| The thesis deals with the stimuli-responsive behavior of temperature and pH sensitive polymer by using laser light scattering (LLS), ultra sensitive differential scanning calorimetry (US-DSC) and quartz crystal microbalance with dissipation (QCM-D), including the phase transition of poly(AMsopropylmethacrylamide) (PNIPMAM) chains in water, the coil-to-globule transition of individual PNIPMAM chains, and the periodic swelling and shrinking of polymeric multilayer induced by chemical oscillation. The main results are as follows:1. The chain molar mass (Mw) and scanning rate effects on association and dissociation of PNIPMAM chains in water were studied by use of LLS and US-DSC. The investigations lead to the following conclusion: (a) PNIPMAM chains form larger aggregates as Mw decreases at a temperature above its lower critical solution temperature. (b) The ratio of average radius of gyration to average hydrodynamic radius (g>/h>) (～0.9) is larger than that of poly(N-isopropylacrylamide) (PNIPAM) aggregates (～0.8), indicating that PNIPMAM chains form looser aggregates, (c) In the heating process, either decreasing the Mw or increasing the heating rate cause the increases of phase transition temperature (Tp), but they leads Tp to decrease in the cooling process. (d) In both heating and cooling process, as the scanning rate increases, the enthalpy change (△H) decreases but Mw decreases. In addition,△H in the cooling process is some larger than that in the heating process, indicating that PNIPMAM chains can be over-dehydrated at a temperature much higher than LCST in heating process.(e) PNIPMAM chains have smaller enthalpy change and entropy change than PNIPAM chains during the phase transition, indicating that PNIPMAM chains have smaller conformational change. Our experiments demonstrate that the additional methyl groups in PNIPMAM chains restrain the intrachain collapse and interchain association, leading the phase transition to occur at a higher temperature.2. The coil-to-globule transition of individual linear PNIPMAM chains was investigated by a combination of a fast infrared laser heating pulse-induced temperature jump, the time-dependent fluorescence and Rayleigh scattering intensity measurements. The Rayleigh scattering intensity remains invariant upon the heating, indicating no interchain association. The fluorescence intensity curve can be well fit by a double exponential function, implying that the coil-to-globule transition is of two distinct kinetic stages. In addition, the two characteristic transition times (τfast andτslow) are consistent with the theoretical prediction. The fast stage can be attributed to the nucleation and initial growth of some "pearls" on the chain, while the slower one is related to the merging and coarsening of the "pearls". Similar kinetics has been observed in the coil-to-globule transition of PNIPAM chains.3. Poly(acrylic acid-co-3-azidopropyl acrylate) (poly(AA-co-Az)) and poly(acrylic acid-co-propargyl acrylate) (poly(AA-co-PA)) were synthesized via reversible addition-fragmentation chain transfer technique. poly(AA-co-Az) and poly(AA-co-PA) were alternatively fabricated into a multilayer via click reaction. The layer-by-layer (LBL) deposition was monitored by QCM-D in real time. The changes in frequency (△f) decrease and changes in dissipation (△D) increase with increasing number of layers indicate the LBL deposition in a linear-growth mode. By use of QCM-D, we have investigated the response of the multilayer under continuous flow of bromate-sulfite-ferrocyanide solution with pH oscillation. As pH varies between 3.1 and 6.6, the△f and△D periodically change with a constant amplitude, clearly indicating the multilayer swells and shrinks oscillatedly. The changes of thickness, shear viscosity and elastic shear modulus further demonstrate the oscillation. Such a film might find an application in the fields of actuators and biosensor. |
PDF Full Text Request