| 초록 |
Two gel states of a PEO-PPO-PEO (Pluronic P103) triblock copolymer in water is investigated using small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), rheology and differential scanning calorimetry (DSC). Turbidity change depending only on the temperature with four distinct regions is observed and large aggregates with sizes larger than 5,000 nm are detected with DLS in the turbid solution region. The first sol-to-gel transition (i.e., the hard gel state I) turns out to be the hexagonal microphase as evidenced by the combined measurement of SANS, SAXS and frequency dependence of both G' and G" in rheology. It is worthwhile to note that the mode of change in G" around the second sol-to-gel transition (i.e., the hard gel state II) is not detected during the cooling scan implying that those gels are not thermoreversible. Based upon the present study, two different gelation mechanisms for aqueous PEO-PPO-PEO triblock copolymer solutions are proposed: the hard gel I is caused by the close-packing of micelles while the hard gel II with turbidity is derived from the macroscopic liquid-liquid phase separation due to the attractive hydrophobic interaction among micellar core phases.
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