Hybrid treated graphene-epoxy coating for spray cooling enhancement of light-emitting diode

Thermally-treated graphene-epoxy coatings not only allow rapid water permeation but also increase the durability of the coating. Therefore, these coatings have been extensively used in phase-change heat-transfer applications. In this study, we reported a further improvement in water permeation rate of graphene-epoxy coating by using a hybrid-treatment, which involves a sequential treatment consisting of plasma-treatment and thermal-treatment. With the hybrid-treatment, we observe up to 99% and 87% decrease in water permeation time, when compare to untreated and thermally-treated graphene-epoxy coatings, respectively. This decrease in water permeation time can be primarily attributed to a dramatic increase in surface roughness (125% and 90% for the untreated and thermally-treated coatings) as well as the increase in silver concentration on the coating surface, leading to rapid spreading of the droplet. By depositing a single droplet on the untreated and hybrid-treated graphene-epoxy coatings, it can be seen that by increasing the temperature of the graphene-epoxy coatings to that near the boiling point of water can lead to higher increase in heat removal rates. Using a simple spray system for the cooling of a light-emitting diode that operates at the boiling point of water, we observe 38% and 25% increase of heat transfer coefficients when the deionized aerosols deposited on the hybrid-treated coatings compared to the uncoated surface and thermal-treated coating, respectively. Since the atmospheric pressure plasma can be generated easily, the cost to conduct plasma-treatment is relatively low compared to thermal-treatment, particularly that via corona discharge.