Extreme Water Uptake of Hygroscopic Hydrogels through Maximized Swelling-Induced Salt Loading

Hygroscopic hydrogels are emerging as scalable and low-cost sorbents for atmospheric water harvesting, dehumidification, passive cooling, and thermal energy storage. However, devices using these materials still exhibit insufficient performance, partly due to the limited water vapor uptake of the hydrogels. Here, the swelling dynamics of hydrogels in aqueous lithiumchloride solutions, the implications on hydrogel salt loading, and the resulting vapor uptake of the synthesized hydrogel-salt composites are characterized. By tuning the salt concentration of the swelling solutions and the cross-linking properties of the gels, hygroscopic hydrogels with extremely high salt loadings are synthesized, which enable unprecedented water uptakes of 1.79 and 3.86 gg-1 at relative humidity (RH) of 30% and 70%, respectively. At 30% RH, this exceeds previously reported water uptakes of metal-organic frameworks by over 100% and of hydrogels by 15%, bringing the uptake within 93% of the fundamental limit of hygroscopic salts while avoiding leakage problems common in salt solutions. By modeling the salt-vapor equilibria, the maximum leakage-free RH is elucidated as a function of hydrogel uptake and swelling ratio. These insights guide the design of hydrogels with exceptional hygroscopicity that enable sorption-based devices to tackle water scarcity and the global energy crisis.

Unusual Temperature Dependence of Water Sorption in Semicrystalline Hydrogels

Water vapor sorption is a ubiquitous phenomenon in nature and plays an important role in various applications, including humidity regulation, energy storage, thermal management, and water harvesting. In particular, capturing moisture at elevated temperatures is highly desirable to prevent dehydration and to enlarge the tunability of water uptake. However, owing to the thermodynamic limit of conventional materials, sorbents inevitably tend to capture less water vapor at higher temperatures, impeding their broad applications. Here, an inverse temperature dependence of water sorption in poly(ethylene glycol) (PEG) hydrogels, where their water uptake can be doubled with increasing temperature from 25 to 50 °C, is reported. With mechanistic modeling of water-polymer interactions, this unusual water sorption is attributed to the first-order phase transformation of PEG structures, and the key parameters for a more generalized strategy in materials development are identified. This work elucidates a new regime of water sorption with an unusual temperature dependence, enabling a promising engineering space for harnessing moisture and heat.

Capillary Transfer of Self-Assembled Colloidal Crystals

Colloidal self-assembly has attracted significant interest in numerous applications including optics, electrochemistry, thermofluidics, and biomolecule templating. To meet the requirements of these applications, numerous fabrication methods have been developed. However, these are limited to narrow ranges of feature sizes, are incompatible with many substrates, and/or have low scalability, significantly limiting the use of colloidal self-assembly. In this work, we study the capillary transfer of colloidal crystals and demonstrate that this approach overcomes these limitations. Enabled by capillary transfer, we fabricate 2D colloidal crystals with nano-to-micro feature sizes spanning 2 orders of magnitude and on typically challenging substrates including those that are hydrophobic, rough, curved, or structured with microchannels. We developed and systemically validated a capillary peeling model, elucidating the underlying transfer physics. Due to its high versatility, good quality, and simplicity, this approach can expand the possibilities of colloidal self-assembly and enhance the performance of applications using colloidal crystals.

A unified approach and descriptor for the thermal expansion of two-dimensional transition metal dichalcogenide monolayers

Two-dimensional (2D) materials have enabled promising applications in modern miniaturized devices. However, device operation may lead to substantial temperature rise and thermal stress, resulting in device failure. To address such thermal challenges, the thermal expansion coefficient (TEC) needs to be well understood. Here, we characterize the in-plane TECs of transition metal dichalcogenide (TMD) monolayers and demonstrate superior accuracy using a three-substrate approach. Our measurements confirm the physical range of 2D monolayer TECs and, hence, address the more than two orders of magnitude discrepancy in literature. Moreover, we identify the thermochemical electronegativity difference of compositional elements as a descriptor, enabling the fast estimation of TECs for various TMD monolayers. Our work presents a unified approach and descriptor for the thermal expansion of TMD monolayers, which can serve as a guideline toward the rational design of reliable 2D devices.

Three-Tier Hierarchical Structures for Extreme Pool Boiling Heat Transfer Performance

Boiling is an effective energy-transfer process with substantial utility in energy applications. Boiling performance is described mainly by the heat-transfer coefficient (HTC) and critical heat flux (CHF). Recent efforts for the simultaneous enhancement of HTC and CHF have been limited by an intrinsic trade-off between them-HTC enhancement requires high nucleation-site density, which can increase bubble coalescence resulting in limited CHF enhancement. In this work, this trade-off is overcome by designing three-tier hierarchical structures. The bubble coalescence is minimized to enhance the CHF by defining nucleation sites with microcavities interspersed within hemi-wicking structures. Meanwhile, the reduced nucleation-site density is compensated for by incorporating nanostructures that promote evaporation for HTC enhancement. The hierarchical structures demonstrate the simultaneous enhancement of HTC and CHF up to 389% and 138%, respectively, compared to a smooth surface. This extreme boiling performance can lead to significant energy savings in a variety of boiling applications.

How Coalescing Bubbles Depart from a Wall

Bubble evolution plays a fundamental role in boiling and gas-evolving electrochemical systems. One key stage is bubble departure, which is traditionally considered to be buoyancy-driven. However, conventional understanding cannot provide the full physical picture, especially for departure events with small bubble sizes commonly observed in water splitting and high heat flux boiling experiments. Here, we report a new regime of bubble departure owing to the coalescence of two bubbles, where the departure diameter can be much smaller than the conventional buoyancy limit. We show the significant reduction of the bubble base area due to the dynamics of the three-phase contact line during coalescence, which promotes bubble departure. More importantly, combining buoyancy-driven and coalescence-induced bubble departure modes, we demonstrate a unified relationship between the departure diameter and nucleation site density. By elucidating how coalescing bubbles depart from a wall, our work provides design guidelines for energy systems which can largely benefit from efficient bubble departure.

Enhancement of Boiling with Scalable Sandblasted Surfaces

Surface engineering has been leveraged by researchers to enhance boiling heat transfer performance, with benefits ranging from improved thermal management to more efficient power generation. While engineered surfaces fabricated using cleanroom processes have shown promising boiling results, scalable methods for surface engineering are still limited despite most real-world industry-scale applications involving large boiling areas. In this work, we investigate the use of sandblasting as a scalable surface engineering technique for the enhancement of pool boiling heat transfer. We vary the size of an abrasive Al₂O₃ sandblasting medium (25, 50, 100, and 150 μm) and quantify its effects on silicon surface conditions and boiling characteristics. The surface morphology and capillary wicking performance are characterized by optical profilometry and capillary rise tests, respectively. Pool boiling results and surface characterization reveal that surface roughness and volumetric wicking rate increase with the abrasive size, which results in improvements in the critical heat flux and the heat transfer coefficient of up to 192.6 and 434.3% compared to a smooth silicon surface, respectively. The significant enhancement achieved with sandblasted surfaces indicates that sandblasting is a promising option for improving boiling performance in industry-scale applications.

Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer

Recent advances in thermally localized solar evaporation hold significant promise for vapor generation, seawater desalination, wastewater treatment, and medical sterilization. However, salt accumulation is one of the key bottlenecks for reliable adoption. Here, we demonstrate highly efficient (>80% solar-to-vapor conversion efficiency) and salt rejecting (20 weight % salinity) solar evaporation by engineering the fluidic flow in a wick-free confined water layer. With mechanistic modeling and experimental characterization of salt transport, we show that natural convection can be triggered in the confined water. More notably, there exists a regime enabling simultaneous thermal localization and salt rejection, i.e., natural convection significantly accelerates salt rejection while inducing negligible additional heat loss. Furthermore, we show the broad applicability by integrating this confined water layer with a recently developed contactless solar evaporator and report an improved efficiency. This work elucidates the fundamentals of salt transport and offers a low-cost strategy for high-performance solar evaporation.

Solar evaporation is promising for sustainable freshwater production but typically limited by salt accumulation. Here, by manipulating natural convection, authors develop a wick-free confined water layer that enables highly efficient and salt rejecting solar evaporation.

Kinetics of Sorption in Hygroscopic Hydrogels

Hygroscopic hydrogels hold significant promise for high-performance atmospheric water harvesting, passive cooling, and thermal management. However, a mechanistic understanding of the sorption kinetics of hygroscopic hydrogels remains elusive, impeding an optimized design and broad adoption. Here, we develop a generalized two-concentration model (TCM) to describe the sorption kinetics of hygroscopic hydrogels, where vapor transport in hydrogel micropores and liquid transport in polymer nanopores are coupled through the sorption at the interface. We show that the liquid transport due to the chemical potential gradient in the hydrogel plays an important role in the fast kinetics. The high water uptake is attributed to the expansion of hydrogel during liquid transport. Moreover, we identify key design parameters governing the kinetics, including the initial porosity, hydrogel thickness, and shear modulus. This work provides a generic framework of sorption kinetics, which bridges the knowledge gap between the fundamental transport and practical design of hygroscopic hydrogels.

Temporal Evolution of Surface Contamination under Ultra-high Vacuum

Ultra-high vacuum (UHV) is essential to many surface characterization techniques and is often applied with the intention of reducing exposure to airborne contaminants. Surface contamination under UHV is not well-understood, however, and introduces uncertainty in surface elemental characterization or hinders surface-sensitive manufacturing approaches. In this work, we investigated the time-dependent surface composition of gold samples with different initial levels of contamination under UHV over a period of 24 h with both experiments and physical modeling. Our results show that surface hydrocarbon concentration under UHV can be explained by molecular adsorption-desorption competition theory. Gold surfaces that were initially pristine adsorbed hydrocarbons over time under UHV; conversely, surfaces that were initially heavily contaminated desorbed hydrocarbons over time. During both adsorption and desorption, the concentration of contaminants tended toward the same equilibrium value. This study provides a comprehensive evaluation of the temporal evolution of surface contamination under UHV and highlights routes to mitigate surface contamination effects.

Rational Fabrication of Nano-to-Microsphere Polycrystalline Opals Using Slope Self-Assembly

Self-assembly of artificial opals has garnered significant interest as a facile nanofabrication technique capable of producing highly ordered structures for optical, electrochemical, biomolecular, and thermal applications. In these applications, the optimum opal particle diameter can vary by several orders of magnitude because the properties of the resultant structures depend strongly on the feature size. However, current opal fabrication techniques only produce high-quality structures over a limited range of sphere sizes or require complex processes and equipment. In this work, the rational and simple fabrication of polycrystalline opals with diameters between 500 nm and 10 μm was demonstrated using slope self-assembly of colloids suspended in ethanol-water. The role of the various process parameters was elucidated through a scaling-based model that accurately captures the variations of opal substrate coverage for spheres of size 2 μm or smaller. For spheres of 10 μm and larger, capillary forces were shown to play a key role in the process dynamics. Based on these insights, millimeter-scale monolayered opals were successfully fabricated, while centimeter-scale opals were possible with sparse sphere stacking or small uncovered areas. These insights provide a guide for the simple and fast fabrication of opals that can be used as optical coatings, templates for high power density electrodes, molecule templates, and high-performance thermo-fluidic devices.

Bottom-Up Synthesized All-Thermal-Catalyst Aerogels for Heat-Regenerative Air Filtration

Airborne particular matter (PM) pollution is an increasing global issue and alternative sources of filter fibers are now an area of significant focus. Compared with relatively mature hazardous gas treatments, state of the art high-efficiency PM filters still lack thermal decomposition ability for organic PM pollutants, such as soot from coal-fired power plants and waste-combustion incinerators, resulting in frequent replacement, high cost, and second-hand pollution. In this manuscript, we propose a bottom-up synthesis method to make the first all-thermal-catalyst air filter (ATCAF). Self-assembled from ∼50 nm diameter TiO₂ fibers, ATCAF could not only capture the combustion-generated PM pollutants with >99.999% efficiency but also catalyze the complete decomposition of the as-captured hydrocarbon pollutants at high temperature. It has the potential of in situ eliminating the PM pollutants from burning of hydrocarbon materials leveraging the burning heat.

Toward Optimal Heat Transfer of 2D-3D Heterostructures via van der Waals Binding Effects

Two-dimensional (2D) materials and their heterogeneous integration have enabled promising electronic and photonic applications. However, significant thermal challenges arise due to numerous van der Waals (vdW) interfaces limiting the dissipation of heat generated in the device. In this work, we investigate the vdW binding effect on heat transport through a MoS₂-amorphous silica heterostructure. We show using atomistic simulations that the cross-plane thermal conductance starts to saturate with the increase of vdW binding energy, which is attributed to substrate-induced localized phonons. With these atomistic insights, we perform device-level heat transfer optimizations. Accordingly, we identify a regime, characterized by the coupling of in-plane and cross-plane heat transport mediated by vdW binding energy, where maximal heat dissipation in the device is achieved. These results elucidate fundamental heat transport through the vdW heterostructure and provide a pathway toward optimizing thermal management in 2D nanoscale devices.

Lactate Dehydrogenase Is a Useful Marker for Predicting the Efficacy of Bevacizumab-containing Chemotherapy in Patients With Metastatic Colorectal Cancer

BACKGROUND/AIM

No biomarkers that predict the benefit from anti-vascular endothelial growth factor (VEGF) antibodies have been identified. It is necessary to discover biomarkers that can identify patients who are more likely to benefit from bevacizumab-containing treatment, especially those who are more likely to benefit from treatment with bevacizumab beyond progression (BBP). Levels of serum lactate dehydrogenase (LDH), reported to be an indirect marker of hypoxia and angiogenesis, may be a useful marker for monitoring the efficacy of suppression of angiogenesis.

PATIENTS AND METHODS

The clinical data of 91 patients with unresectable metastatic colorectal cancer who were treated with bevacizumab-containing chemotherapy as first-line treatment were collected and studied.

RESULTS

In the second-line treatment, the bevacizumab plus chemotherapy group showed significantly better progression-free survival (PFS) in comparison to the chemotherapy-alone group in patients with low post-first-line-treatment serum LDH levels. On the other hand, no significant differences in the PFS rate were observed between the two groups in patients with high post-first-line-treatment serum LDH levels.

CONCLUSION

The post-first-line-treatment serum LDH levels may, therefore, be useful marker for predicting the efficacy of treatment with BBP.

Prognostic Significance of the Immunological Indices in Patients Who Underwent Complete Resection of Pulmonary Metastases of Colorectal Cancer

BACKGROUND/AIM

The neutrophil-to-lymphocyte ratio (NLR) and the density of tumor-infiltrating lymphocytes (TILs) have been reported as immunological prognostic factors for various cancers. We evaluated the association between the prognosis and the immunological status in patients who underwent complete resection of pulmonary metastases of colorectal cancer (CRC).

PATIENTS AND METHODS

We evaluated the associations between the NLR before the resection of pulmonary metastases and the relapse-free survival (RFS) or overall survival (OS), or between the density of TILs in the pulmonary metastasis and the RFS or OS.

RESULTS

The RFS and OS were significantly worse in the NLR-High group than in the NLR-Low group. The RFS was significantly longer in the CD3⁺TILs-High group than in the CD3⁺TILs-Low group.

CONCLUSION

The NLR and the density of TILs may have prognostic significance in patients who undergo complete resection of pulmonary metastases of CRC.

Elevated Postoperative Levels of Serum C-reactive Protein Are Associated With Shorter Long-term Survival After Resection of Colorectal Liver Metastases, Regardless of the Occurrence of Infectious Complications

BACKGROUND/AIM

Recently, elevated levels of postoperative inflammatory markers have been reported to be associated with poorer long-term survival outcomes, regardless of the occurrence of infectious complications, in gastroenterological malignancies. The aim of this study was to evaluate the association between postoperative inflammation and shorter long-term survival after resection of colorectal liver metastases.

PATIENTS AND METHODS

A total of 104 patients who underwent R0 resection for colorectal liver metastases were enrolled. The CRP_max levels were defined as the highest postoperative serum C-reactive protein levels during hospital stay.

RESULTS

The high-CRP_max group had a significantly lower relapse-free survival rate than the low-CRP_max group, regardless of the occurrence of infectious complications.

CONCLUSION

In colorectal liver metastasis as well as other malignancies, elevated postoperative levels of serum C-reactive protein are associated with shorter long-term survival, regardless of the occurrence of infectious complications.

Solar-Driven Soft Robots

Stimuli-responsive materials have been lately employed in soft robotics enabling new classes of robots that can emulate biological systems. The untethered operation of soft materials with high power light, magnetic field, and electric field has been previously demonstrated. While electric and magnetic fields can be stimulants for untethered actuation, their rapid decay as a function of distance limits their efficacy for long-range operations. In contrast, light-in the form of sunlight or collimated from an artificial source (e.g., laser, Xenon lamps)-does not decay rapidly, making it suitable for long-range excitation of untethered soft robots. In this work, an approach to harnessing sunlight for the untethered operation of soft robots is presented. By employing a selective solar absorber film and a low-boiling point (34 °C) fluid, light-operated soft robotic grippers are demonstrated, grasping and lifting objects almost 25 times the mass of the fluid in a controllable fashion. The method addresses one of the salient challenges in the field of untethered soft robotics. It precludes the use of bulky peripheral components (e.g., compressors, valves, or pressurized gas tank) and enables the untethered long-range operation of soft robots.

Microtube Surfaces for the Simultaneous Enhancement of Efficiency and Critical Heat Flux during Pool Boiling

Boiling is an essential process in numerous applications including power plants, thermal management, water purification, and steam generation. Previous studies have shown that surfaces with microcavities or biphilic wettability can enhance the efficiency of boiling heat transfer, that is, the heat transfer coefficient (HTC). Surfaces with permeable structures such as micropillar arrays, in contrast, have shown significant enhancement of the critical heat flux (CHF). In this work, we investigated microtube structures, where a cavity is defined at the center of a pillar, as structural building blocks to enhance HTC and CHF simultaneously in a controllable manner. We demonstrated simultaneous CHF and HTC enhancements of up to 62 and 244%, respectively, compared to those of a smooth surface. The experimental data along with high-speed images elucidate the mechanism for simultaneous enhancement where bubble nucleation occurs in the microtube cavities for increased HTC and microlayer evaporation occurs around microtube sidewalls for increased CHF. Furthermore, we combined micropillars and microtubes to create surfaces that further increased CHF by achieving a path to separate nucleating bubbles and rewetting liquids. This work provides guidelines for the systematic surface design for boiling heat transfer enhancement and has important implications for understanding boiling heat transfer mechanisms.

Transport-Based Modeling of Bubble Nucleation on Gas Evolving Electrodes

Bubble nucleation is ubiquitous in gas evolving reactions that are instrumental for a variety of electrochemical systems. Fundamental understanding of the nucleation process, which is critical to system optimization, remains limited as prior works generally focused on the thermodynamics and have not considered the coupling between surface geometries and different forms of transport in the electrolytes. Here, we establish a comprehensive transport-based model framework to identify the underlying mechanism for bubble nucleation on gas evolving electrodes. We account for the complex effects on the electrical field, ion migration, ion diffusion, and gas diffusion arising from surface heterogeneities and gas pockets initiated from surface crevices. As a result, we show that neglecting these effects leads to significant underprediction of the energy needed for nucleation. Our model provides a non-monotonic relationship between the surface cavity size and the overpotential required for nucleation, which is physically more consistent than the monotonic relationship suggested by a traditional thermodynamics-based model. We also identify the significance of the gas diffuse layer thickness, a parameter controlled by external flow fields and overall electrode geometries, which has been largely overlooked in previous models. Our model framework offers guidelines for practical electrochemical systems whereby, without changing the surface chemistry, nucleation on electrodes can be tuned by engineering the cavity size and the gas diffuse layer thickness.

Polymer Infused Porous Surfaces for Robust, Thermally Conductive, Self-Healing Coatings for Dropwise Condensation

Hydrophobic coatings with low thermal resistance promise a significant enhancement in condensation heat transfer performance by promoting dropwise condensation in applications including power generation, water treatment, and thermal management of high-performance electronics. However, after nearly a century of research, coatings with adequate robustness remain elusive due to the extreme environments within many condensers and strict design requirements needed to achieve enhancement. In this work, we enable long-lasting condensation heat transfer enhancement via dropwise condensation by infusing a hydrophobic polymer, Teflon AF, into a porous nanostructured surface. This polymer infused porous surface (PIPS) uses the large surface area of the nanostructures to enhance polymer adhesion, while the nanostructures form a percolated network of high thermal conductivity material throughout the polymer and drastically reduce the thermal resistance of the composite. We demonstrate over 700% enhancement in the condensation of steam compared to an uncoated surface. This performance enhancement was sustained for more than 200 days without significant degradation. Furthermore, we show that the surfaces are self-repairing upon raising the temperature past the melting point of the polymer, allowing recovery of hydrophobicity and offering a level of durability more appropriate for industrial applications.

Quasi-Newtonian Environmental Scanning Electron Microscopy (QN-ESEM) for Monitoring Material Dynamics in High-Pressure Gaseous Environments

Environmental scanning electron microscopy (ESEM) is a powerful technique that enables imaging of diverse specimens (e.g., biomaterials, chemical materials, nanomaterials) in a hydrated or native state while simultaneously maintaining micro-to-nanoscale resolution. However, it is difficult to achieve high signal-to-noise and artifact-free secondary electron images in a high-pressure gaseous environment due to the intensive electron-gas collisions. In addition, nanotextured substrates can mask the signal from a weakly scattering sample. These drawbacks limit the study of material dynamics under extreme conditions and correspondingly our understanding in many fields. In this work, an imaging framework called Quasi-Newtonian ESEM is proposed, which introduces the concepts of quasi-force and quasi-work by referencing the scattering force in light-matter interactions, to break these barriers without any hardware changes. It is shown that quasi-force is a more fundamental quantity that has a more significant connection with the sample morphology than intensity in the strongly scattering regime. Experimental and theoretical studies on the dynamics of droplet condensation in a high-pressure environment (up to 2500 Pa) successfully demonstrate the effectiveness and robustness of the framework and that the overwhelmed signal of interest in ESEM images can be reconstructed through information stored in the time domain, i.e., frames captured at different moments.

Combining Bevacizumab With Trifluridine/Thymidine Phosphorylase Inhibitor Improves the Survival Outcomes Regardless of the Usage History of Bevacizumab in Front-line Treatment of Patients With Metastatic Colorectal Cancer

BACKGROUND/AIM

The efficacy of trifluridine/thymidine phosphorylase inhibitor (FTD/TPI) plus bevacizumab as later-line treatment for metastatic colorectal cancer (mCRC) has been demonstrated. However, little is known about the impact of a usage history of bevacizumab in front-line treatment on the clinical benefit of combining bevacizumab with FTD/TPI.

PATIENTS AND METHODS

A total of 62 patients with mCRC treated with FTD/TPI±bevacizumab was enrolled and assessed for chemotherapeutic efficacy and adverse events.

RESULTS

Regardless of the usage history of bevacizumab in front-line treatment, the FTD/TPI plus bevacizumab group had a significantly better progression-free survival rate than the FTD/TPI monotherapy group, and no significant differences in the safety profile were observed between the two groups.

CONCLUSION

Combining bevacizumab with FTD/TPI improves the survival outcomes with manageable toxicity, regardless of the usage history of bevacizumab in front-line treatment, in patients with mCRC.

Wide-Field Magnetic Field and Temperature Imaging Using Nanoscale Quantum Sensors

The simultaneous imaging of magnetic fields and temperature (MT) is important in a range of applications, including studies of carrier transport and semiconductor device characterization. Techniques exist for separately measuring temperature (e.g., infrared (IR) microscopy, micro-Raman spectroscopy, and thermo-reflectance microscopy) and magnetic fields (e.g., scanning probe magnetic force microscopy and superconducting quantum interference devices). However, these techniques cannot measure magnetic fields and temperature simultaneously. Here, we use the exceptional temperature and magnetic field sensitivity of nitrogen vacancy (NV) spins in conformally coated nanodiamonds to realize simultaneous wide-field MT imaging at the device level. Our "quantum conformally attached thermo-magnetic" (Q-CAT) imaging enables (i) wide-field, high-frame rate imaging (100-1000 Hz); (ii) high sensitivity; and (iii) compatibility with standard microscopes. We apply this technique to study the industrially important problem of characterizing multifinger gallium nitride high-electron mobility transistors (GaN HEMTs). We spatially and temporally resolve the electric current distribution and resulting temperature rise, elucidating functional device behavior at the microscopic level. The general applicability of Q-CAT imaging serves as an important tool for understanding complex MT phenomena in material science, device physics, and related fields.

High Heat Flux Evaporation of Low Surface Tension Liquids from Nanoporous Membranes

Water is often considered as the highest performance working fluid for liquid-vapor phase change due to its high thermal conductivity and large enthalpy of vaporization. However, a wide range of industrial systems require using low surface tension liquids where heat transfer enhancement has proved challenging for boiling and evaporation. Here, we enable a new paradigm of phase change heat transfer, which favors high volatility, low surface tension liquids rather than water. We utilized a nanoporous membrane of ≈600 nm thickness and <140 nm pore diameters supported on efficient liquid supply architectures, decoupling capillary pumping from viscous loss. Proof-of-concept devices were microfabricated and tested in a custom-built environmental chamber. We used R245fa, pentane, methanol, isopropyl alcohol, and water as working fluids with devices of total membrane area varying from 0.017 to 0.424 cm². We realized a device-level pure evaporation heat flux of 144 ± 6 W/cm² for water, and the highest evaporation heat flux was obtained with pentane at 550 ± 90 W/cm². We developed a three-level model to understand vapor dynamics near the interface and thermal conduction within the device, which showed good agreement with experiments. We then compared pore-level heat transfer of different fluids, where R245fa showed approximately 10 times the performance of water under the same working conditions. Finally, we illustrate the usefulness of a figure of merit extracted from the kinetic theory for evaporation. The current work provides fundamental insights into the evaporation of low surface tension liquids, which can impact various applications such as refrigeration and air conditioning, petroleum and solvent distillation, and on-chip electronics cooling.

Harnessing Heat Beyond 200 °C from Unconcentrated Sunlight with Nonevacuated Transparent Aerogels

Heat at intermediate temperatures (120-220 °C) is in significant demand in both industrial and domestic sectors for applications such as water and space heating, steam generation, sterilization, and other industrial processes. Harnessing heat from solar energy at these temperatures, however, requires costly optical and mechanical components to concentrate the dilute solar flux and suppress heat losses. Thus, achieving high temperatures under unconcentrated sunlight remains a technological challenge as well as an opportunity for utilizing solar thermal energy. In this work, we demonstrate a solar receiver capable of reaching over 265 °C under ambient conditions without optical concentration. The high temperatures are achieved by leveraging an artificial greenhouse effect within an optimized monolithic silica aerogel to reduce heat losses while maintaining high solar transparency. This study demonstrates a viable path to promote cost-effective solar thermal energy at intermediate temperatures.

Thermal Expansion Coefficient of Monolayer Molybdenum Disulfide Using Micro-Raman Spectroscopy

Atomically thin two-dimensional (2D) materials have shown great potential for applications in nanoscale electronic and optical devices. A fundamental property of these 2D flakes that needs to be well-characterized is the thermal expansion coefficient (TEC), which is instrumental to the dry transfer process and thermal management of 2D material-based devices. However, most of the current studies of 2D materials' TEC extensively rely on simulations due to the difficulty of performing experimental measurements on an atomically thin, micron-sized, and optically transparent 2D flake. In this work, we present a three-substrate approach to characterize the TEC of monolayer molybdenum disulfide (MoS₂) using micro-Raman spectroscopy. The temperature dependence of the Raman peak shift was characterized with three different substrate conditions, from which the in-plane TEC of monolayer MoS₂ was extracted on the basis of lattice symmetries. Independently from two different phonon modes of MoS₂, we measured the in-plane TECs as (7.6 ± 0.9) × 10^-6 K^-1 and (7.4 ± 0.5) × 10^-6 K^-1, respectively, which are in good agreement with previously reported values based on first-principle calculations. Our work is not only useful for thermal mismatch reduction during material transfer or device operation but also provides a general experimental method that does not rely on simulations to study key properties of 2D materials.

Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance

Atmospheric water harvesting (AWH) is the capture and collection of water that is present in the air either as vapor or small water droplets. AWH has been recognized as a method for decentralized water production, especially in areas where liquid water is physically scarce, or the infrastructure required to bring water from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and utilizing sorbent materials to collect vapor from the air. In this paper, we first distinguish between the geographic/climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temperature and relative humidity (RH). Because utilizing sorbents has the potential to be more widely applicable to areas which are also facing water scarcity, we focus our discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equilibrium vapor uptake in the material (kg of water uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equilibrium property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances associated with heat and mass transport in the bulk material dramatically change the system performance. We focus our discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of water per m² device per day or L of water per kg adsorbent per day. The former metric is especially important for systems driven by low-grade heat sources because the low power density of these sources makes this technology land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss our previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized water supplies.

A unified relationship for evaporation kinetics at low Mach numbers

We experimentally realized and elucidated kinetically limited evaporation where the molecular gas dynamics close to the liquid–vapour interface dominates the overall transport. This process fundamentally dictates the performance of various evaporative systems and has received significant theoretical interest. However, experimental studies have been limited due to the difficulty of isolating the interfacial thermal resistance. Here, we overcome this challenge using an ultrathin nanoporous membrane in a pure vapour ambient. We demonstrate a fundamental relationship between the evaporation flux and driving potential in a dimensionless form, which unifies kinetically limited evaporation under different working conditions. We model the nonequilibrium gas kinetics and show good agreement between experiments and theory. Our work provides a general figure of merit for evaporative heat transfer as well as design guidelines for achieving efficient evaporation in applications such as water purification, steam generation, and thermal management.

Evaporation plays a key role in applications such as cooling and desalination. Here, the authors experimentally demonstrated a unifying relationship between dimensionless flux and driving potential for evaporation kinetics under different working conditions.

Enhanced Environmental Scanning Electron Microscopy Using Phase Reconstruction and Its Application in Condensation

Environmental scanning electron microscopy (ESEM) is a broadly utilized nanoscale inspection technique capable of imaging wet or insulating samples. It extends the application of conventional scanning electron microscopy (SEM) and has been extensively used to study the behavior of liquid, polymer, and biomaterials by allowing for a gaseous environment. However, the presence of gas in the chamber can severely degrade the image resolution and contrast. This typically limits the ESEM operating pressure below 1000 Pa. The dynamic interactions, which require even-higher sensitivity and resolution, are particularly challenging to resolve at high-pressure conditions. Here, we present an enhanced ESEM technique using phase reconstruction to extend the limits of the ESEM operating pressure while improving the image quality, which is useful for sensing weak scattering from transparent or nanoscale samples. We applied this method to investigate the dynamics of condensing droplets, as an example case, which is of fundamental importance and has many industrial applications. We visualized dynamic processes such as single-droplet growth and droplet coalescence where the operating pressure range was extended from 1000 to 2500 Pa. Moreover, we detected the distribution of nucleation sites on the nanostructured surfaces. Such nanoscale sensing has been challenging previously due to the limitation of resolution and sensitivity. Our work provides a simple approach for high-performance ESEM imaging at high-pressure conditions without changes to the hardware and can be widely applied to investigate a broad range of static and dynamic processes.

Prognostic Significance of the C-Reactive Protein-to-Albumin Ratio in Patients With Metastatic Colorectal Cancer Treated With Trifluridine/Thymidine Phosphorylase Inhibitor as Later-line Chemotherapy

BACKGROUND/AIM

New drugs for metastatic colorectal cancer (mCRC) have been recently developed for use in later-line chemotherapy and have contributed to further prolongation of the survival of patients. However, in later-line chemotherapy, treatment failure may lead to discontinuation of chemotherapy and the transition to best supportive care. Therefore, a biomarker able to predict the effects of later-line chemotherapy is required. The C-reactive protein-to-albumin ratio (CAR), which is an inflammatory marker, has been reported to correlate with therapeutic outcome in patients with mCRC who underwent first-line chemotherapy. However, the significance of the CAR as a marker for predicting the chemotherapeutic outcome in patients with mCRC treated with later-line chemotherapy is unknown.

PATIENTS AND METHODS

We retrospectively reviewed the medical records of 40 patients with mCRC who were treated with trifluridine/thymidine phosphorylase inhibitor (FTD/TPI) as a later-line chemotherapy. The CAR was calculated from the blood samples obtained within 1 week before the initiation of FTD/TPI by dividing the serum C-reactive protein level by the serum albumin level.

RESULTS

According to the receiver operating characteristic curve analysis, we set 0.122 as the CAR cut-off, and patients were classified into groups with high or low CAR. The low-CAR group had a significantly higher disease control rate than the high-CAR group. The progression-free and overall survival rates were significantly better in the low-CAR group than in the high-CAR group. A high-CAR was associated with a greater number of prior regimens, higher serum lactate dehydrogenase level and more organs with metastases, considered to be correlated with the rate of disease progression. However, no significant differences were observed in the incidence of grade 3 or more adverse events, the relative dose intensity, or the rate of discontinuing chemotherapy between the two groups.

CONCLUSION

The CAR may be a useful indicator for predicting the chemotherapeutic outcome in patients with mCRC treated with FTD/TPI as a late-line chemotherapy. The correlation between a high-CAR and poor prognosis was presumed to be due to the rate of cancer growth and increased resistance to chemotherapy rather than an insufficient dose of the drug.

Theoretical and experimental investigation of haze in transparent aerogels

Haze in optically transparent aerogels severely degrades the visual experience, which has prevented their adoption in windows despite their outstanding thermal insulation property. Previous studies have primarily relied on experiments to characterize haze in aerogels, however, a theoretical framework to systematically investigate haze in porous media is lacking. In this work, we present a radiative transfer model that can predict haze in aerogels based on their physical properties. The model is validated using optical characterization of custom-fabricated, highly-transparent monolithic silica aerogels. The fundamental relationships between the aerogel structure and haze highlighted in this study could lead to a better understanding of light-matter interaction in a wide range of transparent porous materials and assist in the development of low-haze silica aerogels for high-performance glazing units to reduce building energy consumption.

Tunable Metal-Organic Frameworks Enable High-Efficiency Cascaded Adsorption Heat Pumps

Rising global standards of living coupled to the recent agreement to eliminate hydrofluorocarbon refrigerants are creating intense pressure to develop more sustainable climate control systems. In this vein, the use of water as the refrigerant in adsorption heat pumps is highly attractive, but such adsorption systems are constrained to large size and poor efficiency by the characteristics of currently employed water sorbents. Here we demonstrate control of the relative humidity of water uptake by modulating the pore size in a family of isoreticular triazolate metal-organic frameworks. Using this method, we identify a pair of materials with stepped, nonoverlapping water isotherms that can function in tandem to provide continuous cooling with a record ideal coefficient of performance of 1.63. Additionally, when used in a single-stage heat pump, the microporous Ni₂Cl₂BBTA has the largest working capacity of any material capable of generating a 25 °C difference between ambient and chiller output.

Passive directional sub-ambient daytime radiative cooling

Demonstrations of passive daytime radiative cooling have primarily relied on complex and costly spectrally selective nanophotonic structures with high emissivity in the transparent atmospheric spectral window and high reflectivity in the solar spectrum. Here, we show a directional approach to passive radiative cooling that exploits the angular confinement of solar irradiation in the sky to achieve sub-ambient cooling during the day regardless of the emitter properties in the solar spectrum. We experimentally demonstrate this approach using a setup comprising a polished aluminum disk that reflects direct solar irradiation and a white infrared-transparent polyethylene convection cover that minimizes diffuse solar irradiation. Measurements performed around solar noon show a minimum temperature of 6 °C below ambient temperature and maximum cooling power of 45 W m^–2. Our passive cooling approach, realized using commonly available low-cost materials, could improve the performance of existing cooling systems and enable next-generation thermal management and refrigeration solutions.

Passive daytime radiative cooling presents a promising low-cost refrigeration solution but has thus far relied on specialized nanophotonic structures. Here Bhatia et al. show a directional approach that decouples solar reflectance and infrared emission to achieve superior cooling performance.

Toward Condensation-Resistant Omniphobic Surfaces

Omniphobic surfaces based on reentrant surface structures repel all liquids, regardless of the surface material, without requiring low-surface-energy coatings. Although omniphobic surfaces have been designed and demonstrated, they can fail during condensation, a phenomenon ubiquitous in both nature and industrial applications. Specifically, as condensate nucleates within the reentrant geometry, omniphobicity is destroyed. Here, we show a nanostructured surface that can repel liquids even during condensation. This surface consists of isolated reentrant cavities with a pitch on the order of 100 nm to prevent droplets from nucleating and spreading within all structures. We developed a model to guide surface design and subsequently fabricated and tested these surfaces with various liquids. We demonstrated repellency to 10 °C below the dew point and showed durability over 3 weeks. This work provides important insights for achieving robust, omniphobic surfaces.

Multiscale Dynamic Growth and Energy Transport of Droplets during Condensation

Condensation is an important physical process and has direct relevance for a range of engineering applications, including heat transfer, antifrosting, and self-cleaning. Understanding the mechanism of droplet growth during condensation is an important aspect, but past works have not typically considered the dynamics of the multiscale process. In this paper, we developed a dynamic growth model, which considers the continuous and multiscale nature of the droplet growth process from several nanometers to hundreds of microns. This model couples the transient phase change heat transfer and two-phase flow both inside and outside the droplet. Accordingly, the energy transport is distinct from the classical pure conduction model. We show that convection near the liquid-vapor interface and inside the droplets plays an increasingly important role as droplets grow and finally dominates the energy transport process. Driven by strong convection, the droplets mix well and the discrete layers of temperature observed in the pure conduction model disappear at the microscale. This model that considers convection can lead to over 4 times higher predicted overall heat transfer than that obtained with the pure conduction model. The interfacial mass flow through the liquid-vapor interface is the dominant factor responsible for the strong convection. We studied the critical radius where convection starts to have a significant influence on droplet growth under different subcooling temperatures and contact angles. Droplets have smaller critical radii under larger subcooling temperatures or larger contact angles, ranging from 0.5 to 20 μm. This work identifies the modes of energy transport in condensation at different scales, which not only enhances our fundamental understanding of individual droplet growth but provides design guidelines for various dropwise and jumping-droplet condensation research.

Specular side reflectors for high efficiency thermal-to-optical energy conversion

The performance of incandescent light bulbs and thermophotovoltaic devices is fundamentally limited by our ability to tailor the emission spectrum of the thermal emitter. While much work has focused on improving the spectral selectivity of emitters and filters, relatively low view factors between the emitter and filter limit the efficiency of the systems. In this work, we investigate the use of specular side reflectors between the emitter and filter to increase the effective view factor and thus system efficiency. Using an analytical model and experiments, we demonstrate significant gains in efficiency (>10%) for systems converting broadband thermal radiation to a tailored spectrum using low-cost and easy-to-implement specular side reflectors.

Gravitationally Driven Wicking for Enhanced Condensation Heat Transfer

Vapor condensation is routinely used as an effective means of transferring heat or separating fluids. Filmwise condensation is prevalent in typical industrial-scale systems, where the condensed fluid forms a thin liquid film due to the high surface energy associated with many industrial materials. Conversely, dropwise condensation, where the condensate forms discrete liquid droplets which grow, coalesce, and shed, results in an improvement in heat transfer performance of an order of magnitude compared to filmwise condensation. However, current state-of-the-art dropwise technology relies on functional hydrophobic coatings, for example, long chain fatty acids or polymers, which are often not robust and therefore undesirable in industrial conditions. In addition, low surface tension fluid condensates, such as hydrocarbons, pose a unique challenge because common hydrophobic condenser coatings used to shed water (with a surface tension of 73 mN/m) often do not repel fluids with lower surface tensions (<25 mN/m). We demonstrate a method to enhance condensation heat transfer using gravitationally driven flow through a porous metal wick, which takes advantage of the condensate's affinity to wet the surface and also eliminates the need for condensate-phobic coatings. The condensate-filled wick has a lower thermal resistance than the fluid film observed during filmwise condensation, resulting in an improved heat transfer coefficient of up to an order of magnitude and comparable to that observed during dropwise condensation. The improved heat transfer realized by this design presents the opportunity for significant energy savings in natural gas processing, thermal management, heating and cooling, and power generation.

Precise control of pore hydrophilicity enabled by post-synthetic cation exchange in metal-organic frameworks

The ability to control the relative humidity at which water uptake occurs in a given adsorbent is advantageous, making that material applicable to a variety of different applications.

The ability to control the relative humidity at which water uptake occurs in a given adsorbent is advantageous, making that material applicable to a variety of different applications. Here, we show that cation exchange in a metal–organic framework allows precise control over the humidity onset of the water uptake step. Controlled incorporation of cobalt in place of zinc produces open metal sites into the cubic triazolate framework MFU-4l, and thereby provides access to materials with uptake steps over a 30% relative humidity range. Notably, the MFU-4l framework has an extremely high water adsorption capacity of 1.05 g g^–1, amongst the highest known for porous materials. The total water capacity is independent of the cobalt loading, showing that cation exchange is a viable route to increase the hydrophilicity of metal–organic frameworks without sacrificing capacity.

Predicting Surface Tensions of Surfactant Solutions from Statistical Mechanics

The importance of surfactants to various industries necessitates a predictive understanding of their surface tension and adsorption behavior in terms of molecular characteristics. Previous models are highly empirical, require fitting parameters, and have limited applicability at various temperatures. Here, we provide a surface tension model based on statistical mechanics that (1) is thermodynamically consistent, (2) provides a higher predictive power, wherein surface tension can be calculated for any tail length, concentration, and temperature from molecular parameters, and (3) provides a physical understanding of the important molecular interactions at play. This model is applicable to both nonionic and ionic surfactants, where the effects of the electric double layer have been taken into account in the latter case. For nonionic surfactants, we were able to extend our model to predict dynamic surface tension as well. We have validated our model with tensiometry experiments for various surfactants, concentrations, and temperatures. In addition, we have validated our model with a diverse set of literature data, wherein agreement within a few mN M^-1 and a correct prediction of phase change behavior is shown. The model could enable a more informed design of surfactant systems and serve as the theoretical basis for theory on more complex surfactant systems such as mixtures.

Nanoporous membrane device for ultra high heat flux thermal management

High power density electronics are severely limited by current thermal management solutions which are unable to dissipate the necessary heat flux while maintaining safe junction temperatures for reliable operation. We designed, fabricated, and experimentally characterized a microfluidic device for ultra-high heat flux dissipation using evaporation from a nanoporous silicon membrane. With ~100 nm diameter pores, the membrane can generate high capillary pressure even with low surface tension fluids such as pentane and R245fa. The suspended ultra-thin membrane structure facilitates efficient liquid transport with minimal viscous pressure losses. We fabricated the membrane in silicon using interference lithography and reactive ion etching and then bonded it to a high permeability silicon microchannel array to create a biporous wick which achieves high capillary pressure with enhanced permeability. The back side consisted of a thin film platinum heater and resistive temperature sensors to emulate the heat dissipation in transistors and measure the temperature, respectively. We experimentally characterized the devices in pure vapor-ambient conditions in an environmental chamber. Accordingly, we demonstrated heat fluxes of 665 ± 74 W/cm² using pentane over an area of 0.172 mm × 10 mm with a temperature rise of 28.5 ± 1.8 K from the heated substrate to ambient vapor. This heat flux, which is normalized by the evaporation area, is the highest reported to date in the pure evaporation regime, that is, without nucleate boiling. The experimental results are in good agreement with a high fidelity model which captures heat conduction in the suspended membrane structure as well as non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work suggests that evaporative membrane-based approaches can be promising towards realizing an efficient, high flux thermal management strategy over large areas for high-performance electronics.

Enhanced water transport and salt rejection through hydrophobic zeolite pores

The potential of improvements to reverse osmosis (RO) desalination by incorporating porous nanostructured materials such as zeolites into the selective layer in the membrane has spurred substantial research efforts over the past decade. However, because of the lack of methods to probe transport across these materials, it is still unclear which pore size or internal surface chemistry is optimal for maximizing permeability and salt rejection. We developed a platform to measure the transport of water and salt across a single layer of zeolite crystals, elucidating the effects of internal wettability on water and salt transport through the ≈5.5 Å pores of MFI zeolites. MFI zeolites with a more hydrophobic (i.e., less attractive) internal surface chemistry facilitated an approximately order of magnitude increase in water permeability compared to more hydrophilic MFI zeolites, while simultaneously fully rejecting both potassium and chlorine ions. However, our results also demonstrated approximately two orders of magnitude lower permeability compared to molecular simulations. This decreased performance suggests that additional transport resistances (such as surface barriers, pore collapse or blockages due to contamination) may be limiting the performance of experimental nanostructured membranes. Nevertheless, the inclusion of hydrophobic sub-nanometer pores into the active layer of RO membranes should improve both the water permeability and salt rejection of future RO membranes (Fasano et al 2016 Nat. Commun. 7 12762).

Design of Lubricant Infused Surfaces

Lubricant infused surfaces (LIS) are a recently developed and promising approach to fluid repellency for applications in biology, microfluidics, thermal management, lab-on-a-chip, and beyond. The design of LIS has been explored in past work in terms of surface energies, which need to be determined empirically for each interface in a given system. Here, we developed an approach that predicts a priori whether an arbitrary combination of solid and lubricant will repel a given impinging fluid. This model was validated with experiments performed in our work as well as in literature and was subsequently used to develop a new framework for LIS with distinct design guidelines. Furthermore, insights gained from the model led to the experimental demonstration of LIS using uncoated high-surface-energy solids, thereby eliminating the need for unreliable low-surface-energy coatings and resulting in LIS repelling the lowest surface tension impinging fluid (butane, γ ≈ 13 mN/m) reported to date.

Response to Comment on "Water harvesting from air with metal-organic frameworks powered by natural sunlight"

In their comment, Bui et al argue that the approach we described in our report is vastly inferior in efficiency to alternative off-the-shelf technologies. Their conclusion is invalid, as they compare efficiencies in completely different operating conditions. Here, using heat transfer and thermodynamics principles, we show how Bui et al's conclusions about the efficiencies of off-the-shelf technologies are fundamentally flawed and inaccurate for the operating conditions described in our study.

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E₂ (high), A₁ longitudinal optical (LO), and E₂ (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

An Ultrathin Nanoporous Membrane Evaporator

Evaporation is a ubiquitous phenomenon found in nature and widely used in industry. Yet a fundamental understanding of interfacial transport during evaporation remains limited to date owing to the difficulty of characterizing the heat and mass transfer at the interface, especially at high heat fluxes (>100 W/cm²). In this work, we elucidated evaporation into an air ambient with an ultrathin (≈200 nm thick) nanoporous (≈130 nm pore diameter) membrane. With our evaporator design, we accurately monitored the temperature of the liquid-vapor interface, reduced the thermal-fluidic transport resistance, and mitigated the clogging risk associated with contamination. At a steady state, we demonstrated heat fluxes of ≈500 W/cm² across the interface over a total evaporation area of 0.20 mm². In the high flux regime, we showed the importance of convective transport caused by evaporation itself and that Fick's first law of diffusion no longer applies. This work improves our fundamental understanding of evaporation and paves the way for high flux phase-change devices.

Coexistence of Pinning and Moving on a Contact Line

Textured surfaces are instrumental in water repellency or fluid wicking applications, where the pinning and depinning of the liquid-gas interface plays an important role. Previous work showed that a contact line can exhibit nonuniform behavior due to heterogeneities in surface chemistry or roughness. We demonstrate that such nonuniformities can be achieved even without varying the local energy barrier. Around a cylindrical pillar, an interface can reside in an intermediate state where segments of the contact line are pinned to the pillar top while the rest of the contact line moves along the sidewall. This partially pinned mode is due to the global nonaxisymmetric pattern of the surface features and exists for all textured surfaces, especially when superhydrophobic surfaces are about to be flooded or when capillary wicks are close to dryout.

Record Atmospheric Fresh Water Capture and Heat Transfer with a Material Operating at the Water Uptake Reversibility Limit

The capture of water vapor at low relative humidity is desirable for producing potable water in desert regions and for heat transfer and storage. Here, we report a mesoporous metal-organic framework that captures 82% water by weight below 30% relative humidity. Under simulated desert conditions, the sorbent would deliver 0.82 g_H2O g_MOF^-1, nearly double the quantity of fresh water compared to the previous best material. The material further demonstrates a cooling capacity of 400 kWh m^-3 per cycle, also a record value for a sorbent capable of creating a 20 °C difference between ambient and output temperature. The water uptake in this sorbent is optimized: the pore diameter of our material is above the critical diameter for water capillary action, enabling water uptake at the limit of reversibility.