The effect of glycerol on the micellization of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and of the ethoxylated nonionic surfactant Brij 58 has been investigated by various experimental techniques. For both surfactants the critical micellar concentration (cmc), determined by surface tension measurements, is almost unaffected by the presence of glycerol in the mixture; only at high glycerol concentrations (20% w/w) does the cmc significantly increase. The area per surfactant molecule at the air–solution interface, A, increases with increasing glycerol weight percentage, wg. Fluorescence quenching measurements indicate that the presence of glycerol induces a lowering of the aggregation number of both surfactants. The glycerol intradiffusion coefficient has been measured by the pulsed-gradient spin–echo NMR technique as a function of glycerol content at constant surfactant concentration. It is almost unaffected by the presence of the surfactants, indicating that no direct glycerol–surfactant interaction occurs in the mixture. The surfactant intradiffusion coefficient has been also measured. In the case of CTAB, it increases with increasing glycerol concentration, a reflection of the decreased aggregation number. For Brij 58, in spite of the lowering of the aggregation number, the surfactant intradiffusion coefficient decreases with increasing glycerol concentration, suggesting an increase of the intermicellar interaction. The experimental evidence shows that for both surfactants the micellization is affected by the presence of glycerol through an indirect, solvent-mediated mechanism. In the case of CTAB, the main effect of glycerol is a lowering of the medium dielectric constant, which enhances the electrostatic interactions in solution. In the case of Brij 58, the results can be interpreted in terms of a salting-out effect according to which glycerol competes with the surfactant for water molecules, causing a dehydration of the surfactant ethoxylic headgroup.

Effect of glycerol on micelle formation by ionic and nonionic surfactants at 25°C / D'Errico, Gerardino; Ciccarelli, Donato; Ortona, ORNELLA GIUSTINA. - In: JOURNAL OF COLLOID AND INTERFACE SCIENCE. - ISSN 0021-9797. - STAMPA. - 286:(2005), pp. 747-754. [10.1016/j.jcis.2005.01.030]

Effect of glycerol on micelle formation by ionic and nonionic surfactants at 25°C

D'ERRICO, GERARDINO;CICCARELLI, DONATO;ORTONA, ORNELLA GIUSTINA
2005

Abstract

The effect of glycerol on the micellization of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and of the ethoxylated nonionic surfactant Brij 58 has been investigated by various experimental techniques. For both surfactants the critical micellar concentration (cmc), determined by surface tension measurements, is almost unaffected by the presence of glycerol in the mixture; only at high glycerol concentrations (20% w/w) does the cmc significantly increase. The area per surfactant molecule at the air–solution interface, A, increases with increasing glycerol weight percentage, wg. Fluorescence quenching measurements indicate that the presence of glycerol induces a lowering of the aggregation number of both surfactants. The glycerol intradiffusion coefficient has been measured by the pulsed-gradient spin–echo NMR technique as a function of glycerol content at constant surfactant concentration. It is almost unaffected by the presence of the surfactants, indicating that no direct glycerol–surfactant interaction occurs in the mixture. The surfactant intradiffusion coefficient has been also measured. In the case of CTAB, it increases with increasing glycerol concentration, a reflection of the decreased aggregation number. For Brij 58, in spite of the lowering of the aggregation number, the surfactant intradiffusion coefficient decreases with increasing glycerol concentration, suggesting an increase of the intermicellar interaction. The experimental evidence shows that for both surfactants the micellization is affected by the presence of glycerol through an indirect, solvent-mediated mechanism. In the case of CTAB, the main effect of glycerol is a lowering of the medium dielectric constant, which enhances the electrostatic interactions in solution. In the case of Brij 58, the results can be interpreted in terms of a salting-out effect according to which glycerol competes with the surfactant for water molecules, causing a dehydration of the surfactant ethoxylic headgroup.
2005
Effect of glycerol on micelle formation by ionic and nonionic surfactants at 25°C / D'Errico, Gerardino; Ciccarelli, Donato; Ortona, ORNELLA GIUSTINA. - In: JOURNAL OF COLLOID AND INTERFACE SCIENCE. - ISSN 0021-9797. - STAMPA. - 286:(2005), pp. 747-754. [10.1016/j.jcis.2005.01.030]
File in questo prodotto:
File Dimensione Formato  
JCIS 2005.pdf

non disponibili

Tipologia: Documento in Post-print
Licenza: Accesso privato/ristretto
Dimensione 292.23 kB
Formato Adobe PDF
292.23 kB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/201941
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 106
  • ???jsp.display-item.citation.isi??? 96
social impact