract

The effect of hydrophilic/hydrophobic balance on phenols as cosolutes in the formation of wormlike micelles (WLM) formed by hexadecyltrimethylammonium bromide (C 16 TAB) was studied.For this purpose, mixtures of phenol, 1-naphthol, 2naphthol, 2,3-dihydroxynaphthalene, and R-1,1'-bi (2-naphthol) and S-1,1 '-bi (2naphthol) in the presence of 100 mmol kg -1 of C 16 TAB.The phase behavior and rheology of these systems were evaluated.All the phenols showed to lead to the formation of WLM in certain concentrations, in addition, the presence of surfactant increased their solubility, as well as the number of hydroxyls in the structure of the cosolute.For phenol, a maximum in viscosity was observed as a function of the cosolute concentration, while for the others a plateau was observed until the point of phase separation.When the cosolutes are deprotonated by the addition of NaOH, the same trends are observed, however, the phase separation occurs by coacervation.Wormlike micelles obtained from the phenolate were shown to have maxwellian behavior close to the maximum in viscosity.The coacervates formed by phenolate were studied by rheology, small angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (Cryo-TEM).The results obtained corroborate the hypothesis of the formation of a network after coacervation.The effect of the form of the aggregate on the chirality of chiral surfactants containing systems was also studied.Spherical micelles of hexadecyl-N,N-dimethyl-N-(S)-(1phenyl)ethylammonium bromide (SC16), and dodecyl-N,N-dimethyl-N-(S)-(1phenyl)ethylammonium bromide (SC12) were studied by circular dichroism (CD), and it was shown that exciton coupling occurs when there is formation of SC12 micelles.This same effect was observed in the case of SC16 at concentrations about 17 times its cmc, attributed to the approximation of the aromatic groups of the surfactant headgroups.The addition of sodium salicylate (NaSal) to the solutions of these surfactants led to the formation of WLM only in the case of SC16.WLM were characterized by rheology, Cryo-TEM, isothermal titration calorimetry (ITC) and CD.From CD, it was possible to observe that the presence of salt set apart the heads of the surfactant molecules, extinguishing the exciton coupling.Still using the CD technique, the cmc of two ionic surfactants (tetradecyltrimethylammonium bromide, C 14 TAB, and sodium dodecylsulfate, SDS) were determined using a chiral molecule (R-1,1'-bi (2-naphtolate) and S-1,1'-bi (2-naphtolate)) as a probe.