Formation Of Stable Dispersions Research Articles

Engineering of CIGS nanoparticle inks for colloidal stability, uniform film formation and application as HTL for perovskite solar cells

In this work, synthesis of CuIn0.75Ga0.25S2 (CIGS) nanoparticles, the formation of stable dispersion, deposition of high-quality films and, fabrication of thin-film Perovskite solar cells are reported. The stability of nanoparticle ink is crucial in the formation of device-quality films. The chalcogenide-based materials are widely used in thin-film solar cells; in particular, Cu(In,Ga)S2 are used as an absorber and hole transporting layer. In the present study, the nanoparticles of about 20 nm size and bandgap of 1.5 eV are synthesized using a heat-up method. A variety of solvents are used as dispersing media and the stability of the inks is evaluated by precise optical monitoring. We observe a clear dependence of ink stability to the polarity index of the solvent, where the best stability occurs at a polarity index of about 0.26–0.36, corresponding to a range of solvents including chloroform. The thin films that are spin-coated using CIGS chloroform ink show large cracks, presumably due to the high vapor pressure of chloroform and evaporation-induced stress in the film. We resolve this problem through low-temperature deposition, which resulted in highly uniform pin-hole and crack-free films. Finally, the optimum deposition condition is used to fabricate perovskite solar cells having about 16.5% efficiency with CIGS as a hole transport layer.

Charge Compensation in Europium-Doped Hafnia Nanoparticles: Solvothermal Synthesis and Colloidal Dispersion

Effective charge compensation of europium in hafnium oxide nanoparticles was achieved at low temperature, allowing high doping incorporation (up to 6 at.%) and enhanced luminescence. The efficiency of the incorporation and charge compensation was confirmed by scanning electron microscope energy dispersive X-ray spectroscopy and powder X-ray diffraction measurements. Despite the known polymorphism of hafnium oxide, when doped to a concentration above 3 at.%, only the pure monoclinic phase was observed up to 6 at.% of europium. Furthermore, the low-temperature solvothermal route allowed the direct formation of stable dispersions of the synthesized material over a wide range of concentrations in aqueous media. The dispersions were studied by diffuse light scattering (DLS) to evaluate their quality and by photoluminescence to investigate the incorporation of the dopants into the lattice.

Stabilization of pristine and oxidized carbon nanotubes dispersions in acidic and alkaline solutions

The possibility of stabilizing aqueous dispersions of carbon nanotubes (CNTs) using phenol-formaldehyde resin (PFR) and aminocumulene (AC) is shown. The preliminary oxidation of CNTs contributes to their higher solubility in the presence of these stabilizing agents. The concentration of pristine and oxidized CNTs in weakly alkaline solutions containing 2.5 g/L of PFR is 3.0 and 11.4 g/L, respectively. AC promotes the formation of stable dispersions in acidic media with the concentrations of pristine and oxidized CNTs, respectively, 3.3 and 20.4 g/L. A decrease in the effective sizes of agglomerates of both pristine and oxidized CNTs in the presence of PFR and AC has been shown by dynamic light scattering method. According to TG/DSC analysis and Raman spectroscopy data, it was concluded that the oxygen-containing groups of oxidized CNTs interact with the surfactants used. Schemes for the formation of hydrogen and chemical bonds between CNTs and PFR or AС were proposed, which made it possible to explain the effect of dispersion.

2D MXene-Molecular Hybrid Additive for High-Performance Ambipolar Polymer Field-Effect Transistors and Logic Gates.

MXenes are highly conductive layered materials that are attracting a great interest for high-performance opto-electronics, photonics, and energy applications.. Their non-covalent functionalization with ad hoc molecules enables the production of stable inks of 2D flakes to be processed in thin-films. Here, the formation of stable dispersions via the intercalation of Ti3 C2 Tx with didecyldimethyl ammonium bromide (DDAB) yielding Ti3 C2 Tx -DDAB, is demonstrated. Such functionalization modulates the properties of Ti3 C2 Tx , as evidenced by a 0.47eV decrease of the work function. It is also shown that DDAB is a powerful n-dopant capable of enhancing electron mobility in conjugated polymers and 2D materials. When Ti3 C2 Tx -DDAB is blended with poly(diketopyrrolopyrrole-co-selenophene) [(PDPP-Se)], a simultaneous increase by 170% and 152% of the hole and electron field-effect mobilities, respectively, is observed, compared to the neat conjugated polymer, with values reaching 2.0 cm2 V-1 s-1 . By exploiting the balanced ambipolar transport of the Ti3 C2 Tx -DDAB/PDPP-Se hybrid, complementary metal-oxide-semiconductor (CMOS) logic gates are fabricated that display well-centered trip points and good noise margin (64.6% for inverter). The results demonstrate that intercalant engineering represents an efficient strategy to tune the electronic properties of Ti3 C2 Tx yielding functionalized MXenes for polymer transistors with unprecedented performances and functions.

Evaluation of the surface energy of dispersed aluminium oxide using owens-wendt theory

Knowing the value of the surface energy of powder materials allows to predict the interaction of the solid phase with liquids, the formation of stable dispersions, durable and resistant to aggressive factors of composites. The application of the Owens-Wendt model for determining the change in the surface energy of aluminium oxide modified by various water repellents is considered. Also, to determine the contact angle of the surface of the modified material, the Washburn method is used, which consists in determining the rate of capillary rise of the test fluid. This method is chosen due to low requirements in the accuracy of measuring equipment and at the same time shows a high degree of accuracy of the results.The object of research is a method for determining the surface energy of powder materials, using aluminium oxide modified with polymethylhydrosiloxane as an example. Surface modifications of the aluminium oxide powder are carried out in a xylene suspension.In the work, the determination of surface energy is carried out in accordance with the Owens-Wendt theory by the graphical method in accordance with the obtained values of the contact angle of the material according to the Washburn method. It is established the shape of the particles of aluminium oxide and their average size, and also calculated the specific surface of the material. A modifier, polymethylhydrosiloxane, is found, with the help of which it is possible to obtain a stable superhydrophobic state, and the optimal concentration by determining the contact angles of the powder material with test liquids according to the method proposed by Washburn.To increase the accuracy of determining the surface energy of the material according to the Washburn method, a mixture of water with ethanol is used, and the components of surface tension are calculated. It is shown that the values of the contact angle of the surface of the dispersed material obtained using a mixture as a test liquid can be used to calculate the values of the components of the surface energy of aluminium oxide. In this case, there is a lack of error in the form of the Cassie state, which is observed for hydrophobic dispersed materials when using water as a test fluid.

Self-assembled supermolecular aggregate supported on boron nitride nanoplatelets for flame retardant and friction application

The scalable preparation and functionalization of two-dimensional (2D) boron nitride (BN) are crucial for its practical applications. Herein, hydroxyl-functionalized BN (OBN) nanoplatelets have been successfully synthesized through a novel two-step method, involving a simple ball milling of bulk BN powders in the assistance of sodium hydroxide, which combine the synergetic effect of mechanical shear forces and chemical peeling, followed by annealing under air condition. The obtained OBN nanoplatelets result in high solubility and form stable dispersions in water or various organic solvents that can be utilized for multiple applications. Then, OBN nanoplatelet was used as platform for embedding supermolecular aggregate (DPCS) via ionic bonding and electrostatic interaction between dicyandiamide and multivalent anions phytic acid connected with cobalt ions (denoted as DPCS@OBN). It is noted that introducing well-characterized DPCS@OBN nanohybrids significantly improve the flame retardancy of epoxy acrylate (EA), i.e., 42.7% and 48.3% reductions in peak heat release rate and total heat release, respectively. In the case of EA/DPCS@OBN system, the storage modulus at 25 °C was dramatically improved by 80.7%, and glass transition temperature was shifted to higher value; the friction coefficient value of EA/DPCS@OBN3.0 composite sharp decline to 0.077, which can be belong to the “superlubrication” phenomena. The excellent properties of these EA composites result from synergetic coupled effect between DPCS supermolecular and BN ultrathin nanoplatelets, as well as good interface interaction between DPCS@OBN and EA matrix.

The synthesis of ultra-high molecular weight poly(1-hexene)s by low-temperature Ziegler-Natta precipitation polymerization in fluorous reaction media

An effective method of 1-hexene polymerization in fluorous reaction media has been developed. When using perfluorinated compounds (FCs) as a solvent, the process, catalyzed by highly active titanium-magnesium catalysts modified with 3,3-bis(methoxymethyl)pentane (BMMP) as an electron-donor, proceeds as a precipitation polymerization, and the reaction products represent highly stereo- and regioregular poly(1-hexene)s in the form of microparticles. In freons, polymerization can be carried out at sub-zero temperatures with monomer conversion up to 50% within 1 h and the formation of UHMW poly(1-hexene)s with Mn ∼2·106 Da. The polymers prepared in FCs demonstrate a high drag reducing effect (up to 40% in n-heptane for 0.25 ppm concentration), exceeding the previously described UHMW poly(1-hexene)s. Polymerization products after mixing with rapeseed oil form stable dispersions of ready-to-use drag reducing agents (DRAs) for pipeline oil transportation.

A review of shampoo surfactant technology: consumer benefits, raw materials and recent developments.

Surfactants form the core of all shampoo formulations, and contribute to a wide range of different benefits, including cleansing, foaming, rheology control, skin mildness and the deposition of benefit agents to the hair and scalp. The purpose of this review was to assist the design of effective, modern, shampoo surfactant technologies. The mechanisms through which surfactants help deliver their effects are presented, along with the appraisal techniques through which surfactant options can be tested and screened for product development. The steps that should be taken to select the most appropriate blend of surfactants are described, and useful information on the most widely used surfactants is provided. The review concludes with an examination of recent developments in 'greener' surfactants, 'sulphate-free' technologies and structured liquid phases for novel sensory properties and for suspending benefit agents.

Access to lanthanoid telluride nanoparticles: Liquid exfoliation of LnTe3 (Ln = La, Ho)

Although many of the nanoparticles containing lanthanoids are deeply investigated, the reports concerning chalcogenide materials are scarce. Comprehensive exploration of properties of these materials requires a proper preparation method avoiding hydrolysis and contamination with oxygen-containing products. Hence, in this case, the top-down approach could be preferable. In this study we demonstrated preparation of LnTe3 (Ln = La, Ho) nanoparticles by liquid exfoliation method. Bulk tritellurides LaTe3 and HoTe3 afford stable dispersions in a number of common organic solvents under ultrasonic treatment. The size and morphology of nanoparticles in colloid solutions as well as films prepared from them were investigated by a number of methods (AFM, TEM, DLS, XRD, Raman). LnTe3 form stable dispersions in alcoholic media with concentration up to 165 mg/L. In these dispersions nanoparticles exist as 1–2 layered charged flakes with lateral size 50–80 nm. The nanoparticles can be reassembled as films, which demonstrated orientation along 0k0 direction.

Spectrophotometric determination of Fe(III) by using casein-functionalized gold nanoparticles

The preparation and application of casein-capped gold nanoparticles (AuNPs) as a specific probe for ferric ions Fe(III) is reported. The functionalized AuNPs exhibit narrow size distribution and form stable dispersions in water of different ionic strengths and basicity. The presence of diverse functional groups from the side chain of peptides warrants colloidal stability of AuNPs and also assists recognition of Fe(III) in versatile conditions. Fe(III) ion reportedly causes the aggregation of AuNPs and a red-shift in absorbance toward longer wavelength (660 nm). A spectrophotometric method is appropriate for selective detection of Fe(III) and the spectral shift is also accompanied by a color change from red to blue. The aggregation of AuNPs is not suppressed after the addition of NaOH or at moderate ionic strength. The resulting spectrophotometric method works for Fe(III) in the concentration range of 0.1 to 0.9 μM and has a detection limit of 450 nM. The AuNP probe can also detect Fe(III) ion content in real samples at the same detection limit, which is much lower than the maximum contaminant level allowed for Fe(III) in drinking water (5.37 μM) by the U.S. Environmental Protection Agency.

Exfoliation of Hexagonal Boron Nitride by Molten Hydroxides

Hexagonal boron nitride (h-BN) nanosheets are prepared by a novel and effective method, in which sodium hydroxide and potassium hydroxide molten salts are used to exfoliate h-BN to obtain nanosheets. BN nanoscrolls are also obtained. The as-prepared products can be readily dispersed in a wide range of solvents, including water and ethanol, and form stable dispersions.

Sequence Specific Association of Tryptic Peptides with Multiwalled Carbon Nanotubes: Effect of Localization of Hydrophobic Residues

A model-free approach has been used to study the association of peptides onto multiwalled carbon nanotubes (MWCNT) in aqueous solution at ambient pH to understand the molecular basis of interaction of the peptides with MWCNT. The peptides obtained by tryptic digestion of cytochrome P450cam from P. putida were allowed to interact with MWCNT, and several peptides were found to bind to the nanotube leading to formation of stable homogeneous dispersion of the bionano conjugates of MWCNT. The peptides bound to the MWCNT were separated from the unbound peptides and sequence analyses by tandem MS/MS technique identified the strongly bound peptides as well as the unbound and the weakly bound peptides. The peptide-MWCNT conjugate was further characterized by TEM as well as Raman, FTIR, vis-NIR absorption, and circular dichroism spectroscopy. A model based on the hydrophobicity of residues in the peptides suggested that the amphiphilic peptides with localized hydrophobic residues at the center or at one end of the sequence form stable dispersions of the peptide-MWCNT conjugates.

Investigation of Phase Separation Behavior and Formation of Plasmonic Nanocomposites from Polypeptide-Gold Nanorod Nanoassemblies

Genetically engineered elastin-like polypeptides (ELP) can be interfaced with cetyltrimethyl ammonium bromide (CTAB)-stabilized gold nanorods (GNRs) resulting in the formation of stable dispersions (nanoassemblies). Increasing the dispersion temperature beyond the ELP transition temperature results in phase separation and formation of solid-phase ELP-GNR matrices (nanocomposites). Here, we investigated different physicochemical conditions that influence nanocomposite formation from temperature-induced phase separation of ELP-GNR nanoassemblies. The presence of cetyltrimethyl ammonium bromide (CTAB), used to template the formation of gold nanorods, plays a significant role in the phase separation behavior, with high concentrations of the surfactant leading to dramatic enhancements in ELP transition temperature. Nanocomposites could be generated at 37 °C in the presence of low CTAB concentrations (<1.5 mM); higher concentrations of CTAB necessitated higher temperatures (60 °C) due to elevated transition temperatures. The concentration of gold nanorods, however, had minimal influence on the phase separation behavior and nanocomposite formation. Further analysis of the kinetics of nanocomposite formation using a mathematical model indicated that CTAB largely influenced the early event of coacervation of ELP-GNR nanoassemblies leading to nanocomposites, but had minimal effect on nanocomposite maturation, which is a later-stage longer event. Finally, nanocomposites prepared in the presence of low CTAB concentrations demonstrated a superior photothermal response following laser irradiation compared to those generated using higher CTAB concentrations. Our results on understanding the formation of plasmonic/photothermal ELP-GNR nanocomposites have significant implications for tissue engineering, regenerative medicine, and drug delivery.

Gd(iii)-doped carbon dots as a dual fluorescent-MRI probe

We describe the synthesis of Gd(III)-doped carbon dots as dual fluorescence-MRI probes for biomedical applications. The derived Gd(III)-doped carbon dots show uniform particle size (3–4 nm) and gadolinium distribution and form stable dispersions in water. More importantly, they exhibit bright fluorescence, strong T1-weighted MRI contrast and low cytotoxicity.

Exploration of Novel Pyrene Labeled Amphiphilic Block Copolymers: Synthesis Via ATRP, Characterization and Properties

A novel initiator containing pyrene, a fluorescent moiety, was prepared by reacting 1-aminopyrene and 2-bromoisobutyl bromide. The structure elucidation of the new initiator was carried out using various spectroscopic tools, as well as through single crystal X-ray diffraction studies. Novel, fluorescent amphiphilic block copolymers with a pyrene end-group, poly(styrene-b-acrylic acid) [P(S-b-AA)], poly(methyl methacrylate-b-dimethylaminoethyl methacrylate) [P(MMA-b-DMAEMA)], poly(styrene-b-tert-butyl acrylate) [P(S-b−t-BA)], poly(styrene-b-dimethylaminoethyl methacrylate) [P(S-b-DMAEMA)] were successfully synthesized by the atom transfer radical polymerization (ATRP) method, using CuBr as the catalyst and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA)/N,N,N′,N″,N″-hexamethyltriethylenetetramine (HMTETA) as the complexing agent. The polymers were characterized by GPC, 1H-NMR, IR and UV-Vis spectroscopies. It was observed that as the polymerization time increased, both the conversion and the molecular weight increased linearly with time. The fluorescence properties of the polymers prepared were recorded. The physical properties and especially the pH dependent swelling properties of the amphiphilic block copolymers have been investigated. The utility of the block copolymers in the formation of stable dispersion of cadmium sulphide nanoparticles was investigated as a model study.

Amine- and Carboxyl- Quantum Dots Affect Membrane Integrity of Bacterium Cupriavidus metallidurans CH34

The present study examines the interaction of amine- and carboxyl- PEG core/shell quantum dots (QDs) with metal resistant bacterium Cupriavidus metallidurans CH34. The evolution of the number of QDs, their hydrodynamic radius, diffusion coefficients, and single particle fluorescence were characterized before and during the contact with bacterium by fluorescence correlation spectroscopy (FCS). The obtained results showed that at nanomolar concentrations the amine- and carboxyl-PEG-QDs with average hydrodynamic radiuses of 16.4 and 13.5 nm, form stable dispersions in the absence and presence of 15 mgC L(-1) HA. The decrease of the number of fluorescent particles in the bacterial medium, determined by FCS, together with the increase of the fluorescence of bacterial cells over the background, found by flow cytometry (FCM), demonstrated the association of QDs to C. metallidurans. Furthermore, QDs enhanced the level of the reactive oxygen species in the bacterial cells and augmented the percentage of the cells with damaged and leaky membranes as probed by FCM in combination with 5-(and-6)-carboxy-27'-dichlorodihydrofluorescein diacetate and propidium iodide stains. No difference in the behavior of amine- and carboxyl-PEG-QDs was found, suggesting that different functional groups in the surface coating have no effect on bacterium-QD interactions under the studied conditions. The presence of HA does not affect the hydrodynamic characteristics of the functionalized QDs, but prevented the damage to the bacterial membrane. The slight decrease in the bacterial growth found after exposure of C. metallidurans to these QDs was attributed to the nanoparticles themselves rather the cadmium, zinc, or selenium ions released from the QDs.

A Simple Method for Preparing Carbon Nanotubes/Clay Hybrids in Water

A simple novel method for preparing multiwalled carbon nanotubes/montmorillonite (MWNTs/MMT) hybrids has been established through mixing pristine MWNTs in MMT aqueous dispersion. The principle of this method is based on the formation of stable dispersion containing both MWNTs and MMT in water, which results from strong interaction between MWNTs and MMT platelets. Sedimentation experiments, measurements of ζ potential, and Raman spectra have been used to confirm the presence of strong interaction between MWNTs and MMT sheets. The morphology observation for the dried MWNTs/MMT hybrids shows that the obtained hybrids are homogeneous, in which MWNTs exist as the state of single nanotubes that are absorbed on the surface and edge of MMT sheets. In addition, poly(ethylene oxide) (PEO) nanocomposites containing both MWNTs and MMTs are prepared by using this method. An obvious synergistic effect of MMT sheets and MWNTs in improving mechanical properties of PEO matrix has been observed.

Liposomes loaded with lipophilic prodrugs of methotrexate and melphalan as convenient drug delivery vehicles

Abstract Liposomal formulations prepared by extrusion from natural phospholipids and 1,2-dioleoylglycerol conjugates of methotrexate and melphalan (egg phosphatidylcholine-phosphatidylinositol–prodrug, 8:1:1, by mol.) were characterized by size, composition and stability. Both prodrugs were shown to incorporate completely into unilamellar liposomes with the mean size below 100 nm and form stable dispersions containing the drug concentrations relevant for systemic injections in animals. For long-term storage, the dispersions can be subjected to deep freezing (- 196 °C) and stored at - 70 °C; before usage, they should be defrosted and treated shortly in an ultrasonic bath. According to the example of methotrexate conjugate, stability of prodrug ester bond in liposomal formulation towards hydrolysis by human plasma esterases during 24-h incubation were established. Also, liposomes bearing methotrexate conjugate were shown to overcome resistance of human leukemia cells related to impaired transport of initial drug across the membrane.

The influence of the ratio between the selenium: Polyvinylpyrrolidone complex components on the formation and morphological characteristics of nanostructures

Optical and spectral methods were used to study nanostructures formed in the reduction of ionic selenium in the selenite-ascorbate redox system in aqueous solutions of polyvinylpyrrolidone, a physiologically active polymer. The weight ratio between the selenium: polymer complex components (ν) was varied over a wide range (ν = 0.01−0.2). The adsorption of a substantial number of macromolecules (up to 1000 at ν = 0.1−0.2) on selenium nanoparticles was observed experimentally. This resulted in the formation of supramolecular spherical nanostructures with a high polymeric shell density. The Gibbs energies of macromolecule-Se0 nanoparticle interactions were calculated for polymeric nanostructures in the region of the formation of stable dispersions. The flow birefringence, dynamic light scattering, and spectrophotometry methods were used to determine the region of saturation of the adsorption capacity of selenium nanoparticles in selenium-containing nanocomposites (ν = 0.1−0.2).

The Influence of Polymer—Selenium Complex Components and the Molecular Weight of the Ionogenic Polymeric Matrix on the Morphologic Characteristics of Selenium-Containing Nanostructures

Several optical methods were used to study nanostructures formed in the reduction of selenium ions in the selenite—ascorbate redox system in an aqueous solution of the poly-N,N,N,N-trimethylmethacryloyloxyethylammonium methyl sulfate polycation. The relation between the molecular weight of the polymeric matrix, which varied over a wide range, Mw = (0.03−13) × 106, and the morphologic characteristics of nanostructures (molecular weight, density, shape, and statistical and hydrodynamic dimensions) was established. The weight ratio between the components of the polymer: selenium complex and the concentration of the polymer in the reaction mixture were shown to substantially influence certain morphologic characteristics of nanostructures. In the region of the formation of stable dispersions, the Gibbs energy of macromolecule—Se0 nanoparticle interactions was calculated. The thermodynamic state of solutions of nanostructures was characterized.