Thin Film Evaporation Research Articles

Capillary transfer: Numerical study of how topology affects the fluid flow rate into a planar microstructure with pseudopotential multiphase Lattice-Boltzmann method

We investigate how topology impacts capillary action with the hope of aiding future thermal engineering decisions. Heat pipes and their two-dimensional variant, vapor chambers are essential components in electronics cooling. With thin-film evaporation as the driving force for such high-heat-flux movers, studies have been done to optimize the thermal performance of different designs. However, the fundamental problem of liquid transportation needs to be addressed exclusively: evaporation can only work as long as the new liquid is continuously being replaced. The device achieves this by the capillary process (or wicking) through the thermal ground (or wicks): a configuration of microstructures attached to the device's walls. Some planar topologies of the structure allow for consistent but slower mass feeding; others offer higher bandwidth but with local flow hindrance, creating a pulsating tendency; certain conditions would even block the capillary flow. Surveying the capillary performance of different two-dimensional designs of the thermal ground, we encounter a topological factor that correlates with this mass transfer rate. We incorporate in the factor the wick's width, its height, and the gap between one microstructure to another. An energy model is studied to explain the underlying influence of the structure topology, while Lattice-Boltzmann method is used to evaluate the capillary dynamics inside the thermal ground. With ultra-thin applications in mind, the paper looks at the length scales of micrometers with a wick height of 50 μm. Overall, we find that tightly packed structures pull the most liquid in the same amount of time; however, we find that two core constraints need to be met: sufficient clearance between structures and freedom of mobility.

A molecular dynamics investigation on the effects of electrostatic forces on nanoscale thin film evaporation

Thin-film evaporation is relevant for electronics cooling, water desalination, and some energy conversion processes, and the overall performance of such applications relies on the adequate understanding of heating-induced phase-change mechanisms. Given the importance of polar compounds, such as alumina, for nanoporous membranes in water desalination, the effects of electrostatic forces on thin-film evaporation were investigated in this paper by means of molecular dynamics simulations. The influence of the electrostatic interactions was assessed by modelling the alumina-water interactions using two approaches: i) accounting for electrostatic and dispersive van der Waals (vdWs) forces between the solid and liquid atoms (LJ+Coulombic model), and ii) considering only dispersive vdWs interactions (LJ model). Additionally, a theoretical model based on the Schrage relationships was developed to compare theory and simulations. The results showed considerable differences in the evaporation rates obtained from the two interfacial models. For the LJ+Coulombic model, the liquid films were 40% thicker, and the maximum evaporation mass flux was lower than the LJ model by a factor of two. The theoretical Schrage relationships deviated from the simulation evaporation fluxes with errors of 2.2-18.1% and 24.0-57.9% for the LJ+Coulombic and LJ models, respectively. These observations suggest that the partial charges in the solid affect the evaporation behavior of water if the films are ∼5 nm or thinner. Moreover, the significant deviations in the evaporation behavior demonstrated the importance of a robust interfacial modelling approach to investigate thin-film evaporation in polar interfaces.

A novel model of liquid film flow and evaporation for thermal protection to a chamber with high temperature and high shear force

Thin liquid film evaporation is a prevailing cooling technique for thermal protection to the inner wall of a chamber with high-intensity combustion. A novel model is developed to investigate the flow and evaporation of liquid film in a rocket combustion chamber with high temperature and high shear force, in which shear stress at the interface between liquid film and high temperature combustion gas with high velocity, capillary pressure of liquid and disjoining pressure associated with liquid film evaporation are taken into account. A numerical algorithm of the backward solution is deliberately adopted to solve this model so as to eliminate the entrance effect caused by different inlet conditions of liquid film. For given temperature and hot gas rate in a chamber, a stably evolution regime of liquid film with the thickness from thick to thin is depicted corresponding to the total process of being sheared into film and being evaporated to dryness. Results indicate that the three forces mentioned above play critical parts in flowing and evaporating of liquid film during its different evolution regimes. It was shown that shear stress and capillary pressure have a positive effect on the flow and evaporation of film, as well as a negative effect from the disjoining pressure. The effects of these forces are different dependent on different initial average thickness of film, and the distribution profile of these forces are totally illustrated in detailed. The prediction of liquid film length, from being injected to being evaporated, by the proposed model is in a good agreement with available experimental data. All findings are expected to provide a fundamental guideline for the design and optimization of efficient thermal protect to the combustion chamber of space engine.

Effect of double cross sectional ratio on performance characteristics of pulsating heat pipes

Effect of double cross sectional ratio on performance characteristics of pulsating heat pipes is experimentally investigated. The cross sectional ratios in the evaporator and condenser sides are different from each other, and this novel gradually constricted geometry provides to boost flow circulation and to maintain a stable performance regardless of orientation. Tests are performed for different values of inclination angle (0°, 30°, 60° and 90°) and filling ratio (20, 40 and 60%). Also, results of originally structured closed loop flat plate pulsating heat pipe (novel design, ND) are compared with those of the conventional pulsating one with uniform cross section (conventional design, CD). Measurements are supported by high speed flow visualization. It is shown that the ND shows better thermal performance than the CD, and when appropriate filling ratio (40%) is provided, the ND presents orientation-independent running. A turn of the ND is divided into three different zones, and a pressure-balance equation is presented following a detailed flow analysis. Rapid bubble growth instability and annular flow pattern characterized by thin film evaporation are two important characteristics observed for the ND.

A Co-Processed API Approach for a Shear Sensitive Compound Affording Improved Chemical Stability and Streamlined Drug Product Processing.

The physical properties of active pharmaceutical ingredients (API) are critical to both drug substance (DS) isolation and drying operations, as well as streamlined drug product (DP) processing and the quality of final dosage units. High aspect ratio, low bulk density, API 'needles' in particular are a hindrance to efficient processing, with a low probability that conventional crystallization routes can modify the challenging morphology. The compound evaluated in this manuscript demonstrated this non-ideal morphology, with the added complexity of shear sensitivity. Modest shear exposure resulted in conversion of the thermodynamically stable crystalline phase to the amorphous phase, with the amorphous phase then undergoing accelerated chemical degradation. Slow filtration during DS isolation resulted in uncontrolled and elevated amorphous levels, while subsequent DP operations including blending, densification and compression increased amorphous content still further. A chemically stable final dosage unit would ideally involve a high bulk density, free flowing API that did not require densification in order to be commercialized as an oral dosage form with direct encapsulation of a single dosage unit. Despite every effort to modify the crystallization process, the physical properties of the API could not be improved. Here, an innovative isolation strategy using a thin film evaporation (TFE) process in the presence of a water soluble polymer alleviated filtration and drying risks and consistently achieved a high bulk density, free flowing co-processed API amenable to direct encapsulation. Characterization of the engineered materials suggested the lower amorphous levels and reduced shear sensitivity were achieved by coating surfaces of the API at relatively low polymer loads. This particle engineering route blurred conventional DS/DP boundaries that not only achieved improved chemical stability but also resulted in a optimized material, with simplified and more robust processing operations for both drug substance and drug product.

Experimental analysis of high temperature flow boiling heat transfer and pressure drop in a plate heat exchanger

• High temperature flow boiling of seven working fluids is experimentally analyzed. • Two heat transfer mechanisms are identified among different working fluids. • A superposition model is developed for the heat transfer coefficient prediction. • The heat transfer coefficient of propane is up to 152% higher than that of R236fa. • Isobutane has the lowest frictional pressure drop among the seven working fluids. Organic Rankine cycle technology has gained worldwide acceptance as an efficient way to utilize low-grade heat sources. Plate heat exchangers are the most common type of heat exchanger employed as evaporators in small-scale organic Rankine cycle units, in which a high saturation temperature is the prevailing working condition. However, there is a lack of research on high temperature flow boiling in plate heat exchangers. This paper presents an experimental analysis on flow boiling heat transfer and pressure drop characteristics in a plate heat exchanger, and the development of prediction methods for the heat transfer coefficient and frictional pressure drop. Seven working fluids, R134a, R236fa, R245fa, R1234ze(E), R1233zd(E), propane and isobutane, were tested at the reduced pressures of 0.45, 0.55 and 0.65, corresponding to saturation temperatures ranging from 55 °C to 141 °C, and various mass fluxes. Two heat transfer mechanisms, nucleate boiling and thin-film evaporation, were identified in the heat transfer processes of the different working fluids, due to the diversity in their thermo-physical properties. Moreover, the results indicate that propane and isobutane have higher heat transfer coefficients than the other working fluids, while R236fa has the lowest heat transfer coefficient. The frictional pressure drops show the same characteristics for all the working fluids, increasing with the increase of the vapor quality and mass flux and the decrease of the saturation temperature. A superposition model presented in the paper achieves a good prediction for the heat transfer data, with a 12.8% mean absolute percentage deviation. A correlation developed in a previous work by the authors enables a prediction with an 11.1% mean absolute percentage deviation for the pressure drop data. The prediction methods presented in the paper will facilitate the modelling and design of plate heat exchanger evaporators in organic Rankine cycle units.

Material-dependent submicrometer particle trapping in capacitively-coupled plasma sheaths in an intermediate collision regime

Understanding submicrometer particle behavior in non-thermal capacitively coupled plasmas (CCPs) is important in the application of CCP reactors in thin-film vapor deposition; nucleated and resuspended particles can deposit on thin films, forming defects. Prior studies of supermicrometer particle behavior in CCP reactors have revealed that particles are trapped in the pre-sheath or sheath regions near electrodes, but have examined in detail neither the trapping of submicrometer particles, nor the influence of particle material properties on trapping. Using laser light scattering (LLS), we examined trapping of submicrometer metal oxide particles (radii in the 211 nm–565?nm range) of 6 distinct material compositions in the pre-sheath/sheath region of a CCP reactor operated at pressures in the 0.5–2.0 Torr range. We specifically focus on trapping near the upper electrode of a horizontally-oriented reactor. In this instance, trapping is brought about by a balance between electrostatic forces and gravitational forces driving particles away from the electrode, with ion drag forces driving particles toward the electrode. LLS measurements reveal that submicrometer particles are trapped near the upper electrode for all particle sizes, types, and operating pressures, with the trapping location at an increased distance away from the electrode with decreased CCP reactor pressure. Interestingly, we find the trapping location shifts slightly farther from the top electrode with increasing material dielectric constant. This suggests that the ion drag force is influenced by particle material properties, though in an unclarified manner. Measured trapping locations are also compared to model predictions where particle charge levels and the ion drag force are calculated using expressions based on ion trajectory calculations in a plasma sheath accounting for ion–neutral collisions. Predicted ion densities required for trapping are a factor of 6–16 higher than calculated at the observed particle trapping locations when applying a dissipative ion–particle encounter model, with more substantial disagreement found when considering a non-dissipative encounter model. In total, our results confirm that submicrometer particle trapping occurs at the upper electrode of CCP reactors, which must be facilitated by a balance largely between electrostatic and gravitational forces opposed by ion drag forces, but suggest future studies will be required to understand how particle material properties affect forces on particles on the plasma volume boundary, and how the ion drag force is sufficiently high to facilitate trapping.

Direct fabrication and characterization of gold nanohole arrays.

We demonstrate a one-step fabrication method to realize desired gold (Au) nanoholes arrays by using a one-photon absorption based direct laser writing technique. Thanks to the optically induced thermal effect of Au material at 532 nm excitation wavelength, the local temperature at the laser focus area can reach as high as 600°C, which induces an evaporation of the Au thin film resulting in a metallic nanohole. By controlling the laser spot movement and exposure time, different two-dimensional Au nanoholes structures with periodicity as small as 500 nm have been demonstrated. This allows obtaining plasmonic nanostructures in a single step without needing the preparation of polymeric template and lift-off process. By this direct fabrication technique, the nanoholes do not have circular shape as the laser focusing spot, due to the non-uniform heat transfer in a no-perfect flat Au film. However, the FDTD simulation results and the experimental measurement of the transmission spectra show that the properties of fabricated plasmonic nanoholes arrays are very close to those of ideal plasmonic nanostructures. Actually, the plasmonic resonance depends strongly on the periodicity of the metallic structures while the heterogeneous form of the holes simply enlarges the resonant peak. Furthermore, it is theoretically demonstrated that the non-perfect circular shape of the Au hole allows amplifying the electromagnetic field of the resonant peak by several times as compared to the case of perfect circular shape. This could be an advantage for application of this fabricated structure in laser and nonlinear optics domains.

Theoretical Analysis of Thin Film Evaporation in the Wicks of Loop Heat Pipes

Abstract In this paper, a thin film evaporation model that includes expressions for energy, mass, and momentum conservation was established through the augmented Young–Laplace model. Based on this model, the effects of pore size and superheating on heat transfer during thin film evaporation were analyzed. The influence of the wick diameter of the loop heat pipe (LHP) on the critical heat flux of the evaporator is analyzed theoretically. The results show that pore size and superheating mainly influence evaporation through changes in the length of the transition film and intrinsic meniscus. The contribution of the transition film area is mainly reflected in the heat transfer coefficient, and the contribution of the intrinsic meniscus area is mainly apparent in the quantity of heat that is transferred. When an LHP evaporator is operating in a state of surface evaporation, a higher heat transfer coefficient can be achieved using a smaller pore size.

Molecular dynamics simulations of thin-film evaporation: The influence of interfacial thermal resistance on a graphene-coated heated silicon substrate

Two-phase liquid cooling on nanoengineered surfaces has shown great promise for tackling overheating in high performance microelectronics. At the nanoscale, phase change heat transfer can be affected substantially by the thermal resistance at the solid–liquid interface (also known as the Kapitza resistance). For example, surface modification by nanocoatings has been shown to efficiently enhance boiling heat transfer. However, there have been few studies on the effect of the Kapitza resistance on thin-film evaporative heat transfer. Here, the transport behavior of a liquid argon nanofilm evaporating on silicon (100) surfaces coated with different layers of graphene is analyzed using non-equilibrium molecular dynamics (MD) simulations. The results show that increasing layers of graphene coatings lead to a 136% increase in the Kapitza resistance and a 62% reduction in the evaporation rate. The large increase in Kapitza resistance is attributed to the strong repellence between graphene and argon molecules, manifested by a higher contact angle. These findings demonstrate the dominant role of interfacial thermal transport in the evaporation behavior of thin liquid films, and provide guidelines for selecting new materials when designing nanoengineered surfaces to realize improved evaporative cooling performance. • MD simulations of evaporation of liquid Ar on Si coated with graphene. • Influence of surface wettability on Kapitza resistance and evaporation. • Strong correlation between evaporative heat transfer and intermolecular interaction at solid–liquid interface.

Air side-stream ammonia stripping in a thin film evaporator coupled to high-solid anaerobic digestion of sewage sludge: Process performance and interactions

Air side-stream ammonia stripping in a thin-film evaporator (TFE) is proposed for the first time to control total ammonia nitrogen (TAN) concentration in a centralized full-scale plant performing high-solid anaerobic digestion (HSAD) of sewage sludge (SS). In this process, anaerobically digesting sludge (ADS) is continuously recirculated from the digester to the TFE unit where ammonia is stripped by an air stream. The stripped ammonia reacts with sulfuric acid in an absorption unit to produce ammonium sulfate. Overall, HSAD coupled to air side-stream ammonia stripping results in a twofold production of fertilizers (i.e. ammonium sulfate and SS digestate) recycling nutrients from organic wastes in agreement with the principles of circular economy. This study evaluates the influence of different operational airflow rates, temperatures and CO2 concentrations on air side-stream ammonia stripping in the TFE without alkali addition and the impact of air-based ammonia stripping on HSAD performance at full-scale. The study also investigates the chemistry and the interaction between the ammonia and carbonate subsystems of ADS and clarifies the stoichiometric relationship between ammonia and CO2 stripping.

Formulation of Piperine-Chitosan-Coated Liposomes: Characterization and In Vitro Cytotoxic Evaluation.

The present research work is designed to prepare and evaluate piperine liposomes and piperine–chitosan-coated liposomes for oral delivery. Piperine (PPN) is a water-insoluble bioactive compound used for different diseases. The prepared formulations were evaluated for physicochemical study, mucoadhesive study, permeation study and in vitro cytotoxic study using the MCF7 breast cancer cell line. Piperine-loaded liposomes (PLF) were prepared by the thin-film evaporation method. The selected liposomes were coated with chitosan (PLFC) by electrostatic deposition to enhance the mucoadhesive property and in vitro therapeutic efficacy. Based on the findings of the study, the prepared PPN liposomes (PLF3) and chitosan coated PPN liposomes (PLF3C1) showed a nanometric size range of 165.7 ± 7.4 to 243.4 ± 7.5, a narrow polydispersity index (>0.3) and zeta potential (−7.1 to 29.8 mV). The average encapsulation efficiency was found to be between 60 and 80% for all prepared formulations. The drug release and permeation study profile showed biphasic release behavior and enhanced PPN permeation. The in vitro antioxidant study results showed a comparable antioxidant activity with pure PPN. The anticancer study depicted that the cell viability assay of tested PLF3C2 has significantly (p < 0.001)) reduced the IC50 when compared with pure PPN. The study revealed that oral chitosan-coated liposomes are a promising delivery system for the PPN and can increase the therapeutic efficacy against the breast cancer cell line.

Performance evaluation of evaporation from micropillar arrays with different pillar topologies

This paper reports the results of our studies on the performance of thin film evaporation, mostly used in the evaporator of an ultra-thin vapor chamber using micropillar arrays. The dry-out heat flux and evaporator surface temperature have been used as the performance metrics. A numerical model has been formulated to solve for the fluid flow and phase change heat transfer considering the capillary pumping action (wicking action) using a cell-by-cell forward approach and validated with results reported in the literature. The solutions of the model equation are then utilized to study the effects of geometry and arrangement of the micropillars within the vapor chamber and to gain further insights into the interplay of the various forces. It is seen that these variations strongly influence the pumping action as well as the shape of the liquid vapor interface thereby impacting the pressure field, flow rate and the dry-out heat flux. A conical shape of the micropillar (having the same volume as that of other shapes) has a significant impact on the dry-out heat flux e.g., reducing the top diameter from 10 to 8 μm results in an 18% reduction. For a rectangular arrangement of the micropillars, the performance is quite sensitive to the transverse and axial spacing. In the range of 30–40 μm of axial and transverse spacing, the dry out heat flux can be altered by as much as 20%. Higher transverse pitch with lower axial pitch is found to be a better combination for a given overall geometry and number of pillars.

Review article: Microscale evaporative cooling technologies for high heat flux microelectronics devices: Background and recent advances

Evaporation of liquid is important in a diverse range of engineering applications, such as ink-jet printing, pesticide spraying, micro- and nanofabrication, thin-film coatings, biochemical assays, deposition of DNA/RNA microarrays, the manufacture of novel optical and electronic materials, and cooling microelectronics and power electronic devices. In particular, evaporation at the microscale has attracted increasing interest as an effective cooling strategy for overcoming the thermal challenges in high heat flux microelectronics devices. A large number of studies have demonstrated the prospect of evaporative heat transfer methods to tackle die-level hotspots reaching 1 kW/cm2 on each high-power tier in a 3D microelectronics device. Furthermore, evaporation at the microscale (thin-film evaporation) can achieve higher heat removal than evaporation at macroscale. However, evaporation is a complicated process involving several physical transport phenomena, and their dominance can vary with variations in device dimensions and other system parameters. This article reviews the literature on the factors affecting microscale evaporation, which include the properties and temperature of the solid substrate, vapor transport in the gas domain, microconvection, and engineered surface features. Techniques to enhance evaporative heat transfer are highlighted. Extending the contact line region effectively enhances evaporative heat transfer, and this technique is employed in surface coatings or micro- and nanostructures, wicking structures, and micro- and nanoporous membranes. The evaporation rate can also be enhanced by manipulating the meniscus shape to provide an energy barrier at sharp edges of micro- and nanostructures. This review also summarizes the theoretical models for estimating evaporation rates, then discusses the physical transport processes associated with evaporation and their corresponding thermal resistances. Because non-invasive, high resolution temperature measurement and visualization are critical for implementing evaporative cooling in high heat flux applications, state-of-art techniques are also discussed. Laser-induced fluorescence techniques are judged the most advanced for temperature measurement, and particle image velocimetry (PIV) is the most advanced means of flow field visualization. This review identifies the most promising evaporative cooling techniques for next generation of ultra-high heat flux microelectronics applications. It also compares the performance of these cooling technologies in a regime plot, providing useful information for designing effective cooling solutions. We end by summarizing the current challenges and discussing the outlook for evaporative cooling technologies, then consider future research needs.

Исследование тепловых свойств изотермических плит при спекании капиллярного сердечника

This paper mainly introduces the sintering process of the monolithic capillary wick and analyzes the influence of different copper powder particle size, filling rate, copper powder shape and heat source size on the heat transfer performance of the isothermal plate. The experimental results show that: (1) For the isothermal plate sintered with spherical copper powder, the capillary force of large particle size copper powder is small, but the flow resistance is also small, and the performance of the isothermal plate sintered with large particle size copper powder is better. (2) In the case of low filling rate, the isothermal plate is dried due to insufficient return fluid. In the case of high filling rate, on the one hand, the thickness of the liquid film at the evaporation end of the isothermal plate is large, resulting in additional thermal resistance. On the other hand, the thin film evaporation mode will be transformed into pool boiling mode, which will reduce the heat transfer performance. (3) Spherical copper powder sintered plate with regular shape has the best performance, while dendritic copper powder sintered plate has relatively high thermal resistance. (4) The heat source area has a great influence on the thermal resistance of the plate. Under the same heating power, the thermal resistance of the small area heat source is much higher than that of the large area heat source; The thermal resistance of sintered copper plate is lower than that of pure copper plate under two heat source areas.

Experimental study on the interfacial heat transfer of sessile droplet evaporation using temperature-sensitive paint

The present work is aimed at analyzing changes in the interfacial temperature distribution and interfacial heat flux distribution during sessile droplet evaporation. In particular, two kinds of nonintrusive measurement techniques, temperature-sensitive paint (TSP) and infrared imaging were used simultaneously. TSP was used to capture the interfacial temperature distribution, and then a one-dimensional unsteady transient model was established to obtain the heat flux distribution. An infrared camera was applied to observe the thermal patterns during droplet evaporation from the top view. Three kinds of liquids, pentane, HFE-7100 and hexane, were used during our experiments, and the experimental results show that the contact line profile captured by TSP was consistent with that captured by an infrared camera. Three stages could be observed during droplet evaporation: initial droplet heating, convection cell evaporation and thin film evaporation. Convection cells could be observed in the infrared images during the second stage, and an obvious temperature gradient at the contact surface could also be seen from the images captured by TSP. In addition, the heat flux at the contact line was higher than that at the centre. Finally, the heat dissipation due to droplet evaporation could also be obtained by double integration of interfacial heat flux data with contact area and evaporation time, which further demonstrated the soundness of the present experimental and calculated methods.

Enhanced flow boiling of HFE-7100 in picosecond laser fabricated copper microchannel heat sink

The enhanced flow boiling heat transfer of HFE-7100 in wavy copper microchannel heat sink was experimentally studied, which was fabricated with the picosecond laser technique. The micro porous structures were naturally formed on the sidewall and bottom of microchannel during the laser fabrication process, which increase the wall surface roughness. In single-phase flow region, the evaluation of performance evaluation criteria (PEC) proves the heat transfer enhancement overcomes the pressure-drop penalty in present wavy microchannel. In two-phase flow region, the flow patterns including bubbly flow, slug flow and annular flow were captured with the visualization technique, three heat transfer modes including heat convection, nucleate boiling and thin film evaporation were analyzed in detail. In wavy microchannel, the nucleate bubble on concave channel sidewall has a different apparent shape with a larger growth rate compared to that on convex one. In the thin film evaporation stage, the thickness of liquid film varies and it depends on the difference in curvatures between bubbles and sinusoidal channel sidewall. Compared to the straight channel, an increase of 28.89% for CHF can be achieved in wavy one, and the heat transfer coefficient enhancements of 60.76% and 52.71% are obtained in wavy one at the nucleate boiling stage and thin film evaporation stage, respectively.

Designing antiviral surfaces to suppress the spread of COVID-19.

Surface engineering is an emerging technology to design antiviral surfaces, especially in the wake of COVID-19 pandemic. However, there is yet no general understanding of the rules and optimized conditions governing the virucidal properties of engineered surfaces. The understanding is crucial for designing antiviral surfaces. Previous studies reported that the drying time of a residual thin-film after the evaporation of a bulk respiratory droplet on a smooth surface correlates with the coronavirus survival time. Recently, we [Chatterjee et al., Phys. Fluids. 33, 021701 (2021)] showed that the evaporation is much faster on porous than impermeable surfaces, making the porous surfaces lesser susceptible to virus survival. The faster evaporation on porous surfaces was attributed to an enhanced disjoining pressure within the thin-film due the presence of horizontally oriented fibers and void spaces. Motivated by this, we explore herein the disjoining pressure-driven thin-film evaporation mechanism and thereby the virucidal properties of engineered surfaces with varied wettability and texture. A generic model is developed which agrees qualitatively well with the previous virus titer measurements on nanostructured surfaces. Thereafter, we design model surfaces and report the optimized conditions for roughness and wettability to achieve the most prominent virucidal effect. We have deciphered that the optimized thin-film lifetime can be gained by tailoring wettability and roughness, irrespective of the nature of texture geometry. The present study expands the applicability of the process and demonstrates ways to design antiviral surfaces, thereby aiding to mitigate the spread of COVID-19.

Heat dissipation performance of grooved-type and copper foam-type vapor chambers

Both grooved-type and copper foam-type vapor chambers are explored and investigated. The overall performance of vapor chamber depends on both axial and spread thermal resistance mutually. The copper foam-type vapor chambers achieved the lowest axial thermal resistance less than 0.2 K/W. The grooved-type sample presented the lowest spread thermal resistance, indicating better temperature uniformity. The visual experiment demonstrated that the evaporating surface of the copper-foam vapor chamber was dominated by the thin film evaporation mechanism at low charging ratio while dominated by the pulsed pool boiling mechanism at large charging ratio. For the grooved-type vapor chamber, the pool boiling mode was observed at any charging ratio.

Formulation of chitosan coated nanoliposomes for the oral delivery of colistin sulfate: in vitro characterization, 99mTc-radiolabeling and in vivo biodistribution studies

Colistin sulfate is a very important antibiotic for the treatment of multidrug-resistant Gram-negative infections. Unfortunately, it has low oral bioavailability and several side effects following parenteral administration. The present study aims to develop chitosan-coated colistin nanoliposomes to improve the stability in the gastrointestinal tract and to enhance the oral delivery of colistin. The chitosan-coated colistin nanoliposomes were obtained via thin-film evaporation and electrostatic deposition methods using either Span 60, Tween 65 or Tween 80 as surfactants with different cholesterol: surfactant: soya lecithin ratios. The influence of systems variables was further characterized by vesicle size analysis, zeta potential (ZP), poly dispersibility index (PDI), and also their entrapment efficiency percentage (EE %) was evaluated. Various systems were formed with vesicle sizes in the nano-range, 155.64 ± 12.53 nm to 315.64 ± 15.90 nm, and EE % of 45.2 ± 2.9% to 81.8 ± 2.9%. Moreover, the ZP value of the prepared nanoliposomes switched from a negative to a positive value after chitosan coating. To track the released colistin in vivo, technetium 99m (99mTc) was incorporated into the optimum system (S-3) system via direct coupling with colistin. Chitosan-coated 99mTc-colistin nanoliposome, 99mTc-colistin suspension, and 99mTc-chitosan-coated nanoliposomes (placebo) were administered orally into bacterial infection (Escherichia coli) bearing mice. The biodistribution results showed that chitosan-coated nanoliposome significantly enhanced the bioavailability of colistin compared to colistin suspension (the commercially available). Moreover, the system effectively improved the localization of colistin at the infected muscle. In conclusion, this approach offers a promising tool for enhanced oral delivery of colistin.