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Modelling Surfactant Dynamics In a System Containig Coallescent Particles

James E. Magee and Flor R. Siperstein. School of Chemical Engineering and Analytical Science, University of Manchester, Po Box 88, Sackville Street, Manchester, M60 1QD, United Kingdom

The use of surfactant self-assemblies and block copolymers as templates in the synthesis of structured materials is widely spread. Although the first materials synthesized with this approach were silica based, the technique has been extended to other metal oxides and inorganic components [1]. The prediction of the final structure and properties of the templated materials is difficult, specially when self-assembly and inorganic condensation occur simultaneously [2], but even when a preformed liquid crystal is used as a template, as in the true liquid crystal templating approach [3], condensation of the inorganic framework around the soft template can lead to its deformation.

Previous work has indicated that equilibrium phase diagrams obtained from Monte Carlo simulations are useful to understand general trends in the behaviour of surfactant-inorganic systems, where phase separation between a surfactant rich and surfactant poor phases is a result of strong interactions between the surfactant head and the inorganic components [4-5]. Nevertheless, in some cases, real systems may not reach equilibrium and the dynamics of the surfactant self-assemblies as inorganic condensation takes place becomes important for the description of the actual material.

We have developed a simple potential (similar to a DLVO potential) that can correctly describe reaction limited aggregation using dissipative particle dynamics (DPD). We have used this potential to model silica nanocasting using a symmetric surfactant liquid crystal as a model template. We will present the evolution of systems starting in different configurations, where the silica is originally a neutral solvent, and therefore dispersed throughout the system, and where the silica initially shows preference for the surfactant heads. The ability of the system to accommodate a silica framework without leading to phase separation is analyzed using different strengths of aggregation.


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[3] A. Monnier, F. Schuth, Q. Huo, D. Kumar, D. Margolese, R. S. Maxwell, G. D. Stucky, M. Krishnamurty, P. Petroff, A. Firouzi, M. Janicke, B. F. Chmelka Science 1993, 261, 12991303.

[4] F. R. Siperstein and K. E. Gubbins, Langmuir, 2003 19, 2049-2057.

[5] A. Patti, A. D. Mackie, and F. R. Siperstein, Langmuir 2007, 23, 67716780.