Preparation and Characterization of Electrosprayed Aerogel/Polytetrafluoroethylene Microporous Materials

This paper presents the preparation of aerogel/polytetrafluoroethylene (PTFE) microporous materials via needleless electrospray technique, by using an aqueous dispersion of polytetrafluoroethylene as the basic spinning liquid. Different contents of aerogel powders were applied to the spinning liquid for electrospraying to investigate the effect on the structural characteristics and various properties of the materials. Cross-section, surface morphology, and particle size distribution of the electrosprayed materials were examined. Surface roughness, hydrophobicity, and thermal conductivity were evaluated and discussed. The results showed that the electrosprayed aerogel/PTFE layers were compact and disordered stacking structures composed of spherical particles with a rough surface. As the aerogel content increased, the electrosprayed materials demonstrated increased surface roughness and improved surface hydrophobicity with a contact angle up to 147.88°. In addition, the successful achievement of thermal conductivity as low as 0.024 (W m−1 K−1) indicated a superior ability of the prepared aerogel/PTFE composites to prevent heat transfer. This study contributes to the field of development of aerogel/PTFE composites via electrospray technique, providing enhanced final performance for potential use as thermal and moisture barriers in textiles or electronic devices.

Effects of environmental temperature and humidity on evaporative heat loss through firefighter suit materials made with semi-permeable and microporous moisture barriers

The goal of this research was to understand how firefighter protective suits perform in different operational environments. This study used a sweating guarded hotplate to examine the effect of environmental temperature (20–45°C) and relative humidity (25–85% RH) on evaporative heat loss through firefighter turnout materials. Four firefighter turnout composites containing three different bi-component (semi-permeable) and one microporous moisture barriers were selected. The results showed that the evaporative resistance of microporous moisture barrier systems was independent of environmental testing conditions. However, absorbed moisture strongly affected evaporative heat loss through semi-permeable moisture barriers coated with a layer of nonporous hydrophilic polymer. Moisture absorption in mild environment (20–25°C) tests, or when testing at high humidity (>85% RH), significantly increased water vapor transmission in semi-permeable turnout systems. It was also found that environmental conditions used in the total heat loss (THL) test (25°C and 65% RH) produced moisture condensation in bi-component barrier systems, making them appear more breathable than could be expected when worn in hotter environments. Regression models successfully qualified the relationships between moisture uptake levels in semi-permeable barrier systems and evaporative resistance and THL. These findings reveal the limitations in relying on THL, the heat strain index currently called for by the NFPA 1971 Standard for Structural Firefighter personal protective equipment, and supports the need to measure turnout evaporative resistance at 35°C (Ret), in addition to THL at 25°C.

Effect of Polymeric Resins on Geotechnical Properties of Black Cotton Soil

Stabilization of black cotton soil is a challenging task for geotechnical engineers since such soil is highly vulnerable to expansive characteristics when the moisture content is increased. Due to its expansive nature, it is also called as swelling or expansive soils. Among the clay minerals, Montmorillonite is mainly responsible for such expansive characteristics. Bore log profile has a cluster of soil specimens including black cotton soil also which is unavoidable. Soil engineers have a serious concern about such expansive soil since it is treacherous for foundation of buildings. To overcome such deficiencies it becomes essential to stabilize the soil conditions. The commonly employed methods to decrease the expansive behaviour are: Chemical stabilization, Mechanical stabilization and installation of moisture barriers. In this paper, chemical stabilization method is adopted. Soil stabilizers, namely, sodium silicate, epoxy resin and polyvinyl alcohol are chosen and are mixed with black cotton soil in varying proportions of 5%, 10% and 15% to study the changes in geotechnical properties. From the results it is evident that polymer treated soils reduce plasticity characteristics and shows better results in geotechnical properties.

Accelerated Hermeticity Testing of Biocompatible Moisture Barriers Used for the Encapsulation of Implantable Medical Devices

Barrier layers for the long-term encapsulation of implantable medical devices play a crucial role in the devices’ performance and reliability. Typically, to understand the stability and predict the lifetime of barriers (therefore, the implantable devices), the device is subjected to accelerated testing at higher temperatures compared to its service parameters. Nevertheless, at high temperatures, reaction and degradation mechanisms might be different, resulting in false accelerated test results. In this study, the maximum valid temperatures for the accelerated testing of two barrier layers were investigated: atomic layer deposited (ALD) Al2O3 and stacked ALD HfO2/Al2O3/HfO2, hereinafter referred to as ALD-3. The in-house developed standard barrier performance test is based on continuous electrical resistance monitoring and microscopic inspection of Cu patterns covered with the barrier and immersed in phosphate buffered saline (PBS) at temperatures up to 95 °C. The results demonstrate the valid temperature window to perform temperature acceleration tests. In addition, the optimized ALD layer in combination with polyimide (polyimide/ALD-3/polyimide) works as effective barrier at 60 °C for 1215 days, suggesting the potential applicability to the encapsulation of long-term implants.