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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

System and method for curved light sheet projection during two-photon polymerization

A laser-based manufacturing system is disclosed for fabricating non-planar three-dimensional layers. The system may have a laser for producing a laser beam with a plurality of optical wavelengths. An optically dispersive element may be used for receiving the laser beam and splitting the beam into a plurality of distinct beam components, wherein each beam component has spatially separated optical spectral components. A phase mask may be used which is configured to receive at least one of the beam components emerging from the dispersive element and to create a modified beam. One or more focusing elements may then be used to receive the modified beam emerging from the phase mask and to focus the modified beam into a non-planar light sheet for use in fabricating a part.

Saha, Sourabh Kumar↗
DOE OSTI2022

Polymeric materials for electrochemical cells and ion separation processes

Polymers of intrinsic microporosity are provided herein. Disclosed polymers of intrinsic microporosity include modified polymers of intrinsic microporosity that include negatively charged sites or crosslinking between monomer units. Systems making use of polymers of intrinsic microporosity and modified polymers of intrinsic microporosity are also described, such as electrochemical cells and ion separation systems. Methods for making and using polymers of intrinsic microporosity and modified polymers of intrinsic microporosity are also disclosed.

Helms, Brett A.↗
DOE OSTI2022

Liquid-free, polymeric reinforcement of nanoscale assemblies

Provided herein is a nanoscale material assembly made up of a plurality of nanoscale structures with a crosslinked polymer thermally deposited on the structures. Also disclosed are methods for preparing the nanoscale material assembly with a deposited crosslinked polymer. Further disclosed are various conditions and materials that when used in the preparation of the nanoscale material assemblies further enhance their mechanical properties. In some embodiments, the nanoscale material assemblies can be either nanoscale yarn assemblies or nanoscale sheet assemblies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Synthesis and Characterization of Polymeric Pore Former Microspheres using Modified Polymer Resin

Porosity in polymer parts is often desired to improve mechanical properties. Individual pores must be small enough that bulk mechanical properties are retained but significant enough to reduce the density of the material. Filler materials can be incorporated into polymer matrices and subsequently removed to create voids. The materials used to create the voids are known as pore-formers. The present research aims to create spherical pores in a silicone matrix by inserting and removing core materials or fillers post-cure. A method was developed to incorporate pore formers into an uncured polymer resin and remove the materials from the matrix. Polyethylene Glycol (PEG) and Polylactic Acid (PLA) microspheres are created and incorporated into silicone matrices as pore formers. Microspheres with controllable size distributions are formed via ultrasonic spray pyrolysis and emulsion formation. Microspheres are removed from the matrix by solvent extraction and calcination. PLA microspheres were modified by hydroxyl addition to the surface to study their solubility in water. PEG-PLA block copolymers are also synthesized and investigated, comparing their physical and chemical properties to the monomers to identify whether the block copolymer microspheres will be more easily removable than their monomeric microspheres. Moreover, other properties including thermal stability, rheology, and mechanical response are studied. The present dissertation provides a comprehensive understanding of the synthesis and characterization of PEG and PLA-based pore formers, toward the future development of feedstock for additive manufacturing porous structures.

Damptey, Ransford↗
DOE OSTI2017

Retention of Cr in Meta-kaolin-based geo-polymeric Materials under Oxidation and Carbonation - 17453

Alkali activated alumino-silicates, often referred to as geo-polymers, are considered promising immobilization matrices for contaminants due to their high sorption capacity, durability and low leachability. For some contaminants they may prove superior to cement pastes that are conventional immobilization materials in waste management applications. However, estimating the retention capacity of some contaminants under environmental conditions that include oxidation and carbonation and may induce a valance change, is complicated. These contaminants tend to be soluble under oxidizing condition and form precipitates under reducing conditions. Thus, contaminant retention is highly dependent on the initial oxidation state at which the metal was introduced, as well as the matrix sorption ability, ability to resist oxidation and carbonation, and the contaminant leachability. Moreover, carbonation in considered one of the most important degradation mechanisms in cementitious material, causing porosity reduction and significant changes in contaminant leachability, however, geo-polymers have considerably lower Ca content relative to cements, or none, and the effect of carbonation on these pastes is less clear. Thus, contaminant release mechanisms and rates must be estimated based upon exposure to various atmospheres appropriate to waste management applications. In this study we aim to estimate the sorption capacity, and leachability of Cr from a meta-kaolin based geo-polymer, doped with Cr, as a function of its oxidation state and carbonation. Cr has a high valance range from +6 to 0 similar to Tc, and is used as its simulant in the current study. Sodium dichromate was used as an oxidized source metal material. To induce reducing conditions, ascorbic acid was added except for experimental control cases. The samples were aged under N{sub 2}, 98% N{sub 2} + 2% CO{sub 2}, CO{sub 2} deficient air and air environments under constant relative humidity. Following aging, samples were subject to equilibrium leaching as a function of pH (EPA Method 1313) and monolith mass transport rate testing (EPA Method 1315). Mass balance calculations, based on the results of a pH dependent leaching test, have shown that oxidized Cr samples lost 85-95% of their Cr content, whereas, the reduced Cr samples lost only 20% of their Cr content. On the other hand, the leachability of Si and Al is much higher in the reduced-Cr samples then in the samples with oxidized Cr, and their natural pH is up to 2.5 pH units lower than that of the oxidizing cases. Thus, we conclude that the combination of the reducing agent and the spike chemistry influence the matrix formation. Sample aging have not resulted in any significant change in the Cr-leaching behavior of the oxidizing matrices in the pH dependent leaching test, although a significant decrease in the natural pH, of 1.5 pH unit, was observed upon exposure to elevated CO{sub 2} levels (2%), probably due to the formation of Na-carbonate species. The pH and leaching behavior of the reduced Cr samples under the various aging conditions have not yielded significant variation either in their natural pH or in their leaching behavior. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Fuel cell cathode and fuel cell system including a polymeric additive

A cathode configured for use within a fuel cell system is provided. The cathode includes a cathode substrate. The cathode further includes a coating disposed upon the cathode substrate and including a fluorocarbon polymer additive configured for sintering at a temperature of less than 200° C. The fluorocarbon polymer additive may be mixed with a catalyst ink coating or may be applied separately as a topcoat layer.

Ramaswamy, Nagappan↗
DOE OSTI2015

Olefin metathesis for effective polymer healing via dynamic exchange of strong carbon-carbon bonds

A method of preparing a malleable and/or self-healing polymeric or composite material is provided. The method includes providing a polymeric or composite material comprising at least one alkene-containing polymer, combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material, and performing an olefin metathesis reaction on the polymer so as to form reversible carbon-carbon double bonds in the polymer. Also provided is a method of healing a fractured surface of a polymeric material. The method includes bringing a fractured surface of a first polymeric material into contact with a second polymeric material, and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon-carbon double bonds with the second polymeric material. Compositions comprising malleable and/or self-healing polymeric or composite material are also provided.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nanocomposite additives based on graphene sheets and silica nanofibers

A method for producing a composite polymeric article, an additive for a polymeric article, and a composite polymeric article are provided. The method generally includes providing a plurality of graphene nanoplatelets, providing a plurality of silica nanofibers, providing a polymeric material, and distributing the plurality of silica nanofibers and the plurality of graphene nanoplatelets within the polymeric material to achieve a composite article. The additive for a polymeric article includes a plurality of graphene nanoplatelets and a plurality of silica nanofibers. The composite polymeric article includes a plurality of graphene nanoplatelets, a plurality of silica nanofibers, and a polymeric matrix. The plurality of graphene nanoplatelets and the plurality of silica nanofibers are distributed within the polymeric matrix. The silica nanofibers have a mean cross sectional diameter of not more than 100 nm.

36 MATERIALS SCIENCE↗