聚氧乙烯-聚氧丙烯-聚氧乙烯聚合物形成微胞之焓變化研究
Other Title
A Study on the Enthalpy Change of Micellization of Pluronics
Date Issued
2007
Abstract
In our experiment, we study the triblock copolymers of poly(ethylene oxide)- poly(propylene oxide)- poly (ethylene oxide) (Pluronics) using high sensitivity differential scanning calorimeter (HSDSC). With the temperature increases, we discussed the factors of micellization by measuring the heat capacity change of system along with the temperature.
When a small amount of surfactants dissolved in the water, the surfactant will be a monomer dispersed in solution. As the temperature increases, the separate monomers will aggregate at a characteristic temperature, which is denoted as critical micelle temperature. At the same time, it is accompanied with large enthalpy change during the micellization. For some surfactants with simple structure, the enthalpy change will decrease with increasing temperature.
In our research, we found that the enthalpy change decreases, as expected, with increasing temperature. However, the enthalpy change starts departing from the linear relationship at higher concentration range. More unusually, it has a positive relationship with temperature at this concentration range. And the transition of enthalpy tendency seems beginning at lower concentrations for larger molecules.
In addition, we also discussed the phase transition of Pluronics solution which occurred at higher temperatures. The transition is simple for the quite high or low PEO/PPO ratio molecules. But there is rich phase behavior for middle PEO/PPO ratio ones. Finally we compared the HSDSC data with the result from isothermal titration calorimeter, and good consistency between these two methods are obtained.
Subjects
聚氧乙烯
聚氧丙烯
微胞
焓
熱卡計
Pluronics
micelle
calorimeter
DSC
enthalpy
Type
thesis