Fabrication and durability characterization of superhydrophobic and lubricant-infused surfaces.

HYPOTHESIS: Practical applications of non-wetting surfaces require good mechanical durability in the wet environments for which they are intended to be used. Durability of non-wetting surfaces is influenced by the surface features, interaction with the functionalization agent, and the lubricant properties that can be tuned independently to identify optimal combination. EXPERIMENTS: In this study, superhydrophobic and lubricant-infused surfaces are fabricated on copper tubes using chemical etching and electrodeposition texturing techniques, six different functionalizing agents, and five different infused lubricants. Through 180 fabrication combinations and 102 durability tests, each parameter is systematically studied for contributions to initial non-wetting behavior and its durability in heated, wet environment, under high-energy water jet impingement, and under accelerated flow conditions. FINDINGS: Among the adsorbing and curing functionalization agents investigated, n-Hexadecyl mercaptan that belongs to the sulfhydryl group and Sylgard-184, respectively, showed high durability in heated water immersion and under jet impingement tests. For lubricant-infused surfaces, lubricants with high surface tension demonstrated high durability in heated water immersion test, whereas durability in hydrodynamic conditions is closely correlated to lubricant viscosity. Results showed that a lubricant-infused surface will maintain its non-wetting properties in dropwise condensation conditions for approximately 1.5 years.

Dilution effect for highly efficient multiple-component organic solar cells.

Although the multiple-component (MC) blend strategy has been frequently used as a very effective way to improve the performance of organic solar cells (OSCs), there is a strong need to understand the fundamental working mechanism and material selection rule for achieving optimal MC-OSCs. Here we present the 'dilution effect' as the mechanism for MC-OSCs, where two highly miscible components are molecularly intermixed. Contrary to the aggregation-induced non-radiative decay, the dilution effect enables higher luminescence quantum efficiencies and open-circuit voltages (VOC) in MC-OSCs via suppressed electron-vibration coupling. The continuously broadened bandgap together with reduced electron-vibration coupling also explains the composition-dependent VOC in ternary blends well. Moreover, we show that electrons can transfer between different acceptors, depending on the energy offset between them, which contributes to the largely unperturbed charge transport and high fill factors in MC-OSCs. The discovery of the dilution effect enables the demonstration of a high power conversion efficiency of 18.31% in an MC-OSC.

Steam condensation heat transfer on lubricant-infused surfaces.

Steam condensation is fundamental to several industrial processes, including power generation, desalination, and water harvesting. Lubricant-infused surfaces (LISs) promote sustained dropwise condensation, leading to significantly higher heat transfer performance that trades off with durability. Here, we present a systematic study on lubricant-infused copper tubes in a partial vacuum environment typical of power plant condensers to elucidate the influence of the design parameters-texturing, functionalizing agent, and lubricant viscosity-on condensation heat transfer performance and durability. Heat transfer effectiveness is introduced as a relevant parameter to quantify the effects of condensation heat transfer coefficient enhancement on the overall system heat transfer performance. Analytical expressions are developed for lubricant retention fraction and heat transfer effectiveness in terms of Bond number, viscosity ratio, and a dimensionless logarithmic mean temperature difference that can be used for predicting the performance of a LIS or for designing surfaces for a desired performance.

There is no difference in footstrike pattern distribution in recreational runners with or without anterior knee pain.

BACKGROUND: There are no studies comparing footstrike pattern distribution between recreational runners with or without anterior knee pain. OBJECTIVE: The aim of this study was to investigate if there was any difference in footstrike pattern between recreational runners with or without anterior knee pain. METHODS: This cross-sectional study involved 62 runners without anterior knee pain and 60 runners with anterior knee pain. We recruited runners in public parks and amateur road running competitions. A 2D record was made using a high-speed camera with an acquisition frequency of 300 Hz and shutter speed of 300s-1. Also, demographic information, running characteristics, knee pain characteristics, and running biomechanics variables were collected. Besides the footstrike pattern, running step length, mean velocity, footstrike angle, and ankle push-off were evaluated. RESULTS: The distribution of rearfoot strike pattern was similar between groups, observed in 96.6 % of the subjects with anterior knee pain and in 93.5 % of the subjects without it. In the secondary analysis, a logistic regression was conducted, and none of the demographic information, running training characteristics, and running biomechanics variables evaluated in this study were associated with runners presenting knee pain. CONCLUSION: Runners with or without anterior knee pain do not differ in regard to footstrike pattern. Both groups had predominantly rearfoot strike patterns, and none of the collected variables were associated with anterior knee pain on runners.

Photoluminescence and Photoconductivity to Assess Maximum Open-Circuit Voltage and Carrier Transport in Hybrid Perovskites and Other Photovoltaic Materials.

Photovoltaic (PV) device development is much more expensive and time-consuming than the development of the absorber layer alone. This Perspective focuses on two methods that can be used to rapidly assess and develop PV absorber materials independent of device development. The absorber material properties of quasi-Fermi level splitting and carrier diffusion length under steady effective 1 Sun illumination are indicators of a material's ability to achieve high VOC and JSC. These two material properties can be rapidly and simultaneously assessed with steady-state absolute intensity photoluminescence and photoconductivity measurements. As a result, these methods are extremely useful for predicting the quality and stability of PV materials prior to PV device development. Here, we summarize the methods, discuss their strengths and weaknesses, and compare photoluminescence and photoconductivity results with device performance for four hybrid perovskite compositions of various bandgaps (1.35-1.82 eV), CISe, CIGSe, and CZTSe.

Overcoming the Photovoltage Plateau in Large Bandgap Perovskite Photovoltaics.

Development of large bandgap (1.80-1.85 eV Eg) perovskite is crucial for perovskite-perovskite tandem solar cells. However, the performance of 1.80-1.85 eV Eg perovskite solar cells (PVKSCs) are significantly lagging their counterparts in the 1.60-1.75 eV Eg range. This is because the photovoltage ( Voc) does not proportionally increase with Eg due to lower optoelectronic quality of conventional (MA,FA,Cs)Pb(I,Br)3 and results in a photovoltage plateau ( Voc limited to 80% of the theoretical limit for ∼1.8 eV Eg). Here, we incorporate phenylethylammonium (PEA) in a mixed-halide perovskite composition to solve the inherent material-level challenges in 1.80-1.85 eV Eg perovskites. The amount of PEA incorporation governs the topography and optoelectronic properties of resultant films. Detailed structural and spectroscopic characterization reveal the characteristic trends in crystalline size, orientation, and charge carrier recombination dynamics and rationalize the origin of improved material quality with higher luminescence. With careful interface optimization, the improved material characteristics were translated to devices and Voc values of 1.30-1.35 V were achieved, which correspond to 85-87% of the theoretical limit. Using an optimal amount of PEA incorporation to balance the increase in Voc and the decrease in charge collection, a highest power conversion efficiency of 12.2% was realized. Our results clearly overcome the photovoltage plateau in the 1.80-1.85 eV Eg range and represent the highest Voc achieved for mixed-halide PVKSCs. This study provides widely translatable insights, an important breakthrough, and a promising platform for next-generation perovskite tandems.

Correlation between Photoluminescence and Carrier Transport and a Simple In Situ Passivation Method for High-Bandgap Hybrid Perovskites.

High-bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a ligand-assisted crystallization (LAC) technique that introduces additives in situ during the solvent wash and developed a new method to dynamically measure the absolute intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation. Further, the measurements enabled optimization of LAC on the 1.75 eV bandgap FA0.83Cs0.17Pb(I0.66Br0.34)3, resulting in an enhancement of the photoluminescence quantum yield (PLQY) of over an order of magnitude, an increase of 80 meV in the quasi-Fermi level splitting (to 1.29 eV), an increase in diffusion length by a factor of 3.5 (to over 1 µm), and enhanced open-circuit voltage and short-circuit current from photovoltaics fabricated from the LAC-treated films.

In pursuit of functional electrospun materials for clinical applications in humans.

Electrospinning is a simple, low-cost and versatile approach to fabricate multifunctional materials useful in drug delivery and tissue engineering applications. Despite its emergence into other manufacturing sectors, electrospinning has not yet made a transformative impact in the clinic with a pharmaceutical product for use in humans. Why is this the current state of electrospun materials in biomedicine? Is it because electrospun materials are not yet capable of overcoming the biological safety and efficacy challenges needed in pharmaceutical products? Or, is it that technological advances in the electrospinning process are needed? This review investigates the current state of electrospun materials in medicine to identify both scientific and technological gaps that may limit clinical translation.