Stable Aqueous Dispersions Research Articles

Thermal performance evaluation of the heat pipe by using 1-pyrene carboxylic-acid functionalized graphene nanofluid

The experiments are conducted to characterize a low-cost nanofluid and evaluate its effect on the sintered-wick heat pipe efficiency. Stable aqueous dispersions of 1-pyrene carboxylic acid (PCA)-functionalized graphene nanofluid were used to investigate the heat transfer characteristics in a sintered wick heat pipe. The various parameters being investigated include different fluids (concentration range from 0.01 to 0.06 mass%), tilt angles of the heat pipe (0 ͦ to 90 ͦ), and input powers (60 W, 80 W, 100 W, and 120 W). The result shows the enhancement of thermal conductivity of nanofluids are in the range of 21% and 40% as concentration and temperature were increased. It is found that the tilt angle of heat pipe has a substantial impact on the thermal properties, which could enhance the thermal performance by 79%. The experimental results indicated that the heat pipe thermal resistance is reduced using these nanofluids. The reduction in thermal resistance was the best at the high heat flux. The most considerable enhancement on overall heat transfer coefficient was achieved at 0.06 mass% by 13.9 kW/K.m2.

A comparative investigation of toxicity of three polymer nanoparticles on acorn barnacle (Amphibalanus amphitrite)

Pollution from plastic waste is increasingly prevalent in the environment and beginning to generate significant adverse impact on the health of living organisms. In this study, we investigate the toxicity of polymer nanoparticles exposed to Acorn Barnacle (Amphibalanus amphitrite) nauplii, as an animal model. Highly stable aqueous dispersion of luminescent nanoparticles from three common polymers: polymethylmethacrylate (PMMA), polystyrene (PS), and polyvinylchloride (PVC), were prepared via nanoprecipitation and fully characterised. Exposure studies of these polymer particles to freshly spawned barnacle nauplii were performed within a concentration range from 1 to 25 mg/L under laboratory-controlled conditions. The exposure to PMMA and PS nanoparticles did not show detrimental toxicity and did not cause sufficient mortality to compute a LC50 value. However, PVC nanoparticles were significantly toxic with a mortality rate of up to 99% at 25 mg/L, and the calculated LC50 value for PVC nanoparticles was 7.66 ± 0.03 mg/L, 95% CI. Interestingly, PVC nanoparticle aggregates were observed to adhere to the naupliar carapace and appendages at higher concentrations and could not be easily removed by washings. To explore the possibility of chemical toxicity of polymer nanoparticles, analysis of the polymer powders which was used to prepare the nanoparticles was conducted. The presence of low molecular weight oligomers such as dimers, trimers and tetramers were observed in all polymer samples. The chemical nature and concentration of such compounds are likely responsible for the observed toxicity to the barnacle nauplii. Overall, our study shows that care should be exercised in generalising the findings of exposure studies performed using one type of plastic particles, as the use of different plastic particles may elicit different responses inside a living organism.

Graphene Oxide of Extra High Oxidation: A Wafer for Loading Guest Molecules.

We present a new modification of graphene oxide with very high content (85 wt %) of oxygen-containing functional groups (hydroxy, epoxy, lactol, carboxyl, and carbonyl groups) that forms stable aqueous dispersion in up to 9 g·L-1 concentration solutions. A novel faster method of the synthesis is described that produces up to 1 kg of the material and allows controlling the particle size in solution. The synthesized compound was characterized by various physicochemical methods and molecular dynamics modeling, revealing a unique structure in the form of a multilayered wafer of several sheets thick, where each sheet is highly corrugated. The ragged structure of the sheets forms pockets with hindered mobility of water that leads to the possibility of trapping guest molecules.

Efficient transition metal dichalcogenides exfoliation by cellulose nanocrystals for ultrabroad-pH/temp stable aqueous dispersions and multi-responsive photonic films

A major challenge in developing 2D transition-metal dichalcogenides nanosheets (TMD ns) as nanofillers, catalysts and photothermal reagents lies in its colloidal stability and scalable production. Herein, a biomimetic hybrid strategy to efficiently exfoliate and stably disperse TMD ns in a low-cost, environment-friendly manner is demonstrated. Cellulose nanocrystal (CNC) with controllable morphology and surface chemistry is acted as ideal assisted exfoliation reagent and stabilizer for highly concentrated and thin-layer TMD ns aqueous dispersions. Ultrabroad-pH/temperature (pH = 1–13, temperature = 1–95 °C) stable aqueous dispersions of TMD ns/CNC hybrids and the self-assembly of CNC allow the successful construction of flexible, rapid, and multi-stimuli responsive photonic films, e.g., mechanical strain, humidity and photothermal, providing an avenue for artificial skin, flexible sensor, and smart screen & window applications.

Application of Vinyl ether Copolymers for Surface Modification of Carbon Black

In this work, the possibility of stabilizing aqueous dispersed systems of carbon with vinyl ether copolymers of various composition and structure was investigated. It was shown that the presence of hydrophobic fragments in the macromolecule chain plays a significant role and positively affects the results of stabilization of aqueous dispersions of carbon particles. It was shown that the composition and molecular architecture of the stabilizing copolymer strongly affects the stabilizing ability in studied systems. Studies have shown that the use of a polymeric stabilizer in combination with ultrasonic treatment of dispersed systems makes it possible to obtain stable, homogeneous, highly dispersed suspensions. At the same time, it was demonstrated that a strong increase in the time and intensity of ultrasonic treatment of the system does not lead to a significant improvement in the results

Stabilization of Aqueous Dispersions of Inorganic Microparticles Under Mechanical Activation

The stability of aqueous dispersed systems of TiO2 and Fe2O3 microparticles in the presence of a water-soluble polymer - ethylhydroxyethylcellulose (EHEC) - has been studied under the condition of using two methods of mechanoactivation of the pigment surface - processing them in a disintegrator and in an ultrasonic field. It is shown that in the absence of a polymer stabilizer, an intense effect on aqueous dispersed systems of pigments leads to rapid coagulation of particles. In the presence of EHEC, a small stabilizing effect is observed, which is significantly enhanced when processing dispersed systems in a disintegrator and in an ultrasonic field. In this case, the stability of dispersed systems depends little on the method of mechanoactivation of their surface, but significantly depends on the duration of the intense exposure.

Stable aqueous dispersions of bare and double layer functionalized superparamagnetic iron oxide nanoparticles for biomedical applications

Abstract Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted the particular interest of scientists from various disciplines since their obtaining to the present day. The physicochemical and pharmacokinetic properties of SPIONs-containing magnetic nanofluids, and their applicability in biomedicine, largely depend on the stability of the colloidal system, particle size, size distribution, net magnetic moment, phase composition, and type and properties of stabilizers. Also, in some cases, when using magnetic nanoparticles for biomedical purposes, it is necessary that the stabilizing ligands of nanoparticles should not significantly change the magnetic properties. From this point of view, the preparation of stable colloidal systems containing bare iron oxide nanoparticles (BIONs) in water at physiological pH attracts particular attention and becomes increasingly popular in scientific circles. This study is focused on the development of the synthesis of aqueous suspensions of SPIONs stabilized with various organic molecules (oleic acid [OA] and poly(ethylene glycol) monooleate - with molecular weights 460 and 860) using a modified controlled chemical coprecipitation reaction, as well as stable nanofluids containing BIONs in an aqueous medium at neutral pH (near-physiological). The obtained samples were characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy, small-angle x-ray scattering (SAXS), dynamic light scattering (DLS), electrophoretic light scattering (ELS), and Vibrating Sample Magnetometry.

Conductive halloysite clay nanotubes for high performance sodium ion battery cathode

It is a practical challenge to find a cathode material for sodium ion batteries (SIBs) with high capacity and low cost. Here, conductive halloysite nanotubes (Hal) were synthesized by wrapping a layer of polypyrrole (PPy) via in situ polymerization as a potential cathode material for SIBs. By functionalization with PPy, the zeta potential of Hal changed from −28.5 mV to +30.1 mV, which showed excellent aqueous dispersion stability. HR-TEM and XPS results also demonstrated that a continuous conductive layer was formed around the tubes. By virtue of the good electrical conductivity and special tubular structure of Hal@PPy, it was applied as cathode for sodium ion battery. The Hal@PPy electrode could maintain a capacity of 126 mAh g−1 after 280 cycles at current density of 200 mA g−1, which suggested a high potential in energy storage fields.

Enhanced anticorrosion properties of water-borne anticorrosive paints based on Zinc/magnesium/nanocarbon (Zn/Mg/NC).

Zinc (Zn) and magnesium (Mg) network structures have been prepared chemically in presence of stable aqueous dispersion of nanocarbon (NC) to form the corresponding hybrid sol gel (HSG) of Zn /Mg /NC. Morphological studies and particle size distribution of the formed (HSG) have been determined via SEM/EDX, TEM and dynamic light scattering (DLS) respectively. The prepared (HSG) of different weight percent (3, 6, 9, 12 %) has been incorporated into ecofriendly anticorrosive water born paint formulations to protect carbon steel from corrosion. The painted metal panels have been tested for degree of rusting and blistering resistance in accordance with ASTMD. The physico- mechanical properties of the coated panels have been also investigated. The effect of the prepared HSG in enhancing corrosion protection efficiency IE% of the painted panels has been monitored by potentiodynamic polarization and electrochemical impedance spectroscopy. The results revealed that as the concentration of the prepared HSG increases as the IE% increases. Maximum inhibition efficiency IE% up to 96.5% was obtained. As far as we know, these featured corrosion resistances for the prepared paint formulations have not been reported yet in the open literature.

Aqueous dispersions of monodisperse Pt, Pd, and Au nanoparticles stabilized by thermosensitive polymer for the efficient reduction of nitroarenes

The reduction of nitroarenes is usually catalyzed by heterogeneous catalysts. In this work, highly stable aqueous dispersions of monodisperse Pt, Pd, and Au nanoparticles stabilized by thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), are conveniently synthesized with the average sizes of 2.3, 3.1, and 2.3 nm, respectively. The modulation of the hydrophilic-hydrophobic nano-environments of the catalysts can be selectively provided by utilizing the temperature-responsive characteristics of PNIPAM. They are effective and thermosensitive pseudohomogeneous catalysts for nitroarenes reduction. The decreasing trend of catalytic activity is as follows: PNIPAM-Au > PNIPAM-Pd > PNIPAM-Pt. The catalytic reduction of nitrobenzene (NB), 4-nitrophenol (4-NP), and o-nitroaniline (o-NA) follow the pseudo-first-order kinetics, and the catalytic rates can be tuned by utilizing their temperature-responsive behavior. PNIPAM-Au nanocatalysts exhibit high turnover frequencies (TOF) up to 84, 12.9, and 40 min−1 for catalytic reduction of NB, 4-NP, and o-NA at 20 °C, respectively, which are one of the highest values ever reported.

Highly Water-Dispersible Graphene Nanosheets From Electrochemical Exfoliation of Graphite.

The electrochemical exfoliation of graphite has been considered to be an effective approach for the mass production of high-quality graphene due to its easy, simple, and eco-friendly synthetic features. However, water dispersion of graphene produced in the electrochemical exfoliation method has also been a challenging issue because of the hydrophobic properties of the resulting graphene. In this study, we report the electrochemical exfoliation method of producing water-dispersible graphene that importantly contains the relatively low oxygen content of <10% without any assistant dispersing agents. Through the mild in situ sulfate functionalization of graphite under alkaline electrochemical conditions using a pH buffer, the highly water-dispersible graphene could be produced without any additional separation processes of sedimentation and/or centrifugation. We found the resulting graphene sheets to have high crystalline basal planes, lateral sizes of several μm, and a thickness of <5 nm. Furthermore, the high aqueous dispersion stability of as-prepared graphene could be demonstrated using a multi-light scattering technique, showing very little change in the optical transmittance and the terbiscan stability index over time.

Concurrent Enhancement of Conductivity and Stability in Water of Poly(3,4‐Ethylenedioxythiophene):Poly(Styrenesulfonate) Films Using an Oxetane Additive

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most used conducting polymer in organic electronics and bioelectronics owing to its high conductivity combined with high optical transparency and availability as a stable colloidal aqueous dispersion, that can be processed as a conducting ink to produce thin and flexible films and electrodes. In this work, water‐resistant films of PEDOT:PSS showing enhanced conductivity are prepared by solely adding one reagent, 3‐methyl‐3‐oxetanemethanol, to PEDOT:PSS aqueous dispersions. The stability of the resultant thin films in water is attributed to the covalent cross‐linking of benzene rings anchored in PSS chains to polyether chains originated from the polymerization of oxetane groups, as indicated by NMR studies. A phase‐segregation within the PEDOT:cross‐linked PSS film is suggested to facilitate charge transport within the PEDOT network and to be at the origin of the improved conductivity. When immersed in water, the films exhibit increased water‐resistance towards resuspension and delamination and exhibit an increase of conductivity, by two to three orders of magnitude, depending on the used raw PEDOT:PSS formulation. The method described in this work is advantageous in originating water‐stable and highly conducting thin films of PEDOT:PSS as it does not involve high temperatures nor strong acids.

Catalytically active membranes for decomposition of organic compounds in aqueous solutions

This work is devoted to the preparation of microfiltration ceramic tubular membranes based on α-Al2O3 with deposited catalytically active layers for use in wastewater treatment processes. Cobalt and manganese oxides were used as the material of the catalytically active layer; deposition was carried out using a mixture of aggregative stable aqueous dispersions of Co3O4 and MnO2 nanoparticles. According to the data of scanning electron microscopy, the thickness of the obtained deposited layers does not exceed 3 μm. X-ray fluorescence analysis confirmed the presence of Mn and Co on the surface of the samples. The resulting membranes with a mass of 10 mg of the deposited layer of the oxide mixture were tested in the methylene blue decomposition reaction in dilute aqueous solutions (1,2 mg/L). The reaction was carried out in a batch reactor at room temperature, complete discoloration of the solution was observed after 180-240 minutes.

Synthesis and characterization of stable aqueous dispersion of silver nanoparticle from citrullus vulgaris seed oil via lecithin

Nanoparticles are known to be of wide applications in various fields of human endeavours. Many methods of syntheses such as physical, chemical are harmful to the environment, thus, this study utilised green production of nanoparticles via waste product such as Citrulus vulgaris seed. Oil was extracted using soxhlet extractor from the prepared Citrulus vulgaris seed. Physico-chemical properties such as percentage yield, acid value, peroxide value were carried out on the Citrulus vulgaris seed oil. Citrulus vulgaris was further processed to form lecithin. The lecithin extracted was characterized for colour, Peroxide Value, Acetone Insoluble (AI), Acid Value, solubility in water and organic solvents. The result of the physico-chemical parameters was in conformity with the standard and various literatures. Therefore, lecithin is processed into dispersed aqueous silver nanoparticles by the addition of silver nitrate. The chemical reaction was monitored progressively using visual assessment, UV-visible and FTIR Spectroscopy. The size and surface of the dispersed silver nanoparticles produced was analysed using Atomic Force Microscopy. Therefore, a dispersed aqueous silver nanoparticle was produced from lecithin made from Citrulus vulgaris seed oil.

Waterborne polyurethane nanocomposite incorporated with phytic acid intercalated layered double hydroxides: A highly stable aqueous dispersion with desired corrosion protection capability

AbstractIn this research, waterborne polyurethane (WPU) nanocomposites incorporated with MgAl‐NO3LDH layered double hydroxide (LDH) and phytic acid intercalated LDH (PA‐LDH) nanostructures were prepared as novel environmental‐friendly corrosion protective coatings. Fourier‐transform infrared spectroscopy, X‐ray diffraction (XRD), thermogravimetric analysis, field emission scanning electron microscope (SEM), and high‐resolution transmission electron microscopy analysis confirmed the prosperous preparation of LDHs nanosheets. Moreover, structural, thermal, thermo‐mechanical, and morphological investigations of prepared WPU/LDHs films were also evaluated. The SEM images exhibited that the intercalation of LDH nanosheets with PA could drastically overcome the agglomeration problem of unmodified LDH within the polyurethane matrix. Based on XRD results, WPU/LDHs films showed a lower micro‐phase separation degree and crystallinity compared to pure WPU film. According to wettability analysis, WPU/PA‐LDH film demonstrated the highest hydrophobicity among samples due to its lowest phase‐separation degree, which causes the castor oil and poly(tetramethylene ether) glycol segments to migrate toward the surface of film from the bulk. Furthermore, the potentiodynamic polarization scanning and electrochemical impedance spectroscopy analysis revealed that the WPU/PA‐LDH sample containing 1.0 wt% of PA‐LDH has a superlative anti‐corrosion performance for SS 304 steel with an inhibition efficiency of 99.9%. This superior anti‐corrosive property benefited from the barrier property and chloride absorption capability of well‐dispersed PA‐LDH nanosheets, deposition of PA on the steel substrate, and improved hydrophobicity of the WPU/PA‐LDH coating.

Preparation and Properties of Biobased, Cationic, Waterborne Polyurethanes Dispersions from Castor Oil and Poly (Caprolactone) Diol

Biobased cationic waterborne polyurethanes (WPUs) were prepared using isophorone diisocyanate (IPDI), N-methyl diethanolamine (N-MDEA), polycaprolactone (PCL) diol, hydrochlotic acid (HCl), and 1,4-butanediol (BDO). To improve the mechanical performance and adhesive strength of the waterborne polyurethane films, different amounts of castor oil (CO) acting as a cross-linking agent were incorporated in the polyurethane structure. The structures of the waterborne polyurethanes were assessed by Fourier-transform infrared spectroscopy (FTIR). The combination of CO had a positive effect on the dispersion and stability properties of WPUs. WPUs containing higher content of CO demonstrated a remarkable enhancement in homogeneity among particles. The stable aqueous dispersion was obtained even when N-MDEA loading was as low as 3.2 wt%; a bonus of this low hydrophilic moiety was the excellent adhesive strength, whose T-peel strength could reach up to 36.8 N/25 mm, about 114% higher than that of WPU (17.2 N/25 mm) without any CO content. The elongation at break of CO7.40%-WPU was 391%. In addition, the fracture mechanism of the waterborne polyurethane films transformed from the brittle failure to the ductile fracture. The experiment results showed the CO-modified WPUs displayed excellent film-forming property, flexibility, and adhesion, which can be employed for constructing the eco-friendly, biodegradable, cationic, waterborne polyurethanes.

One-pot synthesis of silver nanoparticle deposited cellulose nanocrystals with high colloidal stability for bacterial contaminated water purification

Cellulose nanocrystals (CNCs) have been utilized as a scaffold to immobilize silver nanoparticles (AgNPs) for their potential application as an antibacterial agent and bactericidal filler. However, the present implemented strategies involve synthesis by multi-step and utilize environment non-friendly reducing agents for the deposition of AgNPs on CNCs. Furthermore, the long-time aqueous dispersion stability of prepared AgNPs hybrids is another issue of concern for their efficient utilization as an antibacterial filler. We have developed an environmentally benign one-pot method using a biocompatible polyvinyl+pyrolidone (PVP) as a reducing agent to deposit AgNPs on CNCs. The developed method exhibited the uniform in-situ deposition of AgNPs on CNCs. The formed (CNC-PVP-Ag) nanohybrid displayed excellent long time aqueous colloidal stability (8 months), antibacterial and anti-biofouling activities (12.5 µg/mL and 25 µg/mL for E. coli and S. aureus) which is 4 and 2 times lower than AgNPs (w/o CNCs) prepared by the identical process as of CNC-PVP-Ag. As water-borne microbial contaminations are a global water quality concern, the excellent antibacterial and anti-biofouling activity of CNC-PVP-Ag was applied for water purification. An efficient bacterial filtration performance (100% reduction of Escherichia coli viability) was achieved after two filtration cycles.

Surfactant-Free Stabilization of Aqueous Graphene Dispersions Using Starch as a Dispersing Agent.

Attention to graphene dispersions in water with the aid of natural polymers is increasing with improved awareness of sustainability. However, the function of biopolymers that can act as dispersing agents in graphene dispersions is not well understood. In particular, the use of starch to disperse pristine graphene materials deserves further investigation. Here, we report the processing conditions of aqueous graphene dispersions using unmodified starch. We have found that the graphene content of the starch–graphene dispersion is dependent on the starch fraction. The starch–graphene sheets are few-layer graphene with a lateral size of 3.2 μm. Furthermore, topographical images of these starch–graphene sheets confirm the adsorption of starch nanoparticles with a height around 5 nm on the graphene surface. The adsorbed starch nanoparticles are ascribed to extend the storage time of the starch–graphene dispersion up to 1 month compared to spontaneous aggregation in a nonstabilized graphene dispersion without starch. Moreover, the ability to retain water by starch is reduced in the presence of graphene, likely due to environmental changes in the hydroxyl groups responsible for starch–water interactions. These findings demonstrate that starch can disperse graphene with a low oxygen content in water. The aqueous starch–graphene dispersion provides tremendous opportunities for environmental-friendly packaging applications.

High-Yield Production of Nano-Lateral Size Graphene Oxide by High-Power Ultrasonication.

Nanographene oxide (GOn) constitutes a nanomaterial of high value in the biomedical field. However, large scale production of highly stable aqueous dispersions of GOn is yet to be achieved. In this work, we explored high-power ultrasonication as a method to reduce particle size of GO and characterized the impact of the process on the physicochemical properties of the material. GOn was obtained with lateral dimensions of 99 ± 43 nm and surface charge of −39.9 ± 2.2 mV. High-power ultrasonication enabled an improvement of stability features, particularly by resulting in a decrease of the average particle size, as well as zeta potential, in comparison to GO obtained by low-power exfoliation and centrifugation (287 ± 139 nm; −29.7 ± 1.2 mV). Remarkably, GOn aqueous dispersions were stable for up to 6 months of shelf-time, with a global process yield of 74%. This novel method enabled the production of large volumes of highly concentrated (7.5 mg mL−1) GOn aqueous dispersions. Chemical characterization of GOn allowed the identification of characteristic oxygen functional groups, supporting high-power ultrasonication as a fast, efficient, and productive process for reducing GO lateral size, while maintaining the material’s chemical features.

Capsules from synthetic diblock-peptides as potential artificial oxygen carriers

The design of an encapsulation system consisting of a synthetic peptide which is fully biodegradable into non-toxic constituents. This system should be capable of encapsulating perfluorinated hydrocarbons and should be a promising basis for oxygen carriers to be used as artificial blood replacement. A diblock-peptide is synthesised following a phosgene-free method and characterised by 1H-NMR. Subsequently, this diblock-peptide is self-assembled with perfluorodecalin (PFD) to form PFD-filled capsules as potential artificial oxygen carriers allowing for rapid oxygen uptake and release. The diblock-peptide Bu-PAsp10-PPhe10 is successfully synthesised and used to encapsulate PFD. The capsules have a spherical shape with an average diameter of 360 nm in stable aqueous dispersion. NMR measurements prove their physical capability for reversible uptake and release of oxygen. The resulting capsules are expected to be fully biodegradable and possibly could act as oxygen carriers for artificial blood replacement.