Stable Aqueous Suspensions Research Articles

Preparation of stable aqueous suspensions of antimony-doped tin oxide nanoparticles used for transparent and thermal insulation fluorocarbon coating

In order to prepare the highly stable aqueous suspensions of antimony-doped tin oxide (ATO) used for the transparent and thermal insulation fluorocarbon coating, the effect of sodium polyacrylate (PAAS) and polyvinyl alcohol (PVA) on the stability of the suspensions was investigated. The stability and dispersity of the suspensions were characterized using zeta potential analyzer, ultraviolet–visible spectrophotometer, and scanning electron microscope. No sediments were observed after 6-month storage of the ATO suspensions containing 0.1 wt% PAAS and 2.0 wt% PVA. The reason why aqueous suspensions were capable of stabilization was explained from a theoretical perspective. A new model of steric hindrance for colloid particles stabilized by binary dispersant was proposed, which may have positive contribution to other colloid system containing two dispersants. A nano-composite fluorocarbon coating, exhibiting a good thermal insulation and high transmittance, was formed after ATO suspensions were added in fluorocarbon emulsion. The temperature inside the chamber was decreased by 6.0 °C, and 75.0 % visible light rays could pass through the coating.

Water‐Soluble Monolayer Molybdenum Disulfide Quantum Dots with Upconversion Fluorescence

Uniform water‐soluble monolayer MoS2 quantum dots (MQDs) with lateral sizes of ≈2.1 nm, a clearly zigzag‐terminated edge, and a hexagonal lattice structure are achieved using ammonium molybdate, thiourea, and N‐acetyl‐l‐cysteine (NAC) as precursors and the capping reagent in a facile one‐pot hydrothermal approach. MQDs have good dispersity and high stability in aqueous suspension and exhibit a significantly larger direct bandgap (3.96 eV) compared to monolayer MoS2 nanosheets (1.89 eV). Pronounced blue‐shifts in the wavelengths of both the excitonic absorption and intrinsic state emission with activated strong luminescence at room temperature beyond monolayer MoS2 nanosheets is demonstrated. Unusual upconversion photoluminescence is also observed and is caused by two successive transfers of energy from the near‐infrared (NIR) absorption generated by the NAC capping reagent to the hexagonal structure of MQDs. Additional optical properties of MQDs may provide numerous exciting technological applications. Here, MQDs are demonstrated as a highly selective fluorescent reagent for detecting tetracycline hydrochloride under UV and NIR irradiation.

A novel green approach for the preparation of cellulose nanowhiskers from white coir

The aim of this work was to optimize the extraction of cellulose nanowhiskers (CNW) from unripe coconut husk fibers (CHF). The CHF was delignified using organosolv process, followed by alkaline bleaching (5% (w/w) H2O2+4% (w/w) NaOH; 50°C, 90min). The CHF was subsequently hydrolyzed with 30% (v/v) sulfuric acid (60°C, 360min). The process yielded a partially delignified acetosolv cellulose pulp and acetic black liquor, from which the lignin was recovered. The CNW from the acetosolv pulp exhibited an average length of 172±88nm and a diameter of 8±3nm, (aspect ratio of 22±8). The surface charge of the CNW was −33mV, indicating a stable aqueous colloidal suspension. The nanocrystals presented physical characteristics close to those extracted from cellulose pulp made by CHF chlorine-pulping. This approach offers the additional advantage of extracting the lignin as an alternative to eradication.

Simple Criterion for Stability of Aqueous Suspensions of Ultrafine Particles of a Poorly Water Soluble Drug

In this work, a simple criterion is proposed for prediction of a long-term stability of aqueous suspensions of ultrafine particles of a poorly water soluble drug, curcumin. A new "stability parameter" (γ0ε/γε0) has been defined, which is a ratio of nondimensional mechanical (mainly ultrasonic) energy (ε/ε0) to nondimensional solid-liquid interfacial energy (γ/γ0). The stability of aqueous suspensions of curcumin particles over a period of 1 year and 9 months has been correlated with this parameter. In order to calculate this parameter, solid-liquid interfacial energies were first estimated, from nucleation rates, which in turn were calculated from size distributions of curcumin particles precipitated using water as antisolvent. The mechanical energy was then estimated from the intensity of ultrasound and mechanical agitation used during precipitation. It was found that precipitations carried out with higher values of γ0ε/γε0 (more than 100) result in aqueous suspensions with particle size less than 1 μm. It was further observed that these suspensions remain stable (i.e., no or negligible change in average particle size) for a period of 1 year and 9 months. On the other hand, the suspensions of particles precipitated at lower values of γ0ε/γε0 (less than 10) were found to be highly unstable (i.e., the average particle size changes drastically). These results suggest that γ0ε/γε0 can be used as a parameter to engineer stable aqueous suspensions of curcumin particles. Further, it was found that the use of the Mersmann equation to estimate solid-liquid interfacial surface tensions can help in making this criterion predictive.

Nanofibrillar alginic acid‐derived hierarchical porous carbon supercapacitors

A versatile route has been demonstrated for the preparation of hierarchical porous carbon films derived from nanofibrillar alginic acid extracted from brown seaweeds. An acetic acid‐sodium acetate buffer was used to adjust pH of the nanofibrillar alginic acid gels, giving rise to a stable aqueous homogeneous suspension at the concentration of 5.0 wt% and pH ∼4.5. A crack‐free nanofibrillar alginic acid film with a diameter of several centimeters was cast from the suspension. Self‐condensing silica around nanofibrillar alginic acid formed silica‐alginic acid composites that were carbonised and then etched the silica to generate mesoporous carbon films. The aligned mesochannel carbon was originated from the hierarchical parallel organisation of the self‐assembled nanofibrillar alginic acid. The introduction of mesoporosity into the carbon structure afforded the high‐surface‐area mesoporous carbon film‐based supercapacitor that exhibits an ultrahigh‐rate capability and highly electrical capacitance.

Tb2(bpdc)3 and Eu2(bpdc)3 Nanoparticles (bpdc: 2,2ʹ-Bipyridine-4,4ʹ- dicarboxylate) and Their Luminescence

Tb2(bpdc)3 and Eu2(bpdc)3 nanoparticles (bpdc: 2,2ʹ-bipyridine-4,4ʹ-dicarboxylate) have been prepared via straightforward precipitation from aqueous solution. The nanoparticles exhibit mean diameters of 41(5) nm (Tb2(bpdc)3) and 56(4) nm (Eu2(bpdc)3) and show a very good colloidal stability in aqueous suspension. Particle size and chemical composition have been characterized based on electron microscopy, X-ray diffraction, infrared spectroscopy and thermogravimetry. Photoluminescence validates an efficient excitation of Tb3+/Eu3+ via the bpdc ligand as an antenna that leads to intense characteristic green and red emissions. The absolute quantum yields of Tb2(bpdc)3 and Eu2(bpdc)3 have been determined at 28 and 12%, respectively. Although rare-earth metal-based photoluminescence is typically quenched in water due to vibronic loss processes (v(O-H)), here, the antenna effect and the shielding of the metal centers via the bpdc ligand are very efficient, allowing for an intense green and red emission of the Tb2(bpdc)3 and Eu2(bpdc)3 nanoparticles even in aqueous suspension.

The aqueous colloidal suspension of ultrathin 2D MCM-22P crystallites.

The action of a tetrapropylammonium hydroxide solution on lamellar zeolite precursor MCM-22P produced a stable aqueous colloidal suspension which was shown by X-ray diffraction, small angle X-ray scattering and atomic force microscopy to contain ultrathin two-dimensional (2D) crystallites, including one-unit cell thick (i.e., 2.5 nm) monolayers.

Flow of suspensions of carbon nanotubes carrying phase change materials through microchannels and heat transfer enhancement

This work explores the potential of nano-encapsulated phase change materials (PCMs) in applications related to microelectronics cooling. PCMs (wax or meso-erythritol) were encapsulated in carbon nanotubes (CNTs) by a method of self-sustained diffusion at room temperature and pressure. These nano-encapsulated wax nanoparticles alone allowed heat removal over a relatively wide range of temperatures (different waxes have melting temperatures in the range 40-80 °C). On the other hand, nano-encapsulated meso-erythritol nanoparticles allowed heat removal in the range 118-120 °C. The combination of these two PCMs (wax and meso-erythritol) could extend the temperature range to 40-120 °C, when both types of nanoparticles (wax and meso-erythritol intercalated) would be suspended in the same carrier fluid (an oil). The nanoparticles possess a short response time of the order of 10(-7) s. Such nano-encapsulation can also prevent the PCM from sticking to the wall. In this work, experiments with wax-intercalated CNTs, stable aqueous suspensions of CNTs with concentrations up to 3 wt% with and without nano-encapsulated wax were prepared using a surfactant sodium dodecyl benzene sulfonate (NaDDBS). These suspensions were pumped through two channels of 603 μm or 1803 μm in diameter subjected to a constant heat flux at the wall. It was found that the presence of the surfactant in CNT suspensions results in a pseudo-slip at the channel wall which enhances the flow rate at a fixed pressure drop. When aqueous solutions of the surfactant were employed (with no CNTs added), the enhanced convection alone was responsible for a ~2 °C reduction in temperature in comparison with pure water flows. When CNTs with nano-encapsulated wax were added, an additional ~1.90 °C reduction in temperature due to the PCM fusion was observed when using 3 wt% CNT suspensions. In addition, suspensions of meso-erythritol-intercalated CNTs in alpha-olefin oil were used as coolants in flows through the 1803 μm-diameter microchannel. These suspensions (1.5 wt% CNT) revealed a temperature reduction due to the PCM fusion of up to 3.2 °C, and a fusion temperature in the range 118-120 °C.

Production of aqueous dispersions of inorganic graphene analogues by exfoliation and stabilization with non-ionic surfactants

The production of stable aqueous suspensions of several inorganic graphene analogues was performed by exfoliation of the corresponding bulk layered materials via sonication using non-ionic surfactants as dispersing agents.

Solvent-free acetylation of cellulose nanofibers for improving compatibility and dispersion

Cellulose nanofibers (CNFs), as bio-materials derived from wood or non-wood plants, have the advantages of being biodegradable, renewable, low cost, and having good mechanical properties compared to synthetic nanofibers. CNFs have been used as reinforcement in polymeric matrices, however, due to their polar surface, their dispersibility in non-polar solvents and compatibility with hydrophobic matrices are poor. In this work, the chemical modification of CNFs, using acetic anhydride in the presence of pyridine as a catalyst, was studied with the aim of changing the surface properties. Native and chemically modified CNFs were characterized in terms of dynamic absorption, thermal stability, surface chemistry, morphology, and crystal structure. The reaction of acetylation between the acetyl groups and the hydroxyl groups of the CNFs was examined using Fourier transform infrared (FT-IR) analysis, while its extent was assessed by titration. The ester content of CNFs was higher for the acetylated samples compared to the control samples. It was also shown that the crystallinity decreased moderately as a result of esterification. Thermal stability of the modified nanofibers was slightly increased. Unlike native CNFs, a stable aqueous suspension was obtained with the modified nanofibers in both ethanol and acetone. The contact angle measurements confirmed that the surface characteristics of acetylated CNFs were changed from hydrophilic to more hydrophobic. In addition, the obtained acetylated CNFs showed more hydrophobic surface, which is in favor of enhancing the hydrophobic non-polar mediums.

Isolation and characterization of cellulose nanofibers from banana peels

Cellulose nanofibers were isolated from banana peel using a combination of chemical treatments, such as alkaline treatment, bleaching, and acid hydrolysis. The suspensions of chemically treated fibers were then passed through a high-pressure homogenizer 3, 5, and 7 times, to investigate the effect of the number of passages on the properties of the resulting cellulose nanofibers. The cellulose nanofibers isolated in this study had a dry basis yield of 5.1 %. Transmission electron microscopy showed that all treatments effectively isolated banana fibers in the nanometer scale. The micrographs of the process steps used to isolate the nanofibers revealed gradual removal of amorphous components. Increasing number of passages in the homogenizer shortened the cellulose nanofibers while furnishing more stable aqueous suspensions with zeta potential values ranging from −16.1 to −44.1 mV. All the samples presented aspect ratio in the range of long nanofibers, hence being potentially applicable as reinforcing agents in composites. X-ray diffraction studies revealed that homogenized nanofiber suspensions were more crystalline than non-homogenized suspensions. Fourier transform infrared spectroscopy confirmed that alkaline treatment and bleaching removed most of the hemicellulose and lignin components present in the banana fibers. Thermal analyses revealed that the developed nanofibers exhibit enhanced thermal properties. In general, the nanoparticles isolated from the banana peel have potential application as reinforcing elements in a variety of polymer composite systems.

High resolution electrochemical micro-capacitors based on oxidized multi-walled carbon nanotubes

This study reports the preparation of all-solid-state micro-supercapacitors in planar interdigitated configuration based on MWCNTs via the electrophoretic deposition technique. The carbon nanotubes were functionalized with carboxylic groups via a HNO3 concentric solution in order to prevent their agglomeration and obtain a stable aqueous suspension, and to add a pseudo-capacitance contribution to the predominant double-layer capacitance. The electrode materials were characterized in a 3 electrode configuration, and the micro-devices in a two-electrode configuration using electrochemical impedance spectroscopy and cyclic voltammetry in 0.5 M sulfuric acid and a gel of PVA-H3PO4-H2O doped by SiWA electrolyte. Spatial resolution down to 10 μm was obtained for the device with specific capacitance up to 1.8 mF.cm−2 in electrolyte based PVA and a high power density of 1.28 W.cm−2 in 0.5 M H2SO4 electrolyte.

Preparation and Characterization of Cellulose Regenerated from Phosphoric Acid

Native cellulose has a highly crystalline structure stabilized by a strong intra- and intermolecular hydrogen-bond network. It is usually not considered as a good gelling material and emulsion stabilizer due to its insolubility in water. Chemical modification is generally necessary to obtain cellulose derivatives for these applications. In this study, we have shown that, by simply disrupting the hydrogen-bond network of cellulose with phosphoric acid treatment, the regenerated cellulose can be a good gelling material and emulsion stabilizer. Microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis have confirmed that the regenerated cellulose is primarily amorphous with low crystallinity in the structure of cellulose II. Stable aqueous suspensions and opaque gels that resist flowing can be obtained with the regenerated cellulose at concentrations higher than 0.6% and 1.6%, respectively. Moreover, it can effectively stabilize oil-in-water emulsions at concentrations less than 1% by a mechanism that combines network and Pickering stabilization.

Nanodiamonds for surface engineering of orthopedic implants: Enhanced biocompatibility in human osteosarcoma cell culture

Recently, nanodiamonds have attracted interest in biomedical applications such as drug delivery, targeted cancer therapies, fabrication of tissue scaffolds, and biosensors. We incorporated diamond nanoparticles in alginate–bioactive glass films by electrophoretic process to prepare functional coatings for biomedical implants. Turbidity examination by time-resolved laser transmittance measurement revealed that a stable multi-component aqueous suspension of alginate, bioactive glass and diamond particles could be obtained at concentrations of 0.6, 1.3, and 0.65g/l, respectively. Uniform films with ~5μm thickness were deposited on 316 stainless steel foils by employing constant field strength of 15V/cm for 45s. Scanning electron microscopy and simultaneous thermal analysis showed that the composite films were homogeneous and contained ~39wt.% inorganic particles. In vitro bioactivity assessment in simulated body fluid for 4weeks and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using human osteoblast-like cell line (MG-63) and mouse fibroblast cell line (L929) exhibited enhanced biocompatibility and bioactivity of the composite films. Results show advantages of alginate-nanodiamonds in cell culture, tissue engineering, and pharmaceutical applications.

Vasoactive effects of stable aqueous suspensions of single walled carbon nanotubes in hamsters and mice

Single-walled carbon nanotubes synthesized with iron (Fe-SWCNT) or gadolinium (Gd-SWCNT) show promise as high performance multimodal contrast and drug-delivery agents. Our purpose was to evaluate potential vasoactive effects of SWCNT. Stable aqueous solutions of Fe-SWCNTs or Gd-SWCNTs were made using the biocompatible amphiphilic polymer N-(carbonyl-methoxypolyethyleneglycol 2000)-1,2-distearoylsn-glycero-3- phosphoethanolamine (PEG-DSPE). Both aggregated and non-aggregated (sonicated) formulations were tested. The initial vasoactivity of the formulations and their potential for inducing pro-inflammatory endothelial dysfunction were investigated in the hamster cheek pouch and murine cremaster muscle intravital microscopy models. These models provide an assay to test several formulations/dosages in a paired fashion. Abluminal exposure to small arterioles exposes both endothelial and vascular smooth muscle cells. Using abluminal exposures of dosages that would approximate the first pass of an i.v. bolus injection, both Fe-SWCNTs and Gd-SWCNTs were immediately vasoactive. Aggregated formulations induced dilation and non-aggregated formulations induced constriction in both hamsters and mice. Endothelial dysfunction was evident after exposure to either aggregated or non-aggregated forms. General loss of dilator capability was seen after exposure to non-aggregated but not aggregated forms. Thus concentrations mimicking bolus dosing of PEG-DSPE coated SWCNT induce both acute and chronic vascular responses.

Stable Reduced Graphene Oxide Suspension Modified by PAMAM

Poly (amidoanime) (PAMAM) dendrimers contain numerous amino-terminal groups and are highly hydrophilic. These terminal groups make PAMAM molecules adsorbed onto graphene oxide (GO) nanosheets through electrostatic action with oxygen containing groups on graphene oxide nanosheets. The PAMAM molecules react with GO, and form stable aqueous suspension of modified reduced graphene oxide (RGO).

Coagulation–flocculation treatment of municipal wastewater based on anionized nanocelluloses

The synthetic polymers normally used in the coagulation–flocculation treatment of waste water are in most cases derived from oil-based, non-renewable raw materials. Consequently, there has been a growing interest in replacing them with more sustainable natural bio-based alternatives. However, derivatives of cellulose, which is the most abundant biopolymer on earth, are still scarce. In this work dicarboxylic acid nanocellulose (DCC) flocculants were produced by nanofibrillation of periodate and chlorite-oxidized celluloses with a homogenizer. The flocculation performance levels of five such anionic nanocelluloses with variable charge densities were examined in the coagulation–flocculation treatment of municipal waste water and the results compared with the performance of a commercial coagulant and a synthetic polymeric flocculant. In addition, the aldehyde and carboxyl content, charge density (CD), size and stability of each DCC were determined in an aqueous solution. The results showed that all the DCCs synthesized were able to flocculate waste water very efficiently, and the dosages required were similar to that of the commercial reference flocculant. The combined coagulation–flocculation treatment of municipal wastewater resulted in a lower residual turbidity and COD in a settled suspension, with considerably reduced total chemical consumption relative to coagulation with ferric sulphite alone. A high charge density and high nanofibril content of the DCC flocculant gave the best flocculation performance. The DCCs showed high stability in aqueous suspensions over a long period of time and good performance within the chosen pH range.

Study of stability and dispersion composition of calcium hydroxyapatite in aqueous suspensions by capillary zone electrophoresis

The influence of sodium oleate and ultrasonic treatment on the stability of aqueous suspensions of calcium hydroxyapatite is studied by capillary zone electrophoresis. Chances for the assessment of the stability and dispersion composition based on the electrophoretic behavior of particles are demonstrated. For stable suspensions a linear relation of the normalized peak square to the concentration of calcium hydroxyapatite is found. The data of capillary zone electrophoresis are verified with the data of scanning electron microscopy and dynamic light scattering.

Size effect on the optical limiting in suspensions of detonation nanodiamond clusters

We report on the optical limiting (OL) in stable aqueous suspensions of detonation nanodiamond (ND) clusters with average size of 50, 110, and 320 nm. The nanosecond Z-scan measurements at wavelength of 532 nm revealed that the larger the cluster size, the better the OL performance and the higher the ray stability of the ND suspension. Our analysis showed that the nonlinear scattering and the nonlinear absorption are the dominant mechanisms of OL in aqueous ND suspensions.

One-step chemical vapor deposition synthesis of magnetic CNT–hercynite (FeAl2O4) hybrids with good aqueous colloidal stability

A multiwall carbon nanotube (MWCNT)/hercynite (FeAl2O4) hybrid nanomaterial was synthesized by one-step chemical vapor deposition (CVD) using acetylene as precursor and FeOx–AlOOH xerogel as catalyst. The hybrid material was composing by hercynite nanoparticles (diameter 10–50nm) intimately attached to the walls of the MWCNTs. The diameter of the MWCNTs was related to particle size of the catalyst. The hybrid nanomaterial exhibited a characteristic magnetic behavior that can be considered as a combination of superparamagnetism and ferromagnetism, with a saturation magnetization of 5.7emu/g at an applied field of 18kOe and a coercivity of 520Oe. The hybrid displayed a relatively low pHZPC (approx. 3.2) and formed very stable aqueous suspensions at pH 5.5. Controlled oxidation of the hybrid generated oxidized functional groups, as –OH and –COOH, and promoted the transformation of hercynite to hematite. Due to the high dispersibility of the hybrid in water, it presents an interesting potential as nanofiller for hydrophilic polymers.