Study of heat of micellization and phase separation for Pluronic aqueous solutions by using a high sensitivity differential scanning calorimetry
Journal
Colloid and Polymer Science
Journal Volume
288
Journal Issue
18
Pages
1687-1696
Date Issued
2010
Author(s)
Abstract
Heat of micellization and phase separation temperature (known as cloud point) for the poly (ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) (abbreviated by PEO-PPO-PEO) triblock copolymers, the Pluronics F108, F98, F88, F68, F38, P65, and L62, in water are carefully determined by using a high sensitivity differential scanning calorimeter. It is interesting to find out that there exists a maximum heat of micellization for all these Pluronics. In this study, the heat of micellization of all of the Pluronics decreases as the temperature increases, as expected, at high temperature region (low Pluronic concentration region). However, the enthalpy change has a surprisingly positive relationship with temperature at low temperature region (high Pluronic concentration region). The critical micelle temperature consistently decreases as the Pluronic concentration increases. This unexpected behavior of the positive heat capacity changes of Pluronic aqueous solutions at higher concentration region is somewhat related to the variation of water accessible polar (PEO groups) and non-polar (PPO groups) surface areas in the micellization process. Especially, the removal of polar surface area from water may dominate the contribution to the positive heat capacity change upon micellization. In addition, the cloud points of Pluronic solutions are also discussed. The enthalpy-entropy compensation phenomenon for the micellization of Pluronics is discussed, and the enthalpy-entropy compensation temperature is calculated. © Springer-Verlag 2010.
SDGs
Type
journal article