Construction And Mechanical Property Of Bentonite/SiO₂-baseddualnanocomposite Hydrogels

Bentonite is a rich natural clay mineral in China with montmorillonite as main component.Montmorillonite is a layered silicate and the layer thickness is about 1 nm while the layer spacing is 1-2.5 nm.Usually polymer/Bentonite composite is fabricated based on the unique one-dimensional layered nanostructure and cation exchange properties of montmorillonite.However,there is a stronger bonding effect between the Bentonite interlayers when it is dispersed in the water.In order to solve the problem,it is usually necessary to use a cationic surfactant as an intercalator to improve the affinity of clay to organic phase.However,intercalation is not satisfying so that new intercalating agents are demanding for the formation of nanocomposites.To replace the traditional cationic surfactant intercalator,herein,silanization agents containing different functional groups were used as intercalators to expand the interlayer spacing of Bentonite and synthesize dual nanocomposites with excellent mechanical properties.And the effects of different functional groups on the mechanical properties of hydrogels were discussed.Main contents include as follows:Taking advantage of the cation exchange performance of Bentonite,3-aminopropyltrimethoxysilane?APS?with a cationic group was used as an intercalator for Bentonite.P?AM-co-AMPS?/Bentonite/SiO₂ double nanocomposite hydrogels were synthesized using AM and 2-Acrylamido-2-methylpropane sulfonic acid?AMPS?as monomers,combined with free radical copolymerization methods.The effects of different pH in condensation environments and different Bentonite concentrations on the effect of Bentonite intercalation and the mechanical properties of the gels were investigated.The mechanical properties of the gels was significantly improved by the dual nanocomposite mechanism.It was more favorable for intercalation of Bentonite in the dispersion at pH of 9.7.The d-value of the clay was expanded from 1.21 nm to 2.04 nm,and then the Bentonite in the gel reached the exfoliation state through the action of the polymerization heat.The compressive stress of the gel reached 9.61 MPa with the fracture energy was 6639.35 J?m^-2?the water content was 85 wt%?.Vinyltriethoxysilane?VTES?was used as an intercalator for Bentonite due to its small size.Lower concentrations of VTES was more conducive to intercalation of Bentontie,Bentonite reached a exfoliation state at the dispersion stage.The compressive stress of the resultant nanocomposite gel reached 4.65 MPa,and the fracture energy was 6285.59 J·m^-2?the water content of 85 wt%?.The effective cross-linking density of the gel was as high as 77.17 mol?m^-3.When the water content droped to 50 wt%,the compressive stress of the gel increased to more than 25 MPa.Non-vinyl silylation reagent ethyltriethoxysilane?ETES?was used as an intercalator of Bentonite to synthesize PAM/Bentonite/SiO₂ double nanocomposite hydrogel.The effect of Bentonite intercalation was investigated in dispersions and gels with different ETES contents.Low concentrations of ETES were more conducive to Bentonite intercalation.The d-value of Bentonite was expanded to 4.2 nm during the dispersion stage.After polymerization,the Bentonite in the gel appeared to be exfoliated off.The gel showed good stretchability and ductility but poor compressibility.The tensile stress reached 170.62 kPa with extensibility of up to1259%.