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.