surface property and aggregation behavior of a hydrophobically modified cyclodextrin

The surface property of an amphiphilic cyclodextrin 2-O-(hydroxypropyl-N,N-dimethyl-N-dodecylammonio)-β-cyclodextrin (HPDMA-C₁₂-CD) was investigated using oscillating bubble rheometer and electrical conductivity method at different temperatures. The surface tension and dilational viscoelasticity of HPDMA-C₁₂-CD were provided. The results showed that HPDMA-C₁₂-CD could adsorb on the air-water interface, which decreased the surface tension of water efficiently. Critical micelle concentration (cmc) can be clearly defined from the surface tension isotherm. pC₂₀ and π cmc were derived from the surface tension isotherms as well. The thermodynamic parameters (ΔG ⁰ m , ΔH ⁰ m , −TΔS ⁰ m) derived from electrical conductivity indicated that the micellization of HPDMA-C₁₂-CD was entropy-driven at lower temperature, while it was enthalpy-driven at higher temperature. The dilational modulus appeared a maximum value while the phase angle appeared two maxima as a function of HPDMA-C₁₂-CD concentration.