Self-Assembly of Hierarchical Organic Nanoparticles Controlled by Modified Surfactants

Semi-dilute nanoparticles tend to cluster in order to reduce surface area. Element crystallites form densely clustered primary particles associated with high surface area. In contrast, these larger primary particles have lower surface area and slower thermal movement and aggregate into branched mass fractals, forming a dual-level hierarchical structure. Elemental clustering can be controlled using surfactants. In this work a polyethelene oxide (PEO) based surfactant, Triton^TM X-100^®, is used to control clustering of an organic pigment. PEO displays a lower critical solution temperature (LCST) at 66 °C. It has been found that reduced miscibility in the vicinity of the LCST can be used to control clustering. For small clusters significant aggregation occurs while for sufficiently large clusters aggregation does not occur. In this way a thermally controlled hierarchical structure can be produced. The thermally tuned hierarchical structure can be locked in using chemically modified surfactant.