Monitoring the microenvironment inside polymeric micelles using the fluorescence probe 6-propionyl-2-dimethylaminonaphthalene (PRODAN)

Rheological Control of Aqueous Dispersions by Thermoresponsive BAB* Copolymers of Different Architectures

“…To gain additional information on the aggregation process, we added the solvatochromic probe Prodan to the various polymer solutions and followed its temperature-dependent emission spectra for the different copolymer systems. The photoluminescence of this well-known fluorescent dye depends sensitively on the polarity of its local environment. ,− Although being quite complex, , it enables in particular the study of the aggregation of lipids and surfactants in water. ,,, The emission spectra obtained for the different copolymers in aqueous solution as a function of temperature (see Figure , Figures S29a,d,g,j and S30a,d,g,j,m) were analyzed with respect to the wavelength of their emission maximum and to the maximum emission intensity (Figure ).…”

“…25,59−61 Although being quite complex, 62,63 it enables in particular the study of the aggregation of lipids and surfactants in water. 25,26,62,64 The emission spectra obtained for the different copolymers in aqueous solution as a function of temperature (see Figure 10, Figures S29a,d,g,j and S30a,d,g,j,m) were analyzed with respect to the wavelength of their emission maximum and to the maximum emission intensity (Figure 11). As a reference system, we chose the low molar mass surfactant C 12 -β-D-maltoside above and below its critical micelle concentration CMC (CMC ≈ 0.165 mM 65 ) (Figure S29).…”

“…24 These findings strikingly contrast to the presence of only one emission band and its monotonous spectral shift during the process of micellization of low molar mass surfactants, as found for the reference C 12 -β-D-maltoside, in agreement with the literature. 25,64 Therefore, the coexistence of at least two emission bands in the pNPAm and pNiPAm solutions strongly suggests the occurrence of two distinct environments of different polarity, one being a clearly more hydrophobic domain, between which the probe molecules are distributed and exchange rather slowly (slower than the fluorescence lifetime). Presumably, one is the aqueous bulk solution and the other one the polymer-rich phase separating off above the LCST-transition.…”