| Summary: | 碩士 === 國立臺灣大學 === 藥學研究所 === 90 === Pluronics are water-soluble triblock copolymers with a sequence of PEOa-PPOb-PEOa. They are nonionic amphiphilic macromolecules with surface-activities. By varying the compositions of PPO and PEO blocks, a wide range of chemically similar but physicochemically distinct amphiphiles can be made. As a result, Pluronics had widespread pharmaceutical applications.
Monolayer at the air/water interface is the most frequently used model to study the properties of amphiphilic materials at hydrophobic/ hydrophilic interface. In this study, the p-A isotherms were applied to investigate the interfacial properties of the Pluronic monolayers at the air/water interface. The monolayer penetration technique was used to investigate the interactions between the DPPC monolayers existed at the air/water interface and the Pluronics presented in the subphase. We also measured the CMC of Pluronics in aqueous solutions by both fluorescence probe technique and surface tension technique.
The p-A isotherms of several Pluronic monolayers, appeared six different phases including two phase transitions. The phase transition I appeared at the surface pressure between 8~12 mN/m in the p-A isotherms. When Pluronics’ molecular size increase, the occupied area per molecule corresponding to the point where phase transition I started to occur would also increase. The covered range of occupied area for phase transition I increase with the PEO chain length of Pluronic increase. It is most likely that the PEO chains started to deep into the subphase to form so-called “polymer brush” at the phase transition I. The phase transition II appeared in p-A isotherm at the surface pressure between 19~25 mN/m. The occupied area per molecule and surface pressure corresponding to the point where phase transition II startd to occur increased with increasing of the PPO chain length. This may be due to the PPO chains at the air/water interface started to push out and point into the air as the results of chain-chain squeezing among the PPO segments at the phase transition II.
In the studies of interaction between Pluronics and DPPC monolayers, the concentration of Pluronics in the subphase was 2 × 10-4 mg/mL. Even in such low concentration, it was observed that Pluronics penetrate into the DPPC monolayers even when they were in liquid condensed phase. The Pluronics with longer PPO chain length, shorter PEO chain length and large molecular weight have the greater surface activity and penetration ability into the DPPC monolayers. It was found more Pluronics would adsorb to interface from subphase as the DPPC monolayers exist at the air/water interface. Most likely, some kinds of attractive interaction may exist between Pluronics and DPPC monolayers.
Results of pyrene fluorescence probe technique indicated that the CMC values of Pluronics in aqueous solutions decrease with the PPO chain length increase and the PEO chain length decrease. It is found that the influence of PPO chain length was more significant than the other factors. This is consistent with the observations that the hydrophobic interaction between the PPO chains is the main driven force for Pluronic micelles formation.
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