Surface Contacts Strongly Influence the Elasticity and Thermal Conductivity of Silica Nanoparticle Fibers

Granular materials are met in science and engineering disciplines. Controlling the particle contacts is one of the critical issues for the design, engineering, and utilization of desired properties. The achievable fast fabrication of nanoparticles with tunable physical and chemical properties facilitates tailoring the macroscopic properties of particle assemblies through contacts at the nanoscale. Models have developed to predict the mechanical properties of macroscopic granular materials, however, their predicted power in the case of nanoparticle assemblies is still uncertain. Here, we investigate the influence of nanocontacts on elasticity and thermal conductivity of a granular fiber comprised of close-packed silica nanoparticles. A complete elastic moduli characterization is realized by the non-contact and non-destructive Brillouin light spectroscopy which also in situ resolves the stiffness of the constituent particles. In the framework of effective medium models, the strong enhancement of the elastic moduli is attributed to the formation of physical and chemical nanocontacts. The nanoparticle contacts are also responsible for the increase of the fiber thermal conductivity that emphasizes the role of interface thermal resistance which is ignored in the most porosity models. This insight into the fundamental understanding of structure-property relationships advances the manipulation of granular systems at the nanoscale.