Film Temperature Research Articles

Experimental and Simulation Study on Reducing the Liquid Film and Improving the Performance of a Carbon-Neutral Methanol Engine

Methanol is a potential carbon-neutral fuel. It has a high latent heat of vaporization, making it difficult to achieve evaporation and mixing, and it is prone to forming a liquid film, which in turn affects engine performance. To reduce the liquid film and improve engine performance, this work investigates the influence mechanism of injection strategies on the generation of liquid films in the intake port and cylinder of an inline 6-cylinder port fuel injection (PFI) spark-ignition (SI) methanol engine and further explores the optimization scheme for improving engine performance. The results show that the end of injection (EOI) influences the methanol evaporation rate and the methanol–air mixing process, thereby determining the liquid film deposition, mixture distribution, and temperature distribution in the cylinder. As the EOI advances, the higher methanol evaporation rate during the intake process reduces the amount of methanol droplets and the deposition of a liquid film in the cylinder. The in-cylinder temperature is relatively high, while the mixture inhomogeneity slightly increases. As the EOI increases from 170 °CA to 360 °CA, the higher in-cylinder temperature and properly stratified mixture accelerate the early and middle stages of combustion, shorten the ignition delay, advance the center of combustion, and improve the brake thermal efficiency (BTE). However, further advancing the EOI results in the BTE remaining basically unchanged. Optimized injection timing can enhance the BTE by 1.4% to 2.4% under various load conditions. The increase in the EOI contributes to the reduction of HC emissions due to the weakening of the crevice effect with lower masses of methanol droplets and liquid film in the cylinder, while the increase in mixture inhomogeneity leads to an increase in CO emissions. In general, controlling the EOI at around 360 °CA can maintain relatively low CO emissions under various load conditions, while significantly reducing HC emissions by 71.2–76.4% and improving the BTE.

Investigation on the influence of rotational speed on oil film stability of hydrostatic rotary table

Purpose The purpose of this study is to investigate the influence of rotational speed on the oil film stability of the hydrostatic rotary table having double rectangular oil pads. The oil film stability is evaluated based on the oil film stiffness under constant load condition and the displacement response amplitude of the oil film under disturbance load condition. Design/methodology/approach The oil film stability theoretical equations of the double rectangular oil cavity are deduced such as oil film stiffness, damping and dynamic equations. A simulation model is developed to analyze the relationship among oil film temperature, oil film pressure fields and oil film stability. The user-defined function programs are used to control the rotational speed, lubricant viscosity and oil film thickness during the simulation. In addition, an experimental rig is built to test the simulation results. Findings This study shows that oil film stability decreases with increasing rotational speed under constant load and disturbance load. The trend of oil film stability decreased slowly within 30 r/min, and then rapidly. However, since the hydrodynamic pressure effect, the decrease rate of stability is mitigated under constant load and high rotational speeds. Originality/value The conclusions can provide a theoretical basis for improving the oil film stability of machines with similar hydrostatic support structure. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2024-0267/

Thickness Dependent Structural Transition in Ph-BTBT-10 Thin Films and Stabilization of the Ubiquitous Interface Bilayer.

The influence of the film/substrate interface and the role of film thickness on the structural transition temperature for thin films of the asymmetric BTBT derivative 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]-benzothiophene (Ph-BTBT-10) have been addressed by using Kelvin probe force microscopy (KPFM) and synchrotron grazing incidence wide angle X-ray scattering (GIWAXS). Our data strongly suggest that the structural transformation from a single-layer phase to the thermodynamically stable bilayer structure develops from the bottom of the film to its surface. Contrary to observations in other organic semiconductor films, notably, the thinner the Ph-BTBT-10 film, the lower is the transition temperature. This unusual behavior is attributed to the ubiquitous presence of a bilayer at the substrate interface. The evolution over time of an ultrathin film with ≈3 nm nominal thickness (below the interfacial bilayer completion) shows that molecular diffusion and rearrangement at room temperature lead to the bilayer stacking within hours, a result that further supports the role of the bilayer interface on the structural transition from single-layer to bilayer structure. Our findings highlight that both aging and thermal annealing processes need to be optimized based on the specific thickness of the Ph-BTBT-10 film.

Switchable long-distance propagation of chiral magnonic edge states.

The coherent spin waves, magnons, can propagate without accompanying charge transports and Joule heat dissipation. Room-temperature and long-distance spin waves propagating within nanoscale spin channels are considered promising for integrated magnonic applications, but experimentally challenging. Here we report that long-distance propagation of chiral magnonic edge states can be achieved at room temperature in manganite thin films with long, antiferromagnetically coupled spin spirals (millimetre length) and low magnetic Gilbert damping (~3.04 × 10-4). By directly observing the non-reciprocal spin-wave propagation and analysing the strong magnon-magnon coupling in the spiral textures, we elucidate the crucial role of the dynamic dipolar interaction on the birth and hybridization of this chiral magnonic edge state. The observed hybridized magnons with robust chirality can be reversibly and selectively switched on/off by different threshold angles under an external field, indicating great potential for the design of versatile magnonic devices at the nanoscale.

High strength chitosan-based nanocomposites with aligned nanosheets and crosslinked networks.

High strength/toughness nanocomposites are increasingly in demand due to the development needs of high-end applications. However, the aggregation and random orientation of nanofillers and the weak crosslinking of the polymer matrix lead to the degradation of the mechanical properties of nanocomposites. Here, we present a strategy to prepare chitosan-based nanocomposites with aligned nanosheets via the in situ photo-crosslinking of modified chitosan. The well-dispersed and highly aligned nanosheets, as well as the dense covalently crosslinked network between the modified chitosan chains, effectively improve the mechanical properties of the prepared nanocomposites. For example, the chitosan-based nanocomposite films exhibit a tensile strength of up to 340.6 ± 13.4 MPa, a Young's modulus of 8.2 ± 0.2 GPa and a toughness of 22.0 ± 2.5 MJ m-3, which are 4.2, 4.8 and 1.8 times higher, respectively, than those of pure chitosan films. Moreover, the thermal decomposition temperature of the chitosan-based nanocomposite films reaches 286.8 °C, which is 48.5 °C higher than that of pure chitosan films. We consider that our strategy, which constructs a crosslinked chitosan structure with aligned nanofillers, could lead to the development and application of the bio-based composites with excellent mechanical properties.

Polyvinyl acetate–glycidyl methacrylate co-polymer emulsion-based heat-resistant wood adhesive

In this research work, vinyl acetate (VAc) and glycidyl methacrylate (GMA) emulsion copolymers have been developed and tested as wood adhesives. Further, the emulsion samples are formulated with polyvinyl alcohol (PVA) solution, plasticizer, and preservatives, and compared the polyvinyl acetate (PVAc) homo-polymer based adhesive against PVAc-GMA based adhesive sample. Utilizing differential scanning calorimetry (DSC), the glass transition temperatures (Tg) of the polymer films were found. To assess the effectiveness of the adhesives, the tensile shear strength of wood joints under dry and wet conditions was evaluated in compliance with the EN 204 and EN 205 standard. The heat resistance of the wood adhesives was assessed using the EN 14257 standard, which measures the shear stress of wood joints at 80 °C. According to the experimental findings, the amount of GMA in the emulsion caused significant increases in Tg and hardness. The results of DSC, which were confirmed by tests on the hardness of films, showed that the Tg in the GMA-based adhesive was significantly higher than in the PVAc homo-polymer-based adhesive. According to EN 204, the tensile shear strength of a GMA-based adhesive increased by 43.62% after 6 h of bonding in a dry environment and by 75% in a wet environment when compared to a PVAc homopolymer-based adhesive. Comparing the GMA adhesive to a PVAc homopolymer-based glue, the GMA adhesive demonstrated better heat resistance. The technique developed provides a straightforward and useful path to adhesives with better heat, water, and bonding strength resistance.

High photothermal conversion efficiency of RF sputtered Ti4O7 Magneli phase thin films and its linear correlation with light absorption capacity

RF-sputtering is used to deposit Ti4O7-Magneli-phase films onto various substrates at deposition temperatures (Ts) ranging from 25 to 650 °C. Not only the structural, but also electrical conductivity, optical absorbance and photothermal properties of the Ti4O7 films are shown to change significantly with Ts. A Ts of 500 °C is pointed out as the optimal temperature that yields highly-crystalized pure-Ti4O7-Magneli phase with a densely-packed morphology and a conductivity as high as 740 S/cm. The Ti4O7 films deposited at Ts = 450–500 °C also exhibited the highest optical absorption over all the broad (200–1500) nm range. The absorbed sunlight (AM1.5) was efficiently converted into heat by raising the temperature of the Ti4O7 films up to ~ 54 °C. Thus, the external photothermal efficiency (ηext) of the Ti4O7 films, was found to be as high as ~ 74%. This is the highest ηext reported so far for sputtered-Ti4O7 coatings (just ~ 450 nm-thick), highlighting their significant potential for photothermal applications such as desalination, deicing and/or smart windows. Finally, the ηext of the Ti4O7 coatings is demonstrated, for the first time, to be linearly correlated to their integrated light absorption coefficient. This fundamental relationship paves the way towards the design and optimization of highly efficient solar-thermal conversion devices.

Optimization of deposition time and temperature for high-quality PbS thin films via chemical bath deposition

In this study, lead sulfide (PbS) thin films were synthesized using chemical bath deposition (CBD) on glass substrates, employing lead nitrate and thiourea as source of Lead and Sulfur respectively, and triethanolamine was used as complexing agent. The research systematically examined the impact of two key parameters: deposition time (30-90 minutes) and bath temperature (55-90°C), revealing intricate relationships between deposition conditions and film characteristics. Deposition time analysis demonstrated a non-linear transmittance trend, with values changing from 20% at 30 minutes to 8% at 60 minutes, before recovering to 10% at 90 minutes. Additionally, the band gap changed from 2.00 eV at 30 minutes to 1.63 eV at 60 minutes and then increased to 1.70 eV at 90 minutes. Temperature variations showed a progressive decrease in transmittance from 23.75% at 55°C to 11% at 90°C, accompanied by a corresponding band gap reduction from 1.80 eV to 1.50 eV. The optimal conditions for producing high-quality PbS thin films suitable for p-type solar cell applications were determined to be a deposition time of 45 minutes and a bath temperature of 90°C, which effectively balance transmittance and band gap requirements. These findings provide crucial insights for enhancing PbS thin film performance in solar cell and infrared detection technologies, demonstrating the significance of precise parameter control in chemical bath deposition.

Wood adhesive based on polyvinyl alcohol stabilized polyvinyl acetate, vinyl neodecanoate, vinyl trimethoxy silane, and N-methylol acrylamide copolymer emulsion: synthesis and characterization

To improve a polyvinyl acetate (PVAc) emulsion-based glue’s water resistance, this study aims to offer it a controlled ability for cross-linking. Emulsion polymerization was used to synthesize PVAc-vinyl neodecanoate-vinyl trimethoxy silane-n-methyl acrylamide poly (VAc-VeoVa10-VTMO-NMA) copolymers with polyvinyl alcohol (PVA) stabilization. Using Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC), the copolymerization and glass transition temperatures (Tg) of film were analyzed. To assess the effectiveness of the cross-linked emulsions-based adhesive, the tensile shear strength of wood joints under dry and wet conditions was measured in compliance with the EN 204 and EN 205 standards. The experimental results showed that the copolymer-based poly (VAc-VeoVa10-VTMO-NMA) adhesive significantly increased Tg and film hardness when compared to poly (VAc-VeoVa10-VTMO). Tensile shear strength increased by ∼9% in a dry environment after 24 h of bonding (per EN 204) and by ∼18% in a wet environment with poly (VAc-VeoVa10-VTMO-NMA) adhesive, in comparison to a poly (VAc-VeoVa10-VTMO) adhesive. A contact angle test confirmed that cross-linked poly (VAc-VeoVa10-VTMO-NMA) copolymer adhesives performed somewhat better in wet and heat-resistant conditions than cross-linked poly (VAc-VeoVa10-VTMO) copolymer adhesives. The method proposed provides an easy-to-use route to emulsions with enhanced water resistance and bonding strength by including NMA as a reactive co-monomer.

Physical Aging of Poly(methyl methacrylate) Brushes and Spin-Coated Films.

While there is significant attention aimed at understanding how one-dimensional confinement and chain confirmations can impact the glass transition temperature (Tg) of polymer films, there remains a limited focus on similar effects on sub-Tg processes, notably, structural relaxation. Using spectroscopic ellipsometry, we investigated the combined influence of confinement and molecular packing on Tg and physical aging, i.e., the property changes that accompany structural relaxation, at select film thicknesses and aging temperatures (Ta). We used poly(methyl methacrylate) (PMMA) films in the brush and spin-coated morphologies as model systems. We found that whether a PMMA film exhibited a decrease or increase in physical aging rate with confinement was dependent on the morphology. Notably, PMMA brushes exhibited higher physical aging rates compared to similarly thick spin-coated films at all values of Ta. These intriguing findings reveal the strong effects of confinement and molecular packing on the structural relaxation of polymer films. Results from this study have the potential to aid in the design of thin-film materials with controllable long-term glassy-state properties.

Temperature and Flexural Endurances of Aluminum-Doped Zinc Oxide Thin Films on Flexible Polyethylene Terephthalate Substrates: Pathways to Enhanced Flexibility and Conductivity

This work investigates the endurance and performance of aluminum-doped zinc oxide (AZO) thin films fabricated on flexible polyethylene terephthalate (PET) substrates, providing new insights into their degradation linked to mechanical flexing and accelerated thermal cycling (ATC). The current study uniquely combines cyclic bending fatigue at 23 °C and 70 °C with ATC between 0 °C and 100 °C, simulating operational stresses in real-world environments, in contrast to previous research that has focused primarily on either isolated mechanical or thermal effects. The 425 nm thick films showed high transparency and conductivity, making them suitable materials for flexible electronics and optoelectronic devices. In this work, electrical resistivity, one of the most important performance parameters, was investigated after each mechanical or thermal cycle. The results indicate that mechanical cycling at high temperatures can drastically enhance the crack formation and electrical degradation, with an over 250% change in the electrical resistance (PCER) after 12,000 cycles at 70 °C and more than 300% after 500 thermal cycles. The highly deleterious effects of combined stressors on the structural integrity and electrical properties of AZO films are underlined by these observations. This study further suggests that the design of more robust AZO-based materials/coatings would contribute toward achieving better durability in flexible electronic applications. These findings also go hand in glove with the ninth goal of the United Nations’ Sustainable Development Goals, specifically Target 9.5: Enhance Research and Upgrade Industrial Technologies.

Calibration-free thickness and temperature measurement of oil films using broadband near-infrared absorption spectroscopy

Abstract This paper assesses broadband absorption spectroscopy for calibration-free, single-ended thickness and temperature measurements of thin liquid films with a free interface using spectrally resolved intensity measurements. The spectroscopic properties of the liquid in question, here an oil lubricant, are characterized using a Fourier transform infrared spectrometer. This data forms the basis for a measurement model that is used to infer the thickness and temperature of films wetting metal surfaces based on broadband spectral transmission measurements. The technique is demonstrated by inferring the properties of static films of known properties as well as free films on a rotating metal disk.

Tuning the Crystallization Temperature of Titanium Dioxide Thin Films by Incorporating Silicon Dioxide via Supercycle Atomic Layer Deposition

Tuning the Crystallization Temperature of Titanium Dioxide Thin Films by Incorporating Silicon Dioxide via Supercycle Atomic Layer Deposition

Fine Control of Optical Properties of Nb2O5 Film by Thermal Treatment.

Thermal treatment is a common method to improve the properties of optical thin films, but improper thermal treatment processing will result in the degradation of the optical properties of the optical thin film. The thermal stability of niobium oxide (Nb2O5) thin films prepared by magnetron sputtering was systematically studied by analyzing the roughness and morphology of the film under different thermal treatment processes. The results show that the amorphous stability of the Nb2O5 thin film can be maintained up to 400 °C. Before crystallization, with an increase in annealing temperature, the surface roughness of the film has no obvious change, the refractive index decreases, and the elastic modulus and hardness increase. The residual stress was measured by a laser interferometer. The results show that the residual compressive stress is present in the film, and the residual stress decreases with an increase in thermal treatment temperature. Considering the residual stress state, phase composition, mechanical properties, and optical properties of Nb2O5 films at different thermal treatment temperatures, we believe that the spectral position of the optical thin film device can be finely controlled within a 1.6% wavelength, and the thermal treatment temperature of Nb2O5 films prepared by magnetron sputtering should not exceed 400 °C.

(Invited) Semi-Monolithic Integration of Dissimilar Material Classes into Efficient Water Splitting Devices

Materials compatibility is an important issue in multi-junction (MJ) device integration, which has stifled innovation in photoelectrochemistry (PEC) for decades. Essentially, the deposition process of each layer must not damage the previously deposited layers and interfaces in any way. For example, with state-of-the-art chalcopyrite technology, it is impossible to fabricate high-efficiency monolithic MJ devices by directly depositing a wide-bandgap cell on top of a narrow-bandgap CIGSe device, because the required temperatures for high quality films (Tprocess = 500oC) destroy the underlying CdS/CIGSe heterojunction. As a result, the power conversion efficiency (PCE) of monolithically integrated chalcopyrite solid-state tandems has not exceeded 4.3%. The limitation of monolithic integration goes far beyond the chalcopyrite class, as it inherently restricts materials selection to a sub-set of compatible systems while limiting the adoption of emerging promising candidates. An integration scheme in which material classes can be combined, regardless of their nature, while preserving their intrinsic performance could revolutionize manufacturing technologies that rely on material stacking and lead to combinations of different material classes previously not considered for PEC water splitting.In this communication, we report on our recent efforts to develop a novel and scalable integration scheme to combine promising material classes, regardless of their thermal, physical, or chemical compatibility, into low-cost MJ PEC devices. Such a scheme, pioneered by HNEI and known as semi-monolithic integration, relies on 2D layer-assisted exfoliation and room temperature bonding techniques to transfer fully processed cells from their original substrates onto new handles. With this integration scheme, sub-cells of different bandgaps can be successively transferred onto a new host substrate to create a fully functional MJ structure. By design, semi-monolithic integration allows to circumvent all material incompatibilities, enabling new MJ architectures otherwise not possible with conventional monolithic integration.

A Bayesian Inference Approach to Accurately Fitting the Glass Transition Temperature in Thin Polymer Films.

We present a Bayesian inference-based nonlinear least-squares fitting approach developed to reliably fit challenging, noisy data in an automated and robust manner. The advantages of using Bayesian inference for nonlinear fitting are demonstrated by applying this approach to a set of temperature-dependent film thickness h(T) data collected by ellipsometry for thin films of polystyrene (PS) and poly(2-vinylpyridine) (P2VP). The glass transition experimentally presents as a continuous transition in thickness characterized by a change in slope that in thin films with broadened transitions can become particularly subtle and challenging to fit. This Bayesian fitting approach is implemented using existing open-source Python libraries that make these powerful methods accessible with desktop computers. We show how this Bayesian approach is more versatile and robust than existing methods by comparing it to common fitting methods currently used in the polymer science literature for identifying T g. As Bayesian inference allows for fitting to more complex models than existing methods in the literature do, our discussion includes an in-depth evaluation of the best functional form for capturing the behavior of h(T) data with temperature-dependent changes in thermal expansivity. This Bayesian fitting approach is easily automated, capable of reliably fitting noisy and challenging data in an unsupervised manner, and ideal for machine learning approaches to materials development.

Quantitative Eliashberg theory of the superconductivity of thin films

A quantitative theory of the superconductivity of materials confined at the nanoscale in parameter-free agreement with experimental data has been missing so far. We present a generalization, in the Eliashberg framework, of a BCS theory of superconductivity in good metals which are confined along one of the three spatial directions, such as thin films. In this formulation of the Eliashberg equations the approximation of taking the normal density of states as its value at the Fermi level has been removed. By numerically solving these new Eliashberg-type equations, we find the dependence of the superconducting critical temperatureTcon the confinement sizeL, in quantitative agreement with experimental data of Pb and Al thin films with no adjustable parameters. This quantitative agreement provides an indirect confirmation that, upon increasing the confinement, a crossover from a spherical-like Fermi surface, which contains two growing hole pockets caused by the confinement, to a strongly deformed Fermi surface, occurs. This topology of the Fermi sea is implemented in the new Eliashberg-type equations to reproduce the experimentally observed maximum in the critical superconducting temperature vs film thickness of ultra-thin Pb films.

Optimization of superconducting niobium nitride thin films via high-power impulse magnetron sputtering

Abstract We report a systematic comparison of niobium nitride thin films deposited on oxidized silicon substrates by reactive DC magnetron sputtering and reactive high-power impulse magnetron sputtering (HiPIMS). After determining the nitrogen gas concentration that produces the highest superconducting critical temperature for each process, we characterize the dependence of the critical temperature on film thickness. The optimal nitrogen concentration is higher for HiPIMS than for DC sputtering, and HiPIMS produces higher critical temperatures for all thicknesses studied. We attribute this to the HiPIMS process enabling the films to get closer to optimal stoichiometry before beginning to form a hexagonal crystal phase that reduces the critical temperature, along with the extra kinetic energy in the HiPIMS process improving crystallinity. We also study the ability to increase the critical temperature of the HiPIMS films through the use of an aluminum nitride buffer layer and substrate heating.

Highly selective dual gas (NO & NO2) sensing depended on the operating temperature of WO3 thin films sputtered at room temperature

We have studied the effect of film thickness (120, 180, and 286 nm) on the dual gas (NO & NO2) sensing performance of DC magnetron sputtered WO3 thin films deposited at room temperature. WO3 shows strong absorption from visible light to the infrared region. An unusual peak originates at 467.6 nm (film thickness 286 nm) instead of a broadband tail, usually found in WO3, which has been linked with oxygen vacancies. A high response of ∼196 at 150 °C for 50 ppm NO and ∼50 at 250 °C for 50 ppm NO2 is achieved for 286 nm film, which can be associated with Localized Surface Plasmon Resonance while a low response/recovery time of ∼39s/99s is obtained for 120 nm film at 200 °C for NO gas, which is its best operating temperature too (sensor response ∼100). Even under a high humidity (90 %) environment, the sensor detected 50 ppm of NO.

Thermal-Gas-Elastic Coupling Modeling and Performance Analysis of Foil Cylindrical gas Film Seal Considering Speed Slip, Temperature Jump and Shaft Misalignment

Abstract The Compliant foil cylindrical gas film seal is an advanced sealing technology designed for high-speed and high-temperature conditions in a jet engine. Its design involves using a compliant foil to create a cylindrical sealing surface, achieving adaptive sealing in environments with high pressure differences and rotational speeds. For high-speed and high-temperature operation, a speed slip flow model was established by considering film slip flow, wall temperature jump, foil deformation, and gas viscosity-temperature thermal effects. The variations in the lubrication performance of the foil cylindrical gas film seal with changes in shaft misalignment directions, misalignment angles, and operating parameters were investigated. The speed slip leads to a decrease in gas film lift and an increase in leakage. The wall temperature jump phenomenon caused by speed slip leads to a 2.56% decrease in film temperature. The shaft misalignment angles on the high-pressure and low-pressure sides have different impacts on the flow field, with film pressure and temperature differing by 66.78% and 11.19%, respectively.