Studies On Behaviors And Properties Of Polymer At Interface

This thesis deals with the behavior and properties of polymers in solution and at the interface.First,we have investigated temperature modulated photoluminescence of poly(N-isopropylacrylamide)(PNIPAM) grafted quantum dots.Second,we have studied the effect of ions on the sorting of oppositely charged microgels to mimick cell-sorting.Third,we have investigated the enzymatic degradation of poly(ε-caprolactone) in real time by using QCM-D and SPR.The main results are as follows:(1) We have prepared cadmium sulfide(CdS) quantum dots(QDs) grafted with thermoresponsive PNIPAM chains.As temperature increases,PNIPAM chains shrink and aggregate,so that the QDs exhibit enhanced fluorescence emission.At a temperature around the lower critical solution temperature(LCST) of PNIPAM,the fluorescence exhibits a maximum intensity.Our experiments reveal that the fluorescence emission is determined by the interactions between QDs as a function of the interdot distance.The optical interdot distance for the maximum luminescence intensity is～10 nm.The chain length of PNIPAM also has effect on the luminescence. Short PNIPAM chains are difficult to associate and lead to a large interdot distance, so that luminescence intensity slightly changes with temperature.(2) We have prepared two kinds of thermally sensitive oppositely charged polymeric microgels,poly(N-isopropylacrylamide-co-sodium acrylate)(NIPAM-co-SA) and poly(N-isopropylacrylamide-co-vinylbenzyl trimethylammonium chloride) (NIPAM-co-VT) by surfactant-free emulsion polymerization and studied their temperature induced aggregation by use of laser light scattering.Without addition of a salt,NIPAM-co-SA and NIPAM-co-VT microgels in the mixture do not aggregate but shrink upon the heating.In the presence of divalent metal ions,the heating leads to the association of NIPAM-co-SA microgels via the complexation of metal ions and carboxyl groups on the microgel surface when the temperature approaches their lower critical solution temperature(LCST～32℃).Further heating over the LCST results in the adsorption of NIPAM-co-VT microgels on the NIPAM-co-SA aggregate via the electrostatic attraction so that a core-shell structure with a NIPAM-co-SA core and a NIPAM-co-VT shell forms,resembling the biological cell-sorting.On the other hand, divalent anions also mediate the sorting following the Hofmeister series.(3) We have investigated the enzymatic degradation of poly(ε-caprolactone)(PCL) by use of quartz crystal microbalance with dissipation(QCM-D) and surface plasmon resonance(SPR) in situ.The frequency and dissipation responses of QCM-D and the SPR signal responses can well describe the weight loss and the morphological changes of a PCL film.Our experiments reveal that the degradation has much dependence on the crystallinity and morphology of PCL.PCL with lower crystallinity (45%) and small spherulites degrades in a way of layer-by-layer.Both QCM-D and SPR measurements demonstrate the degradation is of first-order.However,PCL with higher crystallinity(55%) and larger spherulites exhibits a more complex degradation behavior;namely,the degradation in crystalline region lags behind that in amorphous region,leading to a microporous structure.