Film Profile Research Articles

Characterization of column flow regimes on horizontal tubes for falling‐film systems: An experimental approach

AbstractThe intertube flow regimes and hydrodynamic behavior of the liquid profile have a significant impact on the functioning of falling‐film evaporators. Column flow is one of the fundamental flow modes, which is actively observed in many industrial evaporators. A high‐speed digital photographic device is utilized to visualize the complete progression of column flow phases for intertube distances of 10/20/30/40 mm and Reynolds number (Re) values ranging from 41 to 583. The Sobel edge detection algorithm is implemented to quantify the flow parameters for each frame of a sequence. The research results indicated that the column flow regime between the inline horizontal tubes can be broadly classified into the following phases: columnar droplet flow, periodic column flow, satellite drops column flow, drift column flow, and mixing liquid film column flow. The findings show that the liquid jet diameters between the tubes range from 1.6 to 8.46 mm, an increase in the liquid jet diameter with Re and a decrease with tube‐to‐tube distance. The axial coverage of the liquid film profile beneath the tube differed from 2.07 to 3.99 mm and over the tube surface ranged from 1.14 to 2.68 mm. The formation of dry spots and flooding is a major problem in the operation of falling‐film heat exchangers. The shape and size of the liquid jet have a direct impact on the interfacial area; understanding the entire progression of column flow regimes, as well as their characteristics, can help designers avoid the aforementioned problem.

Rapid and label-free detection of the troponin in human serum by a TiN-based extended-gate field-effect transistor biosensor

In this article, the TiN sensitive film as a sensing membrane was deposited onto n+-type Si substrate by a DC sputtering technique for extended-gate field-effect transistor (EGFET) pH sensors and detection of cardiac troponin-I (cTn-I) in the patient sera for the first time. The crystal structure, Raman spectrum, element profile, surface roughness, and surface morphology of the TiN sensitive film were characterized by X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy, atomic force microscopy, and scanning electron microscopy, respectively. The sensing performance of the TiN sensitive film is correlated with its relative structural feature. A high sensitivity of 57.49 mV/pH, a small hysteresis voltage of ∼1 mV, and a low drift rate of 0.31 mV/h were obtained in the TiN sensitive film. In addition, the pH sensitivity of this TiN EGFET sensor was preserved approximately 57 mV/pH after operation time of 180 days. Subsequently, the cTn-I antibodies with carboxyl groups activated by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) along with N-hydroxysuccinimide (NHS) were immobilized on the TiN sensitive film functionalizing with 3-aminopropyl triethoxysilane (APTES). After obtaining the successful immobilization of cTn-I antibodies on the TiN EGFET biosensor, the cTn-I antigen specifically binds with its relative antibody. The cTn-I EGFET biosensor showed a high sensitivity of 21.88 mV/pCcTn-I in a wide dynamic range of 0.01–100 ng/mL. Furthermore, the concentrations of cTn-I in patient sera measured by our TiN EGFET biosensors are comparable to those determined by commercial enzyme-linked immuno-sorbent assay kits.

Controlled release of paroxetine from chitosan/montmorillonite composite films

Controlled drug delivery studies popular in pharmaceutical area; polymeric composites prepared with clay has a great potential importance in drug release studies. The aim of the study is to produce biocoposite material suitable for controlled release of Paroxetine Hydrochloride.In this study, chitosan/clay/paroxetine (CS/MMT/PHH and CS/NaMMT/PHH) composite films were prepared to investigate drug release properties of paroxetine (PHH). Films containing various amounts of clay (MMT/NaMMT) (0, 0.1, 0.2, 0.4 g) and glycerol (0.25, 0.50) were prepared by solvent casting method. The structural properties of drug-containing and non-drug containing films were characterized by FT-IR and SEM analysis. The release studies of PHH were done in vitro and pH 7.4 and at 37 °C temperature. The highest percent of drug release was observed with CS/PHH film after 170 h (69%). It was observed that the drug release profiles of chitosan films containing clay (MMT or NaMMT) were better than films without clay. In order to investigate the drug release mechanism, Korsmeyer-Peppas, Higuchi, Zero and First order kinetic models were used.It was determined that release kinetics of the most of films fit the Korsmeyer-Peppas model, and according to this model, drug release occurs through two mechanisms, swelling-controlled and diffusion-controlled. It has been observed that all films containing clay have long-term drug release. Increasing in clay ratio in the composite, caused decrease in drug release rate. PHH loaded CS/MMT/PHH and CS/NaMMT/PHH films showed steady and prolonged drug delivery. Results indicated that prepared CS/MMT/PHH and CS/NaMMT/PHH films has a potential to act as suitable carrier for drugs.

Characterization of the Interfacial Orientation and Molecular Conformation in a Glass-Forming Organic Semiconductor.

The ability to control structure in molecular glasses has enabled them to play a key role in modern technology; in particular, they are ubiquitous in organic light-emitting diodes. While the interplay between bulk structure and optoelectronic properties has been extensively investigated, few studies have examined molecular orientation near buried interfaces despite its critical role in emergent functionality. Direct, quantitative measurements of buried molecular orientation are inherently challenging, and many methods are insensitive to orientation in amorphous soft matter or lack the necessary spatial resolution. To overcome these challenges, we use polarized resonant soft X-ray reflectivity (p-RSoXR) to measure nanometer-resolved, molecular orientation depth profiles of vapor-deposited thin films of an organic semiconductor Tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Our depth profiling approach characterizes the vertical distribution of molecular orientation and reveals that molecules near the inorganic substrate and free surface have a different, nearly isotropic orientation compared to those of the anisotropic bulk. Comparison of p-RSoXR results with near-edge X-ray absorption fine structure spectroscopy and optical spectroscopies reveals that TCTA molecules away from the interfaces are predominantly planar, which may contribute to their attractive charge transport qualities. Buried interfaces are further investigated in a TCTA bilayer (each layer deposited under separate conditions resulting in different orientations) in which we find a narrow interface between orientationally distinct layers extending across ≈1 nm. Coupling this result with molecular dynamics simulations provides additional insight into the formation of interfacial structure. This study characterizes the local molecular orientation at various types of buried interfaces in vapor-deposited glasses and provides a foundation for future studies to develop critical structure-function relationships.

Liquid film distribution around long gas bubbles propagating in rectangular capillaries

We present a systematic analysis of the bubble and liquid film dynamics corresponding to the propagation of long, isolated gas bubbles, within rectangular capillary channels of cross-sectional aspect-ratio ranging from 1 to 8. Direct numerical simulations of the flow are performed using ESI-OpenFOAM v.1812 and its geometric Volume-Of-Fluid solver isoAdvector. The interface curvature, which enters the calculation of the surface tension force in the momentum equation, is calculated with a parabolic reconstruction method. This study covers a range of capillary and Reynolds numbers of, respectively, 0.005≤Ca≤1 and 1≤Re≲1000. The lubrication film surrounding the bubble is always resolved by the computational mesh, and thus the present results are representative of a perfectly wetting fluid. This study shows that rectangular cross-sections promote the formation of an extended liquid film covering the longer wall of the channel. This liquid film exhibits a saddle-like shape and its streamwise evolution varies depending on the channel shape and flow conditions. Although cross-sectional liquid film profiles and corresponding thicknesses are not constant along the bubble, in general the film deposited upon the shorter wall becomes thicker for increasing values of the aspect-ratio, while the thickness of the film deposited upon the longer wall obeys a Ca2/3/(1+Ca2/3) law which, provided that the channel hydraulic radius is the same, is independent of the aspect-ratio at sufficiently small Ca. An empirical correlation is proposed to predict the cross-sectional gas fraction and bubble speed as a function of a modified capillary number, embedding dependencies on both Ca and aspect-ratio, and converging to the asymptotic limit for a quasi-static flow when Ca→0.

Application of artificial neural network to determine the thickness profile of thin film

In this paper, we introduce a novel artificial neural network (ANN) based scheme to estimate the thickness of thin films deposited on a given substrate. Here we consider the visible interference pattern between a plane wave and a diverging wave reflected from the thin film surface that records the thickness information of the thin film. We assume a uniform thickness profile of the film. However, the thickness increases as the deposition takes place. We extract the intensity data along a line through the center of the interference pattern. We train our network by using a number of such line information of known thickness profiles. The performance of the trained network is then tested by estimating the thickness of unknown surfaces. The numerical simulation results show that the proposed technique can be very much useful for automated measurement of thickness, quickly and in real time, during deposition.

Axisymmetric thin film flow on a flat disk foil subject to intense radial electric fields

The presence of intense radial electric fields on a wetted disk foil of fingernail size results in the formation of a large number (up to ∼1000) of cone-jets and electrosprays (Wang et al., “Massively multiplexed electrohydrodynamic tip streaming from a thin disc,” Phys. Rev. Lett., 126, 064502, 2021). This massively multiplexed electrohydrodynamic tip streaming phenomenon offers a simple and convenient way of creating quasi-monodisperse droplets at high throughput. The structure of the axisymmetric liquid film flow on the disk determines the number and distribution of the cone-jets. In this work, we quantitively study the flow of the axisymmetric thin liquid film subjected to a radial electric field. The liquid film profile is found to be concave with a circular ridge, at which multiple Taylor cones are anchored. The liquid film thickness is experimentally quantified with a fluorescence imaging method, and the results are in decent agreement with the film profile model based on the lubrication theory. The velocity field in the liquid film was experimentally obtained by particle tracking velocimetry (PTV). The results shed light on the understanding of the multiplexed electrohydrodynamic tip streaming from a thin disk.

3D Printed Buccal Films for Prolonged-Release of Propranolol Hydrochloride: Development, Characterization and Bioavailability Prediction

Gelatin-polyvinylpyrrolidone (PVP) and gelatin-poly(vinyl alcohol) (PVA) mucoadhesive buccal films loaded with propranolol hydrochloride (PRH) were prepared by semi-solid extrusion 3D printing. The aim of this study was to evaluate the effects of the synthetic polymers PVP and PVA on thermal and mechanical properties and drug release profiles of gelatin-based films. The Fourier-transform infrared spectroscopy showed that hydrogen bonding between gelatin and PVP formed during printing. In the other blend, neither the esterification of PVA nor gelatin occurred. Differential scanning calorimetry revealed the presence of partial helical structures. In line with these results, the mechanical properties and drug release profiles were different for each blend. Formulation with gelatin-PVP and PRH showed higher tensile strength, hardness, and adhesive strength but slower drug release than formulation with gelatin-PVA and PRH. The in silico population simulations indicated increased drug bioavailability and decreased inter-individual variations in the resulting pharmacokinetic profiles compared to immediate-release tablets. Moreover, the simulation results suggested that reduced PRH daily dosing can be achieved with prolonged-release buccal films, which improves patient compliance.

Use of the reflective background oriented schlieren technique to measure free surface deformations in a thin liquid layer non-uniformly heated from below

To measure liquid film surface deformations, we use the Background Oriented Schlieren (BOS) technique with a reflective optical scheme, which includes a random dot pattern located above the liquid surface, and a camera that captures its reflection from the liquid interface. The substrate was covered with a special black coating to minimize stray light reflection, which allowed to provide clear visualization of the dot pattern reflected from the free surface even for very thin liquid films. Local slopes of the film surface cause the dot displacement on the pattern image relative to the pattern image captured in the absence of any free-surface deformations. Hence, the topography of the liquid film surface is encoded by the apparent displacement of the dot pattern. Using the cross correlation image processing, the displacement vector field was determined, which was then substituted in Poisson equation to reconstruct the free-surface profile of the liquid film. The main advantages of this technique are: applicability for liquids with surface temperature inhomogeneities, experimental simplicity, sensitivity and applicability for both transparent and opaque liquids. Using the reflective BOS technique and using substrate with black coating we measure the free-surface deformation field of a thin layer of silicone oil non-uniformly heated from below. Despite the fact that thermocapillary shear stresses tend to decrease the thickness of the liquid layer in hotter regions, in the experiment, a convex deformation of the liquid film surface was observed above the heater for a few seconds immediately after the start of heating. This phenomenon is explained by the expansion of the liquid induced by the heating, due to the dependence of the liquid density on temperature. The measurement results are compared with those obtained in a single point using the confocal sensor. A good agreement is achieved.

Phase structure and its temporal evolution under growing single vapor bubble

A vapor bubble's footprint on a heated surface is composed of dry and wet regions, and their temporal evolution is governed by several forces, such as gravity, vapor inertia, viscous friction, and capillarity. In this Letter, we derive three types of relations that depict the dynamic variations in the length scales for the bubble base, dry area, and thin liquid film under a single vapor bubble. The proposed relations are validated using measurement results from clear images of the phase structure captured by high-speed visualization. Here, we reveal that the viscous friction is a dominant force acting on the bubble expansion process; however, it has been previously ignored for simplicity in dealing with the classical Rayleigh equation. Additionally, the critical role of the liquid wetting character in the vicinity of the moving triple phase line is illuminated to quantify the dry area dynamics. Finally, we find an analytic expression to obtain the thickness profile of the thin liquid film under a bubble based on the well-known Landau and Levich liquid coating theory.

Effects of Navier slip on film condensation heat transfer over upward facing horizontal flat surfaces with free edges

Transport phenomena involving condensate liquids generated from the phase-change heat transfer in microchannels and in engineered superhydrophobic surfaces require consideration of slip effects. Herein, the laminar film condensation over upward facing flat slabs and circular disks of finite sizes with free edges in the presence of wall slip effects is investigated. By considering the Navier slip model and extending the classical Nusselt analysis, the mass, momentum, and energy of the liquid film in two-dimensional/axisymmetric coordinates are solved for the film thickness and the heat transfer rate in non-dimensional form. Numerical solution yields the local structure of the condensate film profile and the Nusselt number for different values of slip coefficient. The results reveals that the condensate film on horizontal surfaces becomes thinner and the overall heat transfer rate is enhanced with an increase in the slip coefficient. In particular, an analysis of the results indicates a power law dependence of the Nusselt number on the non-dimensional slip coefficient with an exponent close to 0.5. Significant enhancement in phase change heat transfer follow from the modification of the local velocity profiles within the condensate film, resulting from the additional momentum gain near the wall surfaces due to increases in slip effects.

Residual-Solvent-Induced Morphological Transformation by Intense Pulsed Light on Spin-Coated and Inkjet-Printed ZnO NP Films for Quantum-Dot Light-Emitting Diodes.

It was demonstrated through a comparison between the spin-coated and inkjet-printed quantum-dot light-emitting diodes' (QLED) performance analysis outcomes that the annealing temperature of a zinc oxide nanoparticle (ZnO NP) electron transport layer (ETL) optimized for intense pulsed light (IPL) via a post-treatment differs depending on the film-formation method used. For a naturally dried ZnO NP ETL formulated without annealing, different film morphologies were observed according to the film-formation method of spin coating and inkjet printing, and the surface-roughness root mean square (RMS) value was increased in an IPL post-treatment due to unevaporated residual solvent. Based on this phenomenon, we classified and analyzed different film profiles according to the deposition method, the presence or absence of annealing, and the annealing temperature.

Dosimetric study of the interplay effect using three-dimensional motion phantom in proton pencil beam scanning treatment of moving thoracic tumours

Abstract Aim: The dosimetric and clinical advantages offered by implementation of pencil beam scanning (PBS) proton therapy for moving thoracic tumours is hindered by interplay effect. The purpose of this study is to evaluate the impact of large proton beam spot size along with adaptive aperture (AA) and various motion mitigation techniques on the interplay effect for a range of motion amplitudes in a three-dimensional (3D) respiratory motion phantom. Materials and Methods: Point doses using ionisation chamber (IC) and planner dose distributions with radiochromic film were compared against the corresponding treatment planning system (TPS) information. A 3D respiratory motion phantom was scanned either for static or 4D computed tomographic (CT) technique for 6-, 10- and 14-mm motion amplitudes in SI direction. For free breathing (FB) treatment, a tumour was contoured on maximum intensity projection scan and an average scan was used for treatment planning. Each FB treatment was delivered with one, three and five volumetric repaintings (VRs). Three phases (CT40–60%) were extracted from the 4D-CT scans of each motion amplitude for the respiratory-gated treatment and were used for the treatment planning and delivery. All treatment plans were made using AA and robustly optimised with 5-mm set-up and 3·5% density uncertainty. A total of 26 treatment plans were delivered to IC and film using static, dynamic and respiratory-gated treatments combinations. A percent dose difference between IC and TPS for the point dose and gamma indices for film–TPS planner dose comparison was used. Results: The dose profile of film and TPS for the static phantom matched well, and percent dose difference between IC and TPS was 0·4%. The percent dose difference for all the gated treatments were below 3·0% except 14-mm motion amplitude-gated treatment. The gamma passing rate was more than 95% for film–TPS comparison for all gated treatment for the investigated gamma acceptance criteria. For FB treatments, the percent dose difference for 6-, 10- and 14-mm motion amplitude was 1·4%, −2·7% and −4·1%, respectively. As the number of VR increased, the percent difference between measured and calculated values decreased. The gamma passing rate met the required tolerance for different acceptance criteria except for the 14-mm motion amplitude FB treatment. Conclusion: The PBS technique for the FB thoracic treatments up to 10-mm motion amplitude can be implemented with an acceptable accuracy using large proton beam spot size, AA and robust optimisation. The impact of the interplay effect can be reduced with VR and respiratory-gated treatment and extend the treatable tumour motion amplitude.

Universal self-similar attractor in the bending-driven levelling of thin viscous films

We study theoretically and numerically the bending-driven levelling of thin viscous films within the lubrication approximation. We derive Green’s function of the linearized thin-film equation and further show that it represents a universal self-similar attractor at long times. As such, the rescaled perturbation of the film profile converges in time towards the rescaled Green’s function, for any summable initial perturbation profile. In addition, for stepped axisymmetric initial conditions, we demonstrate the existence of another, short-term and one-dimensional-like self-similar regime. We also characterize the convergence time towards the long-term universal attractor in terms of the relevant physical and geometrical parameters, and provide the local hydrodynamic fields and global elastic energy in the universal regime as functions of time. Finally, we extend our analysis to the nonlinear thin-film equation through numerical simulations.

Simulation on surface roughness variation of Au thin films by microwave post annealing

A simulation study was performed in order to interpret the experimental results in the previous report on roughness reduction in Au thin films by microwave post annealing in comparison with an electric furnace. The simulation model of this study is based on one-dimensional capillary driven surface diffusion with incorporation of electromigration force due to microwave irradiation. It was shown that alternating microwave electric field does not cancel the atomic migration completely, because of the capillary driven (thermal) effects simultaneously occurring within the alternation period, but is not adequate to account for the variation of the film profiles and the observed wave number spectra. In this study, capillary model was applied to the furnace annealing, and an anisotropic factor in atomic transport by electromigration was introduced in microwave annealing simulations. We reproduced the profiles and spectra changes observed in the experiments by both annealing methods.

Non-linear convective flow of the thin film nanofluid over an inclined stretching surface

To enhance the surface properties of solids the mechanism of thin films is frequently used. Penetration, degradation, stiffness, illumination, diffusion, absorption, and electric performance are all characteristics of a bulk substance medium that a thin film can improve. In nanotechnology, thin film processing can be extremely useful. Therefore, the time-dependent nonlinearly convective stream of thin film nanoliquid over an inclined stretchable sheet with magnetic effect is investigated in current work. The features of mass and heat transport processes are explained using important factors like thermophoresis and Brownian movement. Nonlinear partial differential equations are obtained to model the time-dependent liquid film flow over an inclined surface, which are then turned into couple ordinary differential equations utilizing appropriate alterations. The results of the computation of the model problem are collected using an analytical approach Homotopy Analysis Method and presented the final finding numerically and graphically. During the flow assessment, the impact of individual flow factors such as magnetic, Brownian, and thermophoresis parameters on regular profiles (temperature, velocity, and concentration) are analyzed and found to be quite remarkable. Furthermore, the consequence of M and Nt factors on the velocity, concentration and thermal distribution leads to diminishing conduct. On the other hand, the thermal profile of the liquid film rises in response to the thermophoresis factor. The % wise variation in the skin friction, Nusselt number and Sherwood number versus physical parameters has been obtained and discussed.

2D numerical simulation of tear film dynamics: Effects of shear-thinning properties

The influence of the shear-thinning properties on tear dynamics is analyzed using 2D numerical simulations. The simulations were conducted in conditions close to those of the actual tear film dynamics. The paper deals with the spreading of the shear-thinning tear film on a spherical cornea with blinking. The shear-thinning properties are described using Cross’s rheological model, known as the model that describes well shear-thinning properties of actual tears. We solved the continuity and the momentum equations using the mono-fluid formulation and the volume of fluid (VOF) method. We have examined the influence of rheological properties namely, the time constant, the zero shear viscosity, and the flow behavior index on the tear film profile. The results confirm that the curvature delays the risk of film rupture. The results also indicate that the values of the shear-thinning parameters within the range of the values measured in-vivo are the ones that delay tear-film breakup. These values provide quasi-uniform thin tear film and ensure a low wall shear stress lubrication between the moving eyelid and the cornea surface. The suggested values for the shear-thinning parameters can serve as a starting point for designing efficient artificial tears to alleviate moderate symptoms of dry eye syndrome.

What is transnational Chinese Cinema today? Or, Welcome to the Sinosphere

ABSTRACT A decade ago, I wrote a piece called ‘What Is Transnational Cinema? Thinking from the Chinese Situation’. It argued that knowledge is situational and perspectival; what transnational cinema is depends on when and where you are looking from and writing about. It observed and analysed two current phenomena relevant to understanding what Chinese transnational cinema was then: the growth of cross-border Chinese film production involving the People’s Republic, Hong Kong, Taiwan and more, known as ‘Chinese-language cinemas’ (huayu dianying); and the larger phenomenon of globalisation. This article asks what has changed since and proposes ‘cinemas of the Sinosphere’ as an idea to encompass those changes. However, the term refers to two very different phenomena. First, it responds to the higher profile of films that are part of a Chinese cultural sphere but not in a Sinitic language, rendering the idea of ‘Chinese-language cinemas’ inadequate. Second, it acknowledges the re-emergence of the nation-state and what some people call the ‘Second Cold War’ or what I call a ‘Two Globalizations’ phenomenon, and it refers to the cinema of the People’s Republic of China under the conditions of the Belt and Road Initiative and the non-Chinese cinemas that respond to it.

Dip coating of cylinders with Newtonian fluids

HypothesisThe Landau-Levich-Derjaguin (LLD) theory is widely applied to predict the film thickness in the dip-coating process. However, the theory was designed only for flat plates and thin fibers. Fifty years ago, White and Tallmadge attempted to generalize the LLD theory to thick rods using a numerical solution for a static meniscus and the LLD theory to forcedly match their numeric solution with the LLD asymptotics. The White-Talmadge solution has been criticized for not being rigorous yet widely used in engineering applications mostly owing to the lack of alternative solutions. A new set of experiments significantly expanding the range of White-Tallmadge conditions showed that their theory cannot explain the experimental results. We then hypothesized that the results of LLD theory can be improved by restoring the non-linear meniscus curvature in the equation. With this modification, the obtained equation should be able to describe static menisci on any cylindrical rods and the film profiles observed at non-zero rod velocity. ExperimentTo test the hypothesis, we distinguished capillary forces from viscous forces by running experiments with different rods and at different withdrawal velocities and video tracking the menisci profiles and measuring the weight of deposited films. The values of film thickness were then fitted with a mathematical model based on the modified LLD equation. We also fitted the meniscus profiles. FindingsThe results show that the derived equation allows one to reproduce the results of the LLD theory and go far beyond those to include rods of different radii. A new set of experimental data together with the White-Tallmadge experimental data are explained with the modified LLD theory. A set of simple formulas approximating numeric results have been derived. These formulas can be used in engineering applications for the prediction of the coating thickness.

Single-shot spectrally resolved interferometry for the simultaneous measurement of the thickness and surface profile of multilayer films.

We present a single-shot spectrally-resolved interferometry for simultaneously measuring the film thickness and surface profile of each layer of a patterned multilayer film structure. For this purpose, we implemented an achromatic phase shifting method based on the geometric phase using the polarization characteristics of the light and obtained four phase-shifted interferograms in the spectrally-resolved fringe pattern at the same time by combining a pixelated polarizing camera with an imaging spectrometer. As a result, we could simultaneously measure the reflectance and phase of the sample over a wide wavelength range with a single measurement. To evaluate the validity of the proposed method, we measured a patterned five-layer film specimen and compared our measurement results with those from commercial instruments, an ellipsometer and a stylus profiler, respectively. We confirmed the results matched each other well.