A comparative study on graphene-nanoplatelet and graphene-oxide coatings of enhanced micro-spray cooling for LED thermal management

Effective thermal management of high-power light-emitting diodes (LEDs) is essential to sustain their performance and operational lifetime. This study investigates the enhancement of micro-spray cooling using deionized water on graphene-based coated surfaces, specifically graphene oxide (GO) and graphene nanoplatelets (GNPs). Through a combination of experimental characterization, thermal-optical performance evaluation, and molecular dynamics simulations, the influence of oxygen functional group distribution (basal-plane functionalization in GO versus edge-localized functionalization in GNP) on wettability, water permeation, and phase-change heat transfer is systematically examined. Surface analyses reveal that GNP coatings possess favorable hydrophilicity, a microporous nanoarchitecture, and rapid water transport, whereas GO coatings exhibit pronounced water-pinning effects arising from excessive basal-plane oxidation. Thermal evaluation demonstrates that GNP coatings deliver a 94.6% maximum enhancement in heat transfer coefficient and reduce LED case temperature by up to 26.1 °C relative to bare copper, corresponding to a 16.2% increase in illuminance. In contrast, GO coatings offer limited and power-dependent cooling, with performance deteriorating sharply at elevated heat fluxes due to interfacial delamination. Molecular dynamics simulations corroborate these observations, showing that edge-functionalized GNP structures enable rapid, low-friction water transport, while basal-plane functionalized GO hinders continuous flow. Overall, the results highlight that controlled functionalization and robust interfacial adhesion of graphene-based coatings are critical for achieving efficient and reliable micro-spray cooling in next-generation high-power LED systems. • GNP coating enhances HTC by 94.6% in micro-spray LED cooling. • Up to 26.1 °C LED temperature reduction achieved with GNP. • Edge-functionalized graphene enables sustained thin-film evaporation. • GO coating shows pinning and delamination at high heat flux. • MD model reveals transport governed by functional group localization.