Aqueous dispersions of layered double hydroxide/polyacrylamide nanocomposites: preparation and rheology

Water was used to replace the toxic organic solvent of formamide in preparation of the aqueous dispersions of layered double hydroxide/polyacrylamide (LDH/PAM) nanocomposites, which exhibited greatly enhanced theological properties when compared to those of the neat PAM. First, the nanocomposite dispersions were prepared via a convenient in situ polymerization or solution mixing method, using water to exfoliate the LDH particles instead of formamide as used in the pioneer investigation. The LDH dispersion structure in the nanocomposite dispersion was demonstrated by X-ray diffraction and direct observation. Then, the rheological investigations including sol -> gel transition, dynamic oscillatory frequency sweep and steady shear measurements were carried out. Subsequently, the rheological properties for the aqueous nanocomposite dispersions prepared by the two methods were compared. Finally, the mechanism of the enhancement of rheological properties (the moduli and viscosities) was discussed based on the LDH dispersion microstructure, network formation as well as interfacial interactions between PAM chains and LDH nanoparticles.