Anisotropic Thermal Transport in Tunable Self-Assembled Nanocrystal Supercrystals

TL;DR

This study visualizes and controls heat flow anisotropy in self-assembled nanocrystal supercrystals, revealing how nanocrystal shape and assembly influence directional thermal transport for advanced thermal management.

Contribution

It demonstrates tunable thermal anisotropy in nanocrystal supercrystals through aspect ratio control and provides a modeling framework for predicting heat flow behavior.

Findings

Heat predominantly flows along the long-axis of nanocrystals.

Anisotropy exceeds nanorod aspect ratio in certain assemblies.

Void presence disrupts heat flow, affecting anisotropy.

Abstract

Realizing tunable functional materials with built-in nanoscale heat flow directionality represents a significant challenge that could advance thermal management strategies. Here we use spatiotemporally-resolved thermoreflectance to visualize lateral thermal transport anisotropy in self-assembled supercrystals of anisotropic Au nanocrystals. Correlative electron and thermoreflectance microscopy reveal that nano- to meso-scale heat predominantly flows along the long-axis of the anisotropic nanocrystals, and does so across grain boundaries and curved assemblies while voids disrupt heat flow. We finely control the anisotropy via the aspect ratio of constituent nanorods, and it exceeds the aspect ratio for nano-bipyramid supercrystals and certain nanorod arrangements. Finite element simulations and effective medium modeling rationalize the emergent anisotropic behavior in terms of a simple series resistance model, further providing a framework for estimating thermal anisotropy as a function of material and structural parameters. Self-assembly of colloidal nanocrystals promises an interesting route to direct heat flow in a wide range of applications that utilize this important class of materials.