Small-angle neutron-scattering (SANS) measurements have been performed on 0.3 M sodium dodecyl sulfate (SDS) micellar solutions containing different ammonium salts, NH4X (X ) Cl, Br, I, NO3, or SCN) at 30 °C. The data indicate that an increase in micellar size takes place at all salt concentrations. At 0.1 M NH4X, the aggregation number (n ˜) of the micelle depends upon the nature of coion X, the order being NO3 -= SCN -< I -= Cl -= Br -, a trend almost opposite to what others have observed for spherical micelles. This observation provides information that the order of preference of added ion is dependent on the size and shape of the aggregate. It was concluded that the micellar aggregation number (and size) is governed by factors such as intermicellar interactions which vary at lower and higher salt concentrations and with the micelle/aggregate shapes.
The effect of organic additives (aliphatic/aromatic amines or alcohols)
on the viscosities of aqueous and
0.1 M KBr solutions of 0.05 or 0.1 M cetylpyridinium bromide have been
measured under Newtonian
flow conditions. The viscosity changed dramatically in the
presence of KBr. This is explained by the
favorable conditions produced by the salt which assists the micellar
growth by organic additives with a
concomitant enhancement in viscosity. Reasons for the
effectiveness of these additives are suggested.
The causes of the viscosity decrease at higher concentrations of
the additive are also explained.
The effect of aliphatic and aromatic hydrocarbons on surfactant micellar growth has been investigated by viscosity measurements at 40°C. Aqueous and aqueous KBr (0.1 M) solutions of 0.1 M cetylpyridinium bromide (CPB) showed that the viscosity behavior changed substantially in the presence of KBr. This is attributed to favorable conditions produced by KBr that assist micellar growth by addition of hydrocarbons. Reasons for the effectiveness of the solubilized hydrocarbons are suggested and supported by theoretical arguments. The causes of viscosity decrease at higher aromatic hydrocarbon concentrations are also explained. Micellar growth with soluble aromatic/aliphatic hydrocarbons could also be initiated if a moderate salt concentration is present in CPB micellar solutions. The chainlength, solubilization site, and molar volume of the soluble hydrocarbons all affect the bulk viscosity of the solution. Such surfactant and hydrocarbon combinations may find use in micellar-enhanced ultrafiltration of benzene and its derivatives, but it should be kept in mind that micellar shape may change and be more curved at higher benzene derivative concentrations. JAOCS 74, 797-801 (1997).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.