Non-aqueous Dispersions Research Articles

Electrophoretic Deposition and Characterization of Er-Doped Bi2O3 Cathode Barrier Coatings on Non-Conductive Ce0.8Sm0.2O1.9 Electrolyte Substrates

In this study, the formation of thin-film barrier coatings based on a highly conductive Bi1.60Er0.4O3 (EDB) solid electrolyte on supporting Ce0.8Sm0.2O1.9 (SDC) electrolyte substrates was implemented for the first time using electrophoretic deposition (EPD). The electrokinetic properties of EDB-based suspensions in a non-aqueous dispersion medium of isopropanol modified with small additions of polyethyleneimine (PEI, 0.26 g/L) and acetylacetone (0.15 g/L), as well as in a mixed isopropanol/acetylacetone (70/30 vol.%) medium, were studied. The dependences of the thickness of the EDB coatings on voltage and deposition time were obtained using deposition on a model Ni foil electrode. Preliminary synthesis of a conductive polypyrrole (PPy) polymer film was used to create surface conductivity on non-conductive SDC substrates. The efficiency of using a modified dispersion medium based on isopropanol to obtain a continuous EDB coating 12 μm thick, sintered at a temperature of 850 °C for 5 h, is shown. The microstructure and morphology of the surface of the EDB coating were studied. A Pt/SDC/EDB/Pt cell was used to characterize the coating’s conductivity. The EPD method is shown to be promising for the formation of barrier coatings based on doped bismuth oxide. The developed method can be used for creating cathode barrier layers in SOFC technology.

Using low-field NMR relaxation to optimise particulate dispersions

Formulation of particulate dispersions is a difficult industrial problem, with a multitude of system details influencing the final outcome. Solvent relaxation NMR is shown to help optimise the formulation of particulate dispersions of a range of widely used commercial silicas. Solvent at the particle interface is sensitive to details of the formulation, and it is shown that the average solvent spin-relaxation time in a dispersion can be used to monitor wetted surface area, sample sedimentation, and additive amounts; chemical syntheses and mechanical degradation of silicas are also monitored to optimise the dispersions. The experiments, which can be carried out on bench-top or on-line spectrometers, are not limited to silicas and can be generalised to other particles in a range of aqueous and non-aqueous dispersions, providing useful feedback to the formulator anywhere surfactants, polymers, pH, ionic strength, Hamaker constants, and surface charge play a role in stabilisation. • Rapid NMR relaxation measurements reveal variation in silica surface chemistry. • Breakup of silica aggregates is monitored by NMR relaxation to optimise processing. • NMR relaxation measurements provide facile quality control tests for hydrogels. • Silica particle syntheses are monitored by NMR relaxation.

Solvent Relaxation NMR as a Tool to Study Particle Dispersions in Non-Aqueous Systems

The determination of the NMR spin–spin relaxation rate of water in (purely) aqueous particulate dispersions has been shown to be a convenient and facile experimental approach to probing the composition of near particle surface structures. Here, a systematic study has been undertaken of both non-aqueous and mixed aqueous–non-aqueous solvent particulate dispersions to explore the universality of the solvent relaxation technique. As in the aqueous case, a linear relationship between the surface area present and the solvent relaxation rate is observed, confirming the rapid exchange of the solvent molecules between the surface and the bulk and thereby illustrating the viability of the experimental methodology to study such systems. Crucially, the surface enhancement effect was considerably weaker in non-aqueous systems compared with aqueous dispersions and reflects a potential limitation of the wider deployment of this experimental methodology.

Ionic liquid-containing non-aqueous Pickering emulsions prepared with sterically-stabilized polymer nanoparticles: A highly efficient platform for Knoevenagel reaction

Room temperature ionic liquids (RTILs)-containing Pickering emulsions exhibit promising application potentials because of the integration of the “green” quality and the tunable applications of RTILs with the advantages of Pickering emulsions, such as the high stability and adjustable droplet size. In the present study, sterically-stabilized polymer nanoparticles (SSPNs) were first prepared via the reversible addition-fragmentation chain transfer (RAFT)-mediated non-aqueous dispersion polymerization, in which poly(lauryl methacrylate) (PLMA) and poly(4-vinyl pyridine) (P4VP) acted as the stabilizer block and the core-forming block, respectively. Kinetically-trapped PLMA-b-P4VP spheres and mixed spherical/worm-like morphologies could be achieved at a target copolymer composition. Subsequently, core cross-linked SSPNs (CSSPNs) were obtained by means of chemical cross-linking of P4VP cores of SSPNs with 1,4-dibromobutane in a diluted solution of SSPNs in toluene (0.4 mg/mL). Stable 1-butyl-3-methylimidazolium tetrafluoroborate-in-toluene ([Bmim][BF4]-in-toluene) non-aqueous Pickering emulsions could be formed at a low emulsifier content of 0.005 wt% adopting CSSPNs with mixed spherical/worm-like morphologies as Pickering emulsifiers. Benefiting from large surface areas of Pickering emulsions and unique chemical/physical properties of RTILs, [Bmim][BF4]-in-toluene Pickering emulsions provided readily available platforms for many organic reactions. As a proof of the concept, proline catalyzed Knoevenagel reaction of 4-nitrobenzaldehyde with malononitrile was chosen as a model here. Both high reaction efficiency and good recyclability were observed.

Effect of D-Mannitol on the Microstructure and Rheology of Non-Aqueous Carbopol Microgels.

D-mannitol is a common polyol that is used as additive in pharmaceutical and personal care product formulations. We investigated its effect on the microstructure and rheology of novel non-aqueous Carbopol dispersions employing traditional and time-resolved rheological analysis. We considered two types of sample, (i) fresh (i.e., mannitol completely dissolved in solution) and aged (i.e., visible in crystalline form). The analysis of the intracycle rheological transitions that were observed for different samples revealed that, when completely dissolved in solution, mannitol does not alter the rheological behaviour of the Carbopol dispersions. This highlights that the chemical similarity of the additive with the molecules of the surrounding solvent allows preserving the swollen dimension and interparticle interactions of the Carbopol molecules. Conversely, when crystals are present, a hierarchical structure forms, consisting of a small dispersed phase (Carbopol) agglomerated around a big dispersed phase (crystals). In keeping with this microstructural picture, as the concentration of Carbopol reduces, the local dynamics of the crystals gradually start to control the integrity of the microstructure. Rheologically, this results in a higher elasticity of the suspensions at infinitesimal deformations, but a fragile yielding process at intermediate strains.

Impact of Catalyst Ink Dispersing Solvent on PEM Fuel Cell Performance and Durability

The dispersing solvent used for fuel cell catalyst ink preparation plays a vital role in establishing the resulting morphology of the electrode layers, which in turn will impact the performance of proton exchange membrane (PEM) fuel cells. In this study, we report the impact of various ionomer dispersion solvents on PEM fuel cell performance and durability; two aqueous (1-propanol/water and 2-propanol/water) and several non-aqueous dispersing solvents (ethylene glycol and 1,2-butanediol) are compared. The cathode catalyst layer (CCL) fabricated using inks prepared with 1-propanol/water (3:1, w/w) exhibited the best initial performance followed by the CCL prepared using ethylene glycol. The CCLs made from non-aqueous ethylene glycol and 1,2-butanediol exhibited the best durability upon accelerated stress testing. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy indicated that, after the stress test, the distribution of both the Nafion ionomer and Pt nanoparticles within the CCLs prepared with non-aqueous ionomer dispersions underwent less change than those prepared with aqueous dispersions, which is responsible for the improved durability.

Formulation and processing of novel non-aqueous polyethylene glycol-in-silicone oil (o/o) phase change emulsions

Oil-in-oil phase change emulsions, composed of phase change materials (PCMs) dispersed in a continuous oily medium, have never been reported in the literature. The current study involves the formulation, stabilisation and characterisation of novel anhydrous emulsions of polyethylene glycol (PEG4000) as PCM in silicone oil. Emulsions with different dispersed phase concentrations were evaluated by analysing the viscous flow properties, optical microscopy and modulated differential scanning calorimetry. The results evidence that the emulsions can be pre-stabilised at 80 °C, under high shear conditions, by selecting an adequate silicone surfactant but undergo a severe destabilisation after a cooling and heating cycle. Nevertheless, a post-processing protocol (low shear agitation at 80 °C for 24 h) leads to thermal cycle resistant and storage stable non-aqueous dispersions. This process gives rise to a reduction of the shear-thinning character of the emulsion, shifts the melting and crystallization temperature of the PEG4000 to lower values and reduce its crystallinity. This is attributed to partial compatibility of the crystalline fraction of PEG4000 with other compounds of the emulsion.

Antitumoral Drug-Loaded Biocompatible Polymeric Nanoparticles Obtained by Non-Aqueous Emulsion Polymerization.

Non-aqueous dispersions (NAD) with two types of polymeric nanoparticles (NPs), such as hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic cross-linked poly(vinylpyrrolidone) (PNVP), were synthesized in the present study starting from monomer-in-silicone oil (PDMS) polymerizable non-aqueous emulsions stabilized with the same tailor-made PDMS-based block copolymer. These NPs were loaded with CCisplatin, an antitumoral model drug, directly from the emulsion polymerization step, and it was observed that the presence of the drug leads only to a slight increase of the NPs size, from 120 to 150 nm. The drug release kinetics was evaluated at 37 °C in phosphate buffer at pH = 7.4 and it appeared that the drug release rate from the hydrophilic cross-linked PNVP-based NPs is higher than that from the hydrophobic PCL-based NPs. Moreover, haemolysis tests revealed the fact that these two types of NPs have a good compatibility with the blood. Furthermore, for both the free and drug-loaded NPs, the in vitro cytotoxicity and apoptosis was studied on two types of cancer cell lines, such as MCF-7 (breast cancer cell line) and A-375 (skin cancer cell line). Both types of NPs had no cytotoxic effect but, at a concentration of 500 μg/mL, presented an apoptotic effect similar to that of the free drug.

Design of 2‐hydroxyethyl methacrylate‐functional macromonomer dispersants by semi‐batch cobalt chain transfer polymerization

AbstractAcrylic resins for automotive coatings are produced in nonaqueous dispersions (NAD) of nanometer size. These must be sterically stabilized by oligomeric dispersants, which are complex reactive oligomers possessing vinyl and hydroxyl functionalities, controlling the size of the nanocolloid. Hence, we have developed a kinetic Monte Carlo (kMC) model to improve the molecular structure of 2‐hydroxyethyl methacrylate‐functionalized poly (butyl methacrylate) (pBMA) dispersants of ca. 6,000 g/mol produced via semi‐batch cobalt chain transfer polymerization (CCTP). The kMC‐predicted degree of functionalization is benchmarked against a novel analytic expression suitable for oligomers. Stepwise adjustment of the semi‐batch feed program illustrates the successive improvement in molecular structure of the dispersant product, finally arriving at a functionalization degree close to the theoretical maximum for CCTP.

Gelation kinetics of non-aqueous Carbopol dispersions

The time evolution of the gelation process of non-aqueous Carbopol dispersions in PEG and glycerol was studied experimentally by tracking the evolving viscoelastic properties of the material by means of Fourier Transform Mechanical Spectroscopy (FTMS). A structural conversion degree related to the storage modulus was defined and a kinetic expression to describe its evolution was developed. UV–vis spectroscopy was employed to confirm the mechanism of gelation. It was found that an increase in both the concentration of glycerol and the gelation temperature increased the gelation rate. These trends seem to indicate a diffusion-controlled mechanism of the process, in which the solvent molecules penetrate the cross-linked structure of Carbopol particles, causing their uncoiling and subsequent swelling. Lastly, the kinetic relation found for the structural conversion degree was used to obtain conversion maps, which can be employed as a first guidance to design new continuous gelation formulation processes.

Nonvolatile Colloidal Dispersion of MgO Nanoparticles in Molten Salts for Continuous CO2 Capture at Intermediate Temperatures

The establishment of advanced CO2 capture, utilization, and storage (CCUS) technology is a crucial challenge for the mitigation of serious ongoing climate change. Herein, we report nonaqueous colloidal dispersions of MgO nanoparticles in molten salts as a new class of fluid absorbents for continuous CO2 capture at intermediate temperatures ranging from 200 to 350 °C. The colloidal absorbents were developed by dispersion of the nanoparticles in three different types of thermally stable low-melting point salts: ternary-eutectic alkali-metal nitrates ((Li–Na–K)NO3), tetraphenylphosphonium bis(trifluoromethane)sulfonimide ([P(Ph)4][NTf2]), and their mixtures. The new absorbents show high CO2 uptake performance with acceptable rheological properties at the target temperatures. The analysis of reaction rate kinetics in the uptake of CO2 revealed that CO2 can diffuse quickly into the molten salts to initiate the rapid formation of carbonates on the surfaces of MgO nanoparticles dispersed in these molten salts. T...

Measuring in Situ Length Distributions of Polymer-Wrapped Monochiral Single-Walled Carbon Nanotubes Dispersed in Toluene with Analytical Ultracentrifugation.

The length of a carbon nanotube is an important dimension that has to be adjusted to the requirements of an experiment or application, e.g., through sorting methods. So far, atomic force microscopy (AFM) has been the method of choice for measuring length distributions, despite being an ex situ method with apparent shortcomings. In this work, we explore analytical ultracentrifugation (AUC) as an in situ method for measuring the length distribution of polymer-wrapped (7, 5) single-walled carbon nanotubes dispersed in toluene. This is an AUC study of nanotubes in nonaqueous media, the preferred media for nanotubes used in device fabrication. In AUC, the temporally and spatially dependent change in optical absorption of a sample is measured under centrifugation. The resulting sedimentation curves can be deconvoluted with a standard data processing procedure (SEDFIT), to yield the sedimentation coefficient distribution. However, the conversion of the sedimentation coefficient distribution into a length distribution is nontrivial and requires finding a suitable model for the nanotube friction coefficient. Also, since AUC is based on optical absorption, it yields a volume distribution and not a number distribution as obtained from AFM reference data. By meeting these challenges and finding a surprisingly simple empirical flexible-chain-like model to describe the sedimentation behavior of one specific chiral structure, we suggest AUC as a viable method for measuring in situ nanotube length distributions of nonaqueous dispersions.

Synthesis and Utilization of Low Dispersity Acrylic Macromonomer as Dispersant for Nonaqueous Dispersion Polymerization

The effect of dispersity on the stabilization performance of poly(butyl methacrylate) (P(BMA)) ω-unsaturated macromonomer used as a reactive dispersant in nonaqueous acrylic dispersion (NAD) polymerization is investigated for the first time. Macromonomer with low dispersity (1.3) is synthesized in a one-pot process by the addition of bis(difluoroboryldiphenylglyoximato)cobalt(II) (CoPheBF) as a catalytic chain transfer (CCT) agent to P(BMA) chains mediated by atom transfer radical polymerization (ATRP); addition of the CoPheBF at a BMA monomer conversion of ∼80% leads to good control of chain length and dispersity while achieving a high fraction of terminal double bond (TDB) functionality. The lower dispersity P(BMA) macromonomer provides better stabilization to NAD systems per dispersant chain compared to material of the same number-average molecular weight (∼6000 Da) and TDB functionalization (∼70–75%) but higher dispersity (1.8), as characterized by the smaller average particle sizes and the higher wei...

Design of Acrylic Dispersants for Nonaqueous Dispersion Polymerization: The Importance of Thermodynamics

AbstractPoly(acrylic) nanoparticles produced by nonaqueous dispersion (NAD) radical polymerization are important components in many automotive coating formulations. A series of experiments show that the properties of final dispersions (particle size distribution, viscosity, and stability) correlate to the thermodynamics of the NAD system, as characterized by solubility parameters and solubility distances among the continuous phase, the soluble polymeric dispersant, and the polymer particles. The insights gained have enabled the design of a macromonomer dispersant containing greater than 10 mol% 2‐hydroxyethyl methacrylate, a necessary functional comonomer addition for end‐use properties. Stable NAD products were synthesized by changing the principal component of the dispersant from butyl methacrylate to 2‐ethylhexyl methacrylate.

Electrophoretic deposition of plasma activated sub-micron alumina powder

The positive effect of plasma mediated treatment of powder fraction in water-based dispersion is a rather well documented fact. Despite its importance for ceramic processing, the applicability of plasma treatment of ceramic particles in a non-aqueous dispersions remains unexplored. In the presented article, a specific planar type of dielectric barrier discharge - Diffuse Coplanar Surface Barrier Discharge (DCSBD), operated in atmospheric pressure air was used for the surface activation of sub-micron alumina particles. These were consequently dispersed in organic solvent of 2-propanol and evaluated for the performance during the process of electrophoretic deposition (EPD). The surface of ceramic particles and the dispersion behaviour were investigated using thermogravimetric analysis, XPS, measurement of zeta potential and particle size distribution. Plasma treatment of ceramic particles had a substantial effect on the deposition rate, which caused a significant reduction of surface roughness and slight improvement of the density and mean grain size of the fabricated coatings. Moreover, the plasma treatment resulted in a simultaneous anodic and cathodic EPD.

Graphene–Solvent Interactions in Nonaqueous Dispersions: 2D ROESY NMR Measurements and Molecular Dynamics Simulations

The liquid phase exfoliation of graphite by sonication in nonaqueous solvents like N-methyl-2-pyrrolidone (NMP) provides a simple and scalable route to dispersions of defect-free graphene sheets. The role of the solvent is crucial to the process; it is the interactions of the solvent with the graphene sheets that prevent agglomeration and stabilize the dispersion. Here, we show that the two-dimensional solution nuclear magnetic resonance (NMR) technique, rotating frame Overhauser effect spectroscopy (ROESY), provides a molecular signature of these interactions in graphene–NMP dispersions. Significant differences are observed in the spectra of the dispersions as compared to the pure solvent. Using classical molecular dynamics simulations, we show that these differences arise because of the induced layering of solvent molecules with reduced rotational mobility in the vicinity of the graphene sheets. The reduced mobility of solvent molecules in the dispersion as compared to the bulk solvent are reflected as differences in their two-dimensional ROESY NMR.

Dispersions of Goethite Nanorods in Aprotic Polar Solvents.

Colloidal suspensions of anisotropic nanoparticles can spontaneously self-organize in liquid-crystalline phases beyond some concentration threshold. These phases often respond to electric and magnetic fields. At lower concentrations, usual isotropic liquids are observed but they can display very strong Kerr and Cotton-Mouton effects (i.e., field-induced particle orientation). For many examples of these colloidal suspensions, the solvent is water, which hinders most electro-optic applications. Here, for goethite (α-FeOOH) nanorod dispersions, we show that water can be replaced by polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethylsulfoxide (DMSO), without loss of colloidal stability. By polarized-light microscopy, small-angle X-ray scattering and electro-optic measurements, we found that the nematic phase, with its field-response properties, is retained. Moreover, a strong Kerr effect was also observed with isotropic goethite suspensions in these polar aprotic solvents. Furthermore, we found no significant difference in the behavior of both the nematic and isotropic phases between the aqueous and non-aqueous dispersions. Our work shows that goethite nanorod suspensions in polar aprotic solvents, suitable for electro-optic applications, can easily be produced and that they keep all their outstanding properties. It also suggests that this solvent replacement method could be extended to the aqueous colloidal suspensions of other kinds of charged anisotropic nanoparticles.

Sealing system activated by magnetic induction polymerization

ABSTRACTThis work describes the one‐step production of glycerin based polyurethane/magnetite nanocomposites. The polymerization was performed in a nonaqueous dispersion containing the magnetic nanoparticles and the polar monomers under alternating magnetic field. Fourier transform infrared spectroscopy and crosslink degree tests were useful to conclude that the use of magnetic induction (∼3 min at 9300 W) produced results similar to the ones obtained by the conventional polymerization (∼3 h at 80 °C) in a fraction of the required time. A lost circulation fluid control test also was performed under magnetic induction heating and the system containing 5 wt % of the nanoparticles showed the highest reduction of the fluid flow rate. Scanning electron microscopy and probability density function tests of the best material allowed inferring that composite prepared by magnetic induction presents a non‐Gaussian distribution of the diameter, which is directly related to the observed sealing effect. These results showed that proposed polymer/polymerization system can be very useful to the sealing applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45549.

A study of the electrophoretic deposition of thin-film coatings based on barium cerate nanopowder produced by laser evaporation

The method of laser ablation of a target, followed by condensation, was used to obtain a weakly aggregated BCSO nanopowder from barium cerate. The dispersity, fraction composition of the nanopowder, electrokinetic potential of its nonaqueous dispersions, and electrokinetic parameters of the electrophoretic deposition process were determined. An ultrasonic treatment produced a stable suspension of the BCSO nanopowder in a mixed isopropanol–acetyl acetone medium (70/30 vol %). The suspension is characterized by a high and positive ζ-potential of +30 mV. The electrophoretic deposition onto a dense model cathode was used to obtain thin-film BCSO coatings that are of interest for the technology of solid-oxide fuel cells. The phase composition of the coating was examined. It was found that the successive annealings of the nanopowder at temperatures of 800–1400°C make it possible to reduce the content of unidentified crystalline phases in BCSO to trace levels (< 5 vol %).

Deacidification of acidic books and paper by means of non-aqueous dispersions of alkaline particles: A review focusing on completeness of the reaction

Deacidification refers to chemical treatments meant to slow down the acid hydrolysis and embrittlement of books and paper documents that had been printed on acidic paper. From the early 1800s up to about 1990, papermakers used aluminum sulfate, an acidic compound, in most printing papers. Certain deacidification methods use non-aqueous media to distribute alkaline mineral particles such as MgO within the pages of the treated books. Evidence is considered here as to whether or not the proximity of alkaline particles within such documents is sufficient to neutralize the acidic species present. Because much evidence suggests incomplete neutralization, a second focus concerns what to do next in cases where books already have been treated with a non-aqueous dispersion system. Based on the literature, the neutralization of acidic species within such paper can be completed by partial moistening, by high humidity and pressure, by water condensation, as well as by optional treatments to enhance paper strength and a final drying step.