Stable Colloidal Solutions Research Articles

Plasma Assisted Generation of Micro- and Nanoparticles

In this research, the peculiarities of micro- and nanoparticles generation are considered. Two techniques of micro- and nanoparticles' formation using electric arc and underwater discharge plasma sources are proposed. Molybdenum oxide crystals were deposited on side surface of the bottom electrode (anode) of the free-burning discharge between metallic molybdenum electrodes. Friable layer of MoO<sub>3</sub>, which consists of variously oriented transparent prisms and platelets (up to few hundreds of $mu;m in size), was formed by vapor deposition around the electrode. In the second technique, plasma of the underwater electric spark discharges between metal granules was used to obtain stable colloidal solutions with nanoparticles of 20-100 nm sizes.

Synthesis and optical properties study of nanocomposites based on AuNPs and AgNPs obtained by laser ablation in liquid monomer

In this work, Ag and Au nanoparticles (AgNPs and AuNPs) stable colloid solution were prepared by laser ablation of chemically pure silver rod and gold film in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning electron microscope and vary from 30 to 130 nm. Nanocomposites films were prepared from obtained stable colloid solution by photocuring. To prepare solid film based on aliphatic polymer IDA long molecules cross-linking, 1,6-Hexandiol diacrylate was used. Obtained films were transparent, homogenous and colored in brown for AgNPs and purple for AuNPs-filled nanocomposites. Prepared nanomaterials exhibit strong third-order nonlinear optical responses under CW laser irradiation at 532 nm, which was estimated by using z-scan technique performed with open and close aperture. The real and imaginary parts of third-order nonlinear optical coefficients of the studied nanocomposites were found to be up to Reχ(3) = 1.31 × 10−5 (esu) and Imχ(3) = 7.64 × 10−5 (esu), for samples negative nonlinear refractive index was obtained, which corresponds to self-defocusing effect.

Experimental validation of numerical predictions for forced convective heat transfer of nanofluids in a microchannel

In this study, we postulated and demonstrated that surface conditions have a dominant role in multi-phase flows that leverage stable colloidal nanoparticle suspensions (i.e., nanofluids) in determining their efficacy as heat transfer fluids (HTF). Forced convective heat transfer rates during the flow of de-ionized water (DIW) and aqueous TiO2 nanofluids inside a microchannel were studied numerically as well as experimentally under constant wall temperature boundary conditions. A brief literature review of the theoretical investigations involving the thermal-conductivity of nanofluids as heat transfer fluids (HTF) was also carried out. This enabled the development of a numerical model and computational analysis for forced convective heat transfer of nanofluids in a microchannel using conventional CFD (Computational Fluid Dynamics) techniques. Experimental validation of the numerical predictions was in accordance with the predicted values of the temperature profile near the walls of the microchannel for the base fluid. Anomalous enhancement of the convective heat flux values was observed in the experiments using nanofluids (e.g., an increase of 91.9%). However, this trend was not seen in the computational analysis because the numerical models were based on continuum assumptions and flow features involving nanoparticles in a stable colloidal solution involving non-continuum effects. The anomalous enhancements are postulated to be caused by isolated and dispersed precipitation of nanoparticles on the flow conduits (the precipitated nanoparticles are called ``nanofins'') which in turn enhance the surface area available for heat exchange (this is called the ``nanofin effect''). The numerical validation of nanoparticle precipitation was successfully achieved by additionally considering particle tracking (i.e., DPM: Discrete Phase Model) and two-phase flow modeling based on conventional CFD and HT methods.The ``nanofin effect'' consists of the cumulative influence of several transport mechanisms at the solid-fluid interface on a nanoscale level - arising from the increase in the effective surface area caused by the formation of surface nanofins - which in turn modulates the effective thermal impedance (resistance, capacitance, inductance, etc.) as well as thermal diodic effects. The efficacy of the nanofins depends on various parameters such as the local profiles for the wall temperature, concentration and flow rates of each phase.

Nanoparticles of organic nonlinear optical molecular crystals synthesized by laser ablation in liquid

In this work, nanoparticles of nonlinear optical organic molecular cocrystal DAST (4-dimethylamino-N-methylstilbazolium p-toluenesulfonate) were obtained by pulsed laser ablation in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning electron microscope and were about 200 nm in width. Laser ablation does not lead to photocuring or photodegradation of liquid monomer. Ablation processes was similar to the processes in classical liquids (water, organic solvents). Since in this case the nanoparticles were synthesized directly in the liquid medium of the surfactant monomer, so they are stabilized in it. Nanocomposites films were synthesized on the basis of these stable colloid solution by photocuring. For aliphatic polymer IDA long molecules cross-linking 1,6-Hexandiol diacrylate was used (DIOL). Optical properties of colloid solution and nanocomposites were investigated. It was found that obtained nanoparticles are amorphous form of DAST cocrystal and have a rod-like shape. Also dodecane and polyphenelene ether were tried in this work as liquids with different viscosity to find its effect on size and shape of nanoparticles.

Optical, structural and nonlinear optical properties of laser ablation synthesized Ag nanoparticles and photopolymer nanocomposites based on them

In this work Ag nanoparticles (NPs) stable colloid solution were prepared by laser ablation of chemically pure silver rod in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning electron microscope and vary from 27 to 120nm. Nanocomposites films were prepared from obtained stable colloid solution of AgNPs by photocuring. For aliphatic polymer IDA long molecules cross-linking Diurethane dimethacrylate, 1,6-Hexandiol diacrylate and Tetra (ethylene glycol) diacrylate were used. Prepared nanomaterials exhibit strong third-order nonlinear optical responses, which was estimated by using z-scan technique. The third-order nonlinear optical coefficients of the studied nanocomposites were found to be up to Reχ(3)=1.31×10−5 (esu) and Imχ(3)=7.64×10−5 (esu).

Universal Approach to the Synthesis of Silver Sulfide in the Forms of Nanopowders, Quantum Dots, Core‐Shell Nanoparticles, and Heteronanostructures

Nanostructured silver sulfide is one of the semiconducting chalcogenides most in demand, due to its unique combination of structure, physical, and chemical properties, and its potential applications in optoelectronics, biosensing, and catalysis. Much research has been carried out in the last decade, with the goals of producing silver sulfide in the form of nanopowders, stable colloidal solutions, quantum dots with protective shells, and heteronanostructures by different chemical and physical methods. This review considers the main challenges in the synthesis of all these forms of nanostructured silver sulfide by a universal, simple, and environmentally friendly method without the use or generation of any hazardous substances. Recent experimental studies have revealed that such universal synthesis can be carried out by hydrochemical bath deposition.

A new way of developing nanocomposites based on carbon nanotubes and graphene nanoplatelets

In the present research, phenol-formaldehyde resins were used instead of common surfactants for dispersing carbon nanotubes and graphene nanoplatelets in order to develop new composite materials. The use of such resins makes it possible to increase the concentration of nanoparticles in solution by approximately two orders of magnitude. The presence of reactive groups on the surface of the phenol-formaldehyde-resin-modified carbonnanotubes and graphene nanoplatelets promotes synthesis of a variety of composites. According to the experiments performed herein, the modification of the nanomaterials with the phenol-formaldehyde resin significantly improves their compatibility and provides good water-solubility. While dispersing in water, the aggregates of the carbon nanotubes disappear, giving rise to an ordered structure. Besides, they form stable colloidal solutions at slightly alkaline pH values, but coagulate when decreasing the pH. This effect allows for self-assembly of carbon and composite nanostructures from nanoparticles in solution due to pH adjustment. This enables easy synthesis of hybrid composite materials based on carbon nanotubes, graphene nanoplatelets and phenol-formaldehyde resins.

Two-Component Self-Assembly: Hierarchical Formation of pH-Switchable Supramolecular Networks by π-π Induced Aggregation of Ion Pairs.

Two-component self-assembly is a promising approach to construct functional nanomaterials. Interaction of a flexible guanidiniocarbonyl pyrrole tetra-cation (1) with naphthalene diimide dicarboxylic acid (NDIDC) in aqueous DMSO leads to the formation of supramolecular networks. First, the carboxylate groups of NDIDC bind to the guanidiniocarbonyl pyrrole cations of 1 in a 1:2 stoichiometry. Further π-π induced aggregation then leads to 3D networks, as established by dynamic light scattering studies (DLS), NMR, fluorescence titration, viscosity measurements, AFM, and TEM microscopy. Due to ion pairing, the resulting aggregates can be switched between the monomers and the aggregates reversibly using external stimuli like protonation or deprotonation. At high concentration, a stable colloidal solution is formed, which shows an extensive Tyndall effect. Increasing the concentrations even further leads to formation of a supramolecular gel.

Electrochemical properties of WO3-reduced graphene oxide composite powders prepared by one-pot spray pyrolysis process

In this work, we report the preparation of WO3-reduced graphene oxide (rGO) composite powders by spray pyrolysis process using a stable graphene oxide colloidal solution with ammonium tungstate. The ultrafine WO3 nanocrystals below 10 nm in size are dispersed within the rGO matrix. The bare WO3 powders prepared from the aqueous spray solution of ammonium tungstate are spherical and do not aggregate. The bare WO3 and WO3-rGO composite powders show monoclinic and cubic crystal structures, respectively. The initial discharge capacities of the bare WO3 and WO3-rGO composite powders at a current density of 100 mA g−1 are 771 and 941 mA h g−1, respectively, and their initial Coulombic efficiencies are 67 and 65%, respectively. The discharge capacities of the bare WO3 and WO3-rGO composite powders at the 300th cycle are 282 and 546 mA h g−1, respectively.

Ag2S silver sulfide nanoparticles and colloidal solutions: Synthesis and properties

Powders of silver sulfide Ag2S have been synthesized by hydrochemical bath deposition from aqueous solutions of silver nitrate and sodium sulfide in the presence of sodium citrate or EDTA-H2Na2. Colloidal non-toxic solutions of Ag2S nanoparticles have been prepared by chemical condensation method from the same aqueous solutions. The size of silver sulfide particles in deposited powders and colloidal solutions has been estimated with the use of X-ray diffraction, dynamic light scattering, transmission electron microscopy and Brunauer–Emmett–Teller techniques. By varying the ratio between the concentrations of reagents in the initial reaction mixtures it is possible to deposit Ag2S nanoparticles with pre-assigned average size ranging in the interval from about 500 nm down to about 40 nm. The average size of silver sulfide Ag2S nanoparticles in stable colloidal solutions is equal 10–20 nm. Special attention has been devoted to investigation of stability of synthesized colloidal solutions on the duration of their storage. The UV–Vis absorption spectra of colloidal solutions and optical reflectance of nanopowders of silver sulfide have been studied. Decreasing of average size of Ag2S nanoparticles from ∼500 nm down to ∼60 nm leads to increasing of energy band gap Eg from 0.88 to 1.21 eV. Studied colloidal solutions and nanopowders of silver sulfide possess the potential antibacterial activity.

Fabrication of water-soluble polymer-encapsulated As4S4 to increase oral bioavailability and chemotherapeutic efficacy in AML mice.

Realgar (As4S4) has been demonstrated to be effective for the treatment of acute myeloid leukemia (AML); it has the advantages of no drug resistance and oral administration. Nevertheless, its poor solubility has been an obstacle to its bioavailability, requiring high-dose administration over a long period. We investigated whether crushing realgar crystals to the nanoscale and encapsulating the particles in a water-soluble polymer in one step using hot-melt extrusion would increase the bioavailability of As4S4. Raw As4S4 (r-As4S4) and water-soluble polymer were processed via co-rotating twin screw extrusion. The resulting product (e-As4S4) was characterized by SEM, XRD, and DLS. The cytotoxicity and therapeutic effects of e-As4S4 were evaluated in vivo and in vitro. The results show that e-As4S4 dissolved rapidly in water, forming a stable colloid solution. The average size of e-As4S4 particles was 680 nm, which was reduced by more than 40-fold compared with that of r-As4S4. The bioavailability of e-As4S4 was up to 12.6-fold higher than that of r-As4S4, and it inhibited the proliferation of HL-60 cells much more effectively than did r-As4S4, inducing apoptosis and significantly reducing the infiltration of HL-60 cells into the bone marrow, spleen, and liver. This in turn prolonged the survival of AML mice.

PH‐responsive phenylboronic acid‐modified diamond particles: Switch in carbohydrate capture ability triggers modulation of physicochemical and lectin‐recognition properties

Nanodiamonds (NDs) are new carbon‐based materials that have recently been demonstrated to hold promise in a number of biomedical applications. The production of stable colloidal solutions from ND particles obtained through detonation still remains a challenge, as these particles have a strong tendency to form large aggregates. Herein, is described a 4‐aminophenylboronic acid‐modified ND (ND‐BA) system that can either disperse or aggregate in aqueous solution, in the presence of an appropriate monosaccharide and in response to an external pH trigger. At pH = 8.4, the ND‐BA forms stable colloidal solutions when mannose is present, as a consequence of their ability to sequester the monosaccharide through the formation of sugar boronic ester complexes. A decrease in the pH to 4 triggers the disruption of the boronic acid ester bonds and results in mannose‐release thereby inducing aggregation of the ND‐BA particles. The aggregation–dispersion process is seen to be completely reversible and effectively allows control of the physiochemical properties of the ND‐BA–glycan couple through an external pH stimulus. Moreover, the mannose‐saturated ND‐BA particles are shown to interact selectively with appropriate lectins and this recognition demonstrated to be effectively switched off at low pH values.

Zeta Potential, Size, and Semiconductor Properties of Zinc Sulfide Nanoparticles in a Stable Aqueous Colloid Solution

A stable aqueous colloid solution of zinc sulfide (ZnS) nanoparticles was obtained by chemical condensation using ethylenediaminetetraacetic acid disodium salt. The mechanism of prolonged aggregative stability of solution at pH 7–8 with ~7-nm nanoparticles was determined as a result of the zeta potential measurements by dynamic light scattering. The blue and red shifts of the fundamental absorption edge of zinc sulfide semiconductor nanoparticles associated with the small size of nanoparticles and the defective state of their surface were found by optical spectrophotometry.

Mechanism of the formation of photosensitive nanostructured TiO2 with low content of CdS nanoparticles

A method for synthesizing a CdS/TiO2 composite material, active in the visible region, was described. The CdS/TiO2 composite was obtained by the sol–gel synthesis of nanostructured TiO2 in a medium of a stable colloidal solution of CdS nanoparticles. The TiO2 matrix produced by the sol–gel process is amorphous and contains a nanocrystalline anatase phase, the content of which depends on the Ti(OBu)4 hydrolysis rate. The content of CdS nanoparticles forming in the colloidal solution and participating in the TiO2 matrix sensitization is determined by the initial CdS: Ti(OBu)4 ratio. Although the content of CdS nanoparticles in the composite is low (no more than 3 wt %), the composite demonstrates catalytic activity in the visible region, thus proving the possibility of reducing the content of toxic CdS nanoparticles in the TiO2 matrix without decreasing the photosensitivity of the CdS/TiO2 composite.

Effect of pH of Synthesis on CdS/L-cys Colloidal Solutions Optical Properties

Using the measurements of absorption spectra and photoluminescence, as well as electron microscopic studies, the limits of concentrations of cadmium and sulfur ions and the stabilizer L-cysteine, suitable for obtaining stable colloidal solutions of quantum dots (size 1 - 5 nm) with CdS and high quantum yield. The influence of the initial pH values ​​of the reaction system within 7 - 11 on the absorption edge, photoluminescence and quantum yield of colloidal solutions of CdS / L-cis nanoparticles is shown. The results were systematized using the simplex lattice design of the Chefe method.

Burst nucleation by hot injection for size controlled synthesis of ε-cobalt nanoparticles.

BackgroundReproducible growth of narrow size distributed ε-Co nanoparticles with a specific size requires full understanding and identification of the role of essential synthesis parameters for the applied synthesis method. For the hot injection methodology, a significant discrepancy with respect to obtained sizes and applied reaction conditions is reported. Currently, a systematic investigation controlling key synthesis parameters as injection-temperature and time, metal to surfactant ratio and reaction holding time in terms of their impact on mean (bar{D}mean) and median (bar{D}median) particle diameter using dichlorobenzene (DCB), Co2(CO)8 and oleic acid (OA) as the reactant matrix is lacking.MethodsA series of solution-based ε-Co nanoparticles were synthesized using the hot injection method. Suspensions and obtained particles were analyzed by DLS, ICP-OES, (synchrotron)XRD and TEM. Rietveld refinements were used for structural analysis. Mean (bar{D}mean) and median (bar{D}median) particle diameters were calculated with basis in measurements of 250–500 particles for each synthesis. 95 % bias corrected confidence intervals using bootstrapping were calculated for syntheses with three or four replicas.Resultsε-Co NPs in the size range ~4–10 nm with a narrow size distribution are obtained via the hot injection method, using OA as the sole surfactant. Typically the synthesis yield is ~75 %, and the particles form stable colloidal solutions when redispersed in hexane. Reproducibility of the adopted synthesis procedure on replicate syntheses was confirmed. We describe in detail the effects of essential synthesis parameters, such as injection-temperature and time, metal to surfactant ratio and reaction holding time in terms of their impact on mean (bar{D}mean) and median (bar{D}median) particle diameter.ConclusionsThe described synthesis procedure towards ε-Co nanoparticles (NPs) is concluded to be robust when controlling key synthesis parameters, giving targeted particle diameters with a narrow size distribution. We have identified two major synthesis parameters which control particle size, i.e., the metal to surfactant molar ratio and the injection temperature of the hot OA–DCB solution into which the cobalt precursor is injected. By increasing the metal to surfactant molar ratio, the mean particle diameter of the ε-Co NPs has been found to increase. Furthermore, an increase in the injection temperature of the hot OA-DCB solution into which the cobalt precursor is injected, results in a decrease in the mean particle diameter of the ε-Co NPs, when the metal to surfactant molar ratio left( {frac{[Co]}{[OA]}} right) is fixed at ~12.9.Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-016-0156-1) contains supplementary material, which is available to authorized users.

Self-Assembly of CdSe Nanoplatelets into Stacks of Controlled Size Induced by Ligand Exchange

In this paper we present a simple method for the preparation of highly stable colloidal solutions of individual nanoplatelets (NPls) with increased fluorescence quantum yield and a versatile procedure of NPls self-assembly into stacks of controlled size. Dynamic light scattering technique has been demonstrated to be simple and accurate method for in situ studies of the growth kinetics of NPls aggregates. The self-assembly method introduced in this work is based on the exchange of ligands on the surface of CdSe nanoplatelets. Hexadecylphosphonic acid allows control of the average size (length) of NPls stacks in a broad range by varying its concentration and reaction time. The main mechanism governing controlled formation of NPls stacks is based on strong van der Waals interaction between rigid brushes of alkyl chains on the surface of neighboring NPls. The interaction strength and, consequently, the length and colloidal stability of stacks have been shown to be dependent on type and concentration of differ...

Backward-facing step heat transfer of the turbulent regime for functionalized graphene nanoplatelets based water–ethylene glycol nanofluids

Herein, an experimental study on thermo-physical properties of ethylene glycol-functionalized graphene nanoplatelets/water–ethylene glycol nanofluids (EGGNP-WEG) and a numerical study on the convective heat transfer over a backward-facing step are performed. Accordingly, EGGNP was first synthesized covalently to achieve a stable colloidal solution in water–ethylene glycol mixture. Some characterizations were applied to analyze the surface functionality and morphology of EGGNP-flakes. To study the convective heat transfer coefficient in turbulent regime, a numerical study is performed at different weight fractions of EGGNP.According to the results, a higher weight concentration of EGGNP in basefluid indicates a greater extent of convective heat transfer coefficient and thermal conductivity, implying higher heat transfer rate over a backward-facing step.

Colloidal Hydroxyapatite/Poly(Acrylic Acid) Hybrids Using Calcium Sucrate and Ammoniumdihydrogen Orthophosphate

This manuscript is concerned with a simple and novel method to synthesize hydroxyapatite-poly(acylic acid) hybrid materials for broad range of applications. In this method, hydroxyapatite nanoparticles are synthesized using calcium sucrate and ammoniumdihydrogen orthophosphate in the presence of poly(acrylic acid). Increase in poly(acrylic acid) concentration in the synthesis medium results in the increase in the hydrodynamic radius of particle size allowing increased hydration. Poly(acylic acid) tends to control both crystallite size and colloidal stability. Increase in poly(acrylic acid) concentration decreases the crystallite size of the products but considerably increases their shelf life as stable colloidal solutions. Thermo gravimetric analysis shows that there are no combustible or volatile impurities present in these samples. This is further supported by FT-IR studies, which show three types of interactions between hydroxyapatite nanoparticles and poly(acrylic acid).

The influence of soybean genotypes and HTC processing method on trypsin inhibitor activity of soymilk

Kunitz inhibitor (KTI) and Bowman-Birk trypsin inhibitor (BBI) are inhibitors of digestive enzymes in raw soybeans. Due to their antinutritive properties in the active state, their inactivation by heat treatment is commonly used. Soymilk is a turbid and stable colloidal solution, obtained by thermal treatment of soybean. In this study soymilk was made on a pilot-plant scale from six soybean cultivars using hydrothermal cooking (HTC) as the production method. This procedure is significantly different from the traditional one. The aim of this investigation was to evaluate the impact of the HTC processing for soymilk production and different soybean genotypes on trypsin inhibitor content and activity. Obtained soymilk contained BBI in trace amounts, in the BBI-polymeric forms. The BBI monomeric forms were not detected. The soymilk of the investigated soybean genotypes had very similar KTI levels (2.34-2.99%). Results have suggested that the soybean genotype does not have substantial effects on the levels of KTI, as well as on the value of residual trypsin inhibitor activity (rTIA). The total content of TI and rTIA showed a strong dependence (r=0.91; p<0.05). HTC-soymilk rTIA was <20% (7.15-19.89%). These results have indicated that HTC processed soymilk is applicable for human consumption.