(373b) Continuous Flow Synthesis of Metal Patchy Nanoparticles With Tunable Plasmonic Properties
Patchy nanoparticles comprise core particles partially covered by one or more patches of another material. Due to their surface anisotropy, such nanoparticles have very characteristic functionality and have drawn much attention for their promise in the fields of photonics, sensors, drug delivery, catalysis or self-assembled hierarchical materials. The versatile and scalable synthesis of such particles, an essential prequistive for the continuing development of materials based on patchy particles, presents a significant challenge. Current approaches to partially coat core particles lack potential for scale-up and exploitation due to their dependence on masking, templating, physical vapor deposition or complex organic functionalization procedures. We have shown in a previous study that silver patchy nanoparticles can be synthesized in a facile one-pot approach by mixing non-functionalized core nanoparticles (silica) with a silver precursor (silver nitrate) followed by the addition of a reducing agent (formaldehyde) and a base (ammonia). By this approach, patches form via heterogeneous nucleation due to electrostatic interactions between core and patch precursor and surface growth due to surface diffusion effects. Although this technique allows the facile tuning of the morphology of the silver patches and thereby their plasmonic functionality, the reaction volume and the amount of final product are somewhat limited due to the very fast reaction and the need to use very dilute reactants. In order to scale up the synthesis we have investigated the use of a continuous flow synthesis setup. In this, a double syringe pump delivers reactant solutions at variable flowrates to a thermostated T-mixer and subsequent reaction tube. Since the produced patchy particles have characteristic plasmonic properties, we were able to use an in-line fiber coupled spectrometer to acquire extinction spectra of the particles as they were produced, assisting with optimization of the process parameters. The effect of influencing parameters, such as flow rate, reaction concentrations and temperature on the formation of patches was studied. The results show this system has good reproducibility of making patchy particles and yield (number of core particles possessing a patch) could reach 100%. Furthermore, compared with the batch synthesis, the excellent mixing conditions obtained have permitted a higher concentration tolerance, opening up the possibility of gram-scale production of surface-anisotropic nanoparticles. It is also demonstrated to be as versatile as the batch system, permitting other combinations of core and patch material to be synthesized.