Durable Surface Functionalization for Enhanced Phase-Change Heat Transfer Applications

1.1 The role of phase-change heat transfer in modern technologies

Phase-change heat transfer processes, such as boiling, condensation, evaporation, and freezing, play a central role in a wide spectrum of energy and thermal management technologies. Compared with single-phase heat transfer, phase-change processes can transfer large amounts of energy at relatively small temperature differences, making them highly suitable for high-performance applications. For example, pool boiling is widely used in power generation and thermal desalination, while condensation is integral to refrigeration cycles and atmospheric water harvesting. More recently, the demand for compact and efficient cooling solutions has increased dramatically with the rapid development of microelectronics and power-dense systems, such as data centers, electric vehicles, and high-capacity batteries. In parallel, preventing or mitigating ice formation has become crucial in aerospace, wind energy, and cryogenic applications, where frost accumulation and icing can severely degrade efficiency and safety [1].

1.2 Limitations of conventional surfaces and the need for surface functionalization

Despite many existing applications of phase-change processes, the performance of conventional engineering surfaces often remains suboptimal. Flat metallic substrates, typically used in heat exchangers and thermal devices, offer limited control over liquid-solid interactions and nucleation behavior. As a result, nucleation sites for boiling are scarce, leading to high superheat requirements and early dry-out conditions. In condensation, uncontrolled droplet spreading and film formation reduce heat transfer efficiency. For freezing and icing, conventional surfaces tend to provide strong ice adhesion, which makes ice removal difficult. These intrinsic limitations point to the need for engineered surfaces that can manipulate interfacial phenomena to achieve superior heat transfer performance.

Surface functionalization, that is, tailoring the surface properties to make it suitable for a certain functionality/application, can be performed using many methods and their combinations. The ultimate goal is to tailor surface wettability, roughness, and chemistry in order to control phase-change dynamics. Within boiling, hydrophilic surfaces promote efficient liquid replenishment and delay surface dryout, while hydrophobic surfaces promote early bubble nucleation. Independently, micron and submicron-sized surface features, such as cavities, promote active bubble nucleation. In the field of icing and its mitigation, hydrophobic and superhydrophobic surfaces can inhibit the heterogeneous nucleation of ice, delay frost growth, and facilitate droplet removal under condensation [2]. More advanced designs, such as hierarchical or patterned structures, allow for localized control over wetting and phase-change kinetics, enabling significant enhancements in heat transfer coefficients, critical heat flux, or icephobic performance.

While surface functionalization has demonstrated impressive laboratory-scale results, durability (together with scalability) remains a key barrier to the widespread practical implementation of functionalized surfaces. Many functional coatings, particularly polymer-based or fluorinated layers, degrade under prolonged thermal cycling, mechanical stress, or exposure to UV light. Nanostructured surfaces may lose functionality due to fouling, corrosion, or erosion. In extreme cases, delicate structures may be destroyed by the touch of a finger. In boiling applications, repeated bubble nucleation and departure impose strong thermomechanical stress on the surface, potentially leading to delamination and chemical or morphological changes. In anti-icing applications, repeated freeze–thaw cycles can progressively damage surface textures, remove coatings, and thus diminish the icephobic performance.

Without robust durability, even the most effective functional surfaces cannot represent reliable engineering solutions. Therefore, durable surface functionalization has emerged as a research frontier at the intersection of materials science, surface engineering, and thermal sciences. This chapter provides a comprehensive overview of durable surface strategies for enhanced phase-change heat transfer applications, with a particular focus on boiling heat transfer and anti-icing. First, core concepts in surface engineering are discussed, including surface characteristics and functionalization approaches. This is followed by a survey of recent literature to demonstrate the current state of the art in preparing durable surfaces for phase-change applications. In the following two sections, our research on applying different kinds of durable surfaces to enhance boiling heat transfer or decrease ice adhesion is presented. In the final section, the chapter’s contents are summarized, and an outlook regarding future research directions is provided.

1.3 Applications of durable surfaces for control over phase-change phenomena

Durable functionalized surfaces are required in a wide range of industrial and environmental technologies that rely on efficient heat and mass transfer. The ability to tailor surface wettability, roughness, and chemical composition allows control over phase-change phenomena such as boiling, condensation, evaporation, and freezing. These processes affect the performance of technologies like power generation, refrigeration, water treatment, and energy storage systems. In boiling heat transfer, functionalized surfaces with engineered micro-/nanostructures enhance nucleation site density, reduce bubble departure diameter, and significantly increase the heat transfer coefficient and critical heat flux. Such surfaces are integral to the high-performance cooling of electronic devices and data centers, where maintaining thermal stability under extreme heat fluxes is critical for safety and reliability. Similarly, in heat pipes and vapor chambers used for the thermal management of compact electronics or aerospace systems, maintaining long-term wetting characteristics on wick structures is essential for sustained capillary transport and evaporation–condensation efficiency.

Condensation processes, which are vital for desalination, atmospheric water harvesting, and waste heat recovery, also benefit from durable surface functionalization. Hydrophobic and superhydrophobic coatings promote dropwise condensation, enabling faster droplet removal and continuous exposure of fresh condensing areas, thus enhancing heat transfer rates by an order of magnitude compared to filmwise condensation. In industrial condensers or power plant heat exchangers, where continuous exposure to hot, humid, and sometimes corrosive environments is common, durability against corrosion, scaling, and fouling is another critical factor in achieving economic viability.

Similarly, in anti-icing and de-icing applications, surface coatings that combine low surface energy with optimized roughness contribute to delayed ice nucleation, reduced ice adhesion strength, and minimized energy demand for ice removal in areas including aviation, wind turbines, and refrigeration systems. However, repeated freeze–thaw cycles and mechanical abrasion due to ice shedding or particulate impacts can rapidly deteriorate conventional coatings, requiring new approaches to ensure mechanical robustness alongside functional longevity.

Beyond thermal systems, functionalized surfaces are found in various mass transfer and interfacial transport applications. In membrane distillation [3] and filtration, hydrophobic and omniphobic coatings prevent pore wetting while maintaining high vapor flux and selectivity. In microfluidic systems [4], precisely engineered wettability patterns enable droplet manipulation, separation, and mixing for biomedical assays and chemical synthesis. Coatings on heat exchangers and absorbers enhance wettability and reaction rates in solar thermal collectors [5] and CO₂ capture systems [6], respectively. In energy storage technologies, such as lithium-ion batteries or fuel cells, surface-engineered electrodes [7] improve ion transport and mitigate degradation, while in hydrogen energy systems, textured electrodes [8] influence bubble detachment dynamics and gas transport efficiency at electrodes.

2.1 Surface wettability and contact angle hysteresis

Surface wettability governs how a liquid interacts with a solid surface [9, 10]. It is commonly quantified by the static contact angle formed by a liquid droplet on the surface, as shown in Figure 1(a). The contact angle can be considered a result of the balance of interfacial tensions on the triple contact line, where the droplet meets the surface and the surrounding gas. Surfaces are generally classified as hydrophilic if the contact angle is lower than 90° and hydrophobic if the contact angle exceeds 90°, as shown in Figure 1(b).

In addition to the static contact angle, dynamic contact angles (i.e., the advancing and receding angles) are of vital importance in applications where the triple contact line moves (e.g., during droplet spreading across the surface or during bubble growth in boiling applications [11]). The dynamic contact angles may be evaluated by placing the droplet on a slope or by filling and emptying it via a capillary tube. Dynamic contact angles are shown in Figure 1(c). A related parameter is the contact angle hysteresis, defined as the difference between the advancing and the receding contact angles. Low-hysteresis surfaces facilitate droplet mobility, which is beneficial for dropwise condensation or shedding of supercooled droplets before freezing. High-hysteresis surfaces, by contrast, promote droplet pinning and are less desirable for self-cleaning or anti-icing applications. On a real rough surface, the droplet will mostly be in the Wenzel wetting regime, where the surface micro- and nanostructure are homogeneously wetted [12]. In an extreme case, superhydrophobic behavior with a contact angle above 150° may be observed, where only partial wetting of the surface is present, and the droplet will enter the Cassie-Baxter heterogeneous wetting regime, where the droplet is only partially in contact with the micro- and nanostructure and otherwise supported by entrapped gas [13]. Both wetting states are shown in Figure 1(d). In the context of phase-change heat transfer, wettability strongly influences nucleation of vapor bubbles, bubble departure, and liquid replenishment in boiling, as well as droplet mobility, coalescence, and nucleation in condensation and freezing.

2.2 Surface morphology and topography

The physical state of the surface, as described by its morphology and topography, plays a fundamental role in controlling interfacial phenomena. Roughened or textured surfaces influence wettability through the Wenzel or Cassie–Baxter states, depending on whether liquid penetrates into surface features or rests on top of them. In boiling heat transfer, micro- and nanostructures increase the availability of nucleation sites by providing cavities that trap vapor embryos. This reduces the energy barrier for bubble nucleation, thereby lowering the required wall superheat. Hierarchical topographies, which combine micro- and nanoscale features, can further enhance bubble dynamics by coupling stable nucleation with efficient liquid replenishment. In icing scenarios, topography determines whether supercooled droplets freeze in place or can be shed before solidification. Nanostructures may reduce ice adhesion strength, while combined micro-/nanofeatures improve robustness against droplet impalement. Therefore, the design of surface morphology is fundamental to the manipulation of both thermal and mechanical aspects of phase-change processes.

Phase-change processes are initiated by nucleation events, in which a stable embryo of the new phase forms at the liquid–solid interface. For heterogeneous nucleation on solid surfaces, the energy barrier is strongly dependent on surface chemistry, topography, and wettability. The classical nucleation theory framework shows that the Gibbs free energy barrier decreases in the presence of wettable cavities or defects, making controlled surface structuring a powerful tool for tailoring the nucleation site density. In boiling, the distribution and size of nucleation sites determine the onset of nucleate boiling, bubble departure frequency, and ultimately the critical heat flux. In freezing, heterogeneous nucleation on surface asperities influences the degree of supercooling required for ice formation. Through engineered nucleation-promoting or nucleation-preventing features, surfaces can either promote efficient boiling or suppress premature freezing.

2.3 Thermal resistance of coatings and functional layers

A common approach to surface functionalization involves the application of polymeric, ceramic, or composite coatings. While coatings can impart desirable wettability and chemical stability, they introduce an additional thermal resistance between the substrate and the working fluid. Thick or poorly conductive coatings reduce the effective heat transfer rate and may suppress the benefits of enhanced nucleation [14]. Therefore, the design of functional coatings must carefully balance functional performance with thermal conductivity and thickness constraints. Ultra-thin conformal coatings, such as atomic layer deposition (ALD) films or molecular self-assembled monolayers (SAMs), offer a promising strategy to minimize thermal resistance while still providing chemical durability. In contrast, thick polymeric coatings often degrade boiling heat transfer. This trade-off between interfacial control and thermal transport efficiency represents one of the central challenges in durable surface functionalization.

3.1 Physical modification approaches

Physical modifications rely on altering surface morphology without significantly changing the bulk material. These methods include mechanical cutting and mechanical abrasion, laser treatment, ion beam etching, plasma treatment, shot peening, electric discharge machining, etc.

Mechanical roughening techniques, such as sandblasting, grit blasting, or sanding [15–18], provide scalable surface texturing. However, these methods usually lack fine control over the micro- and nanomorphology, limiting the potential for performance tuning [19].

Laser surface texturing creates well-defined micro- and nanoscale features that can act as nucleation sites for boiling or as asperities, providing the necessary surface morphology to achieve surface superhydrophobicity [20–27]. Laser ablation can produce robust features directly on metals, although roughness may degrade under erosion or fouling over time [28]. Nanosecond [29], picosecond, or femtosecond [30] lasers are commonly employed, with wavelengths spanning from UV to IR. In general, shorter pulses allow for more control over the surface texturing process, but this comes at the expense of the duration of the process and the cost of the equipment. Typical applications include heat-sink and evaporator surfaces in power electronics and compact heat exchangers.

Nanoparticle deposition is another common route, where metallic or ceramic nanoparticles are deposited to increase roughness and surface area [31–34]. Such coatings enhance boiling by increasing nucleation site density but often suffer from weak adhesion and poor mechanical durability.

3.2 Chemical modification approaches

Chemical functionalization involves altering surface energy or chemistry to control wetting and nucleation. These methods include etching in acids, chemical vapor deposition (CVD), sol-gel coatings, silanization, oxidation, and electrochemical treatments.

Self-assembled monolayers enable molecular-level tuning of surface energy [35–39]. They are extremely thin (in the range of nanometers) and thus minimize thermal resistance, but they often degrade under thermal cycling or prolonged immersion in liquids. Self-assembled monolayers tune the surface energy with minimal thermal resistance, which is especially attractive for applications where added thermal resistance must be minimal (e.g., microelectronic cooling interfaces).

Silanization and fluorination are widely used to create hydrophobic or superhydrophobic surfaces. Such coatings effectively delay icing and promote dropwise condensation, but they are vulnerable to abrasion and chemical attack. Furthermore, silanes are not compatible with all substrates as different chemistries target specific substrates: silanes bind hydroxylated oxides (glass, silica, alumina), thiols attach to noble metals (gold, silver, copper), and phosphonic acids form robust bonds with metal oxides (aluminum, titanium, zinc).

Polymeric coatings (e.g., fluoropolymers or PDMS) can impart strong icephobicity and chemical resistance [40–42]. Practical uses include lightweight anti-icing skins (aero surfaces, wind-turbine blades) and conformal protective layers on heat exchangers. However, their relatively low thermal conductivity and significant thickness introduce undesirable thermal resistance in heat transfer applications, such as boiling or protection of heat pump evaporators [26].

3.3 Hybrid and composite approaches

Hybrid strategies combine physical structuring with chemical modification to exploit synergistic effects [43–48]. Typically, physical modification is used to produce a suitable surface micro- and nanotexture (e.g., via direct surface laser texturing), while chemical modification is used to tailor the surface chemistry and, with it, surface wettability (e.g., via chemical vapor deposition of low-surface-energy compounds). In general, such approaches grant the most control over the final surface functionality. Hybrid approaches may result in complex, albeit superior, coatings, for example, including different functional layers such as the adhesion layer (e.g., applied via sol–gel or ALD), a mechanical reinforcement layer (e.g., metal oxides or ceramics), and a functional top layer (e.g., with hydrophobic or antimicrobial properties).

An example of such an approach is the fabrication of polymeric coatings containing metal oxide coatings such as TiO₂, ZnO, or Al₂O₃ to produce nanostructured layers functionalized with hydrophobic chemistries [49–52]. These surfaces often demonstrate improved durability compared to polymer-only coatings. Applications include protective coatings for condenser tubes and process equipment. Nanoparticles may also be additionally functionalized via appropriate ligands [53, 54]. Furthermore, multilayer coatings are emerging as a promising route, where different layers provide adhesion, mechanical strength, and functional properties. Layer-by-layer assembly, sol–gel deposition, or ALD-based hybrids are representative examples.

3.4 Durability-oriented strategies

Recent research has increasingly focused on improving surface durability without compromising functional performance [55]. Various surface modifications have been investigated for harsh boiling environments [28, 56]. Anti-fouling and contamination-resistant layers are relevant for long-term operation in real fluids, where biofouling, scaling, or oil contamination can degrade surface properties. Strategies for thermal and mechanical stability include using robust inorganic coatings, covalent bonding of functional groups, or self-healing polymers that can restore functionality after damage [57, 58]. Hoque et al. [59] offered critical insights into the development of novel superhydrophobic surfaces for enhanced phase-change processes, emphasizing three key challenges: (i) ensuring long-term durability and stability, (ii) utilizing environmentally benign materials (e.g., avoiding per- and polyfluoroalkyl substances), and (iii) achieving scalable fabrication. Simultaneously meeting all three criteria is particularly difficult, especially given the need for ultra-thin surface modifications to minimize added thermal resistance, which can otherwise negate heat transfer improvements. However, such thin coatings often compromise the surface’s resistance to abrasion, thermo-physical degradation, and chemical instability when exposed to highly reactive fluids like de-ionized water.

4.1 Mechanical durability

Phase-change processes often subject surfaces to high mechanical stresses. In boiling applications, bubble nucleation and departure create localized stress that can gradually erode nanostructures or delaminate weakly adhered coatings. In high-flow or spray-cooling systems, fluid impingement and particle erosion can further accelerate surface wear. Similarly, in anti-icing applications, mechanical removal of ice – whether through mechanical scraping, vibration, or aerodynamic forces – can damage delicate surface features.

4.2 Thermal durability

Thermal cycling is another major factor limiting the lifetime of functionalized surfaces. During boiling, surfaces are exposed to repeated high-frequency localized heating and cooling cycles that can induce thermal stresses, leading to cracking, delamination, or morphological degradation of coatings. Materials with mismatched coefficients of thermal expansion are especially prone to failure at the interface between the coating and substrate. In icing and anti-icing applications, freeze–thaw cycles cause the expansion of water upon freezing, exerting stresses that can damage micro- and nanostructures. Long-term exposure to subcooled environments can also alter wettability due to changes in surface chemistry.

4.3 Chemical durability

Surfaces used in real environments are frequently exposed to chemically aggressive fluids (e.g., acidic rainwater). Corrosion is a particularly severe issue for metallic substrates in aqueous systems, where functional coatings may degrade or detach over time. In addition, many hydrophobic or icephobic coatings rely on organic compounds, such as fluoropolymers, which can undergo oxidation or hydrolysis at elevated temperatures. Chemical degradation not only reduces surface functionality but may also introduce contaminants into the system.

4.4 Long-term fouling and contamination

In practical systems, surfaces rarely operate in clean, deionized fluids. Instead, impurities such as salts, organic matter, or particulates are present, leading to fouling or scaling over time [60]. During boiling, the deposition of salts or oxides on heated surfaces can block nucleation sites and increase thermal resistance. In condensation and freezing, contamination layers can alter wettability, diminish droplet mobility, or promote ice adhesion. Biofouling may also occur in systems exposed to natural water sources, further complicating long-term performance.

4.5 Scalability, manufacturability, and testing standardization

Even when a functionalized surface demonstrates promising performance and durability in controlled laboratory conditions, large-scale implementation poses additional challenges. Techniques such as nanofabrication, chemical vapor deposition, or atomic layer deposition offer high precision but are difficult and costly to apply on large heat exchanger surfaces. Conversely, scalable approaches such as spray coating or electrodeposition may sacrifice fine structural control or uniformity.

International standards such as ISO 12944 (for corrosion protection) and ASTM D4060 (for abrasion resistance) help ensure surface durability across industries. These standards define testing procedures like Taber abrasion tests, salt spray tests, and UV exposure simulations to evaluate wear, corrosion, and weathering resistance.

5.1 Theoretical background of enhanced boiling heat transfer

Boiling and associated heat transfer are influenced by many parameters, complicating the modeling and analysis of the underlying physics. Influential parameters include (i) properties of the working fluid (surface tension, density, viscosity, latent heat of vaporization, etc.), (ii) properties of the boiling surface (topography, morphology, shape, and orientation), (iii) interactions between (i) and (ii), such as wettability and capillary wicking, and (iv) environmental conditions such as pressure, gravity, and electromagnetic fields. The interdependence of these parameters further complicates both experimental investigations and the modeling of the boiling process.

When describing pool boiling heat transfer, we mainly rely on three parameters: (i) the heat flux removed from the surface, (ii) surface superheat, defined as the temperature difference between the surface and the evaporating liquid, and (iii) their ratio, that is, the heat transfer coefficient, which defines heat transfer intensity. In practical boiling cooling applications, the aim is to achieve a high heat flux at low surface superheats, which directly corresponds to high heat transfer coefficients. Equally important is the upper limit of the nucleate boiling regime, that is, the critical heat flux, at which the entire surface becomes covered by a vapor film, transitioning the process into film boiling.

The term “boiling curve” was first defined by Nukiyama [61] and represents a graphical relationship between heat flux and surface superheat, that is, the difference between the boiling surface temperature, T_w, and the working fluid temperature, T_∞.A typical boiling curve is shown in Figure 2; its shape is approximately the same for different combinations of fluids and boiling surfaces. At the onset of boiling, at low surface superheats, all heat flux is removed by natural convection. As surface superheat increases, vaporization starts to take place at the onset of nucleate boiling (ONB). In the nucleate boiling regime, the highest heat transfer coefficients at relatively low surface superheats are recorded, making boiling highly suitable for engineering heat transfer applications. At the upper limit of nucleate boiling, the entire surface becomes covered with a vapor film, marking the onset of the critical heat flux (CHF), also called the boiling crisis. The vapor film acts as thermal insulation, hindering heat transfer to the liquid–vapor interface. As a result, surface superheats rise sharply, leading to the film boiling regime, which is generally associated with superheats that are too high for most engineering applications.

Figure 2 also shows the enhancement of the boiling curve typically observed on functionalized surfaces. Three modifications are desirable. Firstly, the onset of nucleate boiling should be shifted toward lower surface superheat to facilitate the transition into the desirable nucleate boiling regime. Secondly, the steepness of the boiling curve should increase, indicating higher heat transfer coefficients. Finally, the uppermost limit of the nucleate boiling regime (i.e., the critical heat flux) should be elevated to increase the range of heat flux values within which the surface can safely and efficiently operate within the nucleate boiling regime. To intensify heat transfer, approaches typically involve modifying the boiling surface, the working fluid, and their interaction. Fluid properties can be changed by adding (nano)particles, surface tension modifiers, or other fluids (binary or multicomponent mixtures). Boiling surface properties can be altered using various treatments or micro/nano-structuring techniques to change morphological and topographical characteristics, and often also through intentional surface chemistry modification to tune fluid–surface interactions. By structuring and modifying the surface, the goal is to influence three main factors that affect boiling heat transfer: (i) the presence of micro- or nanocavities serving as nucleation sites for vapor bubbles, (ii) surface structures that enable liquid wicking (e.g., via porosity) to rewet dry areas, and (iii) topography and morphology that mimic extended surfaces at the micron scale, thereby increasing the active heat transfer area.

5.2 Durability of surfaces exposed to boiling heat transfer

Surface durability is crucial for improving boiling heat transfer, yet it is often overlooked by researchers. In practical applications, surfaces typically operate continuously for years or even decades, making research into long-term surface changes and their impact on boiling heat transfer essential. The stability of boiling surfaces was first investigated nearly a century ago, when Jakob with Fritz [62] and Linke [63] noted reduced boiling efficiency on copper after extended operation, attributing it to the loss of entrapped gas nuclei. Later studies confirmed that long-term boiling progressively lowers nucleation activity [64], with copper oxide transformations playing a central role. Yet, despite these early insights, systematic evaluation of stability has remained relatively sparse. Modern surface-engineering techniques, such as laser texturing or chemical functionalization, bring exceptional short-term performance, but their longevity is not guaranteed.

Superhydrophobicity has long been recognized as a pathway toward enhanced phase-change heat transfer, yet its practical use in nucleate boiling remains elusive. Unlike condensation, where several long-term demonstrations of (super)hydrophobic stability exist [65], boiling subjects surfaces to far harsher thermo-chemo-mechanical stresses. Bubble nucleation and departure cycles, microlayer evaporation, and repeated local heating–cooling cycling induce oxidation, coating degradation, and mechanical wear. These factors can rapidly deteriorate favorable surface properties, leading to wettability transitions and diminished heat transfer performance.

5.3 Fabrication of durable surfaces for enhanced boiling

We hereby summarize our recent systematic work on achieving stable, long-term heat transfer on copper-based superhydrophobic surfaces in DI water. First, we establish the degradation pathways on smooth and laser-textured hydrophobized copper under hundreds of hours of boiling [28]. Afterward, we demonstrate a fabrication strategy to preserve superhydrophobicity on a stochastically hierarchical, fluorine-free boiling interface [24].

Extended pool boiling tests in DI water over hundreds of hours reveal that all copper surfaces – whether smooth, laser-textured, hydrophobized, or combinations thereof – undergo measurable performance deterioration over time. At a fixed heat flux, the surface superheats increase steadily, accompanied by a decrease in heat transfer coefficients. Even surfaces initially engineered for enhanced boiling performance exhibit gradual losses, indicating that boiling-induced degradation mechanisms act universally across different surface states. The magnitude of degradation, however, differs. Smooth reference surfaces show the steepest decline, while laser-textured surfaces, with or without hydrophobization, display up to an order of magnitude slower rate of performance loss. For example, over ~500 hours of operation at 250 kW m⁻², heat transfer coefficients (HTCs) decreased between 29.4% and 36.4% on smooth copper and by 13.5–33.7% on laser-textured surfaces, underscoring the beneficial role of micro- and nanostructuring in stabilizing boiling heat transfer.

Progressive deactivation of nucleation sites was noted during boiling experiments and is attributed to changes in surface chemistry, wetting, topography, and morphology, which were quantified after long-term experiments (Figure 3). While hydrophobization stabilizes the surface in air, hindering VOC-adsorption-driven wetting transitions, such (mono)layers are susceptible to thermochemical breakdown under boiling conditions. Oxidation is another key mechanism, which on smooth copper results in patina-like layers, while on laser-textured surfaces, the high initial oxidation reduces the relative role of further oxide growth. Short-term studies or repeated boiling curve recordings often miss these effects – true oxidative aging only emerges over hundreds of hours. Lastly, the laser-created topography provides abundant nucleation sites but is vulnerable to thermomechanical fatigue. SEM imaging shows that protrusions detach under repeated bubble nucleation and growth cycles, reducing effective roughness and active nucleation site density.

To overcome the combined degradation mechanisms, we developed a six-step fabrication procedure, sequentially combining: (i) nanosecond-laser texturing, (ii) ultrasonication, (iii) UV–ozone activation, (iv) sputtering of a thin gold nanolayer, (v) secondary UV–ozone activation, and (vi) deposition and thermal annealing of a non-fluorinated alkyl phosphonic acid monolayer. The process is shown in Figure 4, and the surface was termed “LT–Au-HDPA” based on the combination of laser texturing (LT), gold sputtering (Au), and hydrophobization with an HDPA monolayer.

This design was inspired by previous research seeking robustness through multi-scale structuring [66] or protective coatings [65], and its individual steps were specifically tailored to mitigate the boiling-induced degradation mechanisms of laser-textured surfaces while avoiding fluorinated chemistries. The interface exhibits extreme water repellency, with advancing/receding contact angles of 171.5°/160.2°. The stochastic hierarchy additionally consists of re-entrant features that facilitate long-term gas entrapment.

5.4 Evaluation of enhanced boiling heat transfer and durability

A summary of the evaluation of the “LT–Au-HDPA” surface’s durability is shown in Figure 5. When subjected to pool boiling in DI water at atmospheric pressure, LT–Au-HDPA exhibited superior heat transfer coefficients compared to smooth reference copper. Across multiple independently prepared samples, HTC values remained consistently higher, with improvements of up to 460%. This increase is not merely transient but sustained throughout extended operation. At a constant heat flux of 250 kW m⁻², where reference samples displayed progressive performance decreases, the LT–Au-HDPA surface maintained a stable HTC for more than 200 hours of uninterrupted boiling (Figure 5(a)), with no degradation of wettability (Figure 5(d)) or morphology. The importance of this result is underscored when contrasted with fluorinated coatings used on similar laser-textured topography, which, while initially providing higher HTCs, exhibited reductions of over 30% after prolonged tests.

An equally significant characteristic of LT–Au-HDPA is its reproducibility. Across 15 boiling curves recorded on three independent samples, the scatter in measured wall superheat was smaller than the experimental uncertainty, typically below 0.3 K. This is in stark contrast to smooth copper, where repeated runs often produce curve shifts of 1 K or more [67] due to changes in wetting or oxidation. Such consistency is critical for practical adoption, as it demonstrates not only the stability of the surface during operation but also the robustness of the fabrication process itself. The stochastic nature of hierarchical morphology does not hinder repeatability; rather, the diversity of structures ensures a wide distribution of possibly active nucleation sites, smoothing out performance variations across samples. The durability of LT–Au-HDPA has been further validated through stress testing – repeated pool boiling curves up to the critical heat flux were recorded (Figure 5(c)), where the sudden transition to film boiling subjects the surface to rapid temperature increases and high local temperatures. In contrast to previous studies, LT–Au-HDPA surfaces retained both their morphology and wetting behavior even after 55 CHF onsets. Additionally, the interface was subjected to air at 400 °C for 20 hours to simulate the case of extended thermal runaway. The complementary evaluation of surface chemistry (Figure 5(b)) and surface roughness (Figure 5(e)) after boiling and stress tests proves the robustness and stability of the developed interface.

6.1 Theoretical background of anti-icing strategies

When a water droplet is exposed to a colder environment (e.g., in contact with a cold surface), it first enters the supercooling stage, where heat is transferred either to the surface in contact with the droplet or to the surrounding atmosphere. As the droplet temperature decreases below the equilibrium freezing point, it remains in a supercooled state until nucleation occurs at a random moment. Nucleation initiates recalescence, a rapid and nearly adiabatic process in which the phase transition from liquid water to ice nuclei releases latent heat. This causes the droplet temperature to abruptly rise back to the freezing point, while newly formed ice nuclei grow and no additional nuclei can form. Recalescence, which transforms a transparent droplet into an opaque one, typically happens on the millisecond time scale. Following this stage, the freezing front propagates through the droplet as ice crystals grow at nearly constant temperature, which takes several seconds to several tens of seconds. Due to water’s anomalous expansion upon solidification, the droplet shape changes, and a distinct tip forms at its apex. Once freezing is complete, the droplet undergoes further cooling as its temperature gradually approaches that of the substrate or surrounding air, continuing until thermal equilibrium with the environment is reached. The overall process is shown in Figure 6(a).

Anti-icing surfaces exhibit one or more mechanisms to prevent ice accumulation or to enable easier removal of ice. The properties can be divided into three main groups: (i) prevention of water accumulation through water repellency, (ii) delay of the freezing process, and (iii) reduction of ice adhesion strength [70, 71]. The complementarity is shown in Figure 6(b).

Reducing water droplet retention on the surface significantly contributes to the anti-icing efficiency of materials. Hydrophobic surfaces lower droplet adhesion by creating unfavorable conditions for wetting, thereby shortening the water – substrate interaction time. The effect is even more pronounced on superhydrophobic surfaces, where droplets easily roll off or rebound upon minimal disturbance, thus substantially decreasing the likelihood of water remaining on the surface long enough for ice nucleation to occur. When droplets remain on the surface despite water repellency, the surface topography and chemical composition can significantly influence the dynamics of the liquid – solid phase transition. Reducing the number of nucleation sites, increasing interfacial energy, and stabilizing a metastable supercooled state allow freezing to be delayed either to a lower temperature or over a longer timescale. Structured metallic substrates with reduced thermal conductivity can also slow down droplet cooling, prolonging the liquid phase. Even when ice forms, low-adhesion surfaces enable its removal at relatively low mechanical forces, which is critical for passive removal by vibrations, impacts, or loads. Reduction of ice adhesion can be achieved through several mechanisms. Micro- and nanoscale cracks act as initiators of ice fracture and reduce adhesion via stress concentration, where stresses locally intensify and trigger crack propagation. Multilayered elastic surfaces allow local deformation and reduce the effective contact area between ice and substrate, as elastomeric layers adapt to stresses and thus decrease adhesion. Hybrid systems combine low surface energy with elasticity and structural features to achieve synergistic effects, where different mechanisms complement one another and enhance overall efficiency.

6.2 Durability of surfaces exposed to icing

Degradation mechanisms of anti-icing surfaces pose a major limitation to their practical application. Even during laboratory wear tests, top layers of coatings and microstructures are damaged, reducing the contact angle, increasing hysteresis, and raising ice adhesion. Mechanical damage occurs when the force required for ice removal exceeds the strength of the substrate or the coating – substrate bond [28]. Repeated freeze–thaw cycles lead to material fatigue and gradual loss of low-adhesion properties. Additional damage can result from abrasion as ice crystals slide across the surface. Thermal stresses caused by mismatched coefficients of thermal expansion between ice, coating, and substrate further increase the risk of damage. Environmental factors such as UV radiation, oxidation, and corrosive agents can permanently alter surface properties and reduce anti-icing effectiveness [34].

To enhance durability, various approaches can be employed. Fluorinated polymer coatings with cross-linked networks exhibit improved stability compared to conventional coatings [17]. Slippery liquid-infused porous surfaces (SLIPS) can sustain low ice adhesion even after multiple freeze–thaw cycles [38].

6.3 Fabrication of durable anti-icing surfaces

We hereby present a methodology for fabricating durable anti-icing surfaces with decreased ice nucleation temperature, decreased ice adhesion strength, and superior resistance to cyclical freeze/thaw degradation.

The durable functionalized surfaces were produced on aluminum plates of 1050A aluminum alloy (H24). A total of four surfaces were developed and tested: (i) an untreated reference surface (untreated), (ii) a surface coated with PDMS (PDMS), (iii) a surface with minimal laser-induced roughness and the PDMS coating (LT1 + PDMS), and (iv) a surface with high laser-induced roughness and the PDMS coating (LT2 + PDMS). The PDMS coating (DOW Sylgard 184) was applied in all cases via dip coating from an n-hexane solution with a PDMS concentration of 10 wt.%, yielding a coating thickness of approximately 1.6 μm [40]. The laser-texturing was performed with a 30 W pulsed nanosecond laser (1,064 nm wavelength, spot diameter 25 μm), using two sets of parameters to either achieve minimum roughness of the surface (LT1) or to produce very deep (>100 μm) structures (LT2). LT1 texture was produced using one pass across the surface at a fluence of 23.9 J/cm², while the LT2 texture was produced using 25 passes at a fluence of 28.7 J/cm². Figure 7 shows a comparison of SEM images of all developed surfaces. The untreated and the PDMS surface (left side of Figure 7) exhibited a roughness of Pa 0.66 μm; no difference in the SEM image was observed due to the low thickness of the coating. The LT1 and LT2 surfaces with the PDMS coating had notably different roughness, with the Pa value for LT1 being 1.46 μm, while the value for LT2 was an order of magnitude greater at 10.1 μm.

6.4 Evaluation of the anti-icing properties and durability

The anti-icing properties of the test surfaces were evaluated through multiple tests. Firstly, the ice nucleation temperature was evaluated by placing several water droplets on the surface in a low-humidity chamber and decreasing the surface temperature until the droplets froze. The temperature of the surface was measured continuously while the droplets were filmed from above to determine the freezing temperature of individual droplets. The number of samples was n = 64 for all surfaces. Secondly, the ice adhesion was measured by freezing water on the surface at −20 °C in a 20 × 20 mm² silicone mold and shearing the ice cube off with a motorized pusher to determine the ice adhesion shear strength. Finally, the wettability of the surfaces was evaluated through the static and advancing contact angles measured using a goniometer. To determine the durability of the surfaces, each surface was exposed to cyclical freeze/thaw degradation, where a small volume of DI water was frozen at approximately −20°C and thawed at approximately +40 °C on the surface in 15 minute intervals. All aforementioned tests were performed on each surface before cyclical testing, after 100 degradation cycles, and after 500 degradation cycles.

The results of ice nucleation temperature measurements are compared in Figure 8, from which it is evident that a very small enhancement of the ice nucleation temperature is provided by all three types of functionalized surfaces. In all cases, the enhancement decreases or even disappears after cyclical testing, which is most noticeable on the PDMS surface with no laser-induced texture. Overall, the most stable performance was exhibited by the LT2 + PDMS surface with high roughness.

Similarly, the ice adhesion shear strength is compared in Figure 9, both before and after cyclical degradation testing. All three functionalized surfaces provided lower adhesion values compared to the untreated surface. However, after the cyclical degradation, the ice adhesion universally increased on all functionalized surfaces. A decrease in ice adhesion on the untreated surface might be attributed to oxidation and passivation during long-term exposure to high-purity water, which high-purity aluminum is prone to. Nevertheless, the PDMS surface still granted notably decreased ice adhesion values even after 500 cycles, while the LT1 exhibited a moderate improvement in comparison with the untreated surface. On the other hand, the LT2 surface, which already exhibited the smallest enhancement before degradation testing, showed notably increased ice adhesion after 500 cycles, which can be attributed to degradation of the PDMS coating, causing the water to penetrate deeper into the surface structure and increase the ice adhesion due to mechanical interlocking of the ice with the high-aspect-ratio surface structures.

Figure 10 shows the static contact angles before and after degradation testing. The results confirm the previous discussion on the major changes to the surface chemistry of the untreated aluminum surface, where the contact angle changed by more than 30°. On the other hand, all three functionalized surfaces with the PDMS coating exhibited rather stable contact angle values.

SEM imaging was performed to evaluate the surface after cyclical degradation testing and ice adhesion measurements. While no changes were observable on the LT1 and LT2 surfaces, peeling of the PDMS coating was observed on the PDMS surface, as revealed in Figure 11. Hence, adhesion of the PDMS layer appears to be the key to enhancing the durability of the functionalized surfaces further.