Charging and stability of needle-like TiO2 nanoparticles were studied. Measured iso electric point (IEP) was pH∼4 and lower than that of spherical ones pH∼6. Heat treatment at 400˚C changed the IEP from 4 to 6. The shift is probably due to shape controller (ethylenediamine). The particles aggregate around IEP and thus are chargestabilized. Experimental hydrodynamic diameters of needle-like particles showed a reasonably good agreement with the theoretical diameter. That is, the particles can be dispersed to primary particles. 1pK Stern and standard electrokinetic models describe electrophoretic mobility of needle-like TiO2, indicating that double layer relaxation is significant for needle-like TiO2. | Communications in Physics, Vol. 24, No. 3S1 (2014), pp. 13-21 DOI: ELECTRIC CHARGING AND COLLOID STABILITY OF FABRICATED NEEDLE-LIKE TiO2 NANOPARTICLES KENTO UENO Graduate School, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan MOTOYOSHI KOBAYASHI AND YASUHISA ADACHI Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan TAKASHI KOJIMA Graduate School of Science and Technology, Chiba University, 1-33 Yayoicho, Inage-ku, Chiba 263-8522, Japan E-mail: Received 04 April 2014 Accepted for publication 24 May 2014 Abstract. Charging and stability of needle-like TiO2 nanoparticles were studied. Measured isoelectric point (IEP) was pH∼4 and lower than that of spherical ones pH∼6. Heat treatment at 400˚C changed the IEP from 4 to 6. The shift is probably due to shape controller (ethylenediamine). The particles aggregate around IEP and thus are chargestabilized. Experimental hydrodynamic diameters of needle-like particles showed a reasonably good agreement with the theoretical diameter. That is, the particles can be dispersed to primary particles. 1pK Stern and standard electrokinetic models describe electrophoretic mobility of needle-like TiO2 , indicating that double layer relaxation is significant for needle-like TiO2 . Keywords: electrophoretic mobility, isoelectric point, 1pK Stern model, double layer relaxation, aggregation, hydrodynamic diameter. I. INTRODUCTION The appearance of nanomaterial leads to significant changes in the world of science and engineering. Chemical and physical properties expected for nanomaterials are determined by their size, shape (morphology), composition, reactivity, and surface chemistry [1]. Titanium dioxide (TiO2 : titania) is a naturally occurring mineral and has emerged as one of the most fascinating nanomaterials in modern era. TiO2 nanoparticles have been extensively used in industrial
