Research On The Polymer Microgel Interaction With Rare Earth Ions

Colloidal particles of temperature-responsive polymers with a submicrometer size range havebeen studied extensively. In this respect, hydrophilic-hydrophobic P(N-isopropylacrylamide)(PNIPAM) latex particles has increasingly attracted the interest of researchers in the field owing totheir temperature induced, dramatic and reversible volume changes in aqueous phase surroundingthe temperature of 32℃ , in which is called as the lower critical solution temperature (LCST),resulting in the corresponding large variation of the colloidal properties of the PNIPAM microgel,especially their particles size, electrophoretic mobility, colloidal stability etc. Therefore, theapplication of PNIPAM latex particles in general have mainly focused on the biomedical field fordiagnostic tests, control release, drug delivery system, chemical separation and coating additivesetc. On the other hand, some of lanthanide ions, especially Terbium and Europium, possessedgood luminescence characteristics (high color purity) based on the 4f electronic transitions, avariety of rare earth compounds activated by Terbium and Europium have been investigated forpractical application. In recent years, the lanthanide ion-containing polymers has been greatlystimulated many peoples to further efforts owing to their potential use in fluorescence and lasersystems, which the linear polymer were generally used as ligand in those researching systems. Itwas found that many researchers have reported on the preparation of the functional polymermicrogel, however, there have been only a few studies related to the study of the fluorescence ofpolymer microgel.In this paper, the preparation and spectral properties of copolymer microgels containing rareearth ions have been investigated. The objectives of this study were to synthesis the binary andternary compounds that not only possessed the outstanding luminescence behavior of rare earth ionsbut also kept the distinctive thermal properties of PNIPAM and its copolymers by adding four rareearth ions (Terbium, Europium, Samarium and Dysprosium) and two organic low molecular weightligands (phenanthroline, thenoyltrifluoroacetone) into the submicron NIPAM/AAc/St copolymermicrogels. At the first of all, The N-isopropylacrylamide and acrylic acid, styrene copolymermicrogels were prepared by two polymerization methods (emulsion polymerization andsurfactant-free emulsion polymerization). Secondly, several series of the complexes of microgelcontaining rare earth ions were prepared and characterized by Transmission Electron Micrography(TEM), Dynamic Laser Scattering (DLS), Zeta potential, Ultraviolet spectroscopy (UV-vis), Fouriertransform infrared transmission spectroscopy (FT-IR) and fluorescence spectroscopy. It would lay afoundation of the further investigation of the interaction of rare earth ions with copolymer microgel.The main results obtained are as follows:(1) The experimental results of TEM, DLS showed that the particle radium of the complex ofmicrogel containing rare earth ion has not been obviously changed after the rare earth ions addinginto copolymer microgel. The results from Zeta potential, UV-vis, and FTIR demonstrated that thereexist at least two interactions between the copolymer microgel and rare earth ion in these complexes,which one is coordination action, and another is electrostatic force. Nevertheless, both of themmaybe change the conformation and conjugated structure of these polymers, eventually leading tothe changes of their spectral properties.(2) The fluorescence emission spectra of Terbium (Europium) binary complexes show theirintensive characteristic emissions, indicating that there exists efficient energy transfer behaviorbetween Terbium (Europium) ion and copolymer microgel ligand. However, other binarycomplexes display merely emission bands of copolymer microgel ligands, indicating that the energylevels of triplet state of copolymer microgel ligands do not match the excited states of other rareearth ions. In ternary complexes, the characteristic emission intensities of rare earth ions weresignificantly increased by the introduction of low molecular weight ligands as a result of synergeticeffect between them. Especially, P(NIPAM-co-AAc)-Tb( Ⅲ )-Phen and P(NIPAM-co-AAc)-Eu(Ⅲ)-TTA are potential luminescent materials in respect that they could not only emit intensivemonochromatic light excited by UV light, but also have stable chemical characters.