Aqueous Dispersion Medium Research Articles

A novel approach for the synthesis of lactic acid-based polymers in an aqueous dispersed medium

In recent years, the search for environmentally friendly monomers has gradually increased as an important field, attracting the attention of researchers worldwide. Our approach to obtaining lactic acid-based polymers entails the use of an environmentally friendly monomer, derived from lactic acid (ELA), presenting double-bond functionality, allowing it to undergo free-radical polymerization, while further having an eco-friendly water-based miniemulsion polymerization process. It has been demonstrated that the ELA/methyl methacrylate (MMA) copolymer can successfully be synthesized. Highly stable latexes were obtained at high conversion. The incorporation of ELA and its effect on the copolymer properties were evaluated; results indicated that polymer properties such as average molar masses and glass transition temperatures are strongly dependent on the ELA composition.

Application of automated electron microscopy imaging and machine learning to characterise and quantify nanoparticle dispersion in aqueous media.

SummaryFor many nanoparticle applications it is important to understand dispersion in liquids. For nanomedicinal and nanotoxicological research this is complicated by the often complex nature of the biological dispersant and ultimately this leads to severe limitations in the analysis of the nanoparticle dispersion by light scattering techniques. Here we present an alternative analysis and associated workflow which utilises electron microscopy. The need to collect large, statistically relevant datasets by imaging vacuum dried, plunge frozen aliquots of suspension was accomplished by developing an automated STEM imaging protocol implemented in an SEM fitted with a transmission detector. Automated analysis of images of agglomerates was achieved by machine learning using two free open‐source software tools: CellProfiler and ilastik. The specific results and overall workflow described enable accurate nanoparticle agglomerate analysis of particles suspended in aqueous media containing other potential confounding components such as salts, vitamins and proteins.Lay DescriptionIn order to further advance studies in both nanomedicine and nanotoxicology, we need to continue to understand the dispersion of nanoparticles in biological fluids. These biological environments often contain a number of components such as salts, vitamins and proteins which can lead to difficulties when using traditional techniques to monitor dispersion. Here we present an alternative analysis which utilises electron microscopy. In order to use this approach statistically relevant large image datasets were collected from appropriately prepared samples of nanoparticle suspensions by implementing an automated imaging protocol. Automated analysis of these images was achieved through machine learning using two readily accessible freeware; CellProfiler and ilastik. The workflow presented enables accurate nanoparticle dispersion analysis of particles suspended in more complex biological media.

Molecular dynamics simulations of surfactant adsorption on carbon nanotubes intended for biomedical applications

Carbon nanotubes (CNTs) are allotropes of carbon with hollow, long structures, having diameters on the nanometer scale. They can be described as rolled-up graphene layers. During the last years, they have been increasingly used in the fields of pharmacy and biomedicine. However, due to their high hydrophobicity, they cannot be easily handled in most solvents of biological interest. To this end, different surfactants have been used to improve their dispersion in aqueous media. In the present work, we investigated the adsorption behavior of two surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), at different concentrations on a CNT surface by classical molecular dynamics (MD) simulations. Our results are presented in terms of distance between surfactant molecules and CNT surfaces, radial distribution functions and interaction energies. In all the models simulated in this work, a strong interaction of both surfactants with the CNT surface is observed, as it is demonstrated by decreasing distances between the surfactants and the CNT during simulation time, the shape of their radial distribution functions, as well as favorable adsorption processes from an energetic point of view.

Unexpectedly High Adsorption Capacity of Esterified Hydroxyapatite for Heavy Metal Removal.

Nanohydroxyapatite (n-HAP) as an environmentally friendly adsorbent of heavy metal ions still requires the rational design of the pore structure and surface characteristic for enhancing their adsorption capacity toward heavy metal ions. A novel one-step strategy was developed to regulate the pore structure and surface characteristic of esterified HAP (n-EHAP) nanocrystals (NCs) for enhancing the adsorption capacity by incorporation of 2-bromo-2-methylpropionate (2-BrMP) groups on the surface of n-EHAP NCs. When using water as the sole solvent, the aggregation of n-EHAP NCs became unavoidable because of incorporation of hydrophobic 2-BrMP groups on n-HAP particle surfaces. The synthesis of uniform and individual n-EHAP NCs was achieved by rational adjustment of the aqueous dispersion medium to avoid agglomeration and precipitation, which was induced by the changing surface characteristic of n-EHAP NCs during the continuing incorporation of hydrophobic 2-BrMP groups in the water/acetone system. The successful incorporation of hydrophobic 2-BrMP groups on the surface of n-EHAP NCs was characterized by X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and liquid nitrogen adsorption isotherms. To explore the potential application in water treatment, a series of systematically designed batch experiments were conducted to determine the influences of the adsorbent dosage, solution pH, and contact time on the adsorption behavior of n-EHAP NCs. Experimental results indicated that the addition of water-soluble acetone greatly promoted the formation of individual n-EHAP NCs without aggregation, and furthermore, the successful incorporation of hydrophobic 2-BrMP groups led to formation of porously structured n-EHAP NCs with a higher surface area and an increasing micro-/mesopore ratio. Compared with pristine n-HAP, n-EHAP NCs exhibited lower crystallinity with smaller crystallite size and demonstrated an ultrahigh adsorption capacity for Pb(II) in acidic solution with a record of close to 2400 mg/g. The improved performance of n-EHAP NCs originated from both the suitable porous structure with a higher micro-/mesoporosity ratio and the existing tethered 2-BrMP group-induced the ester bond, providing more adsorption active affinity sites for heavy metal ions. The highly efficient adsorption (99.99%) was further achieved using tap water spiked with traces of Pb(II) (63 ppb). The presented findings promise the application of n-EHAP NCs in water treatment as an alternative, low-cost, and ecofriendly adsorbent for environmental remediation.

Modified tapioca starch for iron nanoparticle dispersion in aqueous media: potential uses for environmental remediation

Synthesis of cost-effective surface-modified nanoscale zero-valent iron (NZVI) for use in environmental remediation is a challenge. Herein, we report the synthesis of modified tapioca starch-coated NZVI (CNZVI) particles and their application for effective aqueous nitrate remediation. We used 2-octen-1-ylsuccinic anhydride (OSA) to modify the native starch and, thus introduced carboxyl and ester groups for effective binding of the starch to the NZVI surface. Coating NZVI (3 g L−1) with 35% OSA-modified tapioca starch (10 g L−1) significantly improved colloidal stability of CNZVI in deionized (DI) water compared to bare (unmodified) NZVI (p = 0.000). Approximately 66% of CNZVI remained suspended till 2 h as compared to 4% of bare NZVI. Nitrate removal studies (20, 40, and 60 mg $${\text{NO}}_{3}^{ - }$$ –N L−1 and 1 g L−1 of nanoparticles) showed CNZVI removed nitrate effectively (54–71% removal). The nitrate removal by CNZVI followed second-order reactions with surface normalized reaction rate constants ranging from 0.003 to 0.007 L m−2 h−1. Shelf life of the coated nanoparticles was found to be 3 months. High biochemical oxygen demand was expressed during respirometric biodegradation studies indicating ease of biodegradation of the CNZVI particles. Coating NZVI particles with OSA-modified tapioca starch is expected to have widespread scientific and industrial application potentials for ex situ as well as in situ contaminant remediation. The authors opine that the use of tapioca starch as the raw material for coated nanoparticle synthesis will be a value addition for the crop, and thus, nanotechnology will contribute to agricultural economy.

Direct bromination of nano hydroxyapatite strategy towards particle brushes via surface-initiated ATRP for highly efficient heavy metal removal

Aminated n-HAP-g-polyacrylonitrile (n-HAP-g-APAN) particle brushes were developed for highly efficient heavy metal removal based on surface-initiated ATRP (SI-ATRP) and subsequent amination. An efficient one-step method for morphology controlled synthesis of ATRP initiator immobilized n-HAP (n-HAP-Br) was realized by using 2-bromoisobutyric acid as tetherable initiator. Uniform and individually dispersed n-HAP-Br NCs were obtained with controlled morphology and particle size by adding portion of water miscible organic solvents to rational adjusting aqueous dispersion medium. Aminated n-HAP-g-APAN displayed record-high adsorption capacity of heavy meatal ions due to the combined contributions of grafted APAN providing pendent amino diethylenepentamine as chelating groups and n-HAP core towards heavy metal ions (pure n-HAP of qe = 284.4 mg/g vs n-HAP-g-APAN of qe = 944.4 mg/g). The proposed one-step direct bromination of n-HAP strategy provides the preparation of uniform n-HAP NCs ready for polymer grafting and further fabrication of n-HAP-g-polymers via SI-ATRP for various applications depending on the characteristic of grafted polymers.

A Novel Method to Improve the Dispersibility of Silicon Nitride Powders in Aqueous Media

The present study describes a novel method to improve the dispersibility of silicon nitride powders in aqueous media. Specifically, a new Si3N4@g-C3N4 core–shell composite material was synthesized via annealing the mixture of silicon nitride and melamine under a nitrogen atmosphere using heating method. The effects of various initial mass ratios of Si3N4 and melamine on the structure and dispersibility of the composite were systematically investigated. The results of X-ray photoelectron spectroscopy and transmission electron microscope demonstrated that as-obtained Si3N4@g-C3N4 composite powders possess the core–shell structure, whereas the zeta potential and sedimentation analysis showed that they exhibit good dispersion in aqueous media. Furthermore, the colloidal dispersion of the composite powders is most stable when the initial mass ratio of Si3N4 and melamine is 100:3. The coated g-C3N4 could be completely removed in a cryogenic nitrogen atmosphere. The proposed process is expected to provide novel avenues for the study of dispersion of other inorganic powders.

РОЗРОБЛЕННЯ БІОРОЗКЛАДНОЇ ПОЛІМЕРНОЇ КОМПОЗИЦІЇ НА ОСНОВІ КАЗЕЇНУ МОЛОКА

The article sums up the results of the study of milk casein as a biopolymer, which is widely used in food industry, construction, pharmacy, etc. and on the basis of which polymer films for biodegradable materials can be obtained. The analysis draws on data on the structure of milk casein molecules as a complex globular micellar system, which is constructed by nanoscale sub-micelles, interconnected by calcium phosphate sites, with the formation of a casein-calcium phosphate complex. Sub-micelles differ in structure and function, according to which their four fractions are distinguished. The hydrophilic carboxyl groups of the glutamic, aspartic and orthophosphate acids of the κ-casein fraction provide the stabilization of casein micelles in the aqueous medium. Such structure of casein does not allow to receive film materials, they have low technological characteristics, very low durability and elasticity, high fragility. Moreover, they are easily soluble in water.
 Studies have shown that on the basis of casein it is possible to obtain polymer films, provided the use of a polymer composition, in which besides casein there is a modified polysaccharide. To obtain such a composition, carboxymethylcellulose was used, which also has biodegradable properties, however, unlike casein, it is capable of forming sufficiently strong polymer films. The polymer composition was synthesized in two steps: first, an aqueous solution of carboxymethyl cellulose was prepared, to which freshly precipitated casein with a moisture content of 20%, precipitated from skim milk, was added. The composition of the polymer composition was enriched with a number of additives serving as plasticizers, and structure-forming. The triatomic alcohol glycerol and diphenylamine were added as plasticizers too. In order to regulate the structure of the aqueous dispersion medium and prevent the processes of aggregation of casein micelles, calcium chloride solution was injected in the composition. The given polymer composition after polymerization in the air-drying process makes it possible to obtain sufficiently strong composite polymer films, the transparency of which depends on the type of plasticizer selected and the presence of CaCl2.

Biocompatibility and Hyperthermia Efficiency of Sonochemically Synthesized Magnetic Nanoparticles

Hereby, a sonochemical method for synthesis of pure magnetic Fe3O4 nanoparticles (Fe3O4-NPs) in large scale is being introduced. Synthesis proceeds via simple approach, at room temperature, under sonication, using cheap reagents, green antioxidant-reductant reagent and without using inert gas purge as protective atmosphere condition. During this procedure, hydrogen gas releases continuously as valuable byproduct at the anaerobic step of reaction. Characterizations’ results indicate that the final product is pure spherical Fe3O4-NPs, with narrow size distribution and about less than 32[Formula: see text]nm in mean diameter while more than 99% of particles size were less than 40[Formula: see text]nm. According to Vibrational Sampling Magnetometer (VSM) result, NPs pose high saturation magnetization of about 77 (emu/g) and magnetization curve shows superparamagnetic behavior with no hysteresis loop. Also by various weight ratios, these NPs performed stable dispersion in aqueous media for long times. Iron oxide NPs show nontoxicity for lower dosage of 10[Formula: see text][Formula: see text][Formula: see text]g/mL in 24[Formula: see text]h on fibroblast cell. Hyperthermia results show maximum heating efficiency in 100[Formula: see text]KHz for 1[Formula: see text]mg/mL of NPs.

Bis-N,N-aminophosphine (PNP) crosslinked poly(p-tert-butyl styrene) particles: A new support for heterogeneous palladium catalysts for Suzuki coupling reactions

Crosslinked polymer particles carrying hemilabile bis-N,N-aminophosphine (PNP) moieties are obtained by the copolymerization of a PNP-derived monomer bearing four vinyl fragments as cross-linkers, with para-tert-butylstyrene and divinylbenzene, using free radical copolymerization in presence of AIBN, performed in aqueous dispersed medium. This new support was characterized by thermogravimetric analysis, elemental analysis, laser diffraction, solid state NMR. The PNP moiety could allow monochelation to palladium. The resulting insoluble Pd-catalyst revealed to be very active for Suzuki cross-coupling with several substrates, allowing separation of the product from the catalyst by filtration. The final palladium PS-PNP catalyst could be reused for several catalytic cycles.

Stabilization of Silver Nanoparticles in Water with a Cationic Copolymer Based on Poly(Aminoethyl Methacrylate)

It has been shown that a cationic copolymer based on poly(aminoethyl methacrylate) is capable of stabilizing silver nanoparticle dispersions in aqueous media. Nanoparticles have been prepared via chemical reduction of AgNO3 in an aqueous solution with sodium borohydride in the presence of a cationic random terpolymer—poly(2-aminoethyl methacrylate-co-N-methyl-2-aminoethyl methacrylate-co-N,N-dimethyl-2-aminoethyl methacrylate). Spectrophotometry has been employed to show that silver dispersions formed in the presence of the copolymer are stable for a long time (more than half a year). Using dynamic light scattering and scanning electron microscopy, consistent information has been obtained on the sizes and size distribution of the stabilized nanoparticles.

Spontaneous nano-emulsification with tailor-made amphiphilic polymers and related monomers

In general, nano-emulsions are submicron droplets composed of liquid oil phase dispersed in liquid aqueous bulk phase. They are stable and very powerful systems when it regards the encapsulation of lipophilic compounds and their dispersion in aqueous medium. On the other hand, when the properties of the nano-emulsions aim to be modified, e.g. for changing their surface properties, decorating the droplets with targeting ligands, or modifying the surface charge, the dynamic liquid / liquid interfaces make it relatively challenging. In this study, we have explored the development of nano-emulsions which were not anymore stabilized with a classical low-molecular weight surfactant, but instead, with an amphiphilic polymer based on poly(maleic anhydride-alt-1-octadecene) (PMAO) and Jeffamine®, a hydrophilic amino-terminated PPG/PEG copolymer. Using a polymer as stabilizer is a potential solution for the nano-emulsion functionalization, ensuring the droplet stabilization as well as being a platform for the droplet decoration with ligands (for instance after addition of function groups in the terminations of the chains). The main idea of the present work was to understand if the spontaneous emulsification –commonly performed with nonionic surfactants– can be transposed with amphiphilic polymers, and a secondary objective was to identify the main parameters impacting on the process. PMAO was modified with two different Jeffamine®, additionally different oils and different formulation conditions were evaluated. As a control, the parent monomer, octadecyl succinic anhydride (OSA) was also modified and studied in the similar way as that of polymer. The generated nano-emulsions were mainly studied by dynamic light scattering and electron microscopy, that allows discriminating the crucial parameters in the spontaneous process, originally conducted with polymers as only stabilizer.

Highly Stable Aqueous Dispersion of CTAB- Intercalated Reduced Graphene Oxide

Abstract A highly stable aqueous dispersion of reduced graphene oxide is obtained through the chemical reduction of graphene oxide by hydrazine hydrate in presence of cetyltrimethyl ammonium bromide (CTAB). Herein we report the preparation of reduced graphene particles which can be stably dispersed in water. The surfactant serves an effective role in graphene layer exfoliation. The dispersion in aqueous media has been observed over a week period. The reduced graphene particles were characterized by X -ray Diffraction (XRD), Fourier Transformed Infra-red (FTIR) spectroscopy. The morphology of prepared particles was studied by High Resolution Transmission Electron Microscopy (HRTEM).

Increase of aggregative and sedimentation stability of slag suspensions by ultrasound

The paper discusses the relevance of the use of metallurgical wastes crushed to a fine state in the production of building materials. Domain granulated slag (DGS) was used as a research object. A method for introducing fine ground slag (FGS) into the cement composition in the form of a slag suspension instead of mixing water has been developed. To establish the uniform distribution of FGS particles in the cement matrix, the behavior of slag particles in an aqueous dispersion medium was previously studied. The optimal parameters of ultrasonic dispersion of slag suspensions are established: the frequency of ultrasonic vibrations is 44 kHz; temperature of dispersion - 25±2°C; dispersion time - 15 min. It has been established that the application of UST to slag suspensions with the observance of optimal dispersion parameters can increase the aggregative and sedimentation stability of the FGS suspension by 2–3 times as compared with mechanical mixing, accelerate the micelle formation process, and enhance the electrostatic factor of aggregative stability.

Influence of optimal conditions of ultrasonic dispersion on the stability of suspensions of finely ground slags

The preparation in the jet mill of finely ground slag (FGS) from the waste of metallurgical production granulated blast-furnace slag, the obtaining of slag suspensions, and the behavior of FGS particles in an aqueous dispersion medium are considered in the paper. It was found that FGS particles in the suspension form micelles of two types with negative (micelle 1) and positive (micelle 2) charges of FGS surface. To increase the aggregative and sedimentation stability of FGS particles in suspensions, studies were carried out using ultrasonic dispersion. The results of investigations on the detection of optimal dispersion parameters for slag suspensions are presented. It was found that in the absence of temperature control, the process of coagulation of slag particles is accelerated and aggregative and sedimentation stability of suspensions of FGS is reduced. The slag particles in the suspension form aggregates that lead to a deterioration of the strength characteristics of the cement stone using suspensions of FGS. Optimal parameters of ultrasonic dispersion of slag suspensions are established: the frequency of ultrasonic vibrations is equal to 44 kHz; the dispersion temperature is 25 ± 2 °C; the dispersion time is 15 min. It was found that the application of ultrasonic dispersion to slag suspensions with the observance of dispersion conditions can increase the aggregative and sedimentation stability of FGS suspension by 2-3 times in comparison with the mechanical mixing of suspensions. The strength of samples with suspensions of FGS prepared using UST under the recommended dispersing conditions increased by 19 to 39% in the first day; for 28 days of hardening - by 19 - 36%, which allows using slag suspensions in the production of cement composite materials and concretes based on them.

Tuning photosensitized singlet oxygen production from microgels synthesized by polymerization in aqueous dispersed media

Miniemulsion copolymerization of vinyl acetate, N-vinylcaprolactam, vinyl benzyl Rose Bengal and divinyl adipate to synthesize switchable photosensitizer-grafted polymer colloids for interfacial photooxygenation reactions.

Radical polymerization of biobased monomers in aqueous dispersed media

This review highlights the synthesis of biobased monomers from renewable resources for the preparation of polymers by (mini)emulsion and suspension polymerizations.

Efficiency of stabilization of slag suspensions by polycarboxylate

The paper describes the method of stabilization of slag suspensions prepared on the basis of finely ground slag (FGS) with a predominant particle size of 1-7 μm, a plasticizer based on polycarboxylate (polycarboxylate). In suspension, FGS particles form two types of micelles with negative and positive surface charges. It has been established that stabilization with polycarboxylate, which is an anionic long-chain surfactant, affects slag particles with a positive surface charge. The formation of strong and elastic gel-like films on the surface of FGS leads to an increase in the structural and mechanical factor of aggregative stability of slag suspensions. Thus, the stabilization of slag particles by polycarboxylate is ensured by electrostatic, structural and mechanical factors of aggregative stability. It was established experimentally that the introduction of polycarboxylate into the aqueous dispersion medium increases the aggregative and sedimentation stability of slag suspensions. In the first period of particle sedimentation, on average, stability of slag suspensions is increased by 36 times, in the second period - 19 times, in the third period - 4 times. To ensure stability of slag suspensions, the protective number and the optimal concentration of the polycarboxylate are determined. The protective number of the suspension was 0,016 g/l; the optimal concentration of polycarboxylate - 4 g/l.

Computer-Aided Design of Process of Fabrication on Steel of Solid Lubricating Coating Based on Bank Sand

The results of investigation of tribological properties of solid lubricating coatings fabricated on high carbon steel of U8 grade (0.8% of C) using thermo-hydro-chemical treatment (THCT) in an aqueous-dispersion medium based on bank sand are presented. The composition of the medium and the temperature and the time parameters of THCT process were optimized by the friction coefficient of solid lubricating coatings. The diagrams of “parameters of process–property” were constructed using mathematical models. Processing by optimal THCT regime of U8 steel in hydrosol medium of bank sand makes it possible under the condition of lubrication absence to decrease the friction coefficient of steel surface by 5.4 times as compared with rough-sawed surface.

Green synthesized multiple fluorescent nitrogen-doped carbon quantum dots as an efficient label-free optical nanoprobe for in vivo live-cell imaging

In this work, nitrogen-doped carbon quantum dots (N-CQDs) have been synthesized successfully by a simple hydrothermal method and demonstrated its application for multicolor imaging in Caenorhabditis elegans (C. elegans) as an in vivo model. The synthesized N-CQDs were characterized by various physicochemical techniques such as XRD, Raman spectroscopy, ATR-FTIR spectroscopy, XPS, HRTEM, UV–vis spectroscopy, and fluorescence spectroscopy. The synthesized N-CQDs exhibited a strong fluorescence due to the uniform size distribution with nitrogen-containing and oxygen-containing functional groups onto the surface of N-CQDs which induce the excellent dispersibility in aqueous media. The N-CQDs has an excitation-dependent fluorescence behavior and the strongest fluorescence appeared at 411 nm (emission peak position) under the excitation of 340 nm. Also, the N-CQDs displayed a high quantum yield (QY) of 12.5. The fluorescence behaviour of the aqueous N-CQDs suspension retains for a long time up to 1 year. The prolonging fluorescent N-CQDs was utilized as a staining agent for bioimaging and toxicity of N-CQDs on C. elegans that was conducted by killing assay. In-vivo studies suggested that the N-CQDs displayed excellent biocompatibility and successfully used for high-contrast imaging of N-CQDs in living and dead C. elegans. Based on the strongest fluorescence along with excellent aqueous dispersibility and biocompatibility, the green synthesized N-CQDs would be an ideal candidate for many biological applications.