Colloidal magnetic brushes: influence of the magnetic content and presence of short-ranged attractive forces in the micro-structure and field response.

The behavior of supramolecular brushes, whose filaments are composed by sequences of mag- netic and non-magnetic colloidal particles, has been studied using Langevin dynamics simula- tions. Two types of brushes have been considered: Stockmayer brushes (SB) and non-sticky magnetic brushes (NSB). In both cases, the microstructure and the collective behaviour have been analysed for a wide range of magnetic field strengths including the zero-field case. Results show that, for the same magnetic content, SB placed in a magnetic field present an extensibility up to three times larger than NSB. The analysis of the microstructure of SB at zero field shows that magnetic particles belonging to different filaments in the brush self-organize into ring and chain aggregates, while magnetic colloids in NSB mainly remain in a non-aggregated state. Clustering among magnetic particles belonging to different filaments is observed to gradually fade away as the magnetic content of SB filaments increases towards 100%. Under an external field, SB are observed to form chains, threads and sheets depending on the magnetic content and the applied field strength. Chain-like clusters in SB are observed to decrease in size as the magnetic content in filaments increases. A non-monotonic field dependence is observed for the average size of these clusters. In spite of the very different microstructure, both NSB and SB are observed to have a very similar magnetization, especially in high strength fields.