Scalable Nanomanufacturing of Virus‐templated Coatings for Enhanced Boiling

electroplating, [ 4,13 ] and evaporation, [ 14 ] as well as other works using electro-deposition, [ 15 ] oxide growth, [ 15,16 ] carbon nanotube growth, [ 17,18 ] and deep-etched silicon microposts [ 19 ] and hoodoos. [ 20 ] These works have showed substantial increases, with CHF values for water of ≈150–210 W/cm 2 for structures with a single length scale, [ 14,19 ] and ≈220–250 W/cm 2 for hierarchical surfaces with multiple length scales, [ 4,15 ] as compared to ≈50–100 W/cm 2 for non-structured surfaces. [ 4,13,15,19 ] These increases have been attributed to liquid spreading and capillary wicking to delay dry-out, [ 4,12,20,21 ] enhanced nucleation sites, [ 4,12–14 ] and an increase in the three-phase contact line length. [ 15,19 ] While these works demonstrate the potential for superhydrophilic coatings, the fabrication methods used are diffi cult, if not impossible, to implement in real applications. This is particularly true for large-scale thermal systems where such enhancements would have the highest impact. This is due to the use of expensive equipment and processes, as well as the need for controlled and elevated temperatures, and/or specifi c substrates. This work reports the scalable manufacturing of surface-bound nanostructures using self-assembled biological templates. This solution-based room-temperature process is compatible with various metallic surfaces, requires no power or equipment, and is scalable to large areas and complex geometries. As such, it has the potential to enhance heat transfer in several large-scale applications, where traditional approaches are not practical or feasible. Viruses represent simple macromolecular assemblies of defi ned components with known dimensions. These properties have led to the use of viruses in the templated growth and organization of novel nanoscale materials. [ 22 ] One of the best studied is the Tobacco mosaic virus (TMV), a benign plant virus ( Figure 1 a). [ 23 ] The TMV is a rigid rod of 2130 identical coat protein subunits stacked in a helix around a single strand of RNA, resulting in an 18 nm diameter, 300 nm long virion (see supplementary material Section 1.1). The wild-type TMV is stable up to 60 °C and over a pH range of 3.5–9, with recent work showing increased stability through genetic modifi cations. [ 24 ] Using the wild-type virus, nanoparticles and nanowires have been prepared on, and within, the rod-like structure of the TMV using solution-based reduction schemes. [ 25–27 ] The current work uses the TMV1cys, a genetically modifi ed strain that has a cysteine residue added to the TMV coat protein open reading frame. The thiol groups of these amino acids enhance binding through covalent-like interactions allowing the TMV to The enhancement of phase-change heat transfer processes is of critical importance due to their impact on energy, the environment, and water resources, as well as their potential in highpower thermal management systems. [ 1–3 ] Recent studies have shown that micro/nano-structures can be used to substantially alter boiling, [ 4 ] evaporation, [ 5 ] freezing, [ 6 ] and condensation [ 7 ] by infl uencing the nature and behavior of liquid, vapor, and solid interfaces. However, the fabrication methods used in these studies are not easily extended to practical applications, particularly over large-areas, complex geometries, and onto various surface materials. Here, biological templates are used to demonstrate the scalable nanomanufacturing of high-surface-area coatings for enhanced boiling on various materials. Using selfassembly of the Tobacco mosaic virus , pool boiling critical heat fl ux and heat transfer coeffi cient have been increased by up to 200%. The solution-based room-temperature biotemplating process is simple and scalable; it requires no external power or special equipment. The coatings are robust with no physical degradation after 24 h of nucleate boiling on gold, copper, aluminum, and stainless steel surfaces. Additionally, the process is compatible with in situ depositions, allowing for the retrofi tting of existing heat transfer equipment and a means to mitigate fouling via stripping and re-deposition, two issues critical to real-world implementation. Boiling heat transfer is used in a number of industries and plays a critical role in various large-scale applications including chemical processing, water purifi cation, power generation, and HVAC. [ 1,2,8 ] As such, even modest enhancements in boiling would lead to substantial energy and cost savings. In addition to increasing performance in systems already using phasechange, there is an urgent need to develop two-phase cooling technologies for thermal management in high-power electronic and photonic systems. [ 3,9 ] During boiling, heat transfer is driven by transient conduction, microlayer evaporation, and microconvection due to the nucleation, growth, and departure of vapor. [ 10 ]