ABSTRACT
A passive cooling method with great potential to lower space-cooling costs, counteract the urban heat island effect, and slow down worldwide warming is radiant cooling. The solutions available frequently require complex layered structures, costly products, or a reflective layer of metal to accomplish daytime radiative cooling, which restricts their applications in many avenues. Furthermore, single-layer paints have been used in attempts to accomplish passive daytime radiative cooling, but these usually require a compact coating or only exhibit limited cooling in daytime. In our study, we investigated and evaluated in daytime the surrounding cooling outcome with aid of one layer coating composed of BaSO4/TiO2 microparticles in various concentrations implanted in the PVDF-HF polymers on a concrete substrate. The 30% BaSO4/TiO2 microparticle in the PVDF-HF coating shows less solar absorbance and excessive emissivity. The value of solar reflectance is improved by employing micro-pores in the structure of PVDF polymers without noticeable effect on thermal emissivity. The 30% BaSO4/TiO2/PVDF coating is accountable for the hydrophobicity and proportionate solar reflection in the UV band, resulting in efficient solar reflectivity of about 95.0%, with emissivity of 95.1% and hydrophobicity exhibiting a 117.1° water contact angle. Also, the developed coating could cool to about 5.1 °C and 3.9 °C below the surrounding temperature beneath the average solar irradiance of 900 W/m-2. Finally, the results demonstrate that the 30% BaSO4/TiO2/PVDF-HF microparticle coating illustrates a typical figure of merit of 0.60 and is also capable of delivering outstanding dependability and harmony with the manufacturing process.
ABSTRACT
Radiative cooling is a new large-scale cooling technology with the promise of lowering costs and decreasing global warning. Currently, daytime radiative cooling is achieved via the application of reflective metal layers and complicated multilayer structures, limiting its application on a massive scale. In our research, we explored and tested the daytime subambient cooling effect with the help of single-layer films consisting of BaSO4, TiO2, and BaSO4/TiO2 microparticles embedded in PVDF/PTFE polymers. The film, consisting of BaSO4/TiO2 microparticles, offers a low solar absorbance and high atmospheric window emissivity. The solar reflectance is enhanced by micropores in the PVDF/PTFE polymers, without any significant influence on the thermal emissivity. The BaSO4/TiO2/PVDF/PTFE microparticle film attains 0.97 solar reflectance and 0.95 high sky-window emissivity when the broadly distributed pore size reaches 180 nm. Our field test demonstrated that the single-layer BaSO4/TiO2/PVDF/PTFE microparticle film achieved a temperature 5.2 °C below the ambient temperature and accomplished a cooling power of 74 W/m2. Also, the results show that, when the humidity rises from 33% to 38% at 12:30 pm, it hinders the cooling of the body surface and lowers the cooling effect to 8%.
ABSTRACT
Currently, gas separation (GS) membranes are produced from petrochemical-based polymers, but their lifespan is severely impacting the environment. Therefore, there has recently been growing interest in developing ecofriendly biodegradable polymer-based GS membranes. This study developed a polylactic acid (PLA)/polybutylene succinate (PBS) blend composite membrane for GS using the dry/wet phase inversion technique. The influence of the multiwalled carbon nanotube (MWCNT) concentration in the PLA/PBS blend was studied by investigating tensile properties, porosity, percentage crystallinity, contact angle, and gas permeance.The obtained results demonstrate that the addition of MWCNT enhances the tensile strength, porosity, and percentage crystallinity, whereas it decreases the contact angle. The pure gas permeation was investigated at pressures of 2-4 bar at 25 °C. The gas permeation study revealed that the PLA/PBS blend with 0.5% wt. MWCNT enhanced the gas permeance and selectivity at 4 bar. The gas permeance acquired at 25 °C and 4 bar for PLA/PBS reinforced with MWCNT was highest in hydrogen followed by carbon dioxide, argon, and nitrogen. Additionally, a study of the membrane morphology illustrated the uniform dispersion of MWCNT in the PLA/PBS blend. The investigation concluded that membranes containing MWCNT are capable of separating gases at the molecular level, thereby reducing energy consumption.
ABSTRACT
The Canny Edge-Based Distance Transform and Hough Transform algorithms were successfully implemented to analyze the size distribution and the orientation of the electrospun PLA/PBS hybrid fiber. The effect of polymer concentration, voltage, feed rate and needle-collector distance were studied. It was found that feed rate of 0.5 ml/h and needle-collector distance of 12 cm is required to generate smooth and uniform hybrid fibers in the smallest size electrospinning with 6 wt.% polymer at voltage of 20 kV. The stationary flat collector with a swaying needle and fast rotating drum disc with a stationary needle were used for the fiber alignment. In order to improve the size distribution and the orientation of the hybrid fibers it is proposed that the fibers should be collected on the rotary drum disc at 700 rpm or higher speed.
ABSTRACT
Co3O4 sensors with a nanoscale TiO2 or SnO2 catalytic overlayer were prepared by screen-printing of Co3O4 yolk-shell spheres and subsequent e-beam evaporation of TiO2 and SnO2. The Co3O4 sensors with 5 nm thick TiO2 and SnO2 overlayers showed high responses (resistance ratios) to 5 ppm xylene (14.5 and 28.8) and toluene (11.7 and 16.2) at 250 °C with negligible responses to interference gases such as ethanol, HCHO, CO, and benzene. In contrast, the pure Co3O4 sensor did not show remarkable selectivity toward any specific gas. The response and selectivity to methylbenzenes and ethanol could be systematically controlled by selecting the catalytic overlayer material, varying the overlayer thickness, and tuning the sensing temperature. The significant enhancement of the selectivity for xylene and toluene was attributed to the reforming of less reactive methylbenzenes into more reactive and smaller species and oxidative filtering of other interference gases, including ubiquitous ethanol. The concurrent control of the gas reforming and oxidative filtering processes using a nanoscale overlayer of catalytic oxides provides a new, general, and powerful tool for designing highly selective and sensitive oxide semiconductor gas sensors.
ABSTRACT
A comparative study is presented of the hydrolytic and thermal stability of 24 different kinds of monolayers on Si(111), Si(100), SiC, SiN, SiO2, CrN, ITO, PAO, Au, and stainless steel surfaces. These surfaces were modified utilizing appropriate organic compounds having a constant alkyl chain length (C18), but with different surface-reactive groups, such as 1-octadecene, 1-octadecyne, 1-octadecyltrichlorosilane, 1-octadecanethiol, 1-octadecylamine and 1-octadecylphosphonic acid. The hydrolytic stability of obtained monolayers was systematically investigated in triplicate in constantly flowing aqueous media at room temperature in acidic (pH 3), basic (pH 11), phosphate buffer saline (PBS) and deionized water (neutral conditions), for a period of 1 day, 7 days, and 30 days, yielding 1152 data points for the hydrolytic stability. The hydrolytic stability was monitored by static contact angle measurements and X-ray photoelectron spectroscopy (XPS). The covalently bound alkyne monolayers on Si(111), Si(100), and SiC were shown to be among the most stable monolayers under acidic and neutral conditions. Additionally, the thermal stability of 14 different monolayers was studied in vacuum using XPS at elevated temperatures (25-600 °C). Similar to the hydrolytic stability, the covalently bound both alkyne and alkene monolayers on Si(111), Si(100) and SiC started to degrade from temperatures above 260 °C, whereas on oxide surfaces (e.g., PAO) phosphonate monolayers even displayed thermal stability up to â¼500 °C.
