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Results for “Colloidal stability”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Some implications of colloid stability theory for protein crystallization

Colloid stability theory has been applied to protein crystallization and predicts a narrow range of conditions under which crystals can be grown without the agglomeration of protein molecules (colloids) in the bulk solution. It also predicts a critical electrolyte concentration above which agglomeration will always occur. Using this theory, the rapid protein agglomeration occurring during Schlieren experiments as well as a terminal crystal size effect in a fixed container were explained. Following this concept, the supposed 'terminal' crystal size has been at least doubled.

Young, C. C.↗
DOE OSTI2020

Arsenite oxyanions affect CeO 2 nanoparticle dissolution and colloidal stability

While highly reactive cerium oxide nanoparticles (CeO 2 NPs) are widely used in industry, their transport in aquatic systems is not well understood. To fill this knowledge gap, the interactions of CeO 2 NPs with arsenite (As 3+ ), a toxic metalloid and potential co-present contaminant, were investigated with respect to CeO 2 NP colloidal stability, dissolution, and surface redox reactions. Arsenite showed distinctive effects at different concentrations, with a high As 3+ concentration (10 –4 M) inducing 90% of CeO 2 NPs to settle from solution after 8 hours, while lower As 3+ concentrations (10 –5 or 10 –6 M) led to only 20% of CeO 2 NPs settling. The dissolution of NPs was most significant in the 10 –5 M As 3+ system owing to a lesser extent of aggregation, exposing more CeO 2 surface for dissolution. In the three As 3+ concentration systems, >97% of aqueous arsenic remained as As 3+ over 6 hours. On the NP surface, adsorbed As III was oxidized to As V , resulting in 58–70% of the adsorbed arsenic remaining as As III . Simultaneously Ce IV was reduced to Ce III , increasing Ce III on the CeO 2 NP surface from 17% (without arsenite) to 21–25% (with arsenite). Further mechanistic analyses revealed that the adsorption of arsenite was the main contributor to neutralizing the CeO 2 NP surface potential, enhancing particle sedimentation. These findings suggest that the fate and transport of CeO 2 NPs in our experimental systems are strongly affected by arsenite concentration and its adsorption on NPs. Here, the results also highlight the importance of the interplay between NP aggregation, oxidation, and dissolution in predicting the behaviors of CeO 2 NPs and associated toxic elements in aquatic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Inferring effective electrostatic interaction of charge-stabilized colloids from scattering using deep learning

In this article, an innovative strategy is presented that incorporates deep auto-encoder networks into a least-squares fitting framework to address the potential inversion problem in small-angle scattering. To evaluate the performance of the proposed approach, a detailed case study focusing on charged colloidal suspensions was carried out. The results clearly indicate that a deep learning solution offers a reliable and quantitative method for studying molecular interactions. The approach surpasses existing deterministic approaches with respect to both numerical accuracy and computational efficiency. Overall, this work demonstrates the potential of deep learning techniques in tackling complex problems in soft-matter structures and beyond.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High performance Calcium Copper Titanate/Polyimide dielectrics composites enabled through colloidal stabilization

Transition to electrified transportation demands advanced power electronic components with the capability to improve range, reliability, and cost of ownership to accelerate mass market adoption. Thus, improvement in the current designs, manufacturing processes, materials, and components capable of providing reliable and efficient operation at higher temperatures play important roles in meeting future needs. To address these challenges, this article focuses on novel dielectric materials designed to reduce the volume of the most important and bulky component of a power electronic system, a capacitor. A new composite dielectric material was developed by integrating the positive attributes of both polymer and ceramic capacitors to overcome the challenges of state-of-the-art dielectric materials. Further, the developed composite properties have been evaluated and showed promising results, achieving a dielectric constant of 250 at 100 Hz, 25°C, unseen in current literature. Additionally, these materials can function at high temperatures (>150°C) with good breakdown strength, providing promising working conditions for capacitors, especially in electric vehicle applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Colloidal Stability of PFSA-Ionomer Dispersions. Part I. Single-Ion Electrostatic Interaction Potential Energies

Charged colloidal particles neutralized by a single counterion are increasingly important for many emerging technologies. Attention here is paid specifically to hydrogen fuel cells and water electrolyzers whose catalyst layers are manufactured from a perfluorinated sulfonic acid polymer (PFSA) suspended in aqueous/alcohol solutions. Partially dissolved PFSA aggregates, known collectively as ionomers, are stabilized by the electrostatic repulsion of overlapping diffuse double layers consisting of only protons dissociated from the suspended polymer. We denote such double layers containing no added electrolyte as "single ion". Size-distribution predictions build upon interparticle interaction potential energies from the Derjaguin-Landau-Verwey-Overbeek (DLVO) formalism. However, when only a single counterion is present in solution, classical DLVO electrostatic potential energies no longer apply. Accordingly, here a new formulation is proposed to describe how single-counterion diffuse double layers interact in colloidal suspensions. Part II (Srivastav, H.; Weber, A. Z.; Radke, C. J. Langmuir 2024 DOI: 10.1021/acs.langmuir.3c03904) of this contribution uses the new single-ion interaction energies to predict aggregated size distributions and the resulting solution pH of PFSA in mixtures of n-propanol and water. A single-counterion diffuse layer cannot reach an electrically neutral concentration far from a charged particle. Consequently, nowhere in the dispersion is the solvent neutral, and the diffuse layer emanating from one particle always experiences the presence of other particles (or walls). Thus, in addition to an intervening interparticle repulsive force, a backside osmotic force is always present. With this new construction, we establish that single-ion repulsive pair interaction energies are much larger than those of classical DLVO electrostatic potentials. The proposed single-ion electrostatic pair potential governs dramatic new dispersion behavior, including dispersions that are stable at a low volume fraction but unstable at a high volume fraction and finite volume-fraction dispersions that are unstable with fine particles but stable with coarse particles. Finally, the proposed single-counterion electrostatic pair potential provides a general expression for predicting colloidal behavior for any charged particle dispersion in ionizing solvents with no added electrolyte.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Colloidal Stability of PFSA-Ionomer Dispersions Part II: Determination of Suspension pH Using Single-Ion Potential Energies

Perfluorosulfonic acid (PFSA) ionomers serve a vital role in the performance and stability of fuel-cell catalyst layers. These properties, in turn, depend on the colloidal processing of precursor inks. Here, to understand the colloidal structure of fuel-cell catalyst layers, we explore the aggregation of PFSA ionomers dissolved in water/alcohol solutions and relate the predicted aggregation to experimental measurements of solution pH. Not all side chains contribute to measured pH because of burying inside particle aggregates. To account for the measured degree of dissociation, a new description is developed for how PFSA aggregates interact with each other. The developed single-counterion electrostatic repulsive pair potential from Part I is incorporated into the Smoluchowski collision-based kinetics of interacting aggregates with buried side chains. We demonstrate that the surrounding solvent mixture affects the degree of aggregation as well as the pH of the system primarily through the solution dielectric permittivity, which drives the strength of the interparticle repulsive energies. Successful pH prediction of Nafion ionomer dispersions in water/n-propanol solutions validates the numerical calculations. Nafion-dispersion pH measurements serve as a surrogate for Nafion particle-size distributions. The model and framework can be leveraged to explore different ink formulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Impact of secondary salts, temperature, and pH on the colloidal stability of graphene oxide in water

The stability of graphene oxide (GO) in water is extremely relevant because of its application as an adsorbent material, as well as for its fate and behavior in the environment. Zeta potential was used to study the effect of secondary salts (carbonate, sulfate, and phosphate), temperature (20 to 60 °C), and pH (5 to 9) on the stability of six different GOs produced from natural, synthetic, and amorphous graphite—with and without the use of attrition milling. Generally, GOs produced with attrition-milled graphites had lower ζ-potentials than their unmilled counterparts because of their smaller particle sizes and higher concentration of oxygen-containing functional groups. It was observed that GO produced from graphite and synthetic graphite had ζ-potential values lower than –30 mV, even at 30 °C. However, it was observed that all the GOs studied were unstable in the presence of carbonate and sulfate salts at concentrations between 170 and 1695 mg L –1 , as they reached a ζ-potential of –4.1 mV. Density-functional theory electronic structure calculations suggested that the instability of GO in the presence of carbonate and sulfate was caused by the abstraction of a proton resulting in interaction energies E int of 28.3 and 168.9 kJ mol –1 , respectively. Our results suggest that temperatures above 30 °C, as well as carbonate and sulfate salts at concentrations relevant to arid and semi-arid regions, could promote the formation of agglomerates of GO, thus limiting its use and mobility in water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Stabilization of colloidal crystals engineered with nucleic acid

A post-synthetic method for stabilizing colloidal crystals programmed from nucleic acid is disclosed herein. In some embodiments, the method relies on Ag + ions to stabilize the particle-connecting nucleic acid duplexes within the crystal lattice, essentially transforming them from loosely bound structures to ones with very strong interparticle links. In some embodiments, the nucleic acid is DNA. Such crystals do not dissociate as a function of temperature like normal DNA or DNA-interconnected colloidal crystals, and they can be moved from water to organic media or the solid state, and stay intact. The Ag + -stabilization of the nucleic acid (e.g., DNA) bonds is accompanied by a nondestructive contraction of the lattice, and both the stabilization and contraction are reversible with the chemical extraction of the Ag + ions, e.g., by AgCl precipitation with NaCl.

Mirkin, Chad A.↗
DOE OSTI2021

In-situ Investigations on Gold Nanoparticles Stabilization Mechanisms in Biological Environments Containing HSA

Nanoparticles (NPs) developments advance innovative biomedical applications. However, complex interactions and the low colloidal stability of NPs in biological media restrict their widespread utilization. The influence of NPs properties on the colloidal stability for gold NPs with 5 and 40 nm in diameter with two surface modifications, methoxy-polyethylene glycol-sulfhydryl (PEG) and citrate, in NaCl and human serum albumin (HSA) protein solution, is investigated. This study is based on small-angle X-ray scattering (SAXS) methods allowing the in-situ monitoring of interactions in physiological conditions. The PEG coating provides high colloidal stability for NPs of both sizes. For 5 nm NPs in NaCl solution, a stable 3D self-assembled body-centered cubic (BCC) arrangement is detected with an interparticle distance of 20.7 ± 0.1 nm. In protein solution, this distance increases to 21.9 ± 0.1 nm by protein penetration inside the ordered structure. For citrate-capped NPs, a different mechanism is observed. The protein particles attach to the NPs surfaces, and an appropriate concentration of proteins results in a stable suspension. Cryogenic transmission electron microscopy (Cryo-TEM), UV–visible spectroscopy, and dynamic light scattering (DLS) support the SAXS results. The findings will pave the way to design and synthesize NPs with controlled behaviors in biomedical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Medium controlled aggregative growth as a key step in mesoporous silica nanoparticle formation

Near monodisperse mesoporous silica nanoparticles (MSN) represent a promising and rapidly developing type of mesoporous silica materials; however, the vast data on their synthesis remains unorganized and ill-understood. We systematically studied the formation of MSN under basic and neutral conditions using various temperatures, CTAB concentrations, hydrolyzing agents (triethanolamine, ammonia, phosphate buffers), and media with different colloidal stabilization properties (with ethanol as a cosolvent and monovalent salts). In the typical conditions for the preparation of stable MSN colloids, the particle size was controlled by colloidal stabilization by the medium (solvent type, ionic strength, and surfactant concentration) in agreement with the “aggregative growth” mechanism, rather than by solely the hydrolysis and condensation rates conventionally used for data interpretation in the classical nucleation theory. Medium properties (pH, ion types and concentration, polarity) also defined the efficiency of silica-surfactant cooperative self-assembly, which directly affected the porosity, mesopore size and pore wall thickness. Interestingly, this traditional silica-surfactant route showed a limited effect on the particle size, emphasizing the dominating role of colloidal stabilization in the studied reaction conditions. In situ pH measurements showed that every reaction medium has unique pH evolution profiles depending on the buffer capacity, hydrolysis and condensation rates. Reaction systems that fail to maintain the working pH can lead to non-porous products or undesired particle morphology and size distribution. The established particle formation mechanism allowed us to formulate comprehensive guidelines for preparing relatively concentrated colloids of near monodisperse (PDI 5–15%) mesoporous 30–700 nm silica spheres with variable porosity and mesopore size. Here, these findings will be particularly useful in designing new mesoporous silica-containing materials for biomedical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Evaluating the Rheo-electric Performance of Aqueous Suspensions of Oxidized Carbon Black

Here, the macroscopic properties of carbon black suspensions are primarily determined by the agglomerate microstructure built of primary aggregates. Conferring colloidal stability in aqueous carbon black suspensions should thus have a drastic impact on their viscosity and conductivity. Carbon black was treated with strong acids following a wet oxidation procedure. An analysis of the resulting particle surface chemistry and electrophoretic mobility was performed in evaluating colloidal stability. Changes in suspension microstructure due to oxidation were observed using small-angle X-ray scattering. Utilizing rheo-electric measurements, the evolution of the viscosity and conductivity of the carbon black suspensions as a function of shear rate and carbon content was thoroughly studied. The carboxyl groups installed on the carbon black surface through oxidation increased the surface charge density and enhanced repulsive interactions. Electrostatic stability inhibited the formation of the large-scale agglomerates in favor of the stable primary aggregates in suspension. While shear thinning, suspension conductivities were found to be weakly dependent on the shear intensity regardless of the carbon content. Most importantly, aqueous carbon black suspensions formulated from electrostatically repulsive primary aggregates displayed a smaller rise in conductivity with carbon content compared to those formulated from attractive agglomerates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Harnessing Particle Size‐Control and DNA‐Oligo Functionalization in ZIF‐76 for Biological Applications

Abstract Advanced therapeutics require novel nanocarriers to ensure their functionality is preserved during transit. Zeolitic imidazolate frameworks (ZIFs) have emerged as promising materials in this field owing to their combined biocompatibility, high porosity, and tunable chemistry. While a diverse family of ZIFs has been reported, few have been explored beyond the prototypical ZIF‐8. Herein, the size‐controlled synthesis of three distinct ZIF‐76 analogs is demonstrated, overcoming the unique synthetic challenges intrinsic to the lta topology and complex crystallization kinetics associated with the mixed linker approach. This assesses the materials’ platform effectiveness for intracellular delivery first by exploring the structural and colloidal stability in biologically relevant media. To circumvent particle aggregation, fluorescently labeled DNA oligonucleotides are post‐synthetically attached to the ZIF surface. This modification significantly improves the colloidal stability in media and facilitates particle internalization tracking. Finally, the particle‐cell interactions are assessed, revealing rapid cell membrane association with macrophages, but not lung epithelial cells, and ZIF accumulation within macrophages which increased over time. Importantly, this study outlines a generalized approach toward expanding the available library of ZIFs for biological applications, enabling the potential for targeted therapeutic delivery for intracellular infections treatment.

Deneff, Jacob I.↗
DOE OSTI2024

Scalable and adaptable two-ligand co-solvent transfer methodology for gold bipyramids to organic solvents

Large and faceted nanoparticles, such as gold bipyramids, presently require synthesis using alkyl ammonium halide ligands in aqueous conditions to stabilize the structure, which impedes subsequent transfer and suspension of such nanoparticles in low polarity solvents despite success with few nanometer gold nanoparticles of shapes such as spheres. Phase transfer methodologies present a feasible avenue to maintain colloidal stability of suspensions and move high surface energy particles into organic solvent environments. Here, we present a method to yield stable suspensions of gold bipyramids in low-polarity solvents, including methanol, dimethylformamide, chloroform, and toluene, through the requisite combination of two capping agents and the presence of a co-solvent. By utilizing PEG-SH functionalization for stability, dodecanethiol (DDT) as the organic-soluble capping agent, and methanol to aid in the phase transfer, gold bipyramids with a wide-range of aspect ratios and sizes can be transferred between water and chloroform readily and maintain colloidal stability. Subsequent transfer to various organic and low-polarity solvents is then demonstrated for the first time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Stabilized Alumina/Ethanol Colloidal Dispersion for Seeding High Temperature Air Flows

Seeding air flows with particles to enable measurements of gas velocities via laser anemometry and/or particle image velocimetry techniques can be quite exasperating. The seeding requirements are compounded when high temperature environments are encountered and special care must be used in selecting a refractory seed material. The pH stabilization techniques commonly employed in ceramic processing are used to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. The technique is not limited to alumina/ethanol and is also demonstrated with an alumina/H2O system. Other ceramic powders in various polar solvents could also be used once the point of zero charge (pH(sub pzc)) of the powder in the solvent has been determined.

Wernet, Judith H.↗
NASA NTRS1995

Demonstration of a stabilized alumina/ethanol colloidal dispersion technique for seeding high temperature air flows

Laser anemometry enables the measurement of complex flow fields via the light scattered from small particles entrained in the flow. In the study of turbomachinery, refractory seed materials are required for seeding the flow due to the high temperatures encountered. In this work we present a pH stabilization technique commonly employed in ceramic processing to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized, produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. Other metal oxide powders in various polar solvents could also be used once the point of zero charge (pH(pzc)) of the powder in the solvent has been determined. Laser anemometry measurements obtained using the new seeding technique are compared to measurements obtained using Polystyrene Latex (PSL) spheres as the seed material.

Wernet, Mark P.↗