Temperature-sensitivity And Complexation Behavior Of Amphoteric Polyurethane Micelles

In this paper, temperature dependence of APU micelles and complexation behavior of APU/SDS and APU/liposome are studied through light scattering, transmission electron microscopy, fluorescent measurement and UV spectrum methods. Corresponding models are proposed in each part to summarily illustrate our study results.We find that the temperature sensitivity of APU micelles is leaded by PPO segments. Dynamic stable core-shell micelles with small size and narrow size distribution can be obtained at low temperature such as 4°C. When temperature increases from 4°C, core-shell-corona micelles are proposed to form and this conversion is reversible. It is believed that the temperature-sensitivity of APU is important to prepare stable micelles at higher concentration.With increase of SDS concentration, the APU/SDS complexation system turns precipitated from clear, and then the precipitation dissociates and mixture becomes clear again. Three distinct interaction stages are observed. It is supposed that electrostatic attraction and hydrophobic aggregation dominate the complexation process. At extra high SDS concentration, a kind of stable complex micelle with APU core covered by dilayer SDS molecules is suggested to form. As we know from our experiments, the configuration of APU/SDS complex mainly rests with their ratio and is independent of mixed sequence.The similar phenomenon can be observed in APU/liposome complexation as in APU/SDS system. When APU concentration is very low, electrostatic adsorption occurs and the system becomes precipitated. With further addition of APU, the system turned transparent and then bud-like micelles were obtserved. At even higher APU concentration, hexagonal micelles were obtained through hydrophobic insertion of APU into dilayer of liposome. It is also confirmed that there was no interaction in alkali media because APU was identically charged with liposome.