Improving stability of TiO2 particles in water by RF-plasma polymerization of poly(acrylic acid) on the particle surface

The stability of TiO2 particles in water was increased through plasma polymerization of acrylic acid (AA) onto the particles surface. The polymerization was carried out directly upon TiO2 powder by using two radiofrequency (RF) plasma reactors: one inductively coupled and another capacitively coupled. In both cases, a cross-linked polyacrylic acid (PAA) film was formed on TiO2 particles surface, which was characterized by Energy Dispersive Spectroscopy (EDS), Fourier-transformed infrared spectroscopy, (FTIR), Raman Spectroscopy, and X-ray photoelectron spectroscopy (XPS). The stability of the PAA-coated TiO2 particles was determined by their precipitation in water. It was found that a moderate plasma treatment effectively improved the stability of PAA-coated TiO2 particles. At low levels of AA polymerization, the TiO2 particles surface was not modified enough to improve their stability in water; on the other hand, a high degree of AA polymerization led to the formation of large agglomerates, induced by the PAA film, and these particles were not stable. As expected, the particle size and the Z-potential of the PAA-coated particles determined their stability in water. Under the optimum operating conditions of this study, the treated TiO2 particles showed stability as good as that of TiO2 particles modified with a dispersant.