Rapid Evaporation Research Articles

Sandwich-Structured textiles with hierarchically nanofibrous network and Janus wettability for outdoor personal thermal and moisture management

As the interlayer between the skin and the environment, textiles play a vital role in achieving personal comfort and safety by managing the localized human body thermal and moisture conditions. However, intense exercise or sunlight exposure in hot and humid outdoor environments still leads to the accumulation of heat and excessive sweat on the human body. This reduces industrial labor productivity and results in economic losses. Herein, a sandwich-structured textile with a hierarchically nanofibrous network and Janus wettability is demonstrated. This textile exhibits excellent spectral selectivity (with a solar reflectance of 93.4% and a human body infrared emittance of 96.3%), rapid sweat evaporation rate (0.26 g h−1), and directional water transport property (a one-way transport index of 1140%). In a practical scenario, a human body covered by this sandwich-structured textile achieved a temperature drop of ∼ 4.2 °C compared with a commercial cotton textile. Through the integration of decent outdoor radiative cooling and continuous sweat wicking-drying properties, this sandwich-structured textile exhibits enhanced personal thermal and moisture management performance. Consequently, this textile leads to a significant reduction in human sweat consumption and excessive heat stress in outdoor environments.

Drying quality and energy consumption efficient improvements in hot air drying of papaya slices by step-down relative humidity based on heat and mass transfer characteristics and 3D simulation

Convective hot air drying technology is widely used for fruits and vegetables drying process due to its simplicity in usage, small investment, and convenience in operation. However, it is generally considered energy-intensive process with lower drying efficiency and quality because of unprecise control of drying process. In order to solve these problems, step-down relative humidity (RH) hot air drying technology was applied for papaya drying to improve drying efficiency and quality and reduce energy consumption. The effect of constant RH (20%, 30%, 40%, and 50%) and step-down RH of 50% with different holding times (10, 30, 60, and 90 min) and then decrease to 20% on heat and mass transfer process, drying quality, and energy consumption was examined. Results showed that decreasing RH contributed to improvement in the drying rate (DR). Compared to constant RH of 20%, the drying time under initial RH of 50% for 30 min followed by 20% RH shortened by 21.4%. Additionally, under this RH control strategy, the rehydration ratio (RR) and energy consumption achieved their maximum (7.71 ± 0.06) and minimum value (0.015 ± 0.001 kJ/g), respectively. During initial drying stage, high RH improved convective heat transfer coefficient (ht ) values and material temperature increased quickly. Furthermore, high RH contributed to maintaining pore structure formation, which benefited moisture diffusion. When RH was reduced, low RH enhanced convective mass transfer coefficient (hm ) significantly, resulting in rapid diffusion of internal moisture at high temperature, as well as rapid moisture evaporation from the surface. Therefore, step-down RH hot air drying was verified to improve drying of papaya slices, making it energy efficient process. The findings in current work indicate step-down relative humidity strategy is a promising technique to enhance hot air drying process, quality, and energy efficiency of papaya slices.

Synergistic Effect of Anti‐Solvent and Component Engineering for Effective Passivation to Attain Highly Stable Perovskite Solar Cells

Defect passivation is a crucial process for achieving high‐performance perovskite solar cells (PSCs). Herein, the synergistic effect of anti‐solvent and component engineering for effective passivation to attain highly stable PSCs is demonstrated, specifically, for ethyl acetate as the anti‐solvent and CsBr as the additive in the MAPbI3 precursor solution. It is found that the rapid solvent evaporation results in fast nucleation, and the CsBr assists the perovskite grain growth. The synergistic effect of anti‐solvent and additive engineering leads to increased perovskite grain size, reduced defect density, improved quality of the perovskite thin film, and finally, enhanced efficiency and stability of the indium tin oxide/SnO2/perovskite/carbon device. The influence of this synergistic effect on the morphology and photovoltaic performance is systematically investigated. Printable PSCs with hole‐transport‐layer‐free carbon electrodes are designed and constructed, which achieve a champion photoelectric conversion efficiency of 16.45%, fill factor of 72.63%, short circuit current of 19.90 mA cm−2, and open circuit voltage of 1.14 V. Herein, a facile and low‐cost approach is demonstrated to obtain highly stable C‐PSCs and a promising strategy for future commercial application is provided.

Impact of the Drying Temperature during Catalyst Layer Manufacturing on PEM Fuel Cell Performance

The manufacturing process of catalyst coated membranes for polymer electrolyte fuel cells (PEMFC) needs to be transferred to high throughput mass production to meet the increasing demand on the market. After the coating of the catalyst ink, the drying temperature and its profile can change the pore structure and crack appearance of the catalyst layer by influencing the solvent evaporation [1]. Therefore, adjusting the drying parameters to the type of solvents within the catalyst ink can result in beneficial performance gain. Often solvents with low boiling points like isopropanol-water mixtures are used. The rapid evaporation of these solvents could lead to crack formation, which could be avoided by the usage of high boiling point solvents like e.g. ethylene glycol [2,3]. Therefore higher drying temperatures are necessary to ensure a complete removal of the wet components. This leads to the question of the maximum drying temperature which can be applied to speed up the drying process as much as possible.The most temperature sensitive component within the catalyst layer is the ionomer. Drying at high temperatures could lead to degradation and decomposition of the ionomer network within the catalyst layer. However, is the temperature too low, the necessary drying time increases, which would result in higher investment costs for longer drying process lines.Within this study we investigated at first the thermal behavior of short side chain (Aquivion®) and long side chain (Nafion™) ionomer dispersions to analyze their glass transition and melting temperatures with differential scanning calorimetry in the range of 30-400°C. The findings are shown in Figure 1. The glass transition temperature of Aquivion® lies between 154-159°C, whereas Nafion™ is more temperature sensitive with 125-142°C, which is consistent with the literature.In a second step, catalyst layers have been fabricated by screen printing with a catalyst paste including a solvent mixture of ethylene glycol and 1-methoxy-2-propanol [4]. The resulting catalyst layers have platinum loadings of 0.154 mg/cm² on the cathode and 0.05 mg/cm² on the anode side. The drying temperature has been varied between 22°C (ambient air temperature), 110°C, 150°C, 180°C, 200°C and 250°C within a continuous convection dryer. Further, different drying profiles have been applied by comparing to hot plate drying method. All other process parameters have been kept constant. The catalyst layers with different drying temperatures have been tested in-situ by electrochemical operation of the MEA. For Aquivion® as ionomer, the polarization curves are shown in Figure 2 and indicate that drying temperatures above 150°C (glass transition temperature) would lead to significant current density losses at wet and dry conditions. Furthermore, there doesn’t seem to be an optimum drying temperature below the glass transition temperature. Therefore, the best compromise of production throughput and electrochemical performance is reached at a temperature of 150°C, which is near the glass transition temperature of the ionomer.[1] Park H-S, Cho Y-H, Cho Y-H, Jung CR, Jang JH, Sung Y-E. Performance enhancement of PEMFC through temperature control in catalyst layer fabrication. Electrochimica Acta 2007;53(2):763–7.[2] Huang D-C, Yu P-J, Liu F-J, Huang S-L, Hsueh K-L, Chen Y-C et al. Effect of Dispersion Solvent in Catalyst Ink on Proton Exchange Membrane Fuel Cell Performance. Int. J. Electrochem. Sci. International Journal 2011;6:2551–65.[3] Hasegawa N, Kamiya A, Matsunaga T, Kitano N, Harada M. Analysis of crack formation during fuel cell catalyst ink drying process. Reduction of catalyst layer cracking by addition of high boiling point solvent. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2021:127153.[4] Alink R, Singh R, Schneider P, Christmann K, Schall J, Keding R et al. Full Parametric Study of the Influence of Ionomer Content, Catalyst Loading and Catalyst Type on Oxygen and Ion Transport in PEM Fuel Cell Catalyst Layers. Molecules (Basel, Switzerland) 2020;25(7). Figure 1

Co-operative halogen bonds and nonconventional sp-C-H...O hydrogen bonds in 1:1 cocrystals formed between diethynylpyridines and N-halosuccinimides.

The rapid evaporation of 1:1 solutions of diethynylpyridines and N-halosuccinimides, that react together to form haloalkynes, led to the isolation of unreacted 1:1 cocrystals of the two components. The 1:1 cocrystal formed between 2,6-diethynylpyridine and N-iodosuccinimide (C4H4INO2·C9H5N) contains an N-iodosuccinimide-pyridine I...N halogen bond and two terminal alkyne-succinimide carbonyl C-H...O hydrogen bonds. The three-dimensional extended structure features interwoven double-stranded supramolecular polymers that are interconnected through halogen bonds. The cocrystal formed between 3,5-diethynylpyridine and N-iodosuccinimide (C4H4INO2·C9H5N) also features an I...N halogen bond and two C-H...O hydrogen bonds. However, the components form essentially planar double-stranded one-dimensional zigzag supramolecular polymers. The cocrystal formed between 3,5-diethynylpyridine and N-bromosuccinimide (C4H4BrNO2·C9H5N) is isomorphous to the cocrystal formed between 3,5-diethynylpyridine and N-iodosuccinimide, with a Br...N halogen bond instead of an I...N halogen bond.

Numerical modeling of oil spills in the Gulf of Morrosquillo, Colombian Caribbean

This study encompasses the analysis of oil spills occurred in the Gulf of Morrosquillo during the loading procedures of oil tankers in the Coveñas maritime Terminal, by means of numerical simulation experiments of the trajectories and weathering processes of oil spilled, which occurred under specific wind, waves, and ocean currents conditions. A three-dimensional (3D) modelling system, OpenOil, which is part of the open-source OpenDrift trajectory framework was used to simulate two contingencies occurred in July and August 2014. During each event, different volumes of Vasconia crude oil spilled on the sea surface were simulated. The resulting slicks were subject to wind drift, Stokes drift from wave forcing, and ocean currents transporting the oil spilled towards the coast. Oil weathering effects (evaporation, emulsification, and biodegradation) are included in the analysis. To calculate weathering of the oil, OpenOil interfaces with the latest version of the open source ADIOS oil library. It should be noted that meteorological and ocean conditions contribute to the oil pathways that in both periods forced the oil slick towards the central coast of the Gulf. The wind speed is an important factor contributing to the rapid evaporation rates of the oil spilled in the warm waters of the Caribbean Sea; hence, allowing a gradual increase of the water fraction, which could lead to the formation of tar balls found in the affected coasts in the areas simulated by the model. The implementation of OpenOil to predict the oil fate and weathering processes in the Colombian basin prove to be a valuable tool that should be used in this maritime terminal to improve planning and preparedness in case of an oil spill. The simulations could be enhanced with higher resolution databases.

Microstructure formation mechanism of catalyst layer and its effect on fuel cell performance: Effect of dispersion medium composition

The design of the catalyst layer (CL) offers a feasible way to realize the commercialization of proton exchange membrane fuel cells (PEMFCs). An in-depth understanding of catalyst inks is critical to achieving the optimal CL structure and cell performance. In this work, the effects of the solvent evaporation process during ink drying on the formation of the CL microstructure are particularly considered to reveal the structure–property correlations among the catalyst ink, drying process, CL microstructure and fuel cell performance. An increase in the alcohol content of the catalyst ink increases the amount of free ionomers while allowing the ionomer backbone to be more stretched in the dispersion medium. The higher alcohol content contributes to rapid solvent evaporation and thus inhibits the formation of coffee rings; as a result, a more developed ionomer network with a denser pore structure is obtained. Therefore, the alcohol-rich electrode exhibits better proton conduction capability, but higher oxygen transport resistance. For complex fuel cell operating conditions, a catalyst ink formulation with 50 wt% alcohol content is preferred due to its proper ionomer and pore size distribution, providing satisfactory fuel cell performance.

Polymorphism at hexadecanoic-acid crystals investigated through structural and vibrational studies

Hexadecanoic acid (HA) is a saturated fatty acid with wide industrial application due to its important chemical and physical properties. However, understanding of its polymorphic characteristics under a specific growth condition is still an open question. This paper shows HA crystals grown by the slow evaporation method with five different solvents. The polymorphism was evaluated by X-ray diffraction, Raman and Fourier-transform infrared (FT-IR) spectroscopy. Most of the crystals presented two main polymorphic phases, and the C polymorphic form common among samples appeared as a progressive increase with increasing solvent polarity. Nevertheless, solvents with slower evaporation allowed to obtain the Bm form as a minor phase. Furthermore, polar solvents with rapid evaporation allowed the growth of the Em form as a secondary phase. Vibrational analysis on the Raman- and IR-active bands indicated that almost all inter-molecular modes are more likely to gauche conformation than all-trans conformation. This behavior is due to changes in the hydrogen bonds (O−H.O) and, mainly, in the C-C bonds around the carboxylic group (COOH) that form the dimers between the pairs of molecules within the crystalline lattice.

Effect of Corn Stalk Biochar on the Evolution of Water Evaporation and Cracking of Soil

The evolution of water evaporation and cracking of soil affected by corn stalk biochar is experimentally investigated. Water evaporates from the soil surface, causing shrinkage in soil body and forming cracks, which significantly lead to crop nutrient loss, groundwater pollution, and land salinization. Biochar is a recyclable natural material widely used in improving the water retention and suppression of cracking of soils. Free desiccation tests were conducted with adding the biochar contents of 0%, 4%, and 8%. The variation of water evaporation amount and the development of cracking were recorded and disposed. The results show that the evaporation process can be changed due to the addition of biochar contents. The evaporation rate can be divided into three phases of a constant rapid evaporation phase, a fluctuated evaporation phase, and a residual evaporation phase. A sudden increase at around 30% of moisture content in evaporation rate indicated that the crack began to develop and extend greatly, which increased the evaporation surface area. The residual moisture contents of soils with biochar contents of 4% and 8% increased by 105.56% and 88.38% than those of soil without biochar, respectively. The crack ratio reduced by 32.39% and 15.31% with the addition of biochar contents of 4% and 8%, respectively. A three-level crack was observed during evaporation process, where a second and third crack developed less with the addition of biochars. The corn stalk biochar improves the integrity of soil bodies and increases the connection of soil particles for more water storing between the biochar particles and soil particles. It can be concluded that corn stalk biochars are able to delay the evaporation and cracking developing in cohesive soils, which may be beneficial for crops in dry area.

High‐Conductivity Crack‐Free 3D Electrical Interconnects Directly Printed on Soft PDMS Substrates

AbstractNanoparticle 3D printing and sintering is a promising method to achieve freeform interconnects on compliant substrates for applications such as soft robotics and wearable healthcare devices. However, previous strategies to sinter metallic nanoparticles while preserving the soft polymer substrate are rife with problems such as cracking and low conductivity of the metallic features. In this paper, the mechanisms of cracking in nanoparticle‐based 3D printed and sintered stretchable interconnects are identified and architecture and processing strategies are demonstrated to achieve crack‐free interconnects fully embedded in thin (<100 μm in thickness) stretchable polydimethylsiloxane (PDMS) with external connectivity. Capillary forces between nanoparticles developed through rapid solvent evaporation in the colloidal ink is hypothesized to initiate cracking during drying. Additionally, the presence of oxygen promotes the removal of organic surfactants and binders in the nanoparticle ink which increases nanoparticle agglomeration, grain growth, and subsequently conductivity. An experimental step‐wise variation of the thermal/atmospheric process conditions supports this hypothesis and shows that the presence of air during a low temperature drying step reduces the capillary stress to produce crack‐free interconnects with high conductivities (up to 56% of bulk metal) while having an excellent compatibility with the underlying polymer materials. Finally, stretchable interconnects fully‐encapsulated in PDMS polymer, with 3D pillar architectures for external connectivity are demonstrated, thus also solving an important “last‐mile” problem in the packaging of stretchable electronics.

3D numerical simulation of hot airflow in the human nasal cavity and trachea

Background and objectiveThe primary function of the human respiratory system is gas and moisture exchange, and conditioning inhaled air to prevent damage to the lungs and alveoli. In a fire incident, exposed soft tissues contract and the respiratory system may be severely damaged, possibly leading to respiratory failure and even respiratory arrest. The purpose of this study is to numerically simulate hot airflow in the human upper airway and trachea to investigate heat and moisture transfer and induced thermal injuries. MethodsFor analysis, the airflow is assumed to be laminar and steady, and simulations have been carried out at volume flow rates of 5 and 10 L/min, inlet temperatures of 70–240 °C, and relative humidity up to 40%. The mucous layer and surrounding tissues are incorporated into the conducting zone of the model. The blood perfusion is considered at different rates up to 5(Kg/m3.s) to regulate the temperature, and the vapor concentration is coupled with the energy equation. ResultsThe temperature and humidity distribution on the airway wall were calculated for all the studied conditions in order to find the mild and severe burn for different inhaled air temperatures. At the inlet temperatures of 70 and 100 °C, there are mild burns in several nasal cavity regions. At the higher temperatures of 160 and 200 °C, these areas suffer from severe burns and mild burns occur at the superior parts and nasopharynx. Rapid evaporation and tissue destruction will be observed if anyone breathes the 240 °C air. ConclusionsThe results show that the hot inlet temperatures drop below 44 °C when passing through the upper airway, and the lower airway was not affected. Increasing the inlet temperature from 70 to 240 °C extends the burns from mild to severe and the affected areas from the beginning of the nasal cavity to the pharynx.

Synchronously managed water and heat transportation for highly efficient interfacial solar desalination

Interfacial photothermal water evaporation technology has shown great potentials in the fields of water resource exploitation and solar energy utilization. The trade-off between rapid evaporation and salt accumulation has been continuously explored in recent years. Herein, a two-stage evaporator (TSE) that synchronously manages the water and heat transportation is introduced. The TSE is designed to improve the evaporation rate by harvesting the dissipated heat including the radiative and convective heat losses on the surface of the solar absorber together with the conductive heat loss to the insulator. The surface temperature of the upper solar absorber is lower than that of a conventional single-stage evaporator (SSE) with a thermal insulator because energy from the upper evaporation surface is partially transferred to the secondary evaporation surface. Importantly, the typical TSE configuration improves the evaporation rate of the traditional SSE from 1.39 to 1.57 kg m−2 h−1, which excludes the contribution of the ambient energy-assisted heating to evaporation. Importantly, by introducing a unilateral water supply channel, the TSE maintains a high evaporation flux of 1.48 kg m−2 h−1 in saline water with a concentration of up to 20% (w/w). The synchronous scheme of water and heat management provides an effective way to overcome the contradiction between rapid evaporation and salt accumulation.

High-performance Self-powered Perovskite Photodetector Based On Cesium Iodide Doped Spiro-OMeTAD Hole Transport Material

Hole transport materials play an essential role in the performance of perovskite detectors (PDs). Therefore, hole transport materials with excellent performance can significantly promote photoinduced holes' extraction rate and mobility. Spiro-OMeTAD, a small organic molecular material, has high solubility and excellent film-forming properties and is ideal for the hole transport layer (HTL) of photodetectors. In this work, a small amount of CsI is introduced into Spiro-OMeTAD together with Li-TFSI and TBP as additives. It is found that CsI and TBP formed a complex, which inhibited the agglomeration of Li-TFSI in Spiro-OMeTAD, thus preventing the rapid evaporation of TBP from leaving some cracks Spiro-OMeTAD. The photodetectors exhibit broadband response from near-ultraviolet to near-infrared (300–800 nm), achieving fast response (rise/fall time is 54.1/10.7 μs) and low dark current density (9.72 ×10−10 A cm−2). The detector can be self-powered at zero bias voltage, the external quantum efficiency (EQE) is 88%, the Responsivity (R) is 0.48 A W−1, and the detectivity (D*) is close to 2.7 × 1013 Jones. When the photovoltaic detector is placed in a nitrogen-filled glove box without special packaging for more than two months, the EQE remains 98.1% of the original. This study provides a simple method for fabricating a large area of high-performance planar PDs.

Fabrication and Optimization of CdSe Solar Cells for Possible Top Cell of Silicon‐Based Tandem Devices

AbstractSilicon‐based tandem solar cells are regarded as one of the most feasible ways to break the single‐junction Shockley–Queisser limit efficiency and further reduce the cost of solar electricity. Recently, wide‐bandgap (≈1.7 eV) perovskite solar cells have drawn intense research interest as the top cell for Si‐based tandem devices. Despite significant progress in device efficiency, the unsatisfactory stability of perovskites is still a huge concern. Besides halide perovskites, there are many inorganic semiconductors worthy of investigation. It is believed that cadmium selenide, a binary compound enjoying outstanding optoelectronic properties, high stability, and low cost, is very promising as the top cell for Si‐based tandem devices. Herein, the CdSe thin‐film solar cells that have been neglected for 3 decades are revisited. Using rapid thermal evaporation, high‐quality CdSe thin films with large grain size, high‐photoluminescence, small Stokes shift, and intrinsic n‐type conductivity are obtained. Furthermore, CdSe solar cells are redesigned and a champion efficiency of 6.00% is achieved. Through in‐depth analysis, it is identified that bulk and interface defects limit the open‐circuit voltage and hence device performance. This work highlights the great potential of CdSe solar cells as top cells for Si‐based tandem devices.

Coupling AFM, DSC and FT-IR towards Elucidation of Film-Forming Systems Transformation to Dermal Films: A Betamethasone Dipropionate Case Study.

Polymeric film-forming systems have emerged as an esthetically acceptable option for targeted, less frequent and controlled dermal drug delivery. However, their dynamic nature (rapid evaporation of solvents leading to the formation of thin films) presents a true characterization challenge. In this study, we tested a tiered characterization approach, leading to more efficient definition of the quality target product profiles of film-forming systems. After assessing a number of physico-chemico-mechanical properties, thermal, spectroscopic and microscopic techniques were introduced. Final confirmation of betamethasone dipropionate-loaded FFS biopharmaceutical properties was sought via an in vitro skin permeation study. A number of applied characterization methods showed complementarity. The sample based on a combination of hydrophobic Eudragit® RS PO and hydroxypropyl cellulose showed higher viscosity (47.17 ± 3.06 mPa·s) and film thickness, resulting in sustained skin permeation (permeation rate of 0.348 ± 0.157 ng/cm2 h), and even the pH of the sample with Eudragit® NE 30D, along with higher surface roughness and thermal analysis, implied its immediate delivery through the epidermal membrane. Therefore, this study revealed the utility of several methods able to refine the number of needed tests within the final product profile.

Milligram mass metrology for quantitative deposition of liquid samples

Quantitative dispensing of liquids by mass becomes increasingly difficult as sample volume decreases. Whereas ml quantities of liquid can be directly weighed as dispensed on an analytical balance or using pycnometer methods, μl samples are more challenging due to their milligram-scale mass and rapid evaporation. Here, a method for quantitative determination of the mass of μl liquid droplets is proposed. The weighing of a microcapillary pycnometer combined with traceable calibration masses and corrections for sample evaporation allows determination of the droplet mass on the order of 1 mg with relative combined expanded uncertainty of 0.3%.

Experimental Investigation on Spray Evaporation and Dispersion Characteristics of Impinged Biodiesel-Butanol Blends

Abstract The objective of the investigation is to explore the spray evaporation and dispersion characteristics of impinged biodiesel-butanol blends at various n-butanol ratios (0, 10%, 30%, 50%) and ambient conditions. A total of 180 experimental cases were performed in a constant-volume combustion chamber. The liquid- and vapor-phase sprays were captured by backlight imaging technique and Schlieren imaging technique, respectively. Several macroscopic parameters were measured and discussed, including impinged spray structure, width, height, and area. Some novel parameters are derived to analyze spray evaporation and dispersion. Results show that biodiesel blended with 30% n-butanol transits better from liquid-phase to vapor-phase compared with other blends, displaying rapid liquid-phase evaporation an steady vapor-phase dispersion. After wall impingement, an increase in the ambient pressure or temperature hinders the liquid-phase dispersion in the vertical direction significantly, leading to a rapid decrease in the height of the impinged spray. The vapor-phase diffusion rate in the horizontal direction is about four times the rate in the vertical direction, and the rate ratio is slightly affected by ambient conditions and injection pressure. Compared with the free jet, the impinged spray is not beneficial for liquid-phase evaporation and vapor-phase dispersion, presenting larger liquid-phase area and smaller vapor-phase area. However, impinged biodiesel blended with 30% n-butanol displays better spray evaporation and dispersion.

Grotthuss Molecular Dynamics Simulations for Modeling Proton Hopping in Electrosprayed Water Droplets.

Excess protons in water exhibit unique transport properties because they can rapidly hop along H-bonded water wires. Considerable progress has been made in unraveling this Grotthuss diffusion mechanism using quantum mechanical-based computational techniques. Unfortunately, high computational cost tends to restrict those techniques to small systems and short times. Molecular dynamics (MD) simulations can be applied to much larger systems and longer time windows. However, standard MD methods do not permit the dissociation/formation of covalent bonds, such that Grotthuss diffusion cannot be captured. Here, we bridge this gap by combining atomistic MD simulations (using Gromacs and TIP4P/2005 water) with proton hopping. Excess protons are modeled as hydronium ions that undergo H3O+ + H2O → H2O + H3O+ transitions. In accordance with ab initio MD data, these Grotthuss hopping events are executed in "bursts" with quasi-instantaneous hopping across one or more waters. The bursts are separated by regular MD periods during which H3O+ ions undergo Brownian diffusion. The resulting proton diffusion coefficient agrees with the literature value. We apply this Grotthuss MD technique to highly charged water droplets that are in a size regime encountered during electrospray ionization (5 nm radius, ∼17,000 H2O). The droplets undergo rapid solvent evaporation and occasional H3O+ ejection, keeping them at ca. 81% of the Rayleigh limit. The simulated behavior is consistent with phase Doppler anemometry data. The Grotthuss MD technique developed here should be useful for modeling the behavior of various proton-containing systems that are too large for high-level computational approaches. In particular, we envision future applications related to electrospray processes, where earlier simulations used metal cations while in reality excess protons dominate.

Tubular polypyrrole enhanced elastomeric biomass foam as a portable interfacial evaporator for efficient self-desalination

Three-dimensional (3D) materials that capture sunlight for desalination provide one promising solution to acquiring freshwater resources, but salt deposition and mechanical stability provide additional hurdles for continuous operation. Herein, this study presents a sustainable and elastic biomass evaporator (EC-PPy-MO) with the hierarchical micro-nano water transport channel and air cavities formed by hydrophilic tubular polypyrrole seamlessly integrated onto the external surface of biomass foam. The EC-PPy-MO foam exhibits high light absorption ability (∼91%) over a broad wavelength due to the waveguide effect of the polypyrrole with a slender tubular morphology and the hierarchical micro-nano structure in the biomass matrix. The EC-PPy-MO foam helps stabilize a thin water film to provide an efficient evaporative interface surface and ensure effective thermal insulation. As a result, the EC-PPy-MO foam evaporator parallel to the horizontal plane demonstrates a rapid evaporation rate of about 1.8 kg m-2h−1 under 1 sun irradiation. In parallel, the evaporator can maintain efficient evaporation without salt fouling in a solution with 7% NaCl salinity, while largely salt fouling appears when higher than 15% brine. However, EC-PPy-MO with melamine foam support floating in 25 wt% brine can be evaporated for 72 h without significant salt fouling accumulation, up to ∼ 2.8 kg m-2h−1. This is attributed to the fact that the exposed sides of the 3D EC-PPy-MO foam can eliminate the boundary Marangoni phenomenon resulting in the appearance of no significant salt fouling, while the exposed cold evaporation surface enhances the evaporation rate of the EC-PPy-MO foam. More importantly, EC-PPy-MO foam exhibits excellent mechanical stability, chemical stability, and elasticity, as well as remarkable water purification ability.

Tunable Solid-State Thermochromism: Alkyl Chain Length-Dependent Conformational Isomerization of Bianthrones.

The introduction of linear alkoxy chains into bianthrone promoted the aggregation of the minor twisted conformer and made it compete with the major folded conformer in the solid-state. Rapid evaporation approach to the methoxy- and n-butoxy-substituted derivatives provided powder mixtures of folded and twisted conformers as metastable solids. Upon heating the powders, different lengths of alkyl chains converged to different conformers via solid-state isomerization reaction with an apparent color change. Monitoring by FT-IR spectroscopy and powder XRD ensured that these isomerization reactions involve only conformational isomerization without pyrolysis. In addition, single crystal X-ray structure analysis revealed that twisted conformers with longer alkyl chains are stabilized in the solid-state by the synergistic effect of their inter-chain hydrophobic interactions and π-π stacking interactions.