Unique role of β-cyclodextrin in modifying aggregation of Triton X-114 in aqueous solutions

The effect of β-cyclodextrin (β-CD) on the aggregation behavior of a nonionic surfactant, Triton X-114 ((1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol), in aqueous solutions has been studied as a function of temperature by means of turbidity, dynamic light scattering (DLS), transmission electron microscopy (TEM), and rheo-small angle light scattering (rheo-SALS). The Triton X-114 (TX-114) solutions possess unique structural variations and display special aggregate transitions upon β-CD addition. In contrast to the reported aggregate disruption effect of β-CD for dilute nonionic surfactant solutions, aggregate growth is found in the aqueous TX-114 solutions of 93 mM upon β-CD addition. The micelle to vesicle transition induced by β-CD addition, which can greatly influence the turbidity and the viscosity of the solutions, is quantified by the characteristic length and aspect ratio of the aggregates. The characteristic length and aspect ratio of the aggregates change significantly after β-CD addition. It shows that aggregate growth may occur in nonionic surfactant–CD systems, as well as the reported ionic surfactant–CD systems. It is proposed that the CD–CD H-bonds create intermicelle interactions and promote aggregation of the CD/surfactant complexes, resulting in the formation of micrometer-scale phase-separated droplets.