Synthesis And Properties Of Acrylic-based Ionic Nanocomposite Hydrogels

Polymeric hydrogels have been applied in many fields, like agriculture, gardeningand etc due to good water-absorbing and retaining ability. Smart hydrogels have beenfully investigated for potential uses, like drug delivery system, substance seperation,and shape memory materials, because their unique sensitivity to outside stimulus.However, there are some shortcomings for smart hydrogels, like weak mechanicalproperties, which limit the appliction. In this thesis, stimuli-responsive ionicnanocomposite hydrogels (NC hydrogels) with ultrahigh tensibility were synthesizedby in-situ copolymerization of ionic monomers in the aqueous dispersion of Laponiteacted as cross-linking agent. The stability of the Laponite dispersion containing ionicmonomers was investigated in detail. The main contents are included as follows:1. Amphoteric NC hydrogels were synthesized by in-situ copolymerization ofacrylic acid (AA) and N[-3(dimethylamino)propyl] methacrylamide (DMAPMA) inan aqueous dispersion of Laponite XLG. The FTIR spectra and elemental analysisconfirmed the components of the NC hydrogel. Dynamic mechanical analysis (DMA)within linear viscoelasticity confirmed that the network structure was formed with thejunction of the ionic monomers and Laponite platelets. Mechanical analysesdemonstrated that this type of hydrogels had a combination of high tensile strengthand excellent stretchability. The tensile strength was increased by5times up to316kPa when the Laponite content was increased from0.1wt%to20wt%, and amaximum fracture strain of2317%was achieved for hydrogels containing3wt%Laponite. Additionally, the marked improvements in strength were achieved withminimal sacrifice of the tensibility.2. Poly(DMAPMA-co-AMPS-co-AA)/Laponite NC hydrogels were prepared byin-situ polymerization technique using ionic monomers2-acrylamido-2-methlypropane sulfonic acid (AMPS), AA and DMAPMA in Laponitedispersion. It was found that these hydrogels showed improved mechanical properties with tensile strength of196kPa and elongation at break of3805%. Besides, thehydrogel showed pH-sensitive and salt-sensitive behaviors.3. Poly(acrylic acid)/Laponite NC hydrogels with much improved mechanicalproperties were prepared by in-situ polymerization of ionic monomer AA at highcontent (above8wt%) of Laponite dispersion modified by tetrasodium pyrophosphate(Na4P2O7). The hydrogels showed tensile strength of308kPa and elongation at breakof1110%at14wt%clay content.