This paper describes the fabrication and testing of a novel angle-scanning surface plasmon resonance imaging (SPRi) instrument. The combination of two stationary mirrors and two angle-controlled ...mirrors provides high accuracy (up to 10
−3
°) and high-speed angular probing. This instrument minimizes the angle-dependent image artifact that arises due to beam walk, which is the biggest challenge for the use of SPRi with angular modulation (AM). In the work described in this paper, two linear stages were employed to minimize the image artifact by adjusting the location of the angle-controlled mirrors and the camera. The SPRi instrument was used to visualize coalescence during dropwise condensation. The results show that the effect of the environment’s temperature on reflectance was less than 1% when the incident angle was carefully chosen for SPRi with intensity modulation (IM). This means that condensation visualization can be carried out at ambient temperatures, without the need for a Peltier stage or a thermally controlled condensing surface. The concept of pixel neighboring was employed to assess the probability of noise and the standard error of thin film measurement. Experimental analyses during dropwise condensation show (1) the presence of a thin film with thickness of one monolayer, and (2) surface coverage of 0.71 m
2
/m
2
by the thin film in the area between the droplets. In addition, analyses showed the existence of a dry area at the part of the substrate exposed by coalescence to ambient air. The results of this work undermine the validity of the film rupture theory as the dropwise condensation mechanism.
Graphic abstract
Nanofluids as CO2 absorbents have problems involving precipitation or flocculation of the seeding particles. Nanoemulsion CO2 absorbents are expected to solve these problems. In this study, ...nanoemulsion (Dodecane/Methanol) absorbents were proposed and their thermophysical properties and dispersion characteristics were evaluated for mass transfer performance enhancement during CO2 absorption process. Both Span 60 and Tween 60 were selected due to their nonionic surfactant feature and hydrocarbon chemical types of dodecane. The nanoemulsion absorbents were ultrasonically manufactured after adding Span 60 and Tween 60 in a ratio of 4:6 to match the required hydrophile-lipophile balance (HLB = 11). Thermal conductivity and viscosity of nanoemulsion absorbents were measured for various surfactant ratios. Tyndall effects and turbidity measurements were executed to find out the best dispersion stability condition. An optimal ultrasonication time was proposed based on the smallest mean size of nanoemulsion droplets and their uniformity. Both mechanisms of thermophysical properties and dispersion stability of nanoemulsion absorbents were proposed based on cryo transmission electron microscope (TEM) results.
The present study aims to investigate the characteristics of pinning behaviors and local mass flux variations during droplet evaporation at different surface temperatures ranging from 22.5 °C to ...80 °C. An evaporating droplet is visualized by a CMOS camera, and the images are analyzed from droplet deposition to completion of evaporation. We measure the contact angle, the contact diameter, the droplet volume, the total evaporation time, and the pinning time during evaporation. The pinning time and Marangoni number increase with surface temperatures in the range from 20 °C to 50 °C; however, they decrease at surface temperatures higher than 50 °C. Moreover, the present study analyzes the local mass flux variation according to the surface temperature, showing the increase in the local mass flux over time. We also consider the change in vapor concentrations for the heated surfaces to estimate the local mass flux. Indeed, the local mass flux at the contact line becomes much higher; it experiences over a 10-fold increase from 0.1tf to 0.9tf.
Understanding the evaporation characteristics of sessile binary mixture droplets (BMDs) is crucial in various industries, such as surface coating, ink-jet printing, evaporators, fuel combustion, and ...medical diagnosis. The underlying physics of BMDs has not yet been fully explored despite numerous prior studies. This paper reviews the recent studies on evaporating BMD and examines various studied and unaddressed issues. First, we introduce measurement techniques to estimate time-varying mixture concentrations of BMDs during evaporation. Next, the theoretical models that have been developed to predict selective evaporation dynamics of BMDs are reviewed and summarized. Finally, this paper reviews the recent studies that have examined the three distinct stages of the contact line motion and internal flows of BMDs.
Early fire detection is essential for preventing catastrophic events, and fire detectors play a critical role in ensuring fire safety. Among the various types of fire detectors, photoelectric smoke ...detectors are widely used because of their ability to detect smoke at an early stage. The present study investigates the effects of changes in flow directions and inlet size on the smoke detection ability of a photoelectric smoke detector by conducting computational fluid dynamics (CFD) simulations. The results indicated that when the flow direction changes, the components in the optical chamber may hinder the smoke inflow and increase the detector activation time. Moreover, the smoke inlet size was found to affect the carbon monoxide concentration inside the chamber. The velocity magnitude distributions confirmed the correlation between the smoke velocity in the labyrinth structures entering the optical chamber and the detection ability of the smoke detector. These findings suggested that when optimizing the performance of a smoke detector, flow direction, inlet size, and amount of smoke introduced into the optical chamber should be considered. The current study suggested the modified design of the smoke detector to have superior detection ability in both directions compared to the base case in terms of activation time.
The objective of this work is to identify the mechanism of dropwise condensation on a smooth solid surface. We investigate the stable dropwise condensation that occurs at a droplet growth rate of 1 ...µm/s in diameter on a gold-coated glass surface. Additionally, we present our observations on unstable dropwise condensation, i.e., degradation of dropwise condensation of steam on a gold surface. Surface Plasmon Resonance Imaging (SPRi) is used to evaluate the existence and structure of thin films and occurrence of initial nuclei during condensation. SPRi approach used in this study has lateral resolutions of 4–10 µm, thickness resolutions of 0.1–1 nm, and temporal resolutions of 200–10,000 frames per second (FPS). Visualization of the onset of stable dropwise condensation suggests droplets form at heterogeneous nucleation sites and that no film greater than a monolayer exists on the surface before the formation of droplets. Observation of the unstable dropwise condensation of steam shows the existence of water films that are several nanometers thick between droplets. This work shows that neither the nucleation theory nor film rupture theory can individually explain the physics of dropwise condensation. Therefore, there is a need for a more comprehensive theory that can explain the mechanism of dropwise condensation.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to prevent colorectal tumorigenesis. Although antitumor effects of NSAIDs are mainly due to inhibition of cyclooxygenase activity, there is ...increasing evidence that cyclooxygenase-independent mechanisms may also play an important role. The early growth response-1 (EGR-1) gene is a member of the immediate-early gene family and has been identified as a tumor suppressor gene. Tolfenamic acid is a NSAID that exhibits anticancer activity in a pancreatic cancer model. In the present study, we investigated the anticancer activity of tolfenamic acid in human colorectal cancer cells. Tolfenamic acid treatment inhibited cell growth and induced apoptosis as measured by caspase activity and bioelectric impedance. Tolfenamic acid induced EGR-1 expression at the transcription level, and analysis of the EGR-1 promoter showed that a putative ETS-binding site, located at -400 and -394 bp, was required for activation by tolfenamic acid. The electrophoretic mobility shift assay and chromatin immunoprecipitation assay confirmed that this sequence specifically bound to the ETS family protein epithelial-specific ETS-1 (ESE-1) transcription factor. Tolfenamic acid also facilitated translocation of endogenous and exogenous ESE-1 to the nucleus in colorectal cancer cells, and gene silencing using ESE-1 small interfering RNA attenuated tolfenamic acid-induced EGR-1 expression and apoptosis. Overexpression of EGR-1 increased apoptosis and decreased bioelectrical impedance, and silencing of endogenous EGR-1 prevented tolfenamic acid-induced apoptosis. These results show that activation of ESE-1 via enhanced nuclear translocation mediates tolfenamic acid-induced EGR-1 expression, which plays a critical role in the activation of apoptosis.
The long-term stability and superior device reliability through the use of delicately designed metal contacts with two-dimensional (2D) atomic-scale semiconductors are considered one of the critical ...issues related to practical 2D-based electronic components. Here, we investigate the origin of the improved contact properties of alloyed 2D metal–semiconductor heterojunctions. 2D WSe2-based transistors with mixed transition layers containing van der Waals (M–vdW, NbSe2/W x Nb1–x Se2/WSe2) junctions realize atomically sharp interfaces, exhibiting long hot-carrier lifetimes of approximately 75,296 s (78 times longer than that of metal–semiconductor, Pd/WSe2 junctions). Such dramatic lifetime enhancement in M–vdW-junctioned devices is attributed to the synergistic effects arising from the significant reduction in the number of defects and the Schottky barrier lowering at the interface. Formation of a controllable mixed-composition alloyed layer on the 2D active channel would be a breakthrough approach to maximize the electrical reliability of 2D nanomaterial-based electronic applications.
Using surface plasmon resonance imaging (SPRi), we have recently shown for the first time the existence of a monolayer water film between droplets during dropwise condensation. This study examines ...the effect of adsorbed volatile organic compounds (VOCs) on the ultrathin film measurement using SPRi. Further, the work presents the proper surface-treatment process that enables measurements of the ultrathin water layer during high-speed imaging of dropwise condensation at 3000 frame per second. In this study, two methods were applied for cleaning the surface (gold-coated glass)—(1) standard cleaning procedure (SCP) using acetone, isopropyl alcohol, and deionized water and (2) SCP followed by air plasma cleaning. This work discusses the effect of the cleaning procedures on surface roughness, contact angle, and surface chemistry using atomic force microscopy, optical microscopy, and an X-ray photoelectron spectroscope meter. The results showed that SCP before the SPRi is a proper surface-treatment method. The effect of adsorbed VOCs during dropwise condensation on a surface treated with SCP was measured to be 0.0025 (reflectivity unit), which was 70% smaller than the reflectance associated with a monolayer water film. The results of this work confirm a monolayer water film observation during the dropwise condensation, which has been reported before.
The present study aims to measure the solid–liquid interface temperature of an evaporating droplet on a heated surface using a thermoresponsive polymer. Poly(N-isopropylacrylamide) (pNIPAM) was used ...owing to its sensitive optical and mechanical properties to the temperature. We also measured the refractive index variation of the pNIPAM solution by using the surface plasmon resonance imaging (SPRi). In particular, the present study proposed a new method to measure the solid–liquid interface temperature using the correlation among reflectance, refractive index, and temperature. It was found that the reflectance of a pNIPAM solution decreased after the droplet deposition. The solid–liquid interface temperature, estimated from the reflectance, showed a lower value at the center of the droplet, and it gradually increased along the radial direction. The lowest temperature at the contact line region is present because of the maximum evaporative cooling. Moreover, the solid–liquid interface temperature deviation increased with the surface temperature, which means solid–liquid interface temperature should be considered at high temperature to predict the evaporation flux of the droplet accurately.
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