Decoupling particle formation from intraparticle ordering in mesostructured silica colloids Andreas Sundblom a,⇑ , Cristiano L.P. Oliveira b,1 , Jan Skov Pedersen b , Anders E.C. Palmqvist a a Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden b Department of Chemistry and iNANO Interdisciplinary Nanoscience Center, University of Aarhus, DK-8000 Aarhus, Denmark article info Article history: Received 8 November 2010 Received in revised form 12 April 2011 Accepted 20 April 2011 Available online 27 April 2011 Keywords: Mesoporous silica SBA-15 Formation mechanism Inorganic silica source Colloidal particles abstract A synthesis methodology that decouples the formation of silica particles from their internal mesoorder- ing has been developed. This was possible by employing synthesis conditions that combine fast nucle- ation and growth of particles with slow silica condensation. The synthesis developed is based on an inorganic silica source and the nonionic block copolymer Pluronic P123 using a synthesis pH of 3 and con- ditions that result in a stable colloidal suspension. Using a two-step procedure the particles can be first formed and then triggered into developing an ordered internal mesostructure by subsequent addition of silica or Pluronic. This is possible because under the conditions employed the particles are stabilized by relatively weak interactions before the formation of a stable silica network. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Mesostructured silica has received enormous interest since its announcement in the early 1990’s. This has led to the development of a large variety of synthesis routes for its preparation. In order to optimize the material for different applications it is important to be able to control properties such as pore size, mesoorder and particle morphology. To do this it is essential to understand the formation mechanism of these materials. One of the synthesis routes that have gained the most attention is the synthesis of SBA-15 in which non-ionic block copolymers are used as structure directing agent [1,2]. The mechanism of this synthesis has been discussed since the first publication but is still not fully under- stood. One of the main discrepancies between different proposed mechanisms concerns when mesoorder is achieved internally in the formed particles and whether or not a mesoordered structure is obtained directly upon particle formation or if it is a result of a separate subsequent reorganization step following particle formation. A mechanism based on floc formation and precipitation, fol- lowed by an internal rearrangement has been proposed [3,4]. Several other studies also support a mechanism where the silica and Pluronic aggregate before the generation of an ordered struc- ture takes place [5–8]. However, others have suggested mecha- nisms, where the interaction between silica and Pluronic leads to elongated cylindrical hybrid organic–inorganic micelles. These mi- celles then aggregate directly into an ordered structure [9–11]. Recently, a modified synthesis of SBA-15 was presented differ- ing from the conventional synthesis through the silica source used, the synthesis temperature and the pH employed [12,13]. While SBA-15 most often is prepared from tetraethylorthosilicate (TEOS) at pH < 1 at temperatures of 35–60 °C, the modified synthesis is prepared from ion-exchanged water glass at pH 3 and room tem- perature. All these differences are attractive from an industrial per- spective. The final product of the modified synthesis shows some interesting characteristics; the obtained particles are much smaller than the conventional product and the particles can be made col- loidally stable. Futhermore, the final particle size can be controlled by the electrolyte concentration of the reaction solution [13]. In this paper attention is directed to the development of mesoorder in the formed particles to further improve the understanding of this exciting and versatile material. The aim with this study is to illustrate whether or not the particle formation and the ordering of the internal structure can be regarded as two separate processes allowing for tuning of particle properties. The internal structure here refers to the organization of the surfactant and silica inside the particle. The results are discussed within the general context of formation mechanisms for block copolymer-templated synthe- ses and the influence of differences in silica source and pH used is explained. 1387-1811/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2011.04.025 ⇑ Corresponding author. Address: Applied Surface Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden. Tel.: +46 31 772 29 58; fax: +46 31 16 00 62. E-mail address: andreas.sundblom@chalmers.se (A. Sundblom). 1 Present address: Complex Fluids group, Department of Experimental Physics, University of São Paulo, 05314-970 São Paulo, Brazil. Microporous and Mesoporous Materials 145 (2011) 59–64 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso