Poly(N-isopropylacrylamide)–clay hydrogels: Control of mechanical properties and structure by the initiating conditions of polymerization

• Mechanical properties and structure of gels are controlled by redox initiating system.
• The relationships formation–structure–properties of gels are determined.
• Theoretical analysis of mechanical properties of nanocomposite gels is described.
• Both covalent crosslinking and physical interactions are considered at gel formation.

The mechanical properties of the poly(N-isopropylacrylamide) (PNIPA)–clay gels are efficiently controlled by the initiating conditions of the polymerization. The concentration and composition of the redox initiating system, initiator ammonium peroxodisulfate (APS) and activator tetramethylethylenediamine (TEMED), are found to be crucial in the gel synthesis, governing not only the polymerization process, but also the gel structure and mechanical properties. For the description of mechanical properties of nanocomposite gels, the combination of the theory of elasticity with the model of mechanical properties of composites is applied, because the incorporated clay serves both as a crosslinker and as reinforcing nanofiller. Based on this approach, the complex mechanical behavior of the gels is described and the experimental data are explained, including the effect of clay, monomer and the initiators. The results contribute to the elucidation of the relationships between formation, structure and mechanical properties of the nanocomposite gels.

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