Induction of Aggregate Formation of Cationic Polysoaps and Surfactants by Low Concentrations of Additives in Aqueous Solution

Abstract

The induction of aggregate formation of cationic polysoaps ((CL)-Copol Cl-12), cetyltrimethylammonium bromide (CTAB), n-dodecyltrimethylammonium bromide (DTAB), and n-dodecylmethyldiallylammonium bromide (DMDAAB) by low concentrations of Methyl Orange (10-5-10-4 M) and anionic surfactants (concentrations below their cmc's) in aqueous solutions was studied using UV-vis absorption and fluorescence spectroscopy. Reduced viscosities were also investigated as a function of polysoap concentration in the presence of low concentrations of the same additives. It was found that the cationic poly soaps, CTAB, DTAB, and DMDAAB aggregate far below their normal cmc in the presence of Methyl Orange in aqueous solution. The cationic polysoaps exhibited an about 5-fold decrease of the reduced viscosity in the presence of the hydrophobic anionic additives but no decrease of the reduced viscosity was found in the presence of hydrophobic nonionic additives and cationic additives (CTAB, DTAB). Depending on the length of the alkyl chains of the organic anionic additives, a conformational transition of the cationic polysoaps was indicated by changes of the reduced viscosity. Pyrene was used as a fluorescence probe to investigate the conformational state of the cationic polysoap CL-Copol Cl-12 in the presence of low concentrations of additives. Pirene fluorescence spectra revealed the formation of hydrophobic microdomains in the presence of the hydrophobic anionic additives depending on the length of alkyl chains. These domains were not observed in the case of hydrophobic cationic additives and nonionic additives.

Non-cross-linked and cross-linked poly(alkylmethyldiallylammonium halides): synthesis and aggregation behavior

“…Sodium methyl sulfate (SMS) had no effect on the reduced viscosity of CL-CopolC1-12-Br. 31 We conclude that the induction of aggregation of cationic polysoaps below their CAC is governed by both electrostatic and hydrophobic interactions. The formation of a compact coil becomes more favorable in the order SMSS HS`Methyl Orange`SDS.…”

“…In the low concentration range between ca 10 À5 and 10 À3 unit mol l À1 , CopolC1-12-Br and (CL)-CopolC1-12-Br showed striking spectral shifts which are attributed to the formation of hydrophobic microdomains induced by the presence of Methyl Orange (see later). 31 At concentrations above 1.0 Â 10 À3 unit mol l À1 , substantial spectral shifts are observed, revealing that Methyl Orange is now bound at hydrophobic binding sites in hydrophobic aggregates of CopolC1-12-Br and (CL)-CopolC1-12-Br in aqueous solution. The spectral data (!…”

“…Cetyltrimethylammonium bromide (CTAB) and n-dodecyltrimethylammonium bromide (DTAB) did not affect the reduced viscosity whereas the non-ionic surfactant heptaethylene glycol n-dodecyl ether (HEGDE) exerted only a minor effect. 31 By contrast, a low reduced viscosity was observed in the presence of sodium dodecyl sulfate (SDS), while a modest reduction of the reduced viscosity was found in the presence of sodium benzenesulfonate (SBS) and sodium hexyl sulfate (SHS). Sodium methyl sulfate (SMS) had no effect on the reduced viscosity of CL-CopolC1-12-Br.…”

“…69,70 In pure water at low pyrene concentrations (2.0 Â 10 À6 M) this ratio I 1 /I 3 is 1.90. 31,[67][68][69][70][71] If pyrene binds to hydrophobic binding sites in supramolecular assemblies, I 1 /I 3 is reduced by a factor characteristic of the particular microenvironment where the pyrene molecule sits.…”

“…Consistent with the observations based on the reduced viscosity, a modest decrease in I 1 /I 3 was observed for SHS, whereas solutions of SMS, DTAB and HEGDE exhibited the same I 1 /I 3 as found for pure water. 31 Ion-Induced Hydrophobic Aggregates of Cross-Linked Polysoaps below Their CAC 37,38 It is well known that the conformations of proteins can be significantly affected by added salts. Salt effects on the association of small-molecule and macromolecular amphiphiles are currently a topic of great interest.…”