| |
[摘要]：We have measured the thermophysical properties of a series of amphiphilic copolymeric F127 solutions (10-30% w/w) as they have been heated between 15 and 65 degrees C using ramp rates of 0.1-10 degrees C/min to study their kinetics of gelation using rheology and DSC. DLS was used to further characterize micelle size. A complementary set of experiments was conducted adding methylparaben, a model pharmaceutical, in order to investigate how the added solute affected the gelation properties of the system. From the rheology results, our use of power law analysis to determine the gelation temperature (T-gel) indicates that T-gel increases at higher temperature ramp rates as compared to the equilibrium or near-equilibrium ramp condition. An alternative analysis using a log-Boltzmann sigmoidal fitting shows a decreased characteristic gelation time for higher ramp rates as well. The gel temperature decreases with increasing F127 concentration, which is expected. The ordering of the micelles is nearly athermic, however, we identified the secondary ordering peak at higher F127 concentrations. DLS measurements showed an increase in micelle monodispersity in the presence of methylparaben, providing one possible explanation for the resultant rheological behavior. These observations suggest that a more refined microstructural evaluation of triblock copolymer dynamic ordering will resolve both the driving force and kinetics of association of amphiphilic copolymers in solution. |
|
