Superbiphilic Laser‐Microengineered Surfaces with A Self‐Assembled Monolayer Coating for Exceptional Boiling Performance

Abstract

The rapid advancement of engineering systems has spurred the search for innovative thermal management solutions. Boiling, as a phase‐change heat transfer method, has shown promise in heat dissipation, but non‐functionalized surfaces struggle with increasing cooling demands. To improve heat dissipation efficiency across different heat loads, functionalized surfaces with tailored wettability have been proposed. Separately, superhydrophilic and superhydrophobic surfaces each offer benefits and drawbacks in boiling applications but combining them on a single “biphilic” surface simultaneously harnesses their advantages. In this study, laser‐functionalized copper surfaces with spatially tailored wettability are developed by combining two‐step laser texturing with a self‐assembled monolayer coating, while focus is placed on the impact of the size and pitch of superhydrophobic spots. The developed functionalized surfaces exhibit exceptional boiling performance with heat transfer coefficients up to 299 kW m−2 K−1, a 434% enhancement over untreated surfaces. Optimal ratios of superhydrophilic and superhydrophobic areas and optimal spot pitch are identified. Additionally, varying behavior at different heat flux levels is observed, emphasizing the importance of considering thermal loads when determining the optimal surface pattern. This advancement in performance, along with the rapid and cost‐effective functionalization process, represents a significant breakthrough for enhanced thermal management applications.

Aluminum Micropillar Surfaces with Hierarchical Micro- and Nanoscale Features for Enhancement of Boiling Heat Transfer Coefficient and Critical Heat Flux

“…During the laser texturing process, thin layers of aluminum oxide formed atop the squares. This procedure also produced microcavities, which were previously shown to be remarkably effective as preferential nucleation sites during nucleate boiling [ 14 , 15 ]. Laser texturing parameters used for the fabrication of square patches, covered by aluminum oxides, were as follows: scanning speed of 110 mm s −1 , pulse frequency of 110 kHz, pulse width of 45 ns, average power of 30 W, and average pulse fluence of 55.6 J cm −2 .…”

“…The main surface engineering techniques include milling, drilling, electrochemical etching, chemical etching, laser processing, and sintering, among others. For example, surfaces with engineered structures that have demonstrated CHF and HTC improvement include (i) microstructures, comprised of elements like fins [ 10 , 11 ], pillars [ 12 , 13 ], microcavities [ 14 , 15 ], and pores; (ii) nanostructures, made of nano-porous media [ 16 , 17 ], nanotubes [ 18 , 19 ], nanowires [ 20 , 21 ], and nano-coatings [ 22 , 23 ]; and (iii) micro/nano hierarchical structures [ 24 , 25 ].…”

“…Increased surface wettability leads to a delayed CHF incipience, which can be attributed to more intense liquid rewetting, while decreased surface wettability results in promoted bubble formation due to a reduced nucleation energy barrier [ 31 , 32 , 33 ]. The synergy between increased bubble nucleation sites and enhanced liquid replenishment serves to further facilitate boiling heat transfer, a concept that has been advanced by the design of surfaces with locally mixed wettability [ 15 , 34 , 35 ].…”

Fundamentals and Applications of Surface Wetting

“…The wetting behavior on solid surfaces significantly influences the dynamics of phase change processes and their total heat-transfer performance. The pool boiling curves of copper surfaces with varying surface wettability under ambient conditions are illustrated in Figure a . The critical heat flux (CHF) of the bare hydrophilic surface (untreated reference surface) was ∼980 kW/m 2 in the first run.…”

“…Effect of surface wettability on various phase change processes: (a) boiling, (b) condensation (effects of surface wettability and degree of subcooling on (i) condensation behavior, (ii) droplet departure radius, and (iii) condensation heat flux), and (c) frosting. [Panel (a) was reproduced with permission from ref . Copyright 2023, Wiley Online Library, under the terms of the Creative Commons CC BY license ().…”