Influence of binding strength of added electrolytes on the properties of micelles and of micellized radical pairs

• Published in: Langmuir 1992-02, Vol.8 (2), p.475-480
• Main Authors: Lei, Xuegong, Zhao, Guohua, Liu, Youcheng, Turro, Nicholas J
• Format: Article
• Language: English
• Subjects: 400102 - Chemical & Spectral Procedures; 400201 - Chemical & Physicochemical Properties; 400500 - Photochemistry; AROMATICS; CHARGED PARTICLES; CHEMICAL REACTIONS; Chemistry; Colloidal state and disperse state; CONDENSED AROMATICS; DATA; DECOMPOSITION; ELECTROLYTES; Exact sciences and technology; EXPERIMENTAL DATA; GADOLINIUM IONS; General and physical chemistry; HYDROCARBONS; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IONS; KETONES; MAGNETIC FIELDS; MICELLAR SYSTEMS; Micelles. Thin films; NUMERICAL DATA; ORGANIC COMPOUNDS; PHOTOCHEMICAL REACTIONS; PHOTOLYSIS; PYRENE; RADICALS; SPECTROSCOPY; SURFACTANTS
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la00038a028

p-Methyldibenzyl ketone (1), pyrene (2), and 1,3-di-[alpha]-napthylpropane (3) have been employed as probes of the effects of added electrolytes on the properties of micelles and of the effects of an applied magnetic field on the reactivity of micellized radical pairs. The effect of added electrolytes depends on the structure of the surfactant head group, the length of the hydrocarbon chain of surfactants, the added gegenions, and the temperature. The electrolytes added were found to exhibit both a [open quotes]salt effect[close quotes] on the physical properties of micelles, which is related to the strength of their binding to the micellar surface, and a [open quotes]magnetic effect[close quotes], which is related to the ability of a bound cation to relax the triplet state of a micellized radical pair and thereby modify the reactivity of the pair. In aqueous solutions of anionic surfactants, Gd[sup 3+] causes a large magnetic field dependent internal magnetic field effect in addition to a salt effect on micellar properties. The internal magnetic field effect is independent of the length of hydrocarbon chain, but is dependent on the surface density of bound Gd[sup 3+] ions. The salt effect on micellar properties decreases with the increase of the length of hydrocarbon chain of the surfactants and with the surface density of added ions. In aqueous solutions containing neutral TX-100 micelles or cationic micelles (cetyltrimethylammonium bromide, CTAB), Gd[sup 3+] shows only a small salt and a small internal magnetic field effect. Addition of lanthanide salts results in a dramatic increase in the aggregation number of sodium dodecyl sulfate (SDS) micelles. 28 refs., 6 figs., 1 tab.