(525a) Patchy Particles Made Easy: Developing General Colloidal Approaches to Produce Anisotropic Building Blocks for Novel Functional Materials

Conventional applications of small particles generally make use of isotropic interactions to form dense, closely packed layers or dilute dispersions in a matrix. There is however, a growing interest in the exploration of particles with anisotropic properties. On the one hand, anisotropy enables particles to behave as “intelligent” building blocks, assembling according to asymmetrical interactions to form hierarchical structures with novel characteristics. On the other hand, exciting technological possibilities to improve existing materials and processes will be developed. Metallic Janus and patchy particles have drawn much attention in the past few years. They have many potential applications in the field of optics, sensors, drug delivery, catalysis or self-assembled hierarchical materials. However, versatile and scalable methods for forming metallic patches on dielectric nanoparticles are still rather scarce. One common approach is to vacuum deposit noble metal such as gold onto a monolayer of silica or polystyrene particles. Another is to introduce particles at the boundary between two phases with the patch-forming chemical reaction selectively taking place in one phase. In our group a method of fabrication of silver and silver/gold patches on silica nanospheres via heterogeneous nucleation and surface growth has been established. Compared to the abovementioned approaches, our method is based on facile liquid phase colloidal techniques without the need for chemical functionalization or templating and allows the morphology and properties of the nanostructures to be influenced by process variables. Recently we have expanded this work considerably to explore the potential generality of the technique.

In this contribution we will report on the use of different core particles, including silica and anionic and cationic polystyrene nanospheres, which permit modulation of the interactions between core, metal precursor and the growing patch. Our systematic experiments show that while heterogeneous nucleation is promoted by electrostatic driven accumulation of the patch precursor, the interfacial chemistry of the core particle has a critical influence on the mode of growth of gold or silver patches. For instance, for increasing ratios of ascorbic acid (reductant) to the chloroauric ion (gold precursor) the gold patch morphology on cationic polystyrene spheres changes significantly from small nanospheres to finely structured dendritic-like patches. The activation of such surface diffusion-limited growth is considered in the framework of accepted models, like diffusion limited aggregation. We will also report on attempts to control the location of heterogeneous nucleation, a critical step in developing a reliable process for producing patchy particles in large quantities with uniform morphology.