Investigation of Interactions Between Polymer-coated Nano-Y-TZP Particles by AFM

Abstract

It is well known that copolymers of polyacrylic acid (PAA) and polymethacrylic acid (PMAA) are strongly adsorbed on the surfaces of alumina and zirconia [1]. For this reason, inorganic oxides such as alumina, silica, and zirconia were surfacemodi®ed by polymers to improve their compatibility with the organic phase in many important applications [2, 3]. Recently, PAA and NH4PAA were applied to prepare core-shell alumina nanocomposite particles by their interparticle-bridging capability [4, 5]. The kinetics and equilibrium of the process have been studied in detail and it was widely claimed that polymer coatings can balance the interactions between particles by inducing repulsive force to prevent the agglomeration of particles, hence, to promote the homogeneity of the particle surfaces [2, 6]. However, until recently the mechanism was probed in submicrosized Al2O3 [7]; nanosized particles differ from submicroparticles naturally, they are ready to agglomerate, and the interactions between them may demonstrate some diversity in comparison with submicroparticles. Although atomic force microscopy (AFM) is attractive for imaging surface topographies of insulating materials because of its exible nature, until recently, the use of the AFM as a force sensing tool has been limited [7±9]. For the ®rst time, we employ AFM to probe interactions between nano-Y-TZP (yttria stabilized tertragonal zirconia, Y2O3 3 mol %), which is a prospective structural ceramic in many critical environments [10]. In a typical procedure, nanosized Y-TZP powder with a speci®c surface area of 31.55 m gy1 (BET) was synthesized by chemical precipitation [10]; TEM shows that the particle size is about 20 nm (Fig. 1). Polymer dispersants used are NH4PAA (ammonium polyacrylate) and NH4PMAA (ammonium polymethacrylate) (Mw ˆ 10 000). Y-TZP suspensions were prepared by ball milling at least 24 h, the suspensions were adjusted to pH 10 by (CH3)4NOH, dispersant concentration was 2 % dwb (dry weight basis of the powder) for NH4PAA and NH4PMAA, respectively. The suspension was ball milled and then equilibrated for 24 h. The particles were separated by using an LG-10 centrifuge at 2000 rpm for 1 h and the supernatant was removed. The polyelectrolytes-coated nano-Y-TZP particles were dried in vacuo prior to surface characterization and interaction analysis. The surface of the powder was characterized by using a Microlab-310F scanning auger microscope (SAM), indium particles were employed as a template for the anchoring of Y-TZP powder. The interaction was analyzed by AFM (Topometrix explorer, commercial silicon nitride tip with a radius around 50 nm) in dried environment, the force curve is the force between the tip, and the surface of the thin plates formed by high pressure from the powders [7, 8]. Fig. 2 shows the SAM spectra of nano-Y-TZP powder. It is easy to ®nd out from the SAM results that the polymer coated nano-YTZP powder has a carbon peak at about 270 eV, which indicates that the surfaces of the nanoparticles were successfully