Premium
The Clouding of an Anionic Surfactant in Acid Solution: Mechanistic and Analytical Implications
Author(s) -
Charboneau Joey,
Wandruszka Ray
Publication year - 2010
Publication title -
journal of surfactants and detergents
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.349
H-Index - 48
eISSN - 1558-9293
pISSN - 1097-3958
DOI - 10.1007/s11743-009-1174-y
Subject(s) - chemistry , dodecanol , pulmonary surfactant , coacervate , sodium dodecyl sulfate , micelle , critical micelle concentration , hydrolysis , nucleation , chromatography , inorganic chemistry , organic chemistry , aqueous solution , biochemistry
The clouding of sodium dodecyl sulfate (SDS) in strongly acidic solutions has seen analytical use, but its mechanism has generally been misinterpreted. In the present work it was found that as SDS slowly hydrolyzes to form dodecanol, the solution passes through a series of compositions at which the aggregation of surfactant is promoted by nucleation onto traces of insoluble dodecanol. This occurred at concentrations well below the critical micelle concentration of SDS and resulted in mixed aggregates that grew to macroscopic size, giving the solution a cloudy appearance. The increasing dodecanol content eventually caused coalescence into a coacervate phase which evolved into a solid layer of dehydrated dodecanol. The process, which continued over an extended period, depended on the temperature and the concentration and type of acid used. The early stages of SDS aggregation were monitored through the I 1 / I 3 ratio of pyrene fluorescence, which confirmed the existence of micelle‐like aggregates at low surfactant concentration. The mixed SDS/dodecanol systems formed in acid hydrolysis were mimicked in neutral solution by combining the appropriate amounts of SDS, dodecanol, and NaCl. Clouding and the formation of a coacervate phase generally proceeded in a similar manner in these solutions.