Polyurethanes (PUs) consisting of m-xylylene diisocyanate (XDI) exhibit excellent thermal stability and optical properties. To further enhance the optical properties, ...1,3-bis(isocyanatomethyl)cyclohexane (H6XDI) is considered a potential isocyanate for optically clear adhesives; however, a detailed analysis of the adhesion mechanism has not been investigated. Herein, we synthesized PUs using diisocyanates (XDI, H6XDI) and polyols polypropylene glycol (PPG), polycaprolactone diol (PCL), and polycarbonate diol (PCD). To investigate the adhesion mechanism, the interaction between each PUs and functionalized self-assembled monolayers was analyzed using a Surface Forces Apparatus at the nanoscale. Additionally, macroscopic surface energy measurement and probe tack testing were performed. Overall, higher hydrophobic interaction in PCD-containing PUs and predominant hydrogen bonding in PPG-containing PUs was measured. Also, hydrophobic interaction was stronger for H6XDI compared to that of XDI in all polyols. These findings clarified polyol-dependent adhesion mechanisms of XDI- and H6XDI-based PUs and could be used to design PUs with controlled strength of hydrogen bonds and hydrophobic interactions.
Abstract
The development of flexible electronic technology has led to convenient devices, including foldable displays, wearable, e‐skin, and medical devices, increasing the need for flexible ...adhesives that can quickly recover their shape while connecting the components of the device. Conventional pressure sensitive adhesives (PSAs) can improve recoverability via crosslinking, but often have poor adhesive strength. In this study, new types of urethane‐based crosslinkers are synthesized using
m
‐xylylene diisocyanate (XDI) or 1,3‐bis(isocyanatomethyl)cyclohexane (H
6
XDI) as a hard segment, and poly(ethylene glycol) (PEG) group as a soft segment. The PSA with the synthesized H
6
XDI‐PEG diacrylate (HPD) demonstrates a significantly improved recoverability compared to XDI‐PEG diacrylate and a conventional crosslinker 1,6‐hexanediol diacrylate (HDDA) while maintaining high adhesion strength (≈25.5 N 25 mm
−1
). The excellent recovery property of the PSA crosslinked with HPD is further confirmed by 100k folding tests and 10k multi‐directional stretching tests exhibiting high folding and stretching stability. PSA with HPD also shows high optical transmittance (> 90%) even after 20% straining, suggesting its applicability in fields that simultaneously require high flexibility, recoverability, and optical clarity such as foldable displays.
The development of flexible electronic technology has led to convenient devices, including foldable displays, wearable, e‐skin, and medical devices, increasing the need for flexible adhesives that ...can quickly recover their shape while connecting the components of the device. Conventional pressure sensitive adhesives (PSAs) can improve recoverability via crosslinking, but often have poor adhesive strength. In this study, new types of urethane‐based crosslinkers are synthesized using m‐xylylene diisocyanate (XDI) or 1,3‐bis(isocyanatomethyl)cyclohexane (H6XDI) as a hard segment, and poly(ethylene glycol) (PEG) group as a soft segment. The PSA with the synthesized H6XDI‐PEG diacrylate (HPD) demonstrates a significantly improved recoverability compared to XDI‐PEG diacrylate and a conventional crosslinker 1,6‐hexanediol diacrylate (HDDA) while maintaining high adhesion strength (≈25.5 N 25 mm−1). The excellent recovery property of the PSA crosslinked with HPD is further confirmed by 100k folding tests and 10k multi‐directional stretching tests exhibiting high folding and stretching stability. PSA with HPD also shows high optical transmittance (> 90%) even after 20% straining, suggesting its applicability in fields that simultaneously require high flexibility, recoverability, and optical clarity such as foldable displays.
Pressure sensitive adhesives (PSAs) with rapid strain recovery properties are developed by incorporating H6XDI‐PEG diacrylate (HPD), a urethane‐based crosslinker. These PSAs also exhibit excellent adhesive strength and optical transparency, and they are expected to be utilized in flexible surfaces, such as foldable/stretchable displays and wearable devices.
Although non-teaching community hospitals form the majority of healthcare providers in South Korea, there is limited data on antibiotic usage in them. To evaluate the pattern of antibiotic usage and ...its appropriateness in hospitals with < 400 beds in South Korea.
A multicentre retrospective study was conducted in 10 hospitals (six long-term care hospitals, three acute care hospitals, and one orthopaedic hospital), with < 400 beds in South Korea. We analysed patterns of antibiotic prescription in 2019, and their appropriateness in the participating hospitals. For the evaluation of the appropriateness of the prescription, 25 patients under antibiotic therapy were randomly selected at each hospital, over two separate periods. Due to the heterogeneity of their characteristics, the orthopaedics hospital was excluded from the analysis.
The most commonly prescribed antibiotics in long-term care hospitals was fluoroquinolone, followed by beta-lactam/beta-lactamase inhibitor (anti-pseudomonal). In acute care hospitals, these were third generation cephalosporin, followed by first generation cephalosporin, and second generation cephalosporin. The major antibiotics that were prescribed in the orthopedics hospital was first generation cephalosporin Only 2.3% of the antibiotics were administered inappropriately. In comparison, 15.3% of patients were prescribed an inappropriate dose. The proportion of inappropriate antibiotic prescriptions was 30.6% of the total antibiotic prescriptions.
The antibiotic usage patterns vary between non-teaching community hospitals in South Korea. The proportion of inappropriate prescriptions exceeded 30% of the total antibiotic prescriptions.
•A human-motion driven miniaturized EM energy harvester using flux-guided magnet stacks.•Flux-guided magnet stack increases the power density more than three times.•Capable of driving wearable ...electronics through efficient power conditioning circuitry.
We present a miniaturized electromagnetic energy harvester (EMEH) that uses two flux-guided magnet stacks to harvest energy from common human-body-induced motions such as hand-shaking, walking, and slow running. We designed each magnet stack to increase the flux density within a given size of the harvester component, by guiding the flux lines through soft magnetic material and designed the miniaturized EMEH to up-convert the low-frequency vibration generated by human-body-induced motion to a high-frequency vibration by mechanical impact of a spring-less structure. Our use of a spring-less structure eliminates the challenges of designing a practical and reliable low-frequency (<5Hz) oscillator. Our low-frequency oscillator couples the human-body-induced vibration to two high-frequency oscillators (electromagnetic transducer elements). Each high-frequency oscillator consists of the analyzed 2-magnet stack and customized helical compression spring. We fabricated a standard AAA battery sized prototype (3.9cm3) and tested it with different human activities. We were able to generate a maximum 203μW, 32μW, and 78μW average power from hand-shaking, walking, and slow running motion, respectively. This miniaturized structure yields a maximum average power density of 52μWcm−3. We used a rectifier and multiplier circuit as the interface between the harvester and a wearable electronic load (wrist watch) to demonstrate the feasibility and capability of powering small-scale electronic systems from human-body vibration.
•A frequency up-converted miniaturized energy harvester, driven by hand-shaking.•Use of a freely movable ball conquers the inconvenience in resonance issue at frequencies below 10Hz.•Can be ...implemented to hand-held and wearable devices through efficient power conditioning circuitry.
We present a frequency up-converted electromagnetic energy harvester that generates significant power from human-limb motion (hand-shaking). Because the power generated by a vibration energy harvester is proportional to the operating frequency, the proposed energy harvester has been designed to up-convert the applied low-frequency vibration to a high-frequency vibration by mechanical impact. Upon excitation, a freely moveable ball (non-magnetic) within a cylindrical structure periodically hits two magnets suspended on two helical compression springs located at either ends of the cylinder, allowing these to vibrate with higher frequencies. The relative motion between the magnets and coils (wrapped around the outside of the cylinder) induces e.m.f. (voltage). High-frequency oscillators have been designed through the design parameters (i.e., frequency, spring stiffness, mechanical, and electrical damping), to minimize the power loss. A prototype was fabricated and tested both using a vibration exciter and by manual hand-shaking. The fabricated device showed non-resonant behavior during the vibration exciter test. At optimum load condition, the frequency up-converted generators (FUGs) delivered 0.84mW and 0.96mW of average power. A maximum 2.15mW of average power was obtained from the device with series connected FUGs while it was mounted on a smart phone and was hand-shaken. The fabricated device exhibited 0.33mWcm−3 of average power density, which is very high compared to the current state-of-the-art devices, indicating its ability in powering portable and wearable smart devices from extremely low frequency (∼5Hz) vibration.
Understanding of the triboelectric charge accumulation from the view of microcapacitor formation plays a critical role in boosting the output performance of the triboelectric nanogenerator (TENG). ...Here, an electrospun nanofiber-based TENG (EN-TENG) using a poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)/MXene nanocomposite material with superior dielectric constant and high surface charge density is reported. The influence of dielectric properties on the output performance of the EN-TENG is investigated theoretically and experimentally. The fabricated EN-TENG exhibited a maximum power density of 4.02 W/m2 at a matching external load resistance of 4 MΩ. The PVDF-TrFE/MXene nanocomposite improved the output performance of the EN-TENG fourfold. The EN-TENG successfully powered an electronic stopwatch and thermo-hygrometer by harvesting energy from human finger tapping. Moreover, it was utilized in smart home applications as a self-powered switch for controlling electrical home appliances, including fire alarms, fans, and smart doors. This work presents an effective and innovative approach toward self-powered systems, human-machine interfaces, and smart home applications.
Hand, foot, and mouth disease (HFMD) causes characteristic blisters and sores mainly in infants and children, and has been monitored in South Korea through sentinel surveillance since 2009. We ...described the patterns of HFMD occurrence and analyzed the effect of climatic factors on national HFMD incidence. Weekly clinically diagnosed HFMD case rates (per 1,000 outpatients) in sentinel sites and weekly climatic factors, such as average temperature, relative humidity, duration of sunshine, precipitation, and wind speed from 2010 to 2013, were used in this study. A generalized additive model with smoothing splines and climatic variables with time lags of up to 2 weeks were considered in the modeling process. To account for long-term trends and seasonality, we controlled for each year and their corresponding weeks. The autocorrelation issue was also adjusted by using autocorrelation variables. At an average temperature below 18°C, the HFMD rate increased by 10.3% for every 1°C rise in average temperature (95% confidence interval (CI): 8.4, 12.3%). We also saw a 6.6% increase in HFMD rate (95% CI: 3.6, 9.7%) with every 1% increase in relative humidity under 65%, with a 1.5% decrease in HFMD rate observed (95% CI: 0.4, 2.7%) with each 1% humidity increase above 65%. Modeling results have shown that average temperature and relative humidity are related to HFMD rate. Additional research on the environmental risk factors of HFMD transmission is required to understand the underlying mechanism between climatic factors and HFMD incidence.
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