The influence of hydroxy propyl β-cyclodextrin on the micellar to gel transition in F127 solutions investigated at macro and nanoscale levels

Abstract

Micellar to gel phase transition in the aqueous triblock copolymer F127 solutions occurs at higher temperatures in the presence of cyclodextrin and the temperature range corresponding to the gel phase is contracted. These features were observed by dynamic rheometry and the tube inversion method. We investigated further the behaviours of various molecular probes in Pluronic F127 solutions in the absence and in the presence of hydroxypropyl-β-cyclodextrin (HPB) as a function of temperature by continuous wave electron paramagnetic resonance (cw-EPR), Electron Spin Echo Envelope Modulation (ESEEM) and fluorescence spectroscopy, to correlate the observed macroscopic and microscopic changes. The use of molecular probes with different structural particularities allowed the targeting of different regions of F127 micelles which are inhomogeneous at the nanoscale level and the elucidation of the mode in which HPB influences the phase transition in such systems. Dansyl-TEMPO (DT), with a dual character (paramagnetic and fluorescent), spin labelled cyclodextrin (MTCYC), spin labelled Pluronics – L62NO and F127NO, dansyl β-CD (D-β-CD) and pyrene were employed as molecular probes. Both cw-EPR and fluorescence measurements revealed that molecular probes with a more hydrophobic character are more sensitive to phase transition occurring in the studied systems.