Thermal conduction in nanoporous copper inverse opal films

Copper inverse opal films offer an attractive combination of conduction and convection transport properties that yield a low total thermal resistance for microfluidic heat exchanger applications. In this work, we present an integrated synthesis and characterization strategy to fabricate nanoporous copper inverse opal films and to measure the effective thermal conductivity. We synthesize inverse opal films with sub-micron pore diameters using a sacrificial packed multilayer nanosphere bed to mold the geometry of an electrodeposited copper film. We characterize the effective thermal conductivity using the 3ω method, where the nanoporous copper film is deposited directly above a microfabricated and electrically-passivated 3ω device. The effective thermal conductivity is measured to be as large as 170 W m^-1 K^-1. This experimental data is compared to finite element simulations as well as common conduction models for heterogeneous media, including Maxwell´s model and differential effective medium theory. This provides insight into the design of nanoengineered surfaces and two-phase vapor-venting microfluidic heat exchangers for ultrahigh heat flux cooling.