Inorganic nanoparticles in nanocomposite are used to enhance optical responses, improve mechanical properties, or increase thermal stability . For example, small metal particles that have large extinction coefficients due to their surface plasmon resonance provide strong colours. The arrangements of such particles are static with no or minimal mobility of the particles in the cross-linked polymer matrix. Plasmonic particles in colloidal dispersions can move and reversibly change their agglomeration state upon stimulation, which changes colour, reflectivity, and scattering as their plasmonic coupling changes . Here, we demonstrate how the mobility of the dispersion can be brought into a solid material to create an “active nanocomposite”.
We combined the emulsion processing of nanoparticles with composite preparation to encapsulate a colloidal nanoparticle dispersion in a solid matrix via an oil-in-water emulsion . The liquid droplets provide mobility, drastically reduce the time required for switching between the different states, and increase the dynamic range of the switchable property. For example, a hydrogel matrix with encapsulated oil droplets containing alkylthiol-coated gold particles reacts to temperature changes by reversible colour change that is due to the agglomeration of the enclosed particles. In-situ small angle x-ray scattering during repetitive cycling between high and low temperatures was used to confirm that gold nanoparticles inside the material switch between a fully dispersed and an agglomerated stated in a highly reversible process. We present optical spectra to show that the change in plasmonic coupling and scattering intensity of the nanoparticles is responsible for the transition of macroscopic properties, such as color and haze.
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