Stable Aqueous Dispersions Research Articles

Supraparticles from Cubic Iron Oxide Nanoparticles: Synthesis, Polymer Encapsulation, Functionalization, and Magnetic Properties.

Supraparticles (SPs) consisting of superparamagnetic iron oxide nanoparticles (SPIONs) are of great interest for biomedical applications and magnetic separation. To enable their functionalization with biomolecules and to improve their stability in aqueous dispersion, polymer shells are grown on the SPs' surface. Robust polymer encapsulation and functionalization is achieved via atom transfer radical polymerization (ATRP), improving the reaction control compared to free radical polymerizations. This study presents the emulsion-based assembly of differently sized cubic SPIONs (12-30 nm) into SPs with diameters ranging from ∼200 to ∼400 nm using dodecyltrimethylammonium bromide (DTAB) as the surfactant. The successful formation of well-defined spherical SPs depends upon the method used for mixing the SPION dispersion with the surfactant solution and requires the precise adjustment of the surfactant concentration. After purification, the SPs are encapsulated by growing surface-grafted polystyrene shells via activators generated by electron transfer (AGET) ATRP. The polymer shell can be decorated with functional groups (azide and carboxylate) using monomer blends for the polymerization reaction. When the amount of the monomer is varied, the shell thickness as well as the interparticle distances between the encapsulated SPIONs can be tuned with nanometer-scale precision. Small-angle X-ray scattering (SAXS) reveals that cubic SPIONs form less ordered assemblies within the SPs than spherical SPIONs. As shown by vibrating sample magnetometer measurements, the encapsulated SPs feature the same superparamagnetic behavior as their SPION building blocks. The saturation magnetization ranges between 10 and 30 emu/g and depends upon the nanocubes' size and phase composition.

Synthesis of perylene‐PEO hyperdispersants for aqueous graphene dispersion

AbstractGraphene, with excellent thermal conductivity, electrical and corrosion shielding performance has great application potential in the fields of heat dissipation coating, conductive agent and anticorrosion composite coatings. However, due to its large specific surface area, resulting strong aggregation behavior limits its application. Herein, the hyperdispersants with perylene anchoring groups are synthesized through the amidation coupling reaction between diacid anhydride and polyetheramine. The branching degree and length of hydrophilic chains on hyperdispersant are revealed to be the very important factors to affect the dispersion stability of aqueous graphene dispersion. The hyperdispersant with a single hydrophilic chain and the molecular weight 2000 of polyetheramine has the excellent dispersal activity discovered by Rheology, particle size distribution and Raman measurements. The possible mechanism is the strongest anchoring effect of perylene on graphene surface and thus achieving in best effective spatial exclusion stabilization effect of hydrophilic chains.

ORGANOPHILIC BENTONITES OF UKRAINE. 1. SCIENTIFIC PRINCIPLES OF PRODUCTION. THE MECHANISM OF ORGANOPHILIZATION OF THE SURFACE

In connection with the inevitable integration of Ukraine into the EU and the discovery of new deposits of high-quality bentonite clays in Ukraine, the issues of studying, developing and industrially producing organophilic bentonites — analogues of foreign trademarks Bentone, Geltone, Petrotone — are becoming especially relevant. Without structuring additives of such bentones, the normal functioning is impossible of the most important industries: automotive, paint and varnish, petrochemical, oil producing, rubber, foundry, mechanical engineering, cosmetics, etc. This work is intended for the first time in Ukraine to lay the scientific foundations for obtaining such materials based on local mineral raw materials. For this purpose, the adsorption of a number of cationic surfactants (quaternary alkylammonium salts) on 4 montmorillonites of bentonite deposits in Ukraine and its effect on the stability, electrosurface and rheological properties of mineral aqueous dispersions were studied. Based on the obtained X-ray data and the dependences of adsorption, z-potential and yield point of dispersions on the concentration of surfactants, the mechanism of surface organophilization was clarified and optimal conditions for modifying montmorillonites for obtaining structure-forming agents for organic media were determined. It was shown that montmorillonite from the Neporotovskoye deposit is the most promising for this purpose. Bibl. 48, Fig. 12, Tab. 6.

Construction of glycosylated zein-based colloids to simultaneously improve fucoxanthin’s thermal processing adaptability, digestive stability, and oral bioavailability

Fucoxanthin (FX) is a carotenoid found in marine environments with a range of nutritional functions. However, its application in the food industry has been restricted by its vulnerability to deterioration and absorption challenges. This study employed zein to develop hydrophilic colloids to enhance the thermal processing adaptability, gastrointestinal digestive stability, and oral bioavailability of FX. The findings demonstrated that the using glucose for the grafting modification of zein caused a deviation in its isoelectric point, reduced its water contact angle, and altered its secondary structure, resulting in higher hydrophilicity. Using glycosylated zein (GZ) for FX loading yielded homogenous, stable aqueous GZ-FX complex dispersion solutions with an encapsulation efficiency (EE) > 85.00%, a particle size < 210.00nm, a zeta-potential > -30.00mV, and a polydispersity index (PDI) < 0.30. GZ-based encapsulation notably enhanced the thermal stability of FX, retaining approximately 90.00% and 80.00% of the FX at 65 ℃ and 100 ℃, respectively. During in vitro simulated gastrointestinal digestion, GZ-encapsulation of FX demonstrated a retention increase of 30.63% and a 2.31-fold higher micellization rate. The in vivo absorption results showed that GZ-based encapsulation dramatically increased FX oral bioavailability, while its serum, liver, and kidney response levels were 51.49-fold, 5.13-fold and 6.73-fold higher. This study suggests that glycosylated alcohol-soluble proteins are highly effective carriers for delivering carotenoids, with significant application potential in the food industry.

Carbon-based thin films as a suitable alternative to metallized films for the preparation of radioactive sources

A new method for radionuclide labeling by the use of graphene thin films was previously presented. In this work, a comparison among low energy radioactive sources supported on carbonaceous thin films on polyvinyl chloride-polyvinyl acetate copolymer (VYNS), based on the use of aqueous solutions is investigated as a feasible alternative to the traditional metallized films avoiding the downside of the loss of many broken films. Graphene-based materials were prepared by both oxidation-exfoliation-reduction and direct graphite exfoliation routes. In addition, multiwalled carbon nanotubes (MWCNTs) thin films were also evaluated. The stability of both carbonaceous materials aqueous dispersions were studied by using ionic and non-ionic surfactants. Solid carbon-based materials were characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) whereas the colloidal nature of the aqueous dispersions was verified by the measurement of Tyndall effect and the morphology of thin films was evaluated by Scanning Electron Microscopy (SEM). 55Fe solutions were used to prepare the radioactive sources on the thin films by quantitative drop deposition. The quality of spectra was measured in a pressurized proportional counter. Results showed a resolution higher than 0.9 keV for all the tested sources. However, MWCNT-based along with non-surfactant sources presented non-adequate escape peaks and low energy tails. On the contrary, all the graphene-based sources prepared using surfactants to stabilize aqueous solutions presented an energy resolution comparable to that of the metallized source while offering notable advantages in terms of cost efficiency and reliability of the as-prepared supports.

Solubilization of Hydrophobic Astaxanthin in Water by Physical Association with Phytoglycogen Nanoparticles.

Astaxanthin (AXT) is a xanthophyll carotenoid with reported health benefits. Realizing its potential as a bioactive is challenging because of its extremely poor solubility in water. We describe a method to improve the effective solubility of AXT in water through its physical association with phytoglycogen (PG), which is produced in sweet corn as compact, highly branched nanoparticles. We combine PG in water with AXT in acetone, evaporate the acetone, and lyophilize. The result is an AXT-PG complex that can be readily redispersed in water, resulting in stable aqueous dispersions. By characterizing the UV-vis absorbance due to different aggregation states of AXT in the AXT-PG complex, we determined the maximum loading of AXT onto PG to be ∼10% by mass. Our results demonstrate the promise of using PG as a solubilizing agent for hydrophobic compounds in water.

Aqueous Keto-Polyethylene Dispersions from Catalytic Copolymerization of Ethylene and Carbon Monoxide in Water.

Water-soluble [P,O]Ni(II) catalysts enable the direct catalytic nonalternating copolymerization of fundamental comonomers ethylene and carbon monoxide (CO) in water as an environmentally friendly reaction medium. This yields stable aqueous dispersions of high molecular weight polyethylene containing ∼1 mol % of largely isolated in-chain keto groups in the form of particles with sizes between 100 nm and 1 μm. The intermediate species of chain growth resulting from incorporation of polar comonomers are amenable to specific chain termination pathways in conjunction with water.

Prevention of thermal gelation in concentrated whey protein isolate dispersions by using H2O2 and SHMP

In the present study, the effect of hydrogen peroxide (H2O2) and sodium hexametaphosphate (SHMP) on the thermal (121.5 °C for 15 min) stability of aqueous dispersions of whey protein isolate (6 % and 10% w/w) was investigated. Based on findings, H2O2, by oxidizing the sulfhydryl (SH) groups, prevented the formation of S–S bonds, therefore prevented thermal aggregation. The presence of SHMP synergistically enhanced the effect of H2O2 by reducing its required concentration. The majority of H2O2 treated samples remained soluble over long cold storage period. This study proved the abilities of H2O2 and SHMP in preventing protein denaturation and improving the thermal stability of whey protein isolate based drinks.

Influence of Defects and Charges on the Colloidal Stabilization of Graphene in Water.

Mastering graphene preparation is an essential step to its integration into practical applications. For large-scale purposes, full graphite exfoliation appears as a suitable route for graphene production. However, it requires overpowering attractive van der Waals forces demanding large energy input, with the risk of introducing defects in the material. This difficulty can be overcome by using graphite intercalation compounds (GICs) as starting material. The greater inter-sheet separation in GICs (compared with graphite) allows the gentler exfoliation of soluble graphenide (reduced graphene) flakes. A solvent exchange strategy, accompanied by the oxidation of graphenide to graphene, can be implemented to produce stable aqueous graphene dispersions (Eau de graphene, EdG), which can be readily incorporated into many processes or materials. In this work, we prove that electrostatic forces are responsible for the stability of fully exfoliated graphene in water, and explore the influence of the oxidation and solvent exchange procedures on the quality and stability of EdG. We show that the amount of defects in graphene is limited if graphenide oxidation is carried out before exposing the material to water, and that gas removal of water before the incorporation of pre-oxidized graphene is advantageous for the long-term stability of EdG.

Thermodynamic Modeling of Aqueous Nanobubble Dispersion

Summary The amount of gaseous species in water or brine can be greatly enhanced in the form of nanobubble (NB) dispersion. Aqueous NB dispersion has vast industrial applications, potentially in enhanced oil recovery (EOR) and carbon dioxide (CO2) sequestration to control the mobility of gaseous species and the geochemistry associated with CO2 dissolution. Development of such NB technologies depends on a proper understanding of thermodynamic properties of aqueous NB dispersion. The objectives of this research are to analyze the thermodynamic stability of aqueous NB dispersion and to apply a thermodynamic equilibrium model to analyze experimental data. We first present a thermodynamic formulation for modeling aqueous NB dispersion, which clarifies that aqueous NB dispersion occurs in the aqueous phase that is supersaturated by the gaseous species in the system. That is, the gaseous species are present in two modes—dispersion of gas bubbles under capillary pressure and molecule dispersion (supersaturation) in the external aqueous phase. Such a thermodynamic system is referred to as aqueous NB fluid in this research and specified by (NC + 3) variables (e.g., temperature, total volume, components’ mole numbers, and capillary pressure), in which NC is the number of components. We then present a novel implementation of the GERG-2008 equation of state (EOS) in minimization of the Helmholtz free energy to solve for equilibrium properties of aqueous NB fluid. GERG-2008 was used in this research because it is suitable for modeling an aqueous phase that is supersaturated by gaseous species. The thermodynamic equilibrium model was applied to experimental data of aqueous NB fluid with nitrogen (N2) at pressures up to 277 bara (4,019 psia) and 295.15 K (71.6°F). Application of the model to experimental data indicates that a large fraction (0.8–0.9) of the total amount of N2 is in the form of molecule dispersion, but such supersaturation of the aqueous phase is possible because of the presence of NB dispersion with capillary pressure. That is, NB dispersion can increase the gas content in aqueous NB fluid by enabling gas supersaturation in the aqueous phase as a thermodynamic system.

INFLUENCE OF POLYVINYL ALCOHOL ON THE STABILITY OF AQUEOUS DISPERSIONS OF NANODIAMONDS

The stability of aqueous dispersions of detonation nanodiamonds (ND) in the presence of polyvinyl alcohol (PVA) has been studied. It has been established that PVA additives with a concentration above 0.1 wt.% cause the formation of aggregates. To increase the stability of ND dispersions, it was proposed to add a stabilizer, an anionic surfactant sodium dodecyl sulfate (SDS), into the system. As a result of the simultaneous action of the SDS-PVA mixture, the aggregation stability of aqueous dispersions of ND increases markedly; the particle size in the dispersions does not change for several days.

The Influence of Polyvinyl Alcohol on the Stability of Aqueous Dispersions of Nanodiamonds

The Influence of Polyvinyl Alcohol on the Stability of Aqueous Dispersions of Nanodiamonds

Nanoparticles of Push-Pull Triphenylamine-Based Molecules for Light-Controlled Stimulation of Neuronal Activity.

Organic semiconductor materials with a unique set of properties are very attractive for interfacing biological objects and can be used for noninvasive therapy or detection of biological signals. Here, we describe the synthesis and investigation of a novel series of organic push-pull conjugated molecules with the star-shaped architecture, consisting of triphenylamine as a branching electron donor core linked through the thiophene π-spacer to electron-withdrawing alkyl-dicyanovinyl groups. The molecules could form stable aqueous dispersions of nanoparticles (NPs) without the addition of any surfactants or amphiphilic polymer matrixes with the average size distribution varying from 40 to 120 nm and absorption spectra very similar to those of human eye retina pigments such as rods and green cones. Variation of the terminal alkyl chain length of the molecules forming NPs from 1 to 12 carbon atoms was found to be an efficient tool to modulate their lipophilic and biological properties. Possibilities of using the NPs as light nanoactuators in biological systems or as artificial pigments for therapy of degenerative retinal diseases were studied both on the model planar bilayer lipid membranes and on the rat cortical neurons. In the planar bilayer system, the photodynamic activity of these NPs led to photoinactivation of ion channels formed by pentadecapeptide gramicidin A. Treatment of rat cortical neurons with the NPs caused depolarization of cell membranes upon light irradiation, which could also be due to the photodynamic activity of the NPs. The results of the work gave more insight into the mechanisms of light-controlled stimulation of neuronal activity and for the first time showed that fine-tuning of the lipophilic affinity of NPs based on organic conjugated molecules is of high importance for creating a bioelectronic interface for biomedical applications.

Stable graphene oxide-based lyotropic liquid crystals for interfacial lubrication

Lyotropic liquid crystals have lubricating properties due to their ordered assembly and fluidity, whose mesogens are often characterized by amphiphilic properties. Despite the attention that graphene oxide (GO) has been studied as a novel amphiphilic lyotropic mesogen this decade, and GO applied as a lubrication additive has been demonstrated in both oil and water-based systems, little research reveals the interfacial lubrication of GO liquid crystals yet. This work reports that GO aqueous dispersion can form lyotropic liquid crystals above a specific critical concentration of 5.00 mg/mL, providing a form of stable water-based lubricant, which can keep stable for several months and can reduce friction by 37.3% and wear by 25.24%. The liquid crystal phase was verified by polarizing microscope and synchrotron radiation small-angle X-ray scattering, and its rheological properties and viscoelasticity were studied by interfacial rheometer. The formation of lyotropic liquid crystals can enhance the stability of GO aqueous dispersions at high density, simultaneously ensuring friction decrease and anti-wear effect. It is attributed to the stable nematic network by the ordered GO sheets. The ordered assembly structure bears vertical shear force, therefore, reducing the wear. It is also assumed that the wide lateral size of graphene oxide promotes the nematic phase thus smoothes the graphene oxide film composed spontaneously under the coincidence of lamellar liquid crystal and 2D layered material. Through this work, the interlayer lubrication of GO was optimized, and the problem of GO dispersion sedimentation was solved by self-assembly. The range of interfacial lubrication of GO aqueous dispersion has been expanded and the synergistic effect is conducive to the environmentally friendly lubricants.

Preparation, formation mechanism, and performance of nitrocellulose aqueous coating based on the anti-solvent method

The organic solvent-based nitrocellulose (NC) coatings exhibit a high volatile solvent content, leading to significant environmental pollution. Whereas, existing waterborne NC-based coating have demonstrated poor water resistance and complex application methods. Therefore, this study aims to develop a green and highly water-resistant waterborne NC-based coating system utilizing a simple anti-solvent method with two environmentally friendly plasticizers, namely acetyl tributyl citrate (ATBC) and triethyl citrate (TEC), as film-forming additives. The dynamic light scattering (DLS) studies revealed that the particle size of NC-based nanoparticles increased with an increase in ATBC content, while it remained relatively constant with an increase in TEC content. Moreover, the particle size results demonstrated that the storage stability of aqueous dispersions containing NC/ATBC (NA) was superior to those containing NC/TEC (NT). Additionally, the physicochemical properties of aqueous dispersions-based films (Ndis), including film formation, hygroscopicity, water resistance, transparency, thermal stability, and mechanical properties were evaluated using solvent-based films (Nsol) as control samples. The results demonstrated that the Ndis films exhibited a dense and uniform structure, with physical and chemical properties that were essentially comparable to those of Nsol films. However, the mechanical properties of Ndis films were somewhat influenced by the nanoparticle size, leading to reduced mechanical performance when the particle size of nanoparticles in the aqueous dispersion was excessively large. The equilibrium moisture content for NA and NT films were reduced to 1.119% and 1.872%, respectively, at a relative humidity of 95%, in comparison to pure NC films (3.975%). Simultaneously, water contact angle measurements indicated an increase from 77° for pure NC film to 89° for NA film and 82° for NT film. All films exhibited superior transparency characteristics. Overall, NA films display excellent water resistance and transparency as well as good mechanical properties.

Water stable colloidal PVP coated spin crossover nanoparticles.

Stable aqueous dispersions of spin-crossover (SCO) doped [FeII(Htrz)2(trz)](BF4) nanoparticles (NPs) were prepared by using water-soluble polyvinylpyrrolidone (PVP) as protecting polymer. The metal or ligand substitution percentage regulated the ultra-small size and morphology of the NPs. At the same time, the colloidal dispersions showed a complete conversion of the LS state to the HS state of the FeII ion.

Stability of Nano-Sized Aqueous Dispersion of n-Heptadecane to Thermal Cycling

A stable aqueous dispersion of n-heptadecane was prepared by ultrasonification without the addition of surfactants. Using the dynamic light scattering, the characteristic size (hydrodynamic radius) of the dispersion‘s particles (100 nm) was determined. On the basis of temperature dependence measurements of scattered light intensity, the temperatures of melting, crystallization and transition to rotator phase of n-heptadecane particles in the studied dispersion were determined. The results obtained are in good agreement with literature data. It has also been experimentally shown that this aqueous dispersion can withstand up to 400 thermal cycles of heating and cooling from 3 °C to 30 °C, retaining ist colloidal stability. The results obtained allow to consider this dispersion as a promising basis for the development of Phase Change Materials.

Recent Innovations of Mesoporous Silica Nanoparticles Combined with Photodynamic Therapy for Improving Cancer Treatment.

Cancer is a global health burden and is one of the leading causes of death. Photodynamic therapy (PDT) is considered an alternative approach to conventional cancer treatment. PDT utilizes a light-sensitive compound, photosensitizers (PSs), light irradiation, and molecular oxygen (O2). This generates cytotoxic reactive oxygen species (ROS), which can trigger necrosis and/ or apoptosis, leading to cancer cell death in the intended tissues. Classical photosensitizers impose limitations that hinder their clinical applications, such as long-term skin photosensitivity, hydrophobic nature, nonspecific targeting, and toxic cumulative effects. Thus, nanotechnology emerged as an unorthodox solution for improving the hydrophilicity and targeting efficiency of PSs. Among nanocarriers, mesoporous silica nanoparticles (MSNs) have gained increasing attention due to their high surface area, defined pore size and structure, ease of surface modification, stable aqueous dispersions, good biocompatibility, and optical transparency, which are vital for PDT. The advancement of integrated MSNs/PDT has led to an inspiring multimodal nanosystem for effectively treating malignancies. This review gives an overview of the main components and mechanisms of the PDT process, the effect of PDT on tumor cells, and the most recent studies that reported the benefits of incorporating PSs into silica nanoparticles and integration with PDT against different cancer cells.

Polymer-Coated Nanoparticles and Pickering Emulsions as Agents for Enhanced Oil Recovery: Basic Studies Using a Porous Medium Model

Globally the overall oil recovery factors for primary and secondary recovery range from 35% to 45%, and a tertiary recovery method that can enhance the recovery factor by 10–30% could contribute to the energy supply. The use of nanoparticles in enhanced oil recovery (EOR) processes comprises an emerging and well-promising approach. Polymer-coated nanoparticles (PNPs) were synthesized through the free radical polymerization (FRP) of the monomers 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and dodecyl methacrylate (DMA) on the surface of acrylic-modified spherical silica nanoparticles. The obtained PNPs were characterized using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA). Dispersions of PNPs were prepared in salt (NaCl, CaCl2) aqueous solutions, the static oil/water interfacial tension were measured using the Du Nouy ring method, and changes caused based on the oil/water contact angle were recorded optically. The PNP dispersions were used to stabilize and characterize shear-thinning oil-in-water Pickering emulsions. The capacity of the PNP dispersions and Pickering emulsions to mobilize the trapped ganglia of viscous paraffin oil, which remained after successive tests of drainage and primary imbibition, was tested with visualization experiments of the secondary imbibition in a transparent glass-etched pore network. The synthesized SiO2-P(AMPSA-co-DMA) nanoparticles were stable even at high temperatures (~200–250 °C) and displayed excellent stability in aqueous dispersions at high ionic strengths with the presence of divalent cations, and their dispersions generated stable oil-in-water Pickering emulsions with a shear-thinning viscosity. The oil-recovery efficiency is maximized when the most viscous Pickering emulsion is selected, but if energy cost factors are also taken into account, then the less viscous Pickering emulsion is preferable.

Highly Crystalized Cl-Doped SnO2 Nanocrystals for Stable Aqueous Dispersion Toward High-Performance Perovskite Photovoltaics.

Tin dioxide (SnO2 ) with high conductivity and low photocatalytic activity has been reported as one of the best candidates for highly efficient electron transport layer (ETL) in perovskite solar cell (PSC). The state-of-the-art SnO2 layer is achieved by chemical bath deposition with tunable properties, while the commercial SnO2 nanocrystals (NCs) with low tunability still face the necessity of further improvement. Here, a kind of highly crystallized Cl-doped SnO2 NCs is reported that can form very stable aqueous dispersion with shelf life up to one year without any stabilizer, which can facilitate the fabrication of PSCs with satisfactory performance. Compared to the commercial SnO2 NCs regardless of the extrinsic Cl-doping conditions, the intrinsic Cl-doped SnO2 NCs effectively suppress the energy barrier and reduces the trap state density at the buried interface between perovskite and ETL. Consequently, stable PSCs based on such Cl-doped SnO2 NCs achieve a champion efficiency up to ≈25% for small cell (0.085 cm2 ) and ≈20% for mini-module (12.125 cm2 ), indicating its potential as a promising candidate for ETL in high-performance perovskite photovoltaics.