The role of poly(methacrylic acid) conformation on dispersion behavior of nano TiO2 powder

Abstract

To exploit the advantages of nanoparticles for various applications, controlling the dispersion and agglomeration is of paramount importance. Agglomeration and dispersion behavior of titanium dioxide (TiO2) nanoparticles was investigated using electrokinetic and surface chemical properties. Nanoparticles are generally stabilized by the adsorption of a dispersant (polyelectrolyte) layer around the particle surface and in this connection ammonium salt of polymethacrylic acid (Darvan C) was used as dispersant to stabilize the suspension. The dosages of polyelectrolyte were optimized to get best dispersion stability by techniques namely particle charge detector (13.75 mg/g) and adsorption (14.57 mg/g). The surface charge of TiO2 particles changed significantly in presence of dispersant Darvan C and isoelectric point (iep) shifted significantly towards lower pH from 5.99 to 3.37. The shift in iep has been quantified in terms of free energy of interaction between the surface sites of TiO2 and the adsorbing dispersant Darvan C. Free energies of adsorption were calculated by electrokinetic data (-9.8 RT unit) and adsorption isotherms (-10.56 RT unit), which corroborated well. The adsorption isotherms are of typical Langmuir type and employed for calculation of free energy. The results indicated that adsorption occurs mainly through electrostatic interactions between the dispersant molecule and the TiO2 surface apart from hydrophobic interactions. (C) 2011 Elsevier B. V. All rights reserved.