Influence of aminosilane surface modification and dyes adsorption on zeta potential of spherical silica particles formed in emulsion system Teofil Jesionowski * Institute of Chemical Technology and Engineering, Poznan University of Technology, Pl. M. Sklodowskiej-Curie 2, 60-965 Poznan, Poland Abstract Studies were performed on the synthesis of spherical silica in an emulsion system. The obtained silica was subjected to surface modification using N -2-(aminoethyl)-3-aminopropyltrimethoxysilane in order to increase adsorptive properties of the silica surface. On surfaces of the unmodified silica material and the aminosilane-functionalised silica C.I. Reactive Blue 19 and C.I. Acid Red 18 were adsorbed. The obtained silica and its derivatives were subjected to physicochemical evaluation: particle size and polydispersity were examined, specific surface area (BET) was determined, surface composition was defined using elemental analysis. The principal aim of the studies was to define electrokinetic (zeta) potential and determination of its alterations as a function of pH in all types of the tested silica colloids. For the purpose the technique of electrophoretic light scattering (ELS) was applied. Effect of ionic strength on stability of tested colloids was also examined. The tested aminosilane was found to exert critical influence on values of zeta potential and, thus, on values of isoelectric point (i.e.p.). The modified silicas reached peak stability within the pH range of 2  /4 manifesting zeta potential within the range of ( /20) to ( /45) mV. # 2003 Elsevier B.V. All rights reserved. Keywords: Zeta potential; Silica, surface modification; Amino-silane; Organic dye 1. Introduction Familiarity with electrochemical properties of colloids has proven very important for various branches of science and for multiple technological processes including in particular adsorptive pro- cesses. The most important parameter which defines surface properties of solids in aqueous solutions is zeta potential (z). The electrokinetic (zeta) poten- tial has been described in detail in multiple most valuable scientific monographs [1  /8]. Detailed knowledge of colloid characteristics, i.e. of its surface potential, structure of its electric double layer (e.d.l.) or of its isoelectric point (i.e.p.) as well as the data on particle size and shape, homogeneity and surface chemistry allow to understand colloid behaviour in several specific * Tel.:  /48-61-6653-720; fax:  /48-61-6653-649. E-mail address: teofil.jesionowski@put.poznan.pl (T. Jesionowski). Colloids and Surfaces A: Physicochem. Eng. Aspects 222 (2003) 87  /94 www.elsevier.com/locate/colsurfa 0927-7757/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0927-7757(03)00237-1