| Thermosensitive poly(N-isopropylacrylamide)(PNIPAM)aqueous solutions have been investigated widely as intelligent materials and PNIPAM has wonderful application prospects in drug release,drug delivery and so on.Lots of achievements have been obtained by the analysis technology such as FTIR,DSC,NMR and so on.However,the analysis they give about the components contributing to phase separation enthalpy in PNIPAM aqueous solution is still ambiguous.For this problem,a series of different concentrations PNIPAM aqueous solutions were measured systematically by different scanning calorimeter measurement(DSC),and the analysis of FTIR and FLS as the supplementary information was also used to explain.DSC heat flow curves for different concentrations PNIPAM solutions were obtained by both different scanning procedures.Significant difference in the thermal properties is observed in four different concentration regions I)0-24 wt%(water concentration,similarly hereinafter),II)24-50 wt%,III)50-65 wt%,IV)abo ve 65 wt%.The typical demixing enthalpy recovery behavior is observed in region III and IV,but cannot be observed in reigon II.In concentration region I,only one concentration dependent glass transition behavior can be observed.Using steady-state fluorescence spectra investigated that above the LCST the groups are dehydrated,causing coil-to-globule transition followed by further aggregation and formation of so-called mesoglobule.By FTIR our result shows that the interaction of water molecules and polymers is fast in the homogeneous recovery process,further,there is no clear information measured proving existing chemical interaction during isothermal process.The whole work suggests that the demixing enthalpy consists of two parts : 1.the hydrogen bonding between polymer and water molecules which does not vary depending on increasing isothermal time;2.the effect of water molecules on swelling of polymer increases with increasing isothermal time and eventually reaches a stable value. |
PDF Full Text Request