Taming the Coffee Ring Effect: Enhanced Thermal Control as a Method for Thin-Film Nanopatterning.

Predicting and controlling a droplet's behavior on surfaces is very complex due to several factors affecting its nature. These factors play a crucial role in colloidal material deposition and related solution-based manufacturing methods such as printing. A better understanding of the processes governing the droplet in the picoliter regime is needed to help develop novel thin-film manufacturing methods and improve the current ones. This study introduces the substrate temperature as a method to control the droplet's behavior during inkjet printing, especially the coffee-ring phenomena, at an unprecedented temperature range (25-250 °C). To explain the particular behavior of the droplet, this research associates the creation of specific coffee-ring micro/nanostructures at elevated temperatures with the Leidenfrost effect that is responsible for creating a vapor pocket under the drying drop. Herein, we combine experimental data and numerical methods to explain the drying dynamic of the picoliter-size droplet on the substrate at elevated temperatures. The achieved results indicate that the coffee-ring effect is correlated with the heat-transfer changes caused by the Leidenfrost effect and can be controlled and used to produce micro/nanostructured thin films without additional processing steps.

Optimized Morphology and Tuning the Mn3+ Content of LiNi0.5Mn1.5O4 Cathode Material for Li-Ion Batteries.

The advantages of cobalt-free, high specific capacity, high operating voltage, low cost, and environmental friendliness of spinel LiNi0.5Mn1.5O4 (LNMO) material make it one of the most promising cathode materials for next-generation lithium-ion batteries. The disproportionation reaction of Mn3+ leads to Jahn-Teller distortion, which is the key issue in reducing the crystal structure stability and limiting the electrochemical stability of the material. In this work, single-crystal LNMO was synthesized successfully by the sol-gel method. The morphology and the Mn3+ content of the as-prepared LNMO were tuned by altering the synthesis temperature. The results demonstrated that the LNMO_110 material exhibited the most uniform particle distribution as well as the presence of the lowest concentration of Mn3+, which was beneficial to ion diffusion and electronic conductivity. As a result, this LNMO cathode material had an optimized electrochemical rate performance of 105.6 mAh g-1 at 1 C and cycling stability of 116.8 mAh g-1 at 0.1 C after 100 cycles.

Suitable Cathode NMP Replacement for Efficient Sustainable Printed Li-Ion Batteries.

N-methyl-2-pyrrolidone (NMP) is the most common solvent for manufacturing cathode electrodes in the battery industry; however, it is becoming restricted in several countries due to its negative environmental impact. Taking into account that ∼99% of the solvent used during electrode fabrication is recovered, dimethylformamide (DMF) is a considerable candidate to replace NMP. The lower boiling point and higher ignition temperature of DMF lead to a significant reduction in the energy consumption needed for drying the electrodes and improve the safety of the production process. Additionally, the lower surface tension and viscosity of DMF enable improved current collector wetting and higher concentrations of the solid material in the cathode slurry. To verify the suitability of DMF as a replacement for NMP, we utilized screen printing, a fabrication method that provides roll-to-roll compatibility while allowing controlled deposition and creation of sophisticated patterns. The battery systems utilized NMC (LiNi x Mn y Co z O2) chemistry in two configurations: NMC523 and NMC88. The first, well-established NCM523, was used as a reference, while NMC88 was used to demonstrate the potential of the proposed method with high-capacity materials. The cathodes were used to create coin and pouch cell batteries that were cycled 1000 times. The achieved results indicate that DMF can successfully replace NMP in the NMC cathode fabrication process without compromising battery performance. Specifically, both the NMP blade-coated and DMF screen-printed batteries retained 87 and 90% of their capacity after 1000 (1C/1C) cycles for NMC523 and NMC88, respectively. The modeling results of the drying process indicate that utilizing a low-boiling-point solvent (DMF) instead of NMP can reduce the drying energy consumption fourfold, resulting in a more environmentally friendly battery production process.

Stable Colloidal Quantum Dot Inks Enable Inkjet-Printed High-Sensitivity Infrared Photodetectors.

Colloidal quantum dots (CQDs) have recently gained attention as materials for manufacturing optoelectronic devices in view of their tunable light absorption and emission properties and compatibility with low-temperature thin-film manufacture. The realization of CQD inkjet-printed infrared photodetectors has thus far been hindered by incompatibility between the chemical processes that produce state-of-the-art CQD solution-exchanged inks and the requirements of ink formulations for inkjet materials processing. To achieve inkjet-printed CQD solids with a high degree of reproducibility, as well as with the needed morphological and optoelectronic characteristics, we sought to overcome the mismatch among these processing conditions. In this study, we design CQD inks by simultaneous evaluation of requirements regarding ink colloidal stability, jetting conditions, and film morphology for different dots and solvents. The new inks remain colloidally stable, achieved through a design that suppresses the reductant properties of amines on the dots' surface. After drop ejection from the nozzle, the quantum dot material is immobilized on the substrate surface due to the rapid evaporation of the low boiling point amine-based compound. Concurrently, the high boiling point solvent allows for the formation of a thin film of high uniformity, as is required for the fabrication of high-performance IR photodetectors. We fabricate inkjet-printed photodetectors exhibiting the highest specific detectivities reported to date (above 1012 Jones across the IR) in an inkjet-printed quantum dot film. As a patternable CMOS-compatible process, the work offers routes to integrated sensing devices and systems.

Disposable optics for microscopy diagnostics.

The point-of-care testing (POCT) is having increasing role on modern health care systems due to a possibility to perform tests for patients conveniently and immediately. POCT includes lot of disposable devices because of the environment they are often used. For a disposable system to be reasonably utilized, it needs to be high in quality but low in price. Optics based POCT systems are interesting approach to be developed, and here we describe a low-cost fabrication process for microlens arrays for microscopy. Lens arrays having average lens diameter of 222 µm with 300 µm lens pitch were fabricated. The lenses were characterized to have standard deviation of 0.06 µm in height and 4.61 µm in diameter. The resolution limit of 3.9µm is demonstrated with real images, and the images were compared with ones made with glass and polycarbonate lens arrays. The image quality is at the same level than with the glass lenses and the manufacturing costs are very low, thus making them suitable for POCT applications.

Porous thin film barrier layers from 2,3-dicarboxylic acid cellulose nanofibrils for membrane structures.

To fabricate a strong hydrophilic barrier layer for ultrafiltration (UF) membranes, 2,3-dicarboxylic acid cellulose nanofibrils with high anionic surface charge density (1.2 mekv/g at pH 7) and a width of 22 ± 4 nm were used. A simple vacuum filtration method combined with a solvent exchange procedure resulted in a porous layer with a thickness of ∼ 0.85 µm. The fabricated membranes reached high rejection efficiencies (74-80%) when aqueous dextrans up to 35-45 kDa were filtrated to evaluate the molecular weight cut-offs (MWCO). A linear correlation between the barrier layer thickness and the flux rate was observed in all tested cases. Further optimization of the barrier layer thickness can lead to an even more effective structure.

High-strength nanocellulose-talc hybrid barrier films.

Hybrid organic-inorganic films mimicking natural nacre-like composite structures were fabricated from cellulose nanofibers obtained from sequential periodate-chlorite oxidation treatment and talc platelets, using a simple vacuum-filtration method. As a pretreatment, commercial talc aggregates were individualized into well-dispersed talc platelets using a wet stirred media mill with high-shear conditions to promote the homogeneity and mechanical characteristics of hybrids. The nanofiber-talc hybrids, which had talc contents from 1 to 50 wt %, were all flexible in bending, and possessed tensile strength and Young's modulus values up to 211 ± 3 MPa and 12 ± 1 GPa, respectively, the values being remarkably higher than those reported previously for nanofibrillated cellulose-talc films. Because of the lamellar and well-organized structure of hybrids in which the talc platelets were evenly embedded, they possessed a small pore size and good oxygen barrier properties, as indicated by the preliminary results. The talc platelets decreased the moisture adsorption of highly talc-loaded hybrids, although they still exhibited hydrophilic surface characteristics in terms of contact angles.