Preparation And Properties Of Nanocomposite Hydrogels Crosslinked By Clay With Ionic Bonds

In this paper, Na-montmorillonite(MMT) and cationic monomer((3-acrylamidopropyl) trimethylammonium chloride, ATC) were introduced in the preparation of nanocomposite(NC) hydrogels. Three kinds of high performance hydrogel were prepared by using free radical copolymerization, such as PATC/PAAm/MMT nanocomposite double network(DN) hydrogels and PATC/P(AMPS-AAm)/MMT zwitterionic nanocomposite double network(DN) hydrogels. During the preparation of hydrogels, the cation exchange reaction between MMT and ATC(cationic monomer) was happened, so MMT platelets were considered as chemical “plane” cross-linkers. Meanwhile, MMT were acted as physical cross-linkers through absorption of macromolecule chains. The influences of montmorillonite, zwitterion and double network on the swelling behavior, mechanical strength, viscoelastic behavior and microstructure of the ionic NC hydrogels were investigated.The P(ATC-AAm)/MMT nanocomposite hydrogels were synthesized by one-step free radical copolymerization of acrylamide and ATC in presence of MMT and N,N’-methylene-bis-acrylamide used as chemical cross-linker. With increasing the amount of MMT, the crosslinking degree enhanced, which caused a decrease of the swelling degree at equilibrium. Investigations of mechanical properties indicated that NC hydrogels exhibited enhanced strength and toughness, which resulted from the interaction between exfoliated MMT platelets and polymer chains in hydrogels. Dynamic shear measurements showed that both storage modulus and loss modulus increased with increasing the MMT content. XRD and micromolophlogy indicated that the silicate layers of Na-montmorillonite in NC gel were exfolicated and dispersed into NC-hydrogel uniformedly. Due to the chemical and physical interaction between exfoliated MMT platelets and polymer chains in hydrogel, the tensile stress and ultimate strain of the NC hydrogel were improved simultaneity.To strengthen the mechanical properties of the hydrogel, the PATC/PAAm/MMT nanocomposite DN hydrogel had been prepared by a two-steps solution radical polymerization in aqueous media. With increasing the amount of MMT, the equilibrium-swelling ratio of the gels decreased due to the enhanced cross-linking degree. Investigations of compressive and tensile properties indicated that compressive modulus and stress, fracture stress, ultimate strain and Young’s modulus were significantly improved in the presence of MMT. Dynamic shear measurements showed that the storage modulus and loss modulus both increased with addition of MMT. SEM displayed some micro-network structures were observed on the fracture surface, which led to the enhancement of mechanical properties. Moreover, the gels with ammonium cationic monomer(ATC) exhibited good antibacterial effects on E. coli and S. aureus.The PATC/P(AMPS-AAm)/MMT zwitterionic nanocomposite DN hydrogels with excellent mechanical properties had been prepared by addition of AMPS into the second network. The introduction of AMPS decreased the equilibrium swelling ratio of zwitterionic nanocomposite DN hydrogels. It was found that compressive and tensile properties were improved in the presence of AMPS because of the ionic bonds between ATC and AMPS. SEM microscopy revealed that the pore size became smaller and the embedded micro-network structures appeared on the fracture surface of the gels, which accounted for an improvement of mechanical properties. The storage modulus and loss modulus of hydrogel both increased by addition of AMPS.