Surface and interfacial properties of polymer-intercalated layered double hydroxide nanocomposites

The surface and interfacial properties of the layered double hydroxide (LDH) phase Mg6Al2(OH)16CO3·4H2O (LDHCO3) and its nanocomposites with poly(styrenesulfonate) (LDHPSS) and poly(vinylsulfonate) (LDHPVS) were characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, transmission electron microscopy, He pycnometry, and electrophoretic light scattering. Polymer incorporation within the inter-gallery space resulted in a shift of the d003 reflection from 7.7 Å (LDHCO3) to 12.7 Å (LDHPVS) and 21 Å (LDHPSS). This increase in basal plane spacing caused the density of the LDH samples to decrease from 2.05 g/cm3 (LDHCO3) to 1.83 and 1.41 g/cm3 for LDHPVS and LDHPSS nanocomposites, respectively. LDHCO3 exhibited a positive electrophoretic mobility over the pH range from 4–11 with an isoelectric point (iep) at pH 11. However, the LDH nanocomposites displayed a negative electrophoretic mobility over the measured pH range, indicating that the surface properties of the LDH nanocomposites were dominated by negatively charged sulfonate groups from adsorbed polymer molecules.