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Results for “solvent evaporation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Mosaic lateral heterostructures in two-dimensional perovskite

Lateral heterostructures are important for exploring exotic physics, developing new devices and achieving device miniaturization. Endo-epitaxial growth occurring in patterned templates presents a promising strategy to realize extensive patterned areas in heterostructures, as recently demonstrated with two-dimensional (2D) covalent materials. However, the conventional lithography and etching processes used to prepare patterned templates are too aggressive for 2D lead halide perovskites, owing to their inherently soft and unstable ionic lattice. Here we create square holes of controllable size within 2D lead halide perovskites, enabling the fabrication of continuous lateral heterostructures over large areas. We demonstrate that the square holes form through spontaneous etching, a process initiated by internal strain and stabilized along the [100]/[010] crystallographic direction. Furthermore, the size of the square holes can be controlled by adjusting the etching time and temperature. Moreover, by incorporating a rapid solvent evaporation growth technique, the edges of the square holes act as templates for epitaxial growth of another type of perovskite, incorporating different halide or metal ions. Finally, we realized a series of mosaic lateral heterostructures that can emit various colours for light-emitting devices. As a result, this synthesis of diverse 2D perovskite mosaic lateral heterostructures provides valuable insights into the structural characteristics of perovskites and offers a versatile material platform for the development of complex integrated emitting devices.

Organic–inorganic nanostructures↗
DOE OSTI2021

Dynamic processes in transient phases during self-assembly of organic semiconductor thin films

Understanding and manipulating crystallization processes has been an important challenge for solution-processed organic thin films, both for fundamental studies and for fabricating thin films with near-intrinsic charge transport properties. We report an in situ X-ray scattering study of the crystallization of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C 10 ) during its deposition from solution. At temperatures modestly below the smectic-E/crystalline phase boundary, the crystallization goes through a transient liquid crystal state before reaching the final stable crystalline phase. Significant dynamics occur in the first few seconds of the transition, which are observed through fluctuations in the X-ray scattering intensity, and are correlated with the time interval that the transient thin film coexists with the evaporating solvent. The transition to the stable crystalline phase takes minutes or even hours under these conditions, which may be a result of the asymmetry of the molecule. Transient phases are of potential interest for applications, since they can act as a route to self-assembly of organic thin films. However, our observations show that the long-lived monolayer-stacked intermediate state does not act as a template for the bilayer-stacked crystalline phase. Rather, the grain structure is replaced through nucleation, where the nucleation free-energy barrier is related to a potential barrier that prevents molecules to flip their long axis by 180°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Quantitative probing of the fast particle motion during the solidification of battery electrodes

Synchrotron x-ray tomography represents one of the most powerful imaging techniques that can visualize the three-dimensional microstructural complexity with a high spatial resolution. To date, however, the temporal resolution of this technique has been handicapped by the intrinsic limitations in the data acquisition speed and the lack of a suitable data processing method. The present study aims to fundamentally resolve this challenge by implementing a data analysis method that is based on differentiating discrete tomography reconstruction from a continuous scan reconstruction. With this methodological development, we capture and quantify the particle motion during the solidification of battery electrodes and reveal the statistics of the dynamically evolving motion in the drying process, which has been challenging to resolve. We discover that the particle motion exhibits a strong dependence on its geometric location within a drying electrode. Our results also imply that the final electrode quality can be controlled by balancing the solvent evaporation rate and the particle mobility in the region close to the drying surface.

25 ENERGY STORAGE↗
DOE OSTI2021

Self-organization of nanoparticles and molecules in periodic Liesegang-type structures

Chemical organization in reaction-diffusion systems offers a strategy for the generation of materials with ordered morphologies and structural hierarchy. Periodic structures are formed by either molecules or nanoparticles. On the premise of new directing factors and materials, an emerging frontier is the design of systems in which the precipitation partners are nanoparticles and molecules. We show that solvent evaporation from a suspension of cellulose nanocrystals (CNCs) and L -(+)-tartaric acid [ L -(+)-TA] causes phase separation and precipitation, which, being coupled with a reaction/diffusion, results in rhythmic alternation of CNC-rich and L -(+)-TA–rich rings. The CNC-rich regions have a cholesteric structure, while the L -(+)-TA–rich bands are formed by radially aligned elongated bundles. The moving edge of the pattern propagates with a finite constant velocity, which enables control of periodicity by varying film preparation conditions. This work expands knowledge about self-organizing reaction-diffusion systems and offers a strategy for the design of self-organizing materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Pore-Filled PEMs from Poly(Phenylene Sulfonic Acid)s and Electrospun Poly(Phenylene Sulfone) Fiber Mats

A novel, composite, non-PFSA-based fuel cell membrane has been fabricated using a pore filling technique. The membrane consists of a mechanically stabilizing skeleton from an electrospun poly(phenylene sulfone) (PPSU) fiber mat and a thermally crosslinkable poly(phenylene sulfonic acid) (cPPSA) proton conducting ionomer that fills the interfiber voids. cPPSA copolymer was synthesized using Ullmann coupling copolymerization of 4,4-dibromobiphenyl 3,3-disulfonic acid with 1,4-dibromobenzene-2,5-disulfonic, followed by grafting a certain fraction of backbone sulfonic acid groups with biphenyl linker. The PPSU fiber mat was electrospun from NMP/acetone solution. Pore-filling was carried out by pouring a solution of cPPSA in methanol over the mat, followed by heating at 70°C to evaporate solvent. The cPPSA was crosslinked by an additional heating step, in a vacuum oven at 210°C for 5 hours. Here the resultant membrane had excellent proton conductivity, 5 times greater than that of Nafion® 211 in the 40-90% RH range at 80°C.

25 ENERGY STORAGE↗
NASA NTRS1980

Room-temperature adhesive for high-temperature use

PPQ (polyphenylquinoxaline) cures at room temperature, but withstands temperatures between -186 and +402 deg C. Adhesive is applied in chloroform solution. Bond forms as solvent evaporates.

Brooks, J. L.↗
NASA NTRS1988

Fire-Retardant Decorative Inks For Aircraft Interiors

Report describes testing of commercial and experimental fire retardants for incorporation into acrylic printing inks used on aircraft-interior sandwich panels. Films of acrylic ink containing fire-retardant additives prepared by casting on glass plates. Solvent evaporated in vacuum, cast films cured at 80 to 100 degree C for 30 minutes in air-circulating oven. Thermochemical properties of films examined by thermogravimetric analysis and differential scanning calorimetry (DSC). Samples of inks cast on sheets of polyvinylfloride (PVF), and their limiting oxygen indices and smoke evolution measured.

Kourtides, D. A.↗
NASA NTRS1993

Shear-induced surface alignment of polymer dispersed liquid crystal microdroplets on the boundary layer

Polymer dispersed liquid crystal thin films have been deposited on a glass substrate, utilizing the processes of polymerization and solvent evaporation induced phase separation. Liquid crystal microdroplets trapped on the upper surface of the thin film respond to the shear stress due to air or gas flow on the surface layer. Response to an applied step shear stress input on the surface layer has been measured by measuring the time response of the transmitted light intensity. Initial results on the measurements of the light transmission as a function of the air flow differential pressure indicate that these systems offer features suitable for boundary layer and gas flow sensors.

Parmar, D. S.↗
NASA NTRS1993

Gas flow-field induced director alignment in polymer dispersed liquid crystal microdroplets deposited on a glass substrate

Polymer dispersed liquid crystal thin films have been deposited on glass substrates by the processes of polymerization and solvent evaporation induced phase separation. The electron and the optical polarization microscopies of the films reveal that PDLC microdroplets formed during the process of phase separation near the top surface of the film remain exposed and respond to shear stress due to air or gas flow on the surface. Optical response of the film to an air flow-induced shear stress input on the free surface has been measured. Director orientation in the droplets changes with the applied shear stress leading to time varying transmitted light intensity. Director dynamics of the droplet for an applied step shear stress has been discussed from free energy considerations. Results on the measurement of light transmission as a function of the gas flow parameter unambiguously demonstrate the potential of these systems for use as boundary layer and gas flow sensors.

Parmar, D. S.↗
NASA NTRS1996

Solutocapillary Convection Effects on Polymeric Membrane Morphology

Macro voids are undesirable large pores in membranes used for purification. They form when membranes are cast as thin films on a smooth surface by evaporating solvent (acetone) from a polymer solution. There are two un-tested hypotheses explaining the growth of macro voids. One states that diffusion of the non-solvent (water) is solely responsible, while the other states that solutocapillary convection is the primary cause of macro void growth. Solutocapillary convection is flow-caused by a concentration induced surface-tension gradient. Macrovoid growth in the former hypothesis is gravity independent, while in the latter it is opposed by gravity. To distinguish between these two hypotheses, experiments were designed to cast membranes in zero-gravity. A semi-automated apparatus was designed and built for casting membranes during the 20 secs of zero-g time available in parabolic aircraft flight such as NASA's KC-135. The phase changes were monitored optically, and membrane morphology was evaluated by scanning electron microscopy (SEM). These studies appear to be the first quantitative studies of membrane casting in micro-gravity which incorporate real-time data acquisition. Morphological studies of membranes cast at 0, 1, and 1.8 g revealed the presence of numerous, sparse and no macrovoids respectively. These results are consistent with the predictions of the solutocapillary hypothesis of macrovoid growth.

Krantz, William B.↗
NASA NTRS2000

Microencapsulation and Electrostatic Processing Method

Methods are provided for forming spherical multilamellar microcapsules having alternating hydrophilic and hydrophobic liquid layers, surrounded by flexible, semi-permeable hydrophobic or hydrophilic outer membranes which can be tailored specifically to control the diffusion rate. The methods of the invention rely on low shear mixing and liquid-liquid diffusion process and are particularly well suited for forming microcapsules containing both hydrophilic and hydrophobic drugs. These methods can be carried out in the absence of gravity and do not rely on density-driven phase separation, mechanical mixing or solvent evaporation phases. The methods include the process of forming, washing and filtering microcapsules. In addition, the methods contemplate coating microcapsules with ancillary coatings using an electrostatic field and free fluid electrophoresis of the microcapsules. The microcapsules produced by such methods are particularly useful in the delivery of pharmaceutical compositions.

Morrison, Dennis R.↗
NASA NTRS2003

Determination of Lubricants on Ball Bearings by FT-IR using an Integrating Sphere

The lifetime determination of space lubricants is done at our facility by accelerated testing. Several micrograms of lubricant are deposited on the surface of a ball by syringing tens of micro liters of dilute lubricant solution. The solvent evaporates and the mass of lubricant is determined by twenty weighings near the balance reliability limit. This process is timely but does not produce a good correlation between the mass of lubricant and the volume of solution applied, as would be expected. The amount of lubricant deposited on a ball can be determined directly by Fourier Transform - Infrared Spectroscopy using an integrating sphere. In this paper, we discuss reasons for choosing this methodology, optimization of quantification conditions and potential applications for the technique. The volume of lubricant solution applied to the ball gives better correlation to the IR intensity than does the weight.

Street, K. W.↗
NASA NTRS1990

Method for fabricating ceramic filaments and high density tape casting method

An apparatus and method is disclosed for fabricating mats of ceramic material comprising preparing a slurry of ceramic particles in a binder/solvent, charging the slurry into a vessel, forcing the slurry from the vessel into spinneret nozzles, discharging the slurry from the nozzles into the path of airjets to enhance the sinuous character of the slurry exudate and to dry it, collecting the filaments on a moving belt so that the filaments overlap each other thereby forming a mat, curing the binder therein, compressing and sintering the mat to form a sintered mat, and crushing the sintered mat to produce filament shaped fragments. A process is also disclosed for producing a tape of densely packed, bonded ceramic particles comprising forming a slurry of ceramic particles and a binder/solvent, applying the slurry to a rotating internal molding surface, applying a large centrifugal force to the slurry to compress it and force excess binder/solvent from the particles, evaporating solvent and curing the binder thereby forming layers of bonded ceramic particles and cured binder, and separating the binder layer from the layer of particles. Multilayers of ceramic particles are cast in an analogous manner on top of previously formed layers. When all of the desired layers have been cast the tape is fired to produce a sintered tape. For example, a three-layer tape is produced having outer layers of highly compressed filament shaped fragments of strontium doped lanthanum (LSM) particles and a center layer of yttria stabilized zicronia (YSZ) particles.

Collins, Jr., Earl R.↗
NASA NTRS2008

Oxygen Plasma Modification of Poss-Coated Kapton(Registered TradeMark) HN Films

The surface energy of a material depends on both surface composition and topographic features. In an effort to modify the surface topography of Kapton(Registered TradeMark) HN film, organic solutions of a polyhedral oligomeric silsesquioxane, octakis(dimethylsilyloxy)silsesquioxane (POSS), were spray-coated onto the Kapton(Registered TradeMark) HN surface. Prior to POSS application, the Kapton(Registered TradeMark) HN film was activated by exposure to radio frequency (RF)-generated oxygen plasma. After POSS deposition and solvent evaporation, the films were exposed to various durations of RF-generated oxygen plasma to create a topographically rich surface. The modified films were characterized using optical microscopy, attenuated total reflection infrared (ATR-IR) spectroscopy, and high-resolution scanning electron microscopy (HRSEM). The physical properties of the modified films will be presented.

Wohl, C. J.↗
DOE OSTI2021

Method of making a perovskite layer at high speed

A method of making a perovskite layer includes providing a flexible substrate; providing a perovskite solution comprising an initial amount of solvent and perovskite precursor materials and a total solids concentration between 30 percent and 70 percent by weight of its saturation concentration; depositing the perovskite solution on the flexible substrate; removing a first portion of the solvent from the deposited perovskite solution and increasing the total solids concentration of the perovskite solution to at least 75 percent of its saturation concentration with a first drying step; and removing a second portion of the solvent from the deposited perovskite solution with a second drying step having a higher rate of solvent evaporation that causes saturation and a conversion reaction in the deposited perovskite solution resulting in perovskite crystal formation or formation of a perovskite intermediate phase, wherein the first drying step dwell time is at least 5 times longer than the second drying step dwell time.

Christensen, Scott Kenneth↗
DOE OSTI2020

Evaporation-Induced Vertical Alignment Enabling Directional Ion Transport in a 2D-Nanosheet-Based Battery Electrode

2D nanosheets have been widely explored as electrode materials owing to their extraordinarily high electrochemical activity and fast solid-state diffusion. However, the scalable electrode fabrication based on this type of material usually suffers from severe performance losses due to restricted ion-transport kinetics in a large thickness. Here, a novel strategy based on evaporation-induced assembly to enable directional ion transport via forming vertically aligned nanosheets is reported. The orientational ordering is achieved by a rapid evaporation of mixed solvents during the electrode fabrication process. Compared with conventional drop-cast electrodes, which exhibit a random arrangement of the nanosheets and obvious decrease of rate performance with increasing thickness, the electrode based on the vertically aligned nanosheets is able to retain the original high rate capability even at high mass loadings and electrode thickness. Furthermore, combined electrochemical and structural characterization reveals the electrode composed of orientation-controlled nanosheets to possess lower charge-transfer resistances, leading to more complete phase transformation in the active material.

25 ENERGY STORAGE↗
NASA NTRS2005

Sol-Gel Process for Making Pt-Ru Fuel-Cell Catalysts

A sol-gel process has been developed as a superior alternative to a prior process for making platinum-ruthenium alloy catalysts for electro-oxidation of methanol in fuel cells. The starting materials in the prior process are chloride salts of platinum and ruthenium. The process involves multiple steps, is time-consuming, and yields a Pt-Ru product that has relatively low specific surface area and contains some chloride residue. Low specific surface area translates to incomplete utilization of the catalytic activity that might otherwise be available, while chloride residue further reduces catalytic activity ("poisons" the catalyst). In contrast, the sol-gel process involves fewer steps and less time, does not leave chloride residue, and yields a product of greater specific area and, hence, greater catalytic activity. In this sol-gel process (see figure), the starting materials are platinum(II) acetylacetonate [Pt(C5H7O2)2, also denoted Pt-acac] and ruthenium(III) acetylacetonate [Ru(C5H7O2)3, also denoted Ru-acac]. First, Pt-acac and Ru-acac are dissolved in acetone at the desired concentrations (typically, 0.00338 moles of each salt per 100 mL of acetone) at a temperature of 50 C. A solution of 25 percent tetramethylammonium hydroxide [(CH3)4NOH, also denoted TMAH] in methanol is added to the Pt-acac/Ruacac/ acetone solution to act as a high-molecular-weight hydrolyzing agent. The addition of the TMAH counteracts the undesired tendency of Pt-acac and Ru-acac to precipitate as separate phases during the subsequent evaporation of the solvent, thereby helping to yield a desired homogeneous amorphous gel. The solution is stirred for 10 minutes, then the solvent is evaporated until the solution becomes viscous, eventually transforming into a gel. The viscous gel is dried in air at a temperature of 170 C for about 10 hours. The dried gel is crushed to make a powder that is the immediate precursor of the final catalytic product. The precursor powder is converted to the final product in a controlled-atmosphere heat treatment. Desirably, the final product is a phase-pure (Pt phase only) Pt-Ru powder with a high specific surface area. The conditions of the controlled- atmosphere heat are critical for obtaining the aforementioned desired properties. A typical heat treatment that yields best results for a catalytic alloy of equimolar amounts of Pt and Ru consists of at least two cycles of heating to a temperature of 300 C and holding at 300 C for several hours, all carried out in an atmosphere of 1 percent O2 and 99 percent N2. The resulting powder consists of crystallites with typical linear dimensions of <10 nm. Tests have shown that the powder is highly effective in catalyzing the electro-oxidation of methanol.

Narayanan, Sekharipuram↗