Effect of temperature on the aggregation behaviour of nonionic surfactants in aqueous solutions

Abstract

2014 L'effet de la température sur les propriétés micellaires de tensioactifs non ioniques a été étudié par déclin de fluorescence (formation d'excimère intramicellaire) du pyrène solubilisé dans les micelles. Pour les surfactants du type C12H25En (E = groupe oxyde d'éthylène; n = 6, 8, 9) le nombre micellaire moyen en nombre N est pratiquement indépendant de la température T quand T TC-35 (TC = température critique du système). Dans le domaine TC-35 T TC, N augmente avec T, jusqu'à TC. Dans le même domaine on note l'existence d'une migration intermicellaire du pyrène. La vitesse de cette migration augmente très rapidement avec T. Ce processus semble se produire par l'intermédiaire de collisions entre micelles accompagnées d'une fusion temporaire et partielle des micelles. Un autre surfactant non ionique étudié, le Triton X-100, se comporte de façon un peu différente : N augmente avec T et le processus de migration existe dans tout le domaine de température étudié. Abstract. 2014 The effect of temperature on the aggregation behaviour of nonionic surfactants in aqueous solution has been investigated by means of transient fluorescence probing (intramicellar excimer formation by pyrene). For surfactants of the C12H25En type (E = ethyleneoxide group, n = 6, 8, 9) the number average aggregation number N of the micelle is nearly independent of the temperature T when T is below TC-35 (TC = critical temperature). In the range TC-35 T TC, N increases with T, up to TC. In the same range, extensive pyrene migration from micelle to micelle is observed. This process is thought to take place through micelle collisions with temporary and partial merging. Triton X-100 was also investigated and found to behave somewhat differently with an increase of N with T and probe migration in the whole T-range.

Mixed Micellization of Dimeric (Gemini) Surfactants and Conventional Surfactants

“…• C, in agreement with a previous report (36). This has been attributed to a decreased polarity of the ethoxylated chains (56).…”

“…This behavior indicated that probe and/or quencher migration between micelles occurred on the fluorescence time scale as was noted in a previous TRFQ investigation of these two surfactants (36). The equations appropriate to this situation (32)(33)(34)(35) were used for the analysis of the decay curves, and again yielded the values of τ , R, and k q .…”

“…The micelle size is then much more sensitive to additives that increase the cloud temperature (36). Note that the aggregation behavior in the 12-2-12/C 12 E 6 mixture has been investigated by light scattering (11).…”

Aggregation Behavior of Tyloxapol, a Nonionic Surfactant Oligomer, in Aqueous Solution

“…Also N increases much with temperature between 25 and 40°C, as for the nonionic surfactants C m E n (37)(38)(39)(40). Our N values are in very good aggreement with those reported by Brown et al (41), who used TRFQ with the pair pyrene-benzophenone.…”

“…The larger microviscosity of TX100 micelles with respect to micelles of ethoxylated nonionic surfactants C m E n (E ϭ ethoxy group) explains why abnormally low values of the micelle aggregation number were measured in a previous timeresolved fluorescence quenching study of TX100 solutions (37). This study used the formation of excimer by pyrene (15).…”