Modifying Thermal Transport in Colloidal Nanocrystal Solids with Surface Chemistry

Area of Science:

• Materials Science
• Nanotechnology
• Thermal Physics

Background:

• Colloidal nanocrystal (NC) solids are promising materials for thermoelectric applications.
• Understanding thermal transport properties is crucial for optimizing NC solid performance.
• Surface chemistry, particularly the organic ligands, plays a vital role in NC solid properties.

Purpose of the Study:

• To systematically investigate the effect of surface chemistry on thermal transport in colloidal NC solids.
• To elucidate the influence of ligand properties (binding group, length) and NC size on thermal conductivity.
• To identify strategies for tuning the thermal conductivity of NC solids.

Main Methods:

• Utilized lead sulfide (PbS) NCs as a model system.
• Varied ligand binding groups (thiol, amine, halides), ligand lengths (C2-C8 dithiols), and NC diameters (3.3-8.2 nm).
• Measured thermal conductivity and employed effective medium approximation (EMA) modeling.

Main Results:

• Ligand choice altered NC solid thermal conductivity by up to 2.5 times.
• Reduced ligand length increased thermal conductivity by decreasing interparticle distance.
• Increased NC diameter and optimized surface chemistry enhanced thermal conductivity, with surface effects being more pronounced for smaller NCs.

Conclusions:

• Thermal conductivity of NC solids can be tuned over a factor of 4 (0.1-0.4 W/m-K) by controlling surface chemistry and NC size.
• Thermal transport through the ligand matrix is the rate-limiting step.
• Future efforts should focus on optimizing the ligand-ligand interface to enhance thermal conductivity in NC solids.