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Urban heat islands (UHI) are a growing issue due to urbanization, causing citizens to suffer from the inadequate thermal properties of building materials. Therefore, the need for climate-resistant infrastructure is crucial for quality of life. Phase change materials (PCMs) offer a solution by being incorporated into construction materials for thermoregulation. PCMs store and release heat as latent heat, adjusting temperatures through phase changes. Polymeric phase change fibers (PCFs) are an innovative technology for encapsulating PCMs and preventing leaks. This study produced PCFs via wet-spinning, using commercial cellulose acetate (CA, Mn 50,000) as the sheath and polyethylene glycol (PEG 2000) as the core. The PCFs were cut using a hot-cutting method at three different temperatures and washed with distilled water. Morphological analysis was conducted with a bright-field microscope, and chemical analysis was performed using Fourier transform infrared spectroscopy (FTIR) before and after controlled washing. Additionally, the washing baths were analyzed by UV-visible spectroscopy to detect PEG. The PCFs displayed a well-defined core-shell structure. Although some PEG 2000 leakage occurred in unsuccessful cuts, cuts at 50 °C showed sealed ends and less material in the baths, making it viable for civil engineering materials.

Nowadays, the growing concern about improving thermal comfort in different structures (textiles, buildings, and pavements, among others) has stimulated research into phase change materials (PCMs). The direct incorporation of PCMs into composite materials can cause mechanical impacts. Therefore, this study focuses on the design of phase change coaxial fibres (PCFs), using commercial cellulose acetate (CA) or recycled CA obtained from cotton fabrics (CAt) as the sheath and polyethylene glycol (PEG) 2000 as the core, via the wet spinning method; the fibres vary in molecular weight, concentration and ejection velocity. The fibres were assessed for their optical, chemical, thermal, and mechanical properties. The presence of PEG2000 is confirmed in the core of the fibres. Thermal analyses revealed a mass loss at high temperatures, attributable to the presence of PEG2000. Notably, the fibres with CA (Mn 30,000) showed superior thermal and mechanical performance. The melting point of PEG2000 incorporated into these PCFs coincided with the melting point of pure PEG2000 (about 55 °C), with a slight deviation, indicating that PCFs were obtained. Finally, the results point to the application of the fibres in civil engineering materials requiring a phase change between 50 and 60 °C, providing promising prospects for their use in applications requiring thermoregulatory properties.

The development of novel technologies and applications for micro/nano devices is an interdisciplinary subject that demands an integration of several research fields, such as material science, biotechnology, medicine, chemistry, informatics, optics, electronics, mechanics, and micro/nanotechnologies [...]

This paper presents the absorbance and fluorescence optical properties of various phytoplankton species, looking to achieve an accurate method to detect and identify a number of phytoplankton taxonomic groups. The methodology to select the excitation and detection wavelengths that results in superior identification of phytoplankton is reported. The macroscopic analyses and the implemented methodology are the base for designing a lab-on-a-chip device for a phytoplankton group identification, based on cell analysis with multi-wavelength lighting excitation, aiming for a cheap and portable platform. With such methodology in a lab-on-a-chip device, the analysis of the phytoplankton cells’ optical properties, e.g., fluorescence, diffraction, absorption and reflection, will be possible. This device will offer, in the future, a platform for continuous, autonomous and in situ underwater measurements, in opposition to the conventional methodology. A proof-of-concept device with LED light excitation at 450 nm and a detection photodiode at 680 nm was fabricated. This device was able to quantify the concentration of the phytoplankton chlorophyll a. A lock-in amplifier electronic circuit was developed and integrated in a portable and low-cost sensor, featuring continuous, autonomous and in situ underwater measurements. This device has a detection limit of 0.01 µ/L of chlorophyll a, in a range up to 300 µg/L, with a linear voltage output with chlorophyll concentration.

CMOS photodiodes have been widely reported in microsystem applications. This article presents the design and numerical simulation of p–n junction photodiodes, using COMSOL Multiphysics, for three CMOS technologies (0.18 μm, 0.35 μm and 0.7 μm) and three different p–n junction structures: n+/p-substrate, p+/n-well and n-well/p-substrate. For these simulations, the depth junctions and dopant concentrations were set according to the different technologies. Then, each photodiode was spectrophotometrically characterized regarding the current, responsivity and quantum efficiency. The obtained numerical results show that the 0.18 and 0.35 μm CMOS technologies are those with the highest peak of efficiency when visible spectral ranges are needed, comparative to the 0.7 µm technology. Furthermore, the three most common p–n vertical junction photodiode structures were compared. The n+/p-substrate junction photodiode appears to be the one with the highest quantum efficiency in the visible range, which is in agreement with the literature. It can be concluded that the photodiodes’ characteristic curves and dark current values are consistent with reports in the literature. Therefore, this numerical approach allows to predict the photodiodes’ performance, helping to select the best structural design for each required application, before their microfabrication.

Fluorinated greenhouse gases (F-gases) are used for various applications, such as in refrigeration and air conditioning, as substitutes of the ozone-depleting substances. Their utilization has increased drastically over the last few decades, with serious consequences for global warming. The Kigali Amendment to the Montreal Protocol and several national and international legislations, such as the 2014 EU F-gas Regulation, aim to control the utilization and emissions of these gases. In the EU, the phase-down of hydrofluorocarbons (HFCs) is underway, with successive reductions in quotas up to 2050. Under this scenario, efficient strategies for managing the produced and already existing F-gases are of vital importance to guarantee that their effect on the environment is mitigated. Up to now, most of the F-gases recovered from end-of-life equipment or when retrofitting systems are either released into the atmosphere or destroyed. However, in order to put forward a cost-efficient adaptation to the F-gas phase-down, increasing separation and recycling efforts must be made. This critical review aims at providing a revision of the current F-gas management problems and strategies and providing an overview on the innovative strategies that can be applied to contribute to build a sustainable market under circular economy principles.

Moisture content is a quality issue raised by recycling plants in the acceptance of paper and cardboard coming from waste streams. The current way to measure this parameter is by the oven drying method, which is a slow and invasive process, costing time and resources for the recyclers to do this type of quality control. An alternative to such a measurement technique is the use of plate-form devices which indirectly measure the moisture content using the dielectric properties of water and paper. This study has tested this method and developed a representative equation for the use of devices with these properties in the Portuguese market. For that, 48 wastepaper and cardboard bales were tested with both the traditional (oven drying) method and a commercial device equipped with dielectric technology. An equation that fits the studied reality (R2 = 0.76) was achieved, and possible problems regarding the use of this device were tested. The results showed that this type of device could be used as a time- and cost-saving, non-destructive and reliable method in the quality control of wastepaper and cardboard bales.

This paper presents the design, fabrication and characterization of temperature microsensors based on Resistance Temperature Detectors (RTDs) with a meander-shaped geometry. Numerical simulations were performed for studying the sensitivity of the RTDs according to their windings numbers as well as for optimizing their layout. These RTDs were fabricated using well-established microfabrication and photolithographic techniques. The fabricated sensors feature high sensitivity (0.3542 mV/°C), linearity and reproducibility in a temperature range of 35 to 45 °C. Additionally, each sensor has a small size with a strong potential for their integration in microfluidic devices, as organ-on-a-chip, allowing the possibility for in-situ monitoring the physiochemical properties of the cellular microenvironment.