Aggregation of colloidal nanoparticles in polymer matrices

Colloidal nanoparticles may possess many functional properties, whose nature may be electronic, chemical, biological, mechanical, etc. It is often advantageous to incorporate them into a matrix material, e.g., a polymer solution or melt, or an elastomer, in order to obtain a 'nanomaterial' with additional properties brought in by the filler particles. One of the basic but nonetheless crucial properties is the mechanical strength of such polymer nanocomposites, whose rheological (or mechanical) properties are usually better than those of the pure matrix. The precise origin of this mechanical reinforcement effect, however, remains unclear. In this context, some recent studies of the structure and mechanical properties of a special type of nanocomposites are reviewed here. In silica-latex systems, a latex film with silica inclusions is formed from a colloidal solution of both components. During drying of the solution, the formation of silica domains can be controlled via the physico-chemical properties of the solution. Well-defined silica aggregates embedded in a polymer matrix can be generated, and the mechanical properties of the resulting nanocomposite have been shown to be directly correlated to the average structure. We believe that the fine-tuning of the structure of the filler phase opens new perspectives for systematic studies of the reinforcement effect, e.g., by modifying filler-polymer interfacial properties at fixed structure, or by generating original structures.