Film Flow Research Articles

Direct detection method for cusp thickness in wavy thin-film flow using an optical waveguide film

The wave crest (cusp) of the disturbance wave in thin liquid film flow is an important factor contributing to heat/mass transfer, e.g., fuel rods in boiling water reactors, stator/rotor blades in steam turbines, and cleaning/drying wafer processes in semiconductor manufacturing. We developed a new technique for directly detecting the thickness of wave cusps using array-based sensing with an optical waveguide film (OWF). This technique, based on geometrical optics assumptions, simultaneously obtains information on liquid films’ thickness and their interfacial shape, i.e., whether or not the local interface is convex upward. We first performed a pseudo-film flow measurement using a metal specimen to confirm the basic principle. According to the results, a meaningful signal indicating the wave-cusp passage, along with a thickness signal, was detected simultaneously. The OWF signal processing for cusp thickness detection was newly established based on this fact. We then applied this technique to a wavy liquid film flow formed on a flat plate in the entry region. A series of experiments were performed over a wide range of air speeds (jG = 20–70 m/s). As a result, the cusp thicknesses of relatively large waves on the wavy interface were successfully extracted from the OWF output signal. Further, the major thickness variables (i.e., base film thickness, median film thickness, and cusp thickness) were compared with those of conventional thickness estimation methods, which showed reasonable agreement. This paper provides a framework for wavy thin-film flow measurements via OWF that is specialized for directly detecting local thickness profiles.Graphical abstract

Dual solution of thin film flow of fuzzified MHD pseudo-plastic fluid: numerical investigation in uncertain environment

The pseudoplastic fluids have wide range of applications in industrial areas including cyclone separation, bearings, paper fibre separation, heat exchangers and also in food industry. In this regard, the current manuscript investigates the impact of transverse magnetic field on thin pseudo-plastic film flow on a vertical wall in a fuzzy (uncertain) environment. The uncertainty in a model is characterized through triangular fuzzy numbers (TFNs) along with r -cut approach, which is computationally effective in capturing the uncertainties in physical phenomena. This results in the modelling of highly nonlinear fuzzified problem. For solution and analysis purposes, Runge–Kutta Fehlberg (RKF) is utilized. Also, RKF solutions are validated by comparing them to homotopy perturbation solutions in the current manuscript. The impact of r -cut, and fluid parameters including non-Newtonian parameter β, magnetic field M and Stoke's number S t on the upper and lower velocity profiles are captured and analysed numerically and graphically. Analysis reveals that velocity profile decreases with an increase in applied magnetic field at upper and lower bounds. Also, increase in S t and β increases the velocity profile at lower bound, while inverse behaviour is recorded in the case of upper bound. The results also indicate that as r goes from 0 to 1, the crisp solution always lies between upper and lower profiles, and becomes coherent at 1. Moreover, all fuzzy level set values of r ∈ [ 0 , 1 ] satisfy the fuzzy solution in the form of TFN.

Modelling Infiltration Based on Source‐Responsive Method for Improving Simulation of Rapid Subsurface Stormflow

AbstractIn humid hilly regions, macropore preferential flow in soils dominates the distribution of event water, thereby influencing the generation and development of runoff. However, the mechanism of how soil functions on macropore drainage and matrix absorption remains poorly understood due to complex soil water dynamics in a multi‐porosity subsurface network. In this study, based on the source‐responsive method that divides the soil into source‐responsive and diffusive domains, the allocation ratio of infiltrated water in macropores recharging the matrix were derived and it was coupled with PIHM (Penn State Integrated Hydrologic Model) as PIHM‐SRM (PS). By simulating the soil moisture process at profile scale and the runoff process at catchment scale, it was found that the PS overcame the difficulty of most hydrologic models in describing the process of replenishing moisture in dry soil. This leads to more satisfactory performance for flood peaks at the outlet (CCC > 0.84) and soil moisture peaks at three profiles (CCC = 0.97) compared to original PIHM models. Moreover, the separate channel of film flow in the PS further improves the simulation accuracy of peak response speed in subsurface floods under rainstorms (TP > 40 mm). Additionally, sensitivity analysis shows that the storage‐discharge capacity of soil profiles dominates torrential flood forecasting in humid headwaters when considering the influence of macropores. Finally, considering the parameter‐predictive property in the PS, field‐based parameterized strategies are vital for distributed catchment modeling. This will enable the PS to improve flash torrent predictions in headwaters and be applied at catchment scales.

Surface wettability governs brine evaporation and salt precipitation during carbon sequestration in saline aquifers: Microfluidic insights.

Carbon sequestration in deep saline aquifers is a promising strategy for reducing atmospheric CO2 emissions. However, salt precipitation triggered by the evaporation of formation brine into injected supercritical CO2 can cause injectivity and containment issues in near-wellbore regions. Predicting the distribution of precipitated salts and their impact on near-wellbore properties remains challenging. This study investigates the influence of surface wettability on CO2-induced halite precipitation and growth within hydrophilic and hydrophobic microfluidic chips designed to mimic rock-structure porous geometries. A series of high-pressure brine-CO2 flow experiments, direct microscopic observations, and detailed image processing were conducted to explore how substrate wettability affects salt precipitation. The experiments show that wettability markedly controls residual brine relocation, film flow movement, solute consumption, and salt formation. Tracking halite precipitation dynamics revealed distinct crystal formation signatures: hydrophilic chips exhibited irregular, larger aggregation patches, while the hydrophobic network showed more numerous, smaller, and limited aggregations. Large individual crystals were observed in both chips, with a notable dominance in the hydrophobic one. Crystallization dynamics varied, with nucleation and growth occurring earlier, progressing faster, and forming bulkier aggregates in the hydrophilic chip. Despite these differences, the three identified temporal stages of brine evaporation and halite surface coverage were comparable. Spatial analysis along the chips indicated that crystal aggregation properties, such as size and distribution, were position-dependent, with hydrophilic chips exhibiting greater probabilistic variability. These observations underscore the impact of surface wettability on salt precipitation through brine accessibility and capillarity, with implications for mitigating and remediating salt issues in saline aquifers.

Numerical study of unsteady thin film flow and heat transfer of power-law tetra hybrid nanofluid with velocity slip over a stretching sheet using engine oil

This paper explores the effects of velocity slip and power-law nanofluid flow on tetrahybrid nanofluids across a stretching sheet. Tetrahybrid nanofluids, which combine four distinct nanoparticles Ag, SiO2, CuO, and ZnO with engine oil as the base fluid, are investigated for their potential to enhance thermal performance. Engine oil plays a critical role in reducing friction and wear in mechanical systems by forming a protective layer on components such as cylinders, pistons, and bearings. Using MATLAB’s bvp4c, the study solves a set of ordinary differential equations derived from boundary layer equations, applying appropriate similarity transformations. It is observed that two unique velocity profiles intersect at a specific location, which shifts away from the stretching sheet as the velocity slip parameter increases. The findings indicate that tetrahybrid nanofluids offer superior heat transfer rates compared to standard nanofluids, showing improvements of 7.43, 6.27, and 5.35% over hybrid and tri-hybrid nanofluids, respectively. This study provides graphical representations of how various parameters, including the Prandtl number, power-law index, slip parameter, magnetic field parameter, and Reynolds number, affect temperature and velocity profiles. It is revealed that increasing the value of the solid volume fraction causes the tetrahybrid nanofluid velocity to decrease and its temperature to rise. The innovation of this work lies in its detailed examination of tetrahybrid nanofluids, extending beyond earlier research on simpler nanofluids and offering valuable insights for advanced thermal management solutions.

Dynamics of a thin film of fluid spreading over a lubricated substrate

We examine the gravity-driven flow of a thin film of viscous fluid spreading over a rigid plate that is lubricated by another viscous fluid. We model the flow over such a ‘soft’ substrate by applying the principles of lubrication theory, assuming that vertical shear provides the dominant resistance to the flow. We do so in axisymmetric and two-dimensional geometries in settings in which the flow is self-similar. Different flow regimes arise, depending on the values of four key dimensionless parameters. As the viscosity ratio varies, the behaviour of the intruding layer ranges from that of a thin coating film, which exerts negligible traction on the underlying layer, to a very viscous gravity current spreading over a low-viscosity, near-rigid layer. As the density difference between the two layers approaches zero, the nose of the intruding layer steepens, approaching a shock front in the equal-density limit. We characterise a frontal stress singularity, which forms near the nose of the intruding layer, by performing an asymptotic analysis in a small neighbourhood of the front. We find from our asymptotic analysis that unlike single-layer viscous gravity currents, which exhibit a cube-root frontal singularity, the nose of a viscous gravity current propagating over another viscous fluid instead exhibits a square-root singularity, to leading order. We also find that large differences in the densities between the two fluids give rise to flows similar to that of thin films of a single viscous fluid spreading over a rigid, yet mobile, substrate.

Investigation of Atomized Droplet Characteristics and Heat Transfer Performance in Minimum Quantity Lubrication Cutting Technology

ABSTRACTMinimum quantity lubrication (MQL) cutting technology is ecologically friendly and efficient in terms of cooling and lubrication. It has be.en widely used in recent years. The atomization effect of the MQL system was characterized by the average diameter of atomized droplets in this study. Second, the MQL heat transfer experimental platform was built, and the cooling experiments were carried out under different MQL parameters. The heat flux density is linearly related to the heat source temperature under steady‐state conditions, and the nozzle target distance has the greatest influence on the cooling effectiveness. The flow state of the lubricating oil is liquid film flow when the heat source temperature is lower than 120°C. The flow state of the lubricating oil is ditch flow when the heat source temperature is higher than 180°C. The average droplet diameter decreased by 43.7% when the pressure was 0.4 MPa compared with 0.2 MPa. An increase in gas supply pressure can improve the cooling effect of MQL. With the increase in flow rate, the average droplet diameter and steady‐state heat flux do not change significantly. At 270°C, the steady‐state heat flux at a flow rate of 90 mL/h was only 2.99% lower than that at 18 mL/h. The average droplet diameter is the smallest, and the cooling effect is the best when the nozzle diameter is 1.5 mm. The heat transfer effect is the best when the nozzle distance is 20 mm at different temperatures. When the nozzle distance is between 20 and 40 mm, the heat transfer capacity of MQL is the most stable. The heat transfer performance of MQL is helpful to improving the efficiency and quality of cutting, and promoting the implementation of a green manufacturing and sustainable development strategy.

Influence of Ice Growth Mode on the Ice Thickness and Shape Prediction of Two-Dimensional Airfoil

Computational results of aircraft icing and predictions of ice shape are not only determined by the solutions of air-supercooled droplet two-phase flow and icing thermodynamic models of surface water film, but are also influenced by the growth mode of the ice layer. Two ice growth modes were established in a two-dimensional (2D) icing process simulation framework to calculate the ice thickness and ice shape, depending on whether surface deformation of the icing process was considered. Ice accretion simulations were performed with the two ice growth modes for an NACA0012 airfoil under rime ice and mixed ice conditions, and the results of ice amount, ice thickness, and ice shape were compared and analyzed. Under the same amount of ice formation, the ice thickness and ice shape obtained using different ice growth modes vary. The ice thickness and the ice shape size are relatively large without considering surface deformation, whereas the results with growth correction show a certain degree of reduction, which is more noticeable around the leading edge and the ice horns. However, the degrees of difference in ice thickness and ice shape are not the same, and the deviation in ice thickness is more obvious. Furthermore, the ice thickness and ice shape obtained using the ice growth correction mode are more consistent with experimental data and commercial software results, verifying the accuracy of the ice simulation method and the necessity of considering ice surface deformation. This paper is an essential guide for understanding the icing mechanism and accurately predicting two-dimensional ice shape.

Imbibition dynamics in a flattened triangular channel including corner film flow

Imbibition dynamics in a flattened triangular channel including corner film flow

Gradient Nonwettability Controls Water-Film Flowing Features.

The flow of the water film on solid surface depended on the film Reynolds number and wind speed. Moreover, environmental factors had an impact on the flow process. This study explored how surface wettability impacts the stability and detachment of water film under varying conditions. Superhydrophobic surface played a critical role in speeding up the detachment of water film, especially under conditions of strong wind and specific flow dynamics, such as a wind speed of 19 m/s and a Reynolds number of 83. The efficiency in water removal was due to a combination of forces: capillary action, which pulls the water into smaller areas, reduced surface tension, and decreased adhesion between the liquid and surface. These factors worked together to shrink the area of contact, allowing the film to break and detach more easily. The findings suggested that enhancing nonwettability can improve water removal efficiency, with potential applications in fields like aerospace. Furthermore, additional trials across varying wind speeds and Reynolds numbers consistently supported the superior performance of superhydrophobic surface in driving rapid water-film detachment. To advance this effect, a gradient nonwetting surface was introduced, specifically engineered within the superhydrophobic regime, to amplify the velocity of film separation. This design innovation leveraged variations in surface energy across the gradient, which fostered directional water-film movement and accelerated detachment. A comprehensive analysis of the underlying physical mechanisms further elucidated its potential in enhancing water-shedding applications across a range of environmental conditions.

Modeling of interfacial diffusion in adjacent flows of polymer films

Adjacent flow of two polymeric fluids occurs in many industrial processes. Under these processes, entangled polymer chains usually undergo extensional flow and shear flow deformation fields, rendering orientation and stretching within polymer chains. In the present paper, the chain stretching ratio and interfacial diffusion in a symmetric bilayer film in the isothermal adjacent flows in a coextrusion process are modeled using the double constraint release with chain stretching model. Extension-dominant and shear-dominant flows are considered separately for ease of the modeling process. Also, the impact of entanglement density on the reptation relaxation is investigated to determine the entanglement density variation and its effect on the stretching ratios and interfacial diffusion. Our findings show that extension-dominant and shear-dominant deformation fields have different impacts on polymer chain stretching, affecting polymer interfacial chain diffusion. Our findings show that while shear flow with the strength of 30 s−1 increases the stretching ratio by 28%, extensional flow with the same strength increases the stretching ratio by 60% of the maximum stretching ratio for polystyrene chains with an average molecular weight of 200 km/mol at 175 °C. Our results show that initial entanglement density is effective on the chain stretching only in the transition step before chains reach equilibriums. This study highlights the impact of flow conditions and chain configuration in polymers on engineering the diffusion of polymer chains at the interface of layered configurations.

Dual effects of pressure difference for long-wave stratified flow in horizontal microchannels

In this work, the linear stability analysis combining with energy balance theory is performed to clarify the suppressing and boosting long-wave instabilities driven by pressure difference in horizontal microchannels as well as its corresponding physical meanings. It is found that, for a specific fluid combination, there exists a certain relative liquid film thickness (hN,c) at which the disturbance work done by interfacial shear stress over unit wavelength (denoted by ISS) is exactly equal to the total viscous dissipation rate over unit wavelength within both phase bulk flows (denoted by DIStot). When the liquid film thickness (hN) exceeds hN,c, ISS is smaller than DIStot, indicating that the initial disturbance energy cannot be replenished from the primary flow until its completely disappear due to the viscosity dissipation. Conversely, ISS is larger than DIStot, indicating that the initial disturbance can acquire energy from the primary flow and grow up. The strength of suppressing and boosting effect can be influenced by liquid film thickness, flow rate, and channel height. However, the demarcation of the dual effects remains unchanged. An analytical expression of hN,c with respect to the viscosity ratio is established by means of long-wave approximation method, which matches well with the numerical results. The energy balance mechanisms revealed in the present study provide a new insight into the wave mode in the confined space and help the design of microfluidic systems.

Thermocapillary weak viscoelastic film flows on a rotating substrate

Thermocapillary weak viscoelastic film flows on a rotating substrate

Vitamin D3 formation in milk by UV treatment – Novel insights into a rediscovered process

Vitamin D3 is essential for several functions in the human body and the demand is usually covered by natural reactions in skin with UV radiation delivered by the sun. But living beyond a latitude of 35° can lead to a lack of sufficient exposition to the deciding wavelength. Here, many countries fortify their milk prophylactically with artificial vitamin D3. However, the precursor molecule of vitamin D3 (7-deydrocholesterol) is already naturally located in the milk fat globule membrane. Thus, this study deals with the transformation of the naturally occurring 7-dehydrocholesterol into vitamin D3 through UV treatment of the milk - a mechanism that was observed a century ago only indirectly. Different parameters such as temperature (10 - 50°C), fluid flow regimen (turbulent vs. laminar thin film, i.e., 0.6 mm) and wavelength (254, 280 and 313 nm) were investigated in this study for their efficiencies. The UV dose of each experiment was measured with chemical actinometry delivering the actually applied dose reaching the milk. Thus, the connection between applied UV dose and generated vitamin D3 content in the milk measured quantitively with LC-MS/MS was evaluated here that both were not possible a hundred years ago. The experimental results revealed that temperature generally promotes the vitamin D3 formation at 254 nm. Further, a turbulent flow is not as efficiently treated as a laminar thin film flow that is as narrow as 0.6 mm. As expected from absorbance spectra of the precursor molecule 7-dehydrocholesterol, 280 nm turned out to be the most efficient wavelength, followed by intermediate success through irradiation with 254 nm and almost no effect by 313 nm. Generally, it was shown that vitamin D3 concentration of milk was easily increased by UV treatment with today's technologies and that adjustment of certain physical parameters have a significant effect on the efficiency.

Comment on Khan et al. Impact of Thermal Radiation on Magnetohydrodynamic Unsteady Thin Film Flow of Sisko Fluid over a Stretching Surface. Processes 2019, 7, 369

Comment on Khan et al. Impact of Thermal Radiation on Magnetohydrodynamic Unsteady Thin Film Flow of Sisko Fluid over a Stretching Surface. Processes 2019, 7, 369

Flow of viscoelastic films over grooved surfaces with partial wetting

We consider the steady flow of a viscoelastic film over an inclined plane featuring periodic trenches normal to the main flow direction. The trenches have a square cross-section and side length 5–8 times the capillary length. Owing to the orientation of the substrate, the film fails to coat the topographical feature entirely, forming a second gas–liquid interface inside the trench and two three-phase contact lines at the points where the free surface meets the wall of the trench. The volume of entrapped air depends on material and flow parameters and geometric conditions. We develop a computational model and carry out detailed numerical simulations based on the finite element method to investigate this flow. We solve the two-dimensional mass and momentum conservation equations using the exponential Phan-Thien & Tanner constitutive model to account for the rheology of the viscoelastic material. Due to the strong nonlinearity, multiple steady solutions possibly connected by turning points forming hysteresis loops, transcritical bifurcations and isolated solution branches are revealed by pseudo-arc-length continuation. We perform a thorough parametric analysis to investigate the combined effects of elasticity, inertia, capillarity and viscosity on the characteristics of each steady flow configuration. The results of our simulations indicate that fluid inertia and elasticity may or may not promote wetting, while shear thinning and hydrophilicity always promote the wetting of the substrate. Interestingly, there are conditions under which the transition to the inertial regime is not smooth, but a hysteresis loop arises, signifying an abrupt change in the film hydrodynamics. Additionally, we investigate the effect of the geometrical characteristics of the substrate, and our results indicate that there is a unique combination of the geometry and viscoelastic properties that either maximizes or minimizes the wetting lengths.

Influence of Ionic Liquid Film Thickness and Flow Rate on Macrocyclization Efficiency and Selectivity in Supported Ionic Liquid-Liquid Phase Catalysis.

Supported ionic-liquid phase (SILP) technology in a biphasic setting with n-heptane as the transport phase was applied to the Ru-alkylidene-N-heterocyclic carbene (NHC) catalyzed macrocyclization of α,ω-dienes to elucidate the effect of ionic liquid (IL)-film thickness, flow rate as well as substrate and product concentration on macrocyclization efficiency, and Z-selectivity. To understand the molecular-level behavior of the substrates and products at the n-heptane/IL interphase, atomistic molecular dynamics simulations were conducted and correlated with experimental observations. The thickness of the IL layer strongly influences the Z/E ratio of the products in that a thin IL layer favors higher Z/E ratios by confining the catalyst between the pore wall and the liquid-liquid interphase whereas a thick IL layer favors formation of the E-product and Ru-hydride catalyzed isomerization reactions. Also, macrocyclization efficiency, expressed by the ratio of oligomers/macromonocycle (O/MMC), is influenced both by the flow rate and the thickness of the IL layer.

Numerical study of unsteady thin film flow of power-law tetra hybrid nanofluid with velocity slip effect over a stretching sheet using sodium alginate as base fluid

This study examines the influence of power-law nanofluid flow and velocity slip on the heat transfer performance of tetrahybrid nanofluids over a stretching sheet, with the objective of enhancing thermal efficiency in industrial applications. The tetrahybrid nanofluids, consisting of Al2O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Al_2O_3$$\\end{document}, TiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$TiO_2$$\\end{document}, Cu, and Fe3O4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Fe_3O_4$$\\end{document} nanoparticles suspended in a sodium alginate base fluid, represent a novel combination of materials whose collective thermal properties have not been extensively studied. The performance of these tetrahybrid nanofluids is compared to that of hybrid and tri-hybrid nanofluids to evaluate their relative heat transfer capabilities. The boundary layer equations are solved using MATLAB’s bvp4c solver, applying similarity transformations to investigate temperature and velocity profiles under varying parameter conditions. The results indicate that tetrahybrid nanofluids significantly enhance heat transfer rates compared to standard nanofluids, with improvements of 7.43%, 6.27%, and 5.35% over hybrid and tri-hybrid nanofluids, respectively. Furthermore, the analysis reveals that velocity profiles intersect at a specific point, and as the velocity slip parameter increases, the profiles move further away from the stretching sheet. Key factors, such as the Prandtl number, power-law index, slip parameter, magnetic field, and Reynolds number, are also examined for their effects on flow and thermal behavior. The key innovation of this research lies in the introduction of tetrahybrid nanofluids as an advanced medium for heat transfer, providing superior thermal efficiency compared to previously studied nanofluids. This study not only builds upon existing research but also provides new computational insights into the potential applications of tetrahybrid nanofluids in areas like food processing and other industries requiring effective thermal management.

Synergistic Control of Molecular Self-Assembly and Orientation to Enhance the Performance of Organic Field-Effect Transistors Utilizing Solution-Processable Organic Semiconductors

Introduction: Fast development of solution-processable organic semiconductors and their utilization as active components of organic electronic devices has gained momentum in the recent past aiming towards the practical realization of low-cost flexible and printable electronics. The past decade has witnessed significant scientific efforts to improve the charge transport characteristics of organic semiconductors by tuning their chemical structure or by varying the film fabrication techniques to enhance the macromolecular ordering. Due to the quasi-one-dimensional nature of organic conjugated polymers (CPs), their backbone orientation and self-assembly have been extensively explored to improve the optoelectronic characteristics of organic electronic devices. Organic electronic devices quite often need multilayer fabrication of devise components, where control of their morphology along with the various interfaces critically controls the overall performance of the devices. Therefore, there is an urge for the facile fabrication of large-area uniform films with controllable film morphology and minimal interference to the underlying layers. Our group has developed and improvised a novel method of thin film fabrication known as the floating-film transfer method (FTM), which provides not only large-area uniform thin films but also these films exhibit directional molecular orientation. Control of molecular orientation is highly desired to control the extent and directionality (vertical or in-plane) of the charge transport, which needs to be amicably utilized to harness the full potentiality of the device performance under investigation. Results and Discussion: The uniqueness of the FTM lies in 1st of all the fabrication of floating films of solution-processable CPs on an orthogonal liquid substrate followed by its transfer on any desired substrate by stamping, which has been schematically represented in Fig.1(a). Thanks to the isolation of film fabrication and transfer, it is possible to fabricate multilayers of the same or different CPs without having any adverse effect on the underlying layers, which is one of the intriguing issues for thin film fabrication using solution processing. We have demonstrated that controlling the parameters for thin film fabrication using NR-P3HT under FTM led to not only macroscopically oriented thin films but also there was a remarkable enhancement in the field effect mobility (>100 times) of organic field-effect transistors (OFETs) as compared to their spin-coated thin film device counterparts. One of the well-studied CPs, PBTTT-C14 possesses a rigid-rod-like polymeric backbone with liquid-crystalline behaviour, which is rather difficult to orient, and has been reported to impart enhanced carrier mobility when its thin film was annealed at its liquid-crystalline temperature of 180oC. Utilizing highly edge-on oriented thin films of this CP processed by FTM, we have not only demonstrated a very high optical dichroism of >10 but also an OFET mobility of 1.24 cm2/Vs, which is one of the highest reported mobility for this class of CPs as shown in Fig. 1(b). Despite the enhancement in solubility as a function of increasing alkyl-chain length in the P3AT class of CPs, there is a drastic fall in carrier mobility up to 4-5 orders of magnitude. We have recently demonstrated that FTM is capable of solving this issue amicably, where the detrimental influence of alkyl chain length for planer charge carrier transport was not observed making the freedom for the selection of any of P3ATs for OFET applications. Fabrication of a large-area ≈40 cm2 film with uniform orientation was recently reported for poly(3,3‴-dialkylquaterthiophene) (PQT) using FTM. An array of bottom-gate top contact OFETs fabricated along the length of a single large-area (≈15 × 2.5 cm2) thin film demonstrated the average field-effect mobility of 0.03 cm2/V s with a very narrow standard deviation of 12%. It has been found that the pre-conceived notion of the orientation of the FTM thin films is perpendicular to the direction of the flow of thin films is not completely true and the viscous force of not only the liquid substrate but also the CP solution plays a vital role in determining the direction of orientation as shown schematically in Fig. 1(c). Based on combined theoretical and experimental approaches, we have demonstrated the control of the extent and direction of molecular orientation using DPP-TTT, a rigid rod-like donor-acceptor type CP, which is rather difficult to orient owing to its molecular rigidity. Harnessing the synergy of orientation and molecular orientation under FTM using DPP-TTT, a very high field-effect mobility of 12.4 cm2V-1s-1 was recently demonstrated, which is one of the highest values reported for solution-processable organic semiconducting polymers. Results pertaining to the film fabrication by FTM, orientation mechanism, film uniformity and anisotropy along with the application of FTM-processed films towards their suitability of OFETs will be discussed in detail. Figure 1

Investigating the Role of Fluid Dynamics on Cut Width Accuracy in Wet Bevel Cleaning Techniques

As the size of advanced technology nodes keeps scaling down, IC manufacturers continue to push the active die area to the wafer edge. Defects originating from the wafer edge can result in substantial yield loss. Etching and cleaning bevel films and particles is increasingly critical in improving wafer yield performance near the wafer edge. Even though backside center dispense spin (BCS) and bevel nozzle dispense spin (BVS) methods have been developed and employed as two main wet bevel cleaning techniques in high volume manufacturing, the comparison of cut width accuracy between different wet bevel cleaning techniques has not been fully studied. The goal of this study is to investigate and understand the effects of fluid dynamics on cut width accuracy in different wet bevel cleaning techniques (i.e. BCS and BVS). In this study, computational fluid dynamics (CFD) numerical models were developed to study the chemical liquid flow in wet bevel cleaning processes.In the BCS process, the chemical liquid is dispensed through a nozzle below the center of wafer backside while the wafer is spinning. In order to characterize the cut width profile after BCS process, the liquid flow was modeled under the coordinate system of the rotating wafer instead of the regular stationary coordinate system. This special type of model allows understanding how the liquid is distributed on the wafer surface with respect to the rotating wafer, which will be more straightforward to be compared with the measurement of cut width profile.For the BCS process, the simulation results of liquid flow on the wafer backside surface are shown in Fig. 1. Due to the increasing centrifugal force towards the wafer edge, the liquid flow starts to develop some branching patterns. The liquid velocity (Fig. 1(a)) and liquid film thickness (Fig. 1(b)) are not axisymmetric anymore. Fig. 2 shows a vertical cross section of liquid flow at the wafer edge. The frontside etching in BCS relies on this liquid wrap-around flow. Due to the inertia and capillary force effects, the liquid first climbs from wafer backside to frontside as shown in Fig. 2(a). The liquid volume keeps increasing as liquid accumulates around the wafer edge as shown in Fig. 2(b). When the liquid volume at wafer bevel is greater than a certain threshold, the extra liquid will be stripped from the continuous liquid film as shown in Fig. 2(c). Because this wrap-around flow is unstable and periodic, the leading edge of the liquid on wafer frontside always fluctuates during BCS process as shown in Fig. 3. The non-axisymmetric backside flow leads to non-axisymmetric wrap-around flow on the wafer frontside. Because the liquid wrap-around flow is spatially non-axisymmetric and temporally unstable, the cut width profile over the whole perimeter of wafer bevel region can be quite non-uniform as shown in Fig. 4(a).In the BVS process, the chemical liquid is dispensed through a nozzle above the frontside bevel region as shown in Fig. 5. After the liquid jet lands on the rotating wafer, the liquid will develop into a stable circular flow along the wafer edge as shown in Fig. 5(a). A vertical cross section of the liquid film flow is plotted in Fig. 5(b). The inner cut position of the liquid film flow dictates the cut width in the BVS process. Because this circular liquid flow during BVS process is more stable, the cut width profile is more uniform in the BVS process as shown in Fig. 4(b).In practice, the cut width profile after the BCS process is also dependent on the properties of wafer surface such as wafer surface wettability. If the wafer surface is hydrophobic, the liquid flow on the wafer backside surface can break up, which results in very limited wrap-around flow and limited etching at the wafer edge. Therefore it can be difficult to use the BCS technique to etch the hydrophobic bevel films. On the other hand, the circular liquid flow in the BVS process is less affected by the properties of wafer surface because the liquid is directly dispensed over the bevel region. It is much easier to achieve the cut width target using the BVS technique by adjusting operation conditions such as the nozzle position. Since the numerical model developed in this study can accurately represent the flow physics in the BVS process, this CFD model can be adopted as a digital twin of the BVS tool to optimize the BVS process conditions based on the film material properties (e.g., contact angle) to meet the cut width target. Figure 1