Functional Nanocomposites of Lead Telluride Percolating Networks

Advantageous properties that reveal themselves in the nanoscale have attracted focus across a wide range of research fields. A great challenge lies in developing materials that can extend effects at the nanoscale to macroscopic materials. Several methods to address this challenge include nanoparticle superlattices and thin film deposition methods that struggle to achieve sufficient thickness for application as a bulk material, or through the dispersion of active nanoscale materials into a polymer matrix that frequently struggles to incorporate a significant enough volume fraction of the functional inorganic phase. For inorganic functional nanomaterials desired for optoelectronic, thermoelectric, and similar applications that rely on transport of information quanta, the nanomaterials must be organized in a way such that both the particle-to-particle separation is sufficiently short and the inorganic phase forms a percolation path that spans the bulk composite volume.<br/> <br/>Our work reports on a material system that forms a percolation networks of lead telluride (PbTe) nanoparticles (NPs) supported in a polymer matrix for mechanical reinforcement. PbTe NPs are semiconducting materials sought for applications in high energy photon sensing and shielding – due to its high effective atomic number – as well as thermoelectric applications for its attractive ZT figure of merit. The confinement effects displayed in PbTe NPs have promise for greatly reducing thermal losses by suppressing optical phonons which is possible to lead to high resolution photon sensing and enhanced thermoelectric power generation in a properly designed and optimized material. The aqueously dispersed PbTe NPs spontaneously self-assemble into percolating networks, which in turn swells to form a volume-spanning hydrogel, which achieves the goals of close particle-to-particle transport and percolation pathways through bulk volumes.<br/> <br/>The hydrogel form of the PbTe nanostructured network is fragile with a short shelf-life due to water evaporation, and converting from hydrogel to an aerogel or xerogel either results in a brittle solid or collapsed structure. To solve this challenge, the PbTe NP network was infiltrated with one of a variety of hydrophilic monomers/polymers, and subsequently polymerized/crosslinked by UV initiation. The resulting functional PbTe+polymer nanocomposites were confirmed to retain stochastic networks from the assembled PbTe network, while the polymer reinforced the samples to prevent brittle fracture and support the network so it can percolate across macroscopic volumes. The nanocomposites’ mechanical properties were determined by the polymer selection and preparation method. The attenuation of the nanocomposite with neutral particle radiation was quantified and unexpectedly outperforms a simulated material of the same element distribution but homogenous composition. Explanations for these unexpected results are currently being investigated to be able to understand the potential improved interaction of high energy photons with nanostructured materials compared to amorphous devices.