Certain nanoparticles, like inorganic nanocrystals, are plasmonic and interact strongly with resonant frequencies of light. Plasmonic coupling between nanoparticles results in structure-dependent optical properties, and experiments have shown that structures self-assembled from plasmonic nanoparticles are promising for switchable photovoltaics and electrocatalysts. Gels are particularly promising candidate structures because they exhibit structural features on multiple length scales that can be modified continuously, offering unprecedented tunability for functional materials. However, a major challenge to realizing these possibilities is the enormous number of physical parameters and gel structures to screen. Computational methods can accelerate the search for optimal materials, but probing the effective plasmonic properties remains a major bottleneck. The necessary optical calculations require expensive numerical solutions to many-bodied systems of equations and are therefore limited to configurations of only a handful of particles, which are not representative of large-scale structural features and heterogeneities. To address these shortcomings, we have developed a mutual polarization method to rapidly simulate the optical response of nanoparticle materials, allowing for thousands of particles to be probed at a time. We use this computational tool to investigate plasmonic coupling in self-assembled nanoparticle gels and show that the predicted optical properties agree well with corresponding experimental measurements of lab-synthesized gels. Using the detailed information available in simulations, we develop structure-property relations for the plasmonic properties of gels which, in certain cases, can be understood in terms of the underlying equilibrium phase diagram. These insights allow us to establish design principles that connect target collective properties to experimental control knobs.

Mutual polarization method for simulating the plasmonic response of self-assembled nanoparticle gels

ACS Spring 2022

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