Film Temperature Research Articles

Characterization and the physical properties of nano-sized Bi2O3/polymer for energy and high-refractive index applications

The present work focuses on developing nanocomposites for optoelectronics and energy storage devices leveraging the unique physicochemical features of bismuth (III) oxide (Bi2O3) using a polyvinyl pyrrolidone/polyvinyl alcohol matrix (PV(A/P)). Bi2O3 nanofillers (NF) and Bi2O3/PV(A/P) nanocomposite (NC) films were prepared by facile chemical solution approaches. The X-ray (XRD) data and a transmission electron image revealed that the NF exhibits a monoclinic phase, resembling slightly deformed agglomerated spheres. In the FTIR spectrum, different stretching vibrations of Bi-O-Bi bonds were found, along with their complexation and interaction with the reactive groups in the matrix. The SEM revealed a uniform distribution of Bi2O3 NF loading up to 1.5 wt% on the sample’s surface. Thermal analyses (TGA and DSC thermograms) were used to study the thermal stability, melting, and decomposition temperatures of the NC films. The dielectric features were studied under frequencies between 2 × 103 and 8 × 106 Hz and heating from 293 to 393 K. The dielectric constant and energy density were increased with Bi2O3 NF content. This implies that we can utilize the prepared NC for the fabrication of energy storage devices. The influences of the Bi2O3 NF doping level on the transmittance, band gap, Urbach energy, refractive index, conductivity, and other physical parameters were discussed. The modifications induced in the dielectric/optical parameters make the prepared NC films the best candidates for applications requiring a high refractive index, such as optical coatings and integrated photonic devices.

Highly crystalline yttria‐stabilized zirconia and titania thin films on plastic substrates via sol‐gel transfer process

AbstractWe prepared yttria‐stabilized zirconia (YSZ) and titania crystalline thin films on polycarbonate (PC) substrates by the sol‐gel transfer technique that we have developed recently. Precursor gel films were deposited by spin‐coating on a polyimide/polyvinylpyrrolidone mixture layer on Si(100) substrates, and then were calcined at 600°C. The spin‐coating and the calcination were cycled, followed by final firing at 600–1000°C, to obtain 140–190 nm thick, YSZ and titania crystalline thin films. The film densification progressed as the final firing temperature increased, where the porosity calculated from the refractive index decreased down to a few percent. The film thus obtained was heated at 190°C on a hot plate, and a PC substrate was pressed on the film to transfer it to the PC substrate. The transferability quantified by image analysis of the film area was found to be significantly different between the YSZ and titania films. In the case of YSZ films, the area of silicon that was fractured and adhered to the transferred film increased significantly with increasing firing temperature, leading to a decrease down to 0% in the fraction of the successful transfer area without such a damage. On the other hand, the fraction of the successful transfer area remained around 90% irrespective of the firing temperature for the titania films. The surface of the titania films that were fired at 800–1000°C and transferred to PC substrates had voids of several tens nm scale, which may have been formed during anatase‐to‐rutile phase transformation. We thought that the reduced titania/Si(100) contact area due to such void formation facilitated the delamination of the titania films from Si(100) substrates. High temperature firing, which promotes crystallization and densification of films, thus affects differently the film transferability to plastic substrates, depending on the type of films. The work also suggested possible use of titania films as release‐assisting layers.

Layer Exchange Synthesis of SiGe for Flexible Thermoelectric Generators: A Comprehensive Review

AbstractFlexible thermoelectric generators are leading candidates for next‐generation energy‐harvesting devices. Although SiGe, an environmentally‐friendly semiconductor, is the most reliable and widely tested thermoelectric material, it is difficult to form a SiGe layer with high thermoelectric performance at temperatures lower than the heat‐proof temperature of flexible plastic films. In this article, the synthesis of SiGe thermoelectric thin films via the metal‐induced layer exchange phenomenon is reviewed, from its mechanism to device performance. The selection of metal species allows low‐temperature formation (≤500 °C) of p‐ and n‐type SiGe on insulating substrates. Currently, the maximum power factors near room temperature are 850 µW m−1 K−2 for p‐type Si0.4Ge0.6 and 1000 µW m−1 K−2 for n‐type Si0.85Ge0.15. These values are the highest among those of Group IV semiconductor thin films formed at low temperatures. The flexible thermoelectric generator consisting of these p‐ and n‐type SiGe exhibits cross‐sectional and planar power densities of ≈3.0 mW cm−2 and 0.50 µW cm−2, respectively, at a temperature difference of 30 K. Finally, the future challenges of layer exchange for improving the performance of flexible thermoelectric generators based on Group IV semiconductors are discussed.

A Study on the Preparation of a Vulcanizing Mixture and Its Application in Natural Rubber Latex.

The traditional preparation process of natural rubber latex requires tedious treatment of a variety of rubber additives. In this paper, a new process of wet mixed grinding was used to prepare a reinforced vulcanization mixture and a rapid vulcanization effect. The effect of different amounts of vulcanization mixtures on the mechanical properties of natural latex film was studied, and the pre-vulcanization process of latex and the vulcanization process of film were optimized. The results showed that with the increase in the amount of vulcanization mixture, the tensile strength increased from 5.96 MPa to 29.28 MPa, and the tear strength increased from 7.59 kN/m to 52.81 kN/m. When the vulcanization temperature of the latex film is heated from 80 °C to 100 °C, the vulcanization time is shortened by 5~6 times. The new vulcanization mixture prepared in this work has the characteristics of simple production and fast vulcanization speed, which provides a new solution for the development of the latex product industry.

Effect of Poly(propylene carbonate) on Properties of Polylactic Acid-Based Composite Films.

To enrich the properties of polylactic acid (PLA)-based composite films and improve the base degradability, in this study, a certain amount of poly(propylene carbonate) (PPC) was added to PLA-based composite films, and PLA/PPC-based composite films were prepared by melt blending and hot-press molding. The effects of the introduction of PPC on the composite films were analyzed through in-depth studies on mechanical properties, water vapor and oxygen transmission rates, thermal analysis, compost degradability, and bacterial inhibition properties of the composite films. When the introduction ratio coefficient of PPC was 30%, the tensile strength of the composite film increased by 19.68%, the water vapor transmission coefficient decreased by 14.43%, and the oxygen transmission coefficient decreased by 18.31% compared to that of the composite film without PPC, the cold crystallization temperature of the composite film increased gradually from 96.9 °C to 104.8 °C, and PPC improved the crystallization ability of composite film. The degradation rate of the composite film with PPC increased significantly compared to the previous one, and the degradation rate increased with the increase in the PPC content. The degradation rate was 49.85% and 46.22% faster on average than that of the composite film without PPC when the degradation was carried out over 40 and 80 days; the composite film had certain inhibition, and the maximum diameter of the inhibition circle was 2.42 cm. This study provides a strategy for the development of PLA-based biodegradable laminates, which can promote the application of PLA-based laminates in food packaging.

Influence of liquid film shape on evaporation performance of agitated thin film evaporator

Abstract The agitated thin film evaporator (ATFE), which is known for its high efficiency, force the material to form a film through the scraping process of a scraper, followed by evaporation and purification. The complex shape of the liquid film inside the evaporator can significantly affect its evaporation capability. This work explores how change in shape of the liquid films affect the evaporation of the materials with non-Newtonian characteristics, achieved by changing the structure of the scraper. Examining the distribution of circumferential temperature, viscosity, and mass transfer of the flat liquid film shows that the film evaporates rapidly in shear-thinning region. Various wavy liquid films are developed by using shear-thinning theory, emphasizing the flow condition in the thinning area and the factors contributing to the exceptional evaporation capability. Further exploration is conducted on the spread patterns of the wavy liquid film and flat liquid film on the evaporation wall throughout the process. It is noted that breaking the wavy liquid film on the evaporating wall during evaporation is challenging due to its film-forming condition. For which the fundamental causes are demonstrated by acquiring the data regarding the flow rate and temperature of the liquid film. The definitive findings of the analysis reveal a significant improvement in the evaporation capability of the wavy liquid film. This enhancement is attributed to increasing the shear-thinning areas and maintaining the overall shape of the film throughout the entire evaporation process.

Capsicum leaf protein-based bionanocomposite films for packaging application: Effect of corn starch content on film properties

The addition of corn starch (CS) enhances the interfacial adhesion of the film-forming liquids (FFLs), weakening the internal relative molecular motion. As a result, the rheological properties and zeta potential values of the FFLs were affected. A tight spatial network structure between capsicum leaf protein (CLP), lignocellulose nanocrystals (LNCs) and CS can be formed through intermolecular entanglement and hydrogen bonding interactions. The crystallinity, thermal degradation temperature, tensile strength and water contact angle of the protein-based bionanocomposite films (PBBFs) increased with increasing CS addition. This is due to the transformation of the secondary space structure of the CLP inside the PBBFs and the increase in cohesion. However, the excessive addition of CS forms aggregated clusters on the surface of PBBFs, which increases the surface roughness of PBBFs and causes more light scattering. Therefore, the brightness and yellowness values of the PBBFs increase, and the transmittance decreases.

Theoretical Study of the Phonon and Electrical Conductivity Properties of Pure and Sr-Doped LaMnO3 Thin Films.

The film thickness, temperature, substrate and doping dependence of the phonon energy ω and damping γ, as well as the electrical conductivity, of pure and Sr-doped LaMnO3 thin films near the phase transition temperature TN are investigated using a microscopic model and the Green's function technique. Due to the strong spin-phonon interaction, there appears a kink at TN in the temperature dependence of ω(T) and γ(T). The softening and hardening of the ω = 495 cm-1 (A1g) and ω = 614 cm-1 (B2g) modes is explained by the different sign of the anharmonic spin-phonon interaction constant R. The damping increases with T for both cases because it is proportional to R2. ω decreases whereas γ increases with an increasing Sr concentration. This is due to the strain caused by the difference between the ionic radii of the La and Sr ions. The film thickness dependence is also considered. ω and γ increase strongly with the decreasing film thickness. The electrical conductivity is enhanced after the doping of the LMO thin films with Sr, which could be used for energy storage applications. The observed results are in good qualitative agreement with the experimental data.

Comparative study on the effects of chitosan, carrageenan, and sodium alginate on the film-forming properties of fish skin gelatin

Polysaccharides are commonly used to improve the film-forming properties of gelatin due to their wide range of sources, safety, and edible properties. However, there has been no systematic study comparing the effects of different polysaccharides on the film-forming properties of gelatin. Effects of chitosan, carrageenan, and sodium alginate on the optical properties, mechanical properties, thermal stability, hydrophilicity, and structure properties of gelatin films were systematically compared. Adding chitosan effectively reduced the ultraviolet transmittance of gelatin film. With an increase in chitosan concentration from 2 g/L to 8 g/L, the melting transition temperature (Tm) of gelatin film increased from 74 °C to 101 °C. Additionally, water vapor permeability decreased from 2.2 ± 0.23 (g.mm)/m2.h.kpa to 1.2 ± 0.18 (g.mm)/m2.h.kpa and water solubility decreased from 75% to 66%. Adding carrageenan and sodium alginate respectively increased the Tm of gelatin film to 92 °C and 84 °C; however, their addition reduced hydrophobicity and elongation at break for gelatin films. X-ray diffraction results suggested good compatibility between gelatin and all three polysaccharides while Fourier transform infrared spectrum results confirmed hydrogen bond interaction between gelatin and polysaccharides with a more orderly structure observed in gelatin films after adding polysaccharides.

Optimization of Mg-Al Layered Double Hydroxide Film Preparation and Corrosion Resistance Study on AZ91D Mg Alloy by Multivariate Polynomial Regression Fitting.

Layered double hydroxide (LDH) films have received extensive attention for their unique physical barrier function and ion exchange properties, which make them promising candidates for corrosion protection of magnesium alloys. In this paper, we used the multiple polynomial regression fitting method to establish a regression equation for the electrochemical corrosion resistance with the reaction temperature (T), pH, and reaction time (t) of the Mg-Al LDH film on the AZ91D magnesium alloy. The goodness of fit, confidence, and residual analyses confirmed the high accuracy of the model equation. According to the calculation using the fmincon function, the best corrosion resistance of the prepared samples could be achieved when the parameters are T = 135 °C, pH = 12.0, and t = 15 h. Then, the experimental results showed that the corrosion current density (Icorr) of the obtained LDH film under the above conditions could be 1.07 × 10-7 A/cm2, approximately 3 orders of magnitude lower than the magnesium alloy substrate, after immersion in a 3.5 wt % NaCl solution for 180 h, the surface structure of the LDH film did not change significantly, and the Icorr was still 2 orders of magnitude higher than that of the magnesium alloy substrate. Hence, a synergistic effect equation for the reaction temperature, pH, and reaction time on the corrosion resistance of the LDH film on a magnesium alloy surface prepared by the hydrothermal method was obtained. Moreover, using this equation, we obtained an LDH film with good corrosion resistance and durability, providing theoretical guidance for optimizing the process of preparing the LDH film by the hydrothermal method in practical applications.

Controlling the Superconducting Critical Temperature and Resistance of NbN Films through Thin Film Deposition and Annealing

Controlling the Superconducting Critical Temperature and Resistance of NbN Films through Thin Film Deposition and Annealing

Slip flow and thermal characteristics in gas thrust bearings with rough surfaces

PurposeThis study aims to investigate the rarefaction effects on flow and thermal performances of an equivalent sand-grain roughness model for aerodynamic thrust bearing.Design/methodology/approachIn this study, a model of gas lubrication thrust bearing was established by modifying the wall roughness and considering rarefaction effect. The flow and lubrication characteristics of gas film were discussed based on the equivalent sand roughness model and rarefaction effect.FindingsThe boundary slip and the surface roughness effect lead to a decrease in gas film pressure and temperature, with a maximum decrease of 39.2% and 8.4%, respectively. The vortex effect present in the gas film is closely linked to the gas film’s pressure. Slip flow decreases the vortex effect, and an increase in roughness results in the development of slip flow. The increase of roughness leads to a decrease for the static and thermal characteristics.Originality/valueThis work uses the rarefaction effect and the equivalent sand roughness model to investigate the lubrication characteristics of gas thrust bearing. The results help to guide the selection of the surface roughness of rotor and bearing, so as to fully control the rarefaction effect and make use of it.

Optical and electronic properties of BCN films deposited by magnetron sputtering.

Boron carbonitride (BCN) films containing hybridized bonds involving B, C, and N over wide compositional ranges enable an abundant variety of new materials, properties, and applications; however, their electronic performance is still limited by the presence of structural and electronic defects, yielding sluggish mobility and electrical conductivity. This work reports on mechanically stable BCN films and their corresponding optical and electronic properties. The ternary BCN films consisting of hybridized B-C-N bonds have been achieved by varying N2 flow by the radio frequency magnetron sputtering method. The BCN films show a bandgap value ranging from 3.32 to 3.82eV. Hall effect measurements reveal an n-type conductivity with an improved hall mobility of 226cm2/V s at room temperature for the optimal film. The n-BCN/p-Si heterojunctions exhibit a nonlinear rectifying characteristic, where the tunneling behavior dominates the injection regimes due to the density of defects, i.e., structural disorder and impurities. Our work demonstrates the tunable electrical properties of BCN/Si p-n diodes and, thus, is beneficial for the potential application in the fields of optics, optoelectronics, and electrics.

Aggregation induced strong photoluminescence at room temperature in large-area C8BTBT thin films

Study of optical properties of 2,7-dioctyl[1]benzothieno[2,3-b]benzothiophene (C8BTBT) is promising for applications in low-cost and flexible optoelectronic devices. Here, we systematically investigated the thickness dependent structural and photophysical properties of large-area C8BTBT films. The large-area C8BTBT thin films of different thickness below 80 nm were prepared by off-centre spin coating method. Grazing incidence X-ray diffraction measurements confirm the highly crystalline nature of the thin films and reveal that crystal coherence length increases with increase of film thickness. The film morphology and its thickness were studied using atomic force microscopy. Further, optical absorption and emission behaviors of the thin films were analyzed. The results show strong ultraviolet (UV) emissions at room temperature. The photoluminescence behaviour of higher-thickness films differs from that of lower-thickness films. The thickness dependent UV emission spectra are explained in terms of defects and aggregation behavior of C8BTBT thin films. We determine the impact of thickness and aggregation (J- and H-type) on emission behaviors of the C8BTBT thin films. Our findings open a new avenue for the future optimization and prospective applications in photonics based on two-dimensional organic semiconductors.

Electronic and Structural Disorder of the Epitaxial La0.67Sr0.33MnO3 Surface.

Understanding and tuning epitaxial complex oxide films are crucial in controlling the behavior of devices and catalytic processes. Substrate-induced strain, doping, and layer growth are known to influence the electronic and magnetic properties of the bulk of the film. In this study, we demonstrate a clear distinction between the bulk and surface of thin films of La0.67Sr0.33MnO3 in terms of chemical composition, electronic disorder, and surface morphology. We use a combined experimental approach of X-ray-based characterization methods and scanning probe microscopy. Using X-ray diffraction and resonant X-ray reflectivity, we uncover surface nonstoichiometry in the strontium and lanthanum alongside an accumulation of oxygen vacancies. With scanning tunneling microscopy, we observed an electronic phase separation (EPS) on the surface related to this nonstoichiometry. The EPS is likely driving the temperature-dependent resistivity transition and is a cause of proposed mixed-phase ferromagnetic and paramagnetic states near room temperature in these thin films.

Supercritical heat transfer of Novec 649 refrigerant in a minichannel with various inclination angles: Horizontal to vertically downward flows

The study of organic fluids under supercritical conditions has been less extensive than that of supercritical carbon dioxide and water. In addition, most studies on supercritical heat transfer have focused on horizontal or vertical channels, with limited research on inclination angles. Therefore, the focus of this study was to investigate the supercritical heat transfer of organic fluid (Novec 649) in a miniaturized channel across various inclination angles. The experimental findings reveal that the heat transfer coefficient (HTC) increases with an increase in the fluid's bulk temperature at a given mass flux and with an increase in the mass flux at a given bulk temperature. Notably, the HTC in horizontal flow channels marginally surpasses that in non-horizontal channels. The buoyancy effect, found to be non-dominant in a studied channel, does not lead to heat transfer deterioration. In vertical flow channels, under the experimental conditions, the acceleration parameters exceeded the threshold values, suggesting a potential significance of the acceleration effect. Particularly at higher mass fluxes, the acceleration parameter peaked as the film temperature approached the fluid's pseudocritical value. We further developed the supercritical heat transfer correlation by introducing an inclination angle parameter, achieving a mean absolute error of 12.7 %.

Splay aligned liquid crystal network photoactuators for integrated microfluidic pumps

As lab-on-a-chip devices aim to incorporate complex and multi-step microfluidic workflows, active fluid control within these platforms is critical. We use a splay aligned liquid crystal network (LCN) photoactuator, capable of deformation upon blue light illumination, as a stimuli responsive material to create integrated fluidic elements. After optimization of the manufacturing parameters, a well-defined actuator material is attained. Illumination with a 455 nm light emitting diode (LED) at 41 mW cm−2 achieves deflection of a 3 × 8 × 0.05 mm LCN film by 380 µm, generating forces of 1.1 mN. The actuator response is stable over time and scalable by light intensity, temperature, and size of the LCN film. By combining with a polydimethylsiloxane (PDMS) membrane, integration into a microfluidic chip is demonstrated and fluid movement of 77 nL in a 2 s stroke is attained. In a pumping setup, the LCN film functions as pumping membrane and two passive PDMS check valves complete the integrated micropump. Constant pumping rates of 0.1 µL min−1 are achieved. An advantage of this micropump setup lies in the non-contact actuation method, which allows for easy integration into microfluidic chips, without the need for chip-to-world connections. Furthermore, with the simple manufacturing procedure and the low operating power, important requirements for application in point-of-care settings are fulfilled.

Numerical and experimental investigation of textured journal bearings for friction reduction

This work investigates the mechanisms for friction reduction in textured journal bearings. The measured friction of laser-etched connecting-rod big-end shells was compared with a non-textured reference under engine-like conditions. Experiments covered several working conditions, and the friction and lubricant film temperatures were measured for three texture configurations. The origin of the verified friction reduction was explored using a numerical model that simulates the hydrodynamic lubrication and global thermal effects. The simulation results accurately matched the friction measurements, revealing that the microscopic mechanisms of reduction in lubricant shear stress and effective viscosity due to texture-induced cavitation act simultaneously to reduce the friction coefficient for the textured shells. The findings have practical applications for the optimal design of textured hydrodynamic bearings.

Large eddy simulation of boundary layer combustion of hydrogen and hydrocarbon fuel films in a modeled scramjet combustor

Supersonic fuel film cooling is a promising way to simultaneously reduce the severe wall heat and friction load of the internal passage in a scramjet engine when operating at hypersonic conditions. Large eddy simulations were performed to investigate the cooling and wall friction characteristics of hydrogen and hydrocarbon films under inert and reactive circumstances. The results show that the essential difference of the turbulent state in the mixing layer contributes to the totally different behaviors of the cooling and wall friction reduction performances of the two fuel films. The turbulent transport processes between the hydrogen film and the mainstream are much weaker as compared to the case of hydrocarbon film, making inert hydrogen rather superior in cooling and friction reduction applications. Besides, the increase of wall temperature for hydrogen film under the inert case is mainly driven by the loss of hydrogen with high heat capacity instead of by direct heat addition. However, the film cooling performance severely deteriorates when the hydrogen film burns due to presence of severe heat release sources near the wall. On the other hand, combustion of hydrocarbon film in the boundary layer can remarkably improve its originally barely-satisfactory cooling and friction reduction performance to the level comparable to that of hydrogen film, due to the suppression of turbulent transport processes in the mixing layer and presence of heat absorption sources near the wall. Overall, the hydrogen film is more advantageous in friction reduction, while the hydrocarbon film is more suitable for cooling.

Compensating thermal bending of the runner disk in hydrodynamic thrust bearings: Simple approach for passively improving the performance of gas bearings

This paper presents a method for passively compensating thermal bending distortions of the thrust disk in gas thrust bearings by passive approaches. Thermal bending displays a prominent problem in hydrodynamic thrust bearings, especially in connection with air bearings. Axial temperature gradients cause the rotor disk to dish which in turn diminishes the lubricating gap topology and reduces the load capacity of the bearing. Consequently, the bearing performance is decreased and the bearing may even fail. The here proposed straightforward solutions are small changes in the rotor and runner disk design and are therefore rather simple and inexpensive to adopt. They comprise asymmetric mass distributions, recesses, disk cuts, and dual-material rotor disks. In order to show the benefit for the thrust bearing performance, detailed multiphysical numerical simulations of a representative rotor assembly with a foil thrust bearing are presented. The fully coupled finite element model calculates the deformations of the foil package (2D Reissner–Mindlin type shell equations), lubricating air film pressure (2D compressible Reynolds equation), air film temperatures (3D energy equation), and thermo-elastic deformations of the rotor and rotor disk (2D Navier-Lamé equations including centrifugal forces and thermal stresses). When the proposed design changes are applied, the model predicts reduced thermal bending, marked improvements in load capacity as well as decreased temperatures. The load capacity increase ranges up to 43% for an optimized design when compared against a standard symmetric design. Also, the sensitivity of different design parameters is discussed in detail. The suggested disk design changes may be applied to a broad variety of rotor-bearing systems. However, the design has to be tailored to the specific and individual machine operating conditions.