The Chemical-Physical Processes Behind Self-assembly

Abstract

This first chapter introduces the models and theories necessary for a basic understanding of mesoporous materials self-assembly. The self-assembly process that drives the formation of an organized mesoporous structure depends on several chemical-physical processes that must be properly designed and governed. In particular, the interaction between the supramolecular template and the inorganic silica building blocks is a critical parameter, such as the organization of the amphiphilic surfactant into micelles. Different organization pathways drive self-assembly, but the thermodynamic and the kinetics of the processes involved should follow specific relationships to achieve order. The Thermodynamics of Self-assemblyThe formation of an ordered mesostructure through self-assembly is governed by the simultaneous occurrence of different chemical-physical phenomena which address the system towards order or disorder [1].The thermodynamics of the entire self-assembly process depends on the free energy variation, G mes , associated with the organization of the individual components, which contribute to the formation of an ordered structure of mesoscopic scale (2-50 nm). If G mes < 0 the system evolves to self-organization [2]. The configuration of the ordered mesophase would represent a minimum of energy.The total free energy of self-assembly, in absence of external fields, is given by the contribution of four processes:(1) G org . The formation of micelles, that is, the supramolecular templates whose organization would determine the structure and topology of the pores, is associated with the free energy, G org . Organic micelles are formed through non-covalent bonds and will depend on the amphiphilic nature of the molecules.(2) G inorg . The formation of the supporting structure of the mesoporous material occurs through covalent bonds and the free energy associated with the