Abstract:
Self-organization of amphiphilic calixarenes oxyethylated at a lower rim has been investigated in water and water-organic solutions. In the range of isotropic solutions three types of structural transitions were indicated by a complex of methods. The first critical point indicated by surface tension, dynamic light scattering and atomic force microscopy methods is probably connected with the formation of " infinite" organized structures (of hundreds nanometers in size) through the open association model. This aggregative phenomenon covers the concentration range below 10-3M. In the case of aqueous calixarene solutions these large aggregates co-exist with small micelle-like particles and undergo a rearrangement with an increase in the concentration. The second structural transition occurs beyond 10-3M. It is revealed in aqueous calixarene solutions by surface tension, spine probe, viscosimetry and dynamic light scattering methods. Small aggregates (~10nm in diameter) are formed in this range through a closed model typical for conventional surfactants. The third transition indicated by viscosimetry and in single case by tensiometry can be connected with an elongation of aggregates. The polarization microscopy and X-ray diffraction studies reveal the anisotropic behavior with the concentration of solutions. Parameters of the existence of liquid crystalline mesophases are found to be influenced by the structure of substituents at both the upper and lower rims, as well as by the nature of solvent. © 2010 Elsevier B.V.
