Network parameters of poly(N-isopropylacrylamide)/montmorillonite hydrogels: Effects of accelerator and clay content

The results of network parameters of poly(N-isopropylacrylamide)/montmorillonite (PNIPAAm/MMT) hydrogels prepared with two different types and concentrations of accelerators (tetramethylethylenediamine, TEMED and quaternary TEMED containing decyl bromide, QTEMED) using three different clay contents (1.0, 3.0, and 5.0wt% of total monomer concentration) at two different polymerization temperatures (10 and 32°C) were presented and discussed. It was observed that when the reaction temperature of PNIPAAm crosslinked with MMT was chosen as 10°C both volume swelling ratios (i.e., thermodynamic interaction) and shear moduli, G increased. In hydrogels, thermodynamic interaction is reflected by polymer-water interaction parameter (χ). The lower is the value of χ, the stronger is the interaction between polymer and water, and the lower is the interaction between hydrophobic groups or between polymer chains. In addition, increase in MMT content was slightly affected on these intermolecular interactions. Therefore, this effect that combines high-shear modulus with lower value of χ in the same molecular structure was defined as clay content-independent diffusion behavior. On the other hand, in the case of the hydrogels synthesized with the higher concentration of TEMED and MMT, the values of χ and G decreased. These facts were interpreted that increase in both accelerator concentration and clay content, for fixed NIPAAm concentration made the number of effective crosslinks between MMT layers smaller.