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

Abstract

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.