High solids loading ceramic colloidal dispersions in UV curable media via comb-polyelectrolyte surfactants Yoram De Hazan a, * , Judit Heinecke a,b , Alfred Weber b , Thomas Graule a,c a Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for High Performance Ceramics, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland b TU Clausthal, Institute of Mechanical Process Engineering, Leibnizstrasse 19, D-38678 Clausthal-Zellerfeld, Germany c TU Freiberg, Institute of Ceramic, Glass and Construction Materials, D-09596 Freiberg, Germany article info Article history: Received 26 February 2009 Accepted 6 May 2009 Available online 12 May 2009 Keywords: Al 2 O 3 ZnO Nanoparticle Comb-polyelectrolyte Nanocomposite Acrylate Rheology UV Cure Thick film abstract Ceramic articles and ceramic/polymer composites with complex 3d shapes can be produced by rapid pro- totyping techniques such as stereolithography of ceramic dispersions in UV curable resins. Nanometer and submicrometer ceramic particles are advantageous for high resolution microstructures, surface qual- ity and reduced sintering temperatures. Frequently, special surfactants are needed to maximize solids loading while maintaining suitable rheological properties for stereolithography applications (viscosity <5 Pa s, 30 1/s). We present here a general scheme for relatively high loading/low viscosity dispersions of nanometer and submicrometer particles in UV curable resins using comb-polyelectrolyte surfactants. In the present approach, adsorption is favorably carried out in aqueous media and the dry particles with adsorbed surfactant are transferred to the organic media through centrifugation, washing, drying and dry milling. The method is demonstrated for Al 2 O 3 , ZnO and mixed Al 2 O 3 /ZnO colloidal dispersions. Disper- sions containing >48 vol% particles suitable for stereolithography have been achieved. Dispersions con- taining 36 vol% particles are predicted to have viscosities in the range suitable for direct inkjet printing applications at 75 °C. The particle stabilization and transfer schemes, rheological behavior and UV curing characteristics are presented. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction Ceramic and ceramic/polymer composites with complicated 3d shapes can be manufactured layer by layer by rapid prototyping techniques such as stereolithography of ceramic dispersions in UV curable media. Stereolithography relies on relatively UV trans- parent dispersions having viscosities lower than 5 Pa s (30 1/s) [1]. Numerous studies of dispersions of micrometer and submicrome- ter powders in organic and aqueous media have been made [1– 9]. Organic systems are advantageous due to the wide choice of monomers and oligomers for composite formulation and fast cur- ing. Nanometer and submicrometer ceramic particles are advanta- geous for high resolution microstructures, surface quality and reduced sintering temperatures. Although few particle types can be efficiently dispersed in organic UV curable monomer mixtures [10], special surfactants are frequently needed to increase particle solids loading to the levels required for ceramic processing (>40 vol%) [2,4–9]. Comb-polyelectrolyte surfactants find increased application due to their ability to sterically or electrosterically disperse nano- particles in aqueous media in a broad pH range under high ionic strength (e.g. in the concrete industry) and high temperature con- ditions [11–13, and references therein]. The comb-polyelectrolyte backbone is designed to have good affinity to the particle surface, while the side-chain density, length and polarity can be tailored to provide efficient dispersing properties in a variety of dispersing media [14–16]. In this work we develop comb-polyelectrolyte stabilized disper- sions in UV curable monomer mixtures suitable for stereolithogra- phy applications. The adsorption of the surfactants is carried out in aqueous media under favorable and controlled pH conditions. The transfer scheme of particles with adsorbed surfactants from aque- ous to the organic media is presented. The method is demonstrated for Al 2 O 3 and ZnO nanometer and submicrometer particles and their mixed particle dispersions. 2. Experimental 2.1. Materials The nanosize ceramic particles explored in this study are shown in Table 1 along with their surface area measured by the BET meth- od with SA3100 (Beckman Coulter, USA). ZnO (60 nm) and CeO 2 (<25 nm) nanoparticles and two types of Al 2 O 3 particles were stud- ied, TMDAR from Taimei Chemical Co., LTD, Japan (TM, a-Al 2 O 3 , 0021-9797/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2009.05.012 * Corresponding author. Fax: +41 44 823 4150. E-mail address: yoram.dehazan@empa.ch (Y. De Hazan). Journal of Colloid and Interface Science 337 (2009) 66–74 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis