Ultralow Thermal Conductivity in Organoclay Nanolaminates Synthesized via Simple Self-Assembly

Because interfaces impede phonon transport of thermal energy, nanostructuring can transform fully dense solids into ultralow thermal conductivity materials. Here we report a simple self-assembly approach to synthesizing organoclay nanolaminates with cross-planar thermal conductivities below 0.10 W m–1 K–1a 5-fold decrease compared to unmodified clay. These organoclays are produced via alkylammonium cation exchange with colloidally dispersed montmorillonite clay sheets followed by solvent casting. Time-domain thermoreflectance (TDTR) is used to evaluate the thermal conductivity of the organoclay nanolaminates. Variations in both organic layer thickness and cation chemistry are investigated. At these interface densities (1.0–1.5 interfaces/nm), we demonstrate that thermal conductivity is relatively independent of nanolaminate spacing. A simple series resistance model describes the behavior and gives an interfacial thermal conductance value of ≈150 MW m–2 K–1 for the organic/clay interface, consistent with similar organic–inorganic interfaces. The wide range of compositional substitutions and structural variations possible in these materials, make organoclays a versatile new platform for investigating the underlying physics of nanolaminate structures.