Novel Behavior of Heat of Micellization of Pluronics F68 and F88 in Aqueous Solutions

Abstract

It is well understood that the heat of micellization for surfactants is monotonically decreased along with an increase in temperature. However, this behavior for polymeric surfactants has never been carefully examined. In this study, the heat of micellization of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers (Pluronics F68 and F88) in water as a function of temperature is carefully examined by using a high-sensitivity differential scanning calorimeter (HSDSC). The critical micelle temperature (CMT) decreases along with an increase in the concentration of Pluronic F68 (or F88). The heat of micellization decreases along with an increase in the temperature, as expected, when the CMT is higher than 55 and 42 degrees C for Pluronics F68 and F88, respectively. It is interesting to observe that the heat of micellization increases along with the temperature while the temperature is below 55 and 42 degrees C for Pluronics F68 and F88, respectively. The enthalpy-entropy compensation phenomenon for the micellization of Pluronics F68 and F88 in connection with the hydrophobicity is discussed.

A concise analysis of the effect of temperature and propanediol-1, 2 on Pluronic F127 micellization using isothermal titration microcalorimetry

“…The compensation temperature T c is 298.08 K. This value is very close to that obtained for Pluronics F88 and 68 (294.9 K) [45] but slightly larger than the one obtained by other research work [42] (281.9 K) for 12 Pluronics. Noteworthy is that the linear correlation between enthalpy and entropy change has often been observed in studies of the isothermal process where, typically, the temperature or the composition of the solvent is varied in a systematic way [42,43,[45][46][47].…”

What can isothermal titration microcalorimetry experiments tell us about the self‐organization of surfactants into micelles?

“…This is a manifestation of the hydrophobic effect with its enthalpy-entropy compensation (Tanford, 1980;Moroi, 1992;Paula et al, 1995). Importantly, the linear correlation between enthalpy and entropy has been observed when the temperature and the composition of the micellization medium are varied in a systematic way (Figure 4) (Jolicoeur and Philip, 1974;Paterson et al, 1997;Tsui et al, 2008;Bouchemal et al, 2009).…”

Glycine elicited self-assembly of amphiphilic star block copolymers with contradistinct hydrophobicities

“…Hence, we performed HSDSC measurements to determine the CMT of T1304 and T1307. HSDSC has been extensively used as a powerful technique to evaluate CMT of block copolymers [52][53][54]. During the heating process, a sharp endothermic peak can be observed.…”