ESPCI web site
We report the synthesis and the characterization of transparent and purely elastic hybrid hydrogels of poly(N,N dimethylacrylamide) (PDMA) and poly(acrylic acid) (PAA) swollen by potassium silicate solutions.
The structure and properties of each organic and inorganic part of these original systems are controlled by a large number of parameters. A 4-steps approach is proposed to identify progressively the phenomena controlling the structure properties relationships.
On the basis of the phantom network model, the analysis of the mechanical (compression, creep) and thermodynamic (swelling) properties of PAA and PDMA gels prepared in water allowed to identify and to quantify topological defects in gel structures; these latter being more important in the case of PAA gels.
The introduction of KOH during the synthesis has two main effects on the structure and properties of the hydrogels: a chemical degradation of the monomers, leading to a decrease of elastic moduli, as well as a modification of defect proportion in the network structure.
Gels prepared in presence of colloidal silica particles have also been investigated. For PDMA, we checked the polymer chains adsorption on silica surfaces and characterized its influence on the mechanical properties. In the case of PAA chains, it was not possible to obtain a transparent gel.
Finally, transparent PAA/silicates gels have been prepared by simultaneous polymerization of the organic network and silica dissolution. The gels present a purely elastic behavior determined by the PAA concentration as well as by the competition, in basic medium, between the silica dissolution and the chemical degradation of the organic monomers.