The effects of divalent metal ions on the micellar properties of sodium dodecyl sulfate

• Published in: Journal of colloid and interface science Vol. 35; no. 1; pp. 53 - 59
• Main Authors: Oko, Michael U, Venable, Raymond L
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1971
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(71)90184-6

Critical micelle concentrations and micellar molecular weights have been determined for sodium dodecyl sulfate in the presence of nitrates of copper, lead, zinc, and magnesium and critical micelle concentrations have been determined with sodium nitrate and silver nitrate as the added electrolytes. The thickness of the ionic atmosphere at the critical micelle concentration has been found to be 34.1 Å with no electrolyte present and 33.6 Å with 9.66 × 10 −6 M sodium or silver nitrate and was found to increase upon addition of the 2:1 electrolytes. This is explained in terms of molecular and ionic interactions. Micellar molecular weights were found to be 14,200 in the absence of extraneous electrolyte, 14,700 in the presence of 4.86 × 10 −4 M copper II, zinc, and magnesium, 18,000 with 4.83 × 10 −4 M lead, and 25,000 with 9.66 × 10 −4 M zinc. Part of the change in micellar molecular weight is attributed to replacement of sodium ions with heavier ions, especially in the case of lead.