title: Ultralow thermal conductivity in organoclay nanolaminates synthesized via simple self-assembly.
abstract: 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.
authors.affiliation: Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Losego
authors.forename: Ian P
authors.initials: IP
authors.lastname: Blitz
authors.forename: Richard A
authors.initials: RA
authors.lastname: Vaia
authors.forename: David G
authors.initials: DG
authors.lastname: Cahill
authors.forename: Paul V
authors.initials: PV
authors.lastname: Braun
mesh_terms: D000538:Aluminum Silicates / Q000138:chemical synthesis* / Q000737:chemistry; D000077215:Clay; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature
chemical_list: D000538:Aluminum Silicates; D000077215:Clay