Refinement of nanoporous copper by dealloying the Al-Cu alloy in NaOH solution containing sodium dodecyl sulfate.

This work reports the refinement of nanoporous copper (NPC) ligaments by introducing the sodium dodecyl sulfate (SDS) surfactant in the dealloying process. The Al80Cu20 (at%) alloy precursor is chemically dealloyed in a mixed solution of NaOH and SDS surfactant, producing NPC with a hierarchical microstructure. Micron-scaled skeletons that build up higher level networks consist of geometrically similar nano-scaled bi-continuous ligament-pore networks at the lower level. It has been found that the size of the ligaments in the lower level networks reduces from ∼32 nm to ∼24 nm with increasing SDS concentration to 1 mM. Further increasing the SDS concentration to 5 mM only leads to a slight ligament size decrease to ∼21 nm. Remarkably, nano-sized cones are formed on the lower level network surface in the dealloying solution containing 1 mM SDS, and the cone number greatly rises when the SDS concentration increases to 5 mM. The surface diffusivity of Cu adatoms is evaluated based on the experimental data, and the refinement of the ligament as well as the formation of cones are associated with the decreased surface diffusivity and the retarded Cu adatom motions with the addition of SDS. Quantum chemical calculations and molecular dynamics simulations are performed to model the adsorption behavior of SDS. It has been found that the SDS-substrate interaction increases with the number of SDS molecules before SDS reaches saturation.