Conformal micro-nano hierarchical surface engineering of aluminum heat sinks via solution-processed etching and layer-by-layer assembly for enhanced heat dissipation

초록

Aluminum heat sinks employ high-aspect-ratio fins to maximize surface area; however, their low emissivity and limited surface functionality constrain both radiative and convective heat transfer. Surface engineering offers an effective route to enhance passive heat dissipation while preserving the original form factor. Nevertheless, many existing surface treatments require high-temperature or vacuum conditions, making conformal coatings on complex fin geometries challenging and costly. Furthermore, since surface modifications can distinctly alter radiative and convective heat transfer, their individual contributions must be decoupled under natural convection to clarify the underlying enhancement mechanisms. Herein, we develop a solution-processed micro-nano hierarchical surface engineering strategy by integrating crystallographically selective HCl etching with conformal layer-by-layer (LbL) assembly of multiwalled carbon nanotube (MWCNT)-polyethyleneimine (PEI) coatings. The chemical etching produces cuboidal microstructures that increase the effective surface area and form microcavities, thereby enhancing emissivity and radiative heat transfer. Subsequently, a scalable LbL process uniformly deposits nanoporous MWCNT-PEI coatings with tunable thicknesses (5-15 bilayers, similar to 50-138 nm) on etched high-aspect-ratio fins. The percolated one-dimensional MWCNT network forms nanoscale porous layers that modify near-wall thermal transport and contribute to convective heat transfer, while also increasing the radiative contribution owing to the high emissivity of the carbon network. Under steady-state electrical heating at 2.2-9.4 W, all treated heat sinks outperform the untreated counterpart, with lower thermal resistance and higher overall heat-transfer coefficient. Among them, the 10-bilayer hierarchical surface delivers the best performance, a 14.8% increase in overall heat-transfer coefficient. Decomposition analysis reveals that the hierarchical architecture effectively balances radiative and convective contributions, yielding a combined enhancement that surpasses singly treated surfaces and enables practical tuning for high-performance passive cooling.

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