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IR spectroscopy in combination with 2DCOS and PCMW is employed to illustrate the dynamic hydration behavior of PVCL in water, which exhibits a typical type I continuous LCST behavior. PCMW easily determines the transition temperature to be about 43.5 oC during heating and about 42.5 oC during cooling and the transition temperature range to be 39.5-45 oC. On the other hand, 2DCOS is used to discern the sequence order of different species in PVCL and concludes that hydrogen bonding transformation predominates at the first stage below LCST while hydrophobic interaction predominates at the second stage above LCST. In combination with MD simulation results, we find that there exists a distribution gradient of water molecules in PVCL mesoglobules ranging from a hydrophobic core to a hydrophilic surface. Due to the absence of self-associated hydrogen bonds and topological constraints, PVCL mesoglobules would form a “sponge-like” structure which can further continuously expel water molecules upon increasing temperature; while PNIPAM with self-associated hydrogen bonds forms mesoglobules with a “cotton ball-like” structure without an apparent distribution gradient of water molecules and does not change much upon increasing temperature. |
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