Constant Humidity Environment Research Articles

Enhancing perovskite solar cells performance via sewing up the grain boundary

Grain boundaries (GBs) are inevitable for the solution-processed perovskite polycrystalline films, but they become the weakest regions when the film undergoes degradation, especially unreacted PbI2 prefers to locate at GBs. Herein, this issue is solved by applying hydroxyl functionalized ionic liquids (ILs) on perovskite solar cells (PSCs). The ILs sew up the GBs continuously through in situ formation of a plumbite complex with residual PbI2. By sewing-up the GBs, the PSCs afford a notable increase in both power conversion efficiency (PCE, from 21.49% to ∼24.00%) and device stability (remaining over 80% of the initial PCE after 600 h at 60 ℃, 90% of the initial PCE after 2000 h in a constant humidity environment of 40% RH, and 85% of its PCE under continuously light illumination for 700 h). These improvements are ascribed to the precise passivation of related defects, optimization of interfacial energy level, suppression of the charge recombination, and enhancement of charge collection through sewing-up the GBs. This “sewing-up grain boundaries” method is highly promising toward construction of robust films for solution-process PSCs.

Water-Regulated Lead Halide Perovskites Precursor Solution: Perovskite Structure Making and Breaking

Identifying the impact of water on iodoplumbate complexes in various solutions is essential for linking the coordination environment of the perovskite precursor to its final perovskite solar cell (PSC) properties. In this study, we propose a digital twin approach based on X-ray absorption fine structure and molecular dynamic simulation to investigate the structure evolution of iodoplumbate complexes in precursor solutions as a function of storage time under a constant humidity environment. A full picture about what water does in the perovskite formation process is brought out, and the “making and breaking” role of water molecules is uncovered to link the structure of iodoplumbate complexes to its final properties. This study sheds light on a full picture about what water does in the perovskite formation process and the role of water, which will lead to developing water-involved strategies for consistent PSC fabrication under ambient conditions.

A Humidity-Powered Soft Robot with Fast Rolling Locomotion.

A range of soft robotic systems have recently been developed that use soft, flexible materials and respond to environmental stimulus. The greatest challenge in their design is the integration of the actuator, energy sources, and body of robots while achieving fast locomotion and well-defined programmable trajectories. This work presents such a design that operates under constant conditions without the need for an externally modulated stimulus. By using a humidity-sensitive agarose film and overcoming the isotropic and random bending of the film, the robot, which we call the Hydrollbot, harnesses energy from evaporation for spontaneous and continuous fast self-rolling locomotion with a programmable trajectory in a constant-humidity environment. Moreover, the geometric parameters of the film were fine-tuned to maximize the rolling speed, and the optimised hydrollbot is capable of carrying a payload up to 100% of its own weight. The ability to self-propel fast under constant conditions with programmable trajectories will confer practical advantages to this robot in the applications for sensors, medical robots, actuation, etc.

Probing of ultrahigh optical Q-factors of individual liquid microdroplets on superhydrophobic surfaces using tapered optical fiber waveguides

We report measurements of ultrahigh quality factors (Q-factors) of the optical whispering-gallery modes excited via a tapered optical-fiber waveguide in single glycerol–water microdroplets standing on a superhydrophobic surface in air. Owing to the high contact angle of the glycerol–water mixture on the superhydrophobic surface (>155°), microdroplets with the geometry of a truncated sphere minimally distorted by gravity and contact line pinning effects could be generated. Q-factors up to 2.3×106 were observed for such droplets with radii of 100–200 μm exposed to the ambient atmosphere in a closed chamber with controlled relative humidity. Placement of microdroplets in a constant humidity environment permitted prolonged characterization of Q-factors for individual microdroplets. We found that the Q-factors in air were stable over more than 1 h and their measured values were limited mostly by the thermally induced droplet shape fluctuations.

Mixed-mode fatigue behavior of degraded toughened epoxy adhesive joints

Open-faced asymmetric double cantilever beam (ADCB) specimens of toughened epoxy-aluminum adhesive joints were aged either in a constant humidity environment or a cyclically changing environment to study the mixed-mode fatigue behavior. Under constant humidity environments, the fatigue threshold strain energy release rate initially decreased with aging time until it reached a constant minimum value for long times. In contrast, the crack growth rates continued to increase with aging time. It is hypothesized that at crack growth rates close to threshold the fatigue behavior is governed by the epoxy matrix, whereas at relatively high crack growth rates the fatigue behavior is governed by the loss of the rubber toughening mechanism. Increasing the aging temperature accelerated the degradation of the joints leading to a reduction in the time to reach the constant minimum value and increased the crack growth rates. Under a cyclic aging environment with intermittent salt spray, neither the threshold strain energy release rate nor the crack growth rates degraded until four weeks of aging. The superior fatigue performance of these joints compared to joints aged in constant humidity environments was due to the lower water concentrations in the adhesive while aging. This conclusion was supported by moisture uptake measurements of the adhesive in deionised and salt water environments that showed simple Fickian behavior at room temperature and dual-Fickian behavior at higher temperature. The salt water environment produced osmotic pressure that decreased the moisture concentration in the second stage of diffusion.

Tensile and Tensile-Mode Fatigue Testing of Microscale Specimens in Constant Humidity Environment

A tensile and tensile-mode-fatigue tester has been developed for testing microscale specimens in high humidity environments in order to investigate the fracture mechanisms of microelectromechanical materials. A humidity control system was installed on a tensile-mode fatigue tester equipped with an electrostatic force grip. A specimen and a griping device were inserted into a small chamber and the humidity was controlled by air flow from a temperature and humidity chamber. The humidity stability was within ±2%RH for humidities in the range 25–90%RH for eight hours of testing. Fatigue tests were performed on single-crystal silicon (SCS) specimens in constant humidity environments and laboratory air for up to 106 cycles. The gauge length, width, and thickness of the SCS specimens were 100 or 500 μm, 13.0 μm, and 3.3 μm, respectively. The average tensile strength was 3.68 GPa in laboratory air; this value decreased in high humidity environments. Fatigue failure was observed during cyclic loading at stresses lower than the average strength. A reduction in the fatigue strength was observed at high relative humidities. Different fracture origins and fracture behaviors were observed in tensile tests and fatigue tests, which indicates that the water vapor in air affects the fatigue properties of SCS specimens.

Evapotranspiration Measurement in Controlled Environment Chambers: A Comparison between Time Domain Reflectometry and Accumulation of Condensate from Cooling Coils

The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity environment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give information on soil water status or root activity. The objective of this study was to compare ET measurements from the condensate system with ET calculated from measurements of water content by TDR. Data from an irrigation × carbon dioxide (CO2) study on potato (Solanum tuberosum L.) were used for this study. The soil water contents in the growth chamber soilbins were monitored once an hour at five vertical depths with three measurement locations per depth using an automated TDR system. The correspondence between daily ET rates for the two systems was good. Maximum daily ET rates were near 6.1 to 7.1 mm cm−2 d−1 (7–8 L d−1 on a chamber basis) and differences were on the order to 0.89 to 1.8 mm cm−2 d−1 (1–2 L d−1). At the higher daily ET rates, the daily values from the two methods were closer. The correspondence between hourly measurements of ET measured from the condensate system and calculated from TDR water contents was poor due to instrument and soil variability. A significant source of error was vertical variation in water content in the soil between horizontally placed TDR probes, especially during irrigation events. Evapotranspiration estimates from TDR measurements were much more robust for calculation of water use over a period of time. Data from the condensate system were most useful for quantification of diurnal transpiration rates and were better correlated with radiation.

Studies on Desorption Behaviour of Garlic (Allium sativum Linn.) Slices

Moisture desorption properties of garlic (Allium sativum cv. 0282) were investigated at 40, 50 and 60oC temperature and relative humidity's ranging from 11% to 82% using the gravimetric static method. The garlic slices Were allowed to equilibrate in constant humidity environment maintained by lair solutions. The effect of temperature and equilibrium relative humidity, on the Equilibrium moisture Contant was highly significant (P<0.0001). Four Models namely, Chung-Pfost, modified, Henderson, modifted Halsey and modified exponential were evaluated (the correlation coefficient and sum of squares of residuals, SSR) to determine the best fit for the experimental data The modified Henderson, modified Halaey and modified exponential models were found" adequate and mathematically similar. The modified exponential model was found superior for characterizing the desorption behaviour of garlic slices in the temperature and relative humidity range investigated.

PREDICTING THE SORPTION BEHAVIOUR OF GARLIC SLICES

ABSTRACT Moisture desorption properties of fresh garlic (cv. Early Californian) were investigated at 20 °C to 70°C and relative humidities ranging from 11% to 85% using the gravimetric static method. The slices were allowed to equilibrate in a constant humidity environment (hygrostats) maintained by salt solutions. The effect of temperature and relative humidity on the equilibrium moisture content was highly significant (P<0.0001). Four models available in the literature, namely the Chung-Pfost, modified Halsey, modified Henderson and the Guggenheim-Anderson-de Boer (GAB) were evaluated (the correlation coefficient, F-ratio and plots of residuals) to determine the best fit for the experimental data. On the basis of the F-test, The modified Henderson model was found adequate and the GAB model superior for characterising the sorption behaviour of garlic slices in the temperature and water activity range investigated.

Variation of the hydrogen ion concentration of healthy intact skin.

Beckman glass and calomel electrodes were used in conjunction with a Beckman model G pH meter to determine the hydrogen ion concentration of the skin surface. Three types of experiment, carried out on male and female subjects, were designed primarily to study the degree of normal variability of the skin reaction and the related E.M.F., in view of measurements being made on the potentials of tumors. The experiments were (a) 20 min. studies, (b)26 hr. studies and (c) 48 day studies. The short term studies showed that in all cases the skin pH readings reached an equilibrium value after two to four minutes and remained quite steady to the end of the experiment. The diurnal variation of the skin reaction in all subjects followed a cyclic path which exhibited excellent reciprocal correlation with environmental temperature. Subjects kept in a constant temperature, constant humidity environment did not show this cyclic pattern in their readings. Oral administration of atropine excluded the possibility of sweat gland activity influencing the temperature dependence. Long term studies on both male and female subjects showed wide variation in absolute readings and little or no evidence of a cyclic nature could be observed or statistically shown.