Colloidal Dispersions In Water Research Articles

Surface Adsorption and Photoinduced Degradation: A Study of Spinel Ferrite Nanomaterials for Removal of a Model Organic Pollutant from Water.

Spinel oxide nanocrystals are attractive materials for photoinduced advanced oxidation processes that degrade organic pollutants in water due to their chemical stability and tunability, visible light absorption, and magnetic recoverability. However, a systematic understanding of the structural and chemical factors that control the reactivity of specific spinel oxide nanocrystal materials toward photoinduced degradation processes is lacking. This Perspective illustrates these knowledge gaps through an investigation into the impacts of surface chemistry and composition of spinel ferrite nanocrystals of formula MFe2O4 (M = Mg, Fe, Co, Ni, Cu, Zn) on their ability to remove a model organic pollutant (methyl orange (MO)) from water. We identify two mechanisms by which the nanocrystals remove MO from water: (i) surface adsorption and (ii) photoinduced degradation under visible light irradiation in the presence of hydrogen peroxide via the photo-Fenton reaction. Nanocrystals that do not contain any surface ligands are more effective at removing MO from water than nanocrystals that contain surface ligands, despite our observation that the ligand-less nanocrystals do not form stable colloidal dispersions in water, while ligand-coated nanocrystals are colloidally stable. For many of the spinel ferrite compositions studied here, the fraction of methyl orange removal via adsorption to the nanocrystal surface in the absence of photoexcitation is larger than the fraction removed under irradiation. Our data indicate that the composition-dependent surface charge of the nanocrystals controls the degree of surface adsorption of the charged MO molecule. Overall, these results demonstrate that careful consideration of the impacts of surface chemistry on the behavior of spinel ferrite nanocrystals is required to accurately assess and subsequently understand their activity toward the photoinduced degradation of organic molecules.

Synthesis, Crystal Structure, and Antibacterial Properties of Silver-Functionalized Low-Dimensional Layered Zirconium Phosphonates.

New insoluble layered zirconium phosphate carboxyaminophosphonates (ZPs), with the general formula Zr2(PO4)H5[(O3PCH2)2N(CH2)nCOO]2·mH2O (n = 3, 4, and 5), have been prepared and characterized. The crystal structure for n = 3 and 4 samples was determined ab initio from X-ray powder diffraction data. The structure for n = 3 was monoclinic in space group C2/c with the following unit cell parameters: a = 34.346(1) Å, b = 8.4930(2) Å, c = 9.0401(2) Å, and β = 97.15(1)°. The structure for n = 4 was triclinic in space group P1̅ with the following unit cell parameters: a = 17.9803(9) Å, b = 8.6066(4) Å, c = 9.0478(3) Å, α = 90.466(3)°, β = 94.910(4)°, and γ = 99.552(4)°. The two structures had the same connectivity as Zr phosphate glycine diphosphonate (n = 1), as previously reported. By intercalation of short amines, these layered compounds were exfoliated in single lamella or packets of a few lamellae, which formed colloidal dispersions in water. After a thorough characterization, the dispersed lamellae were functionalized with Ag nanoparticles, which were grown in situ on the surface of exfoliated lamellae. Finally, their antimicrobial activity was tested on several Gram-positive and Gram-negative bacteria. All of these systems were found to be active against the four pathogens most frequently isolated from orthopedic prosthetic infections and often causative of nosocomial infections. Interestingly, they were found to express powerful inhibitory activity even against bacterial strains exhibiting a relevant profile of antibiotic resistance such as Staphylococcus aureus ATCC 700699.

Polymer Micro and Nanoparticles Containing B(III) Compounds as Emissive Soft Materials for Cargo Encapsulation and Temperature-Dependent Applications.

Polymer nanoparticles doped with fluorescent molecules are widely applied for biological assays, local temperature measurements, and other bioimaging applications, overcoming several critical drawbacks, such as dye toxicity, increased water solubility, and allowing imaging of dyes/drug delivery in water. In this work, some polymethylmethacrylate (PMMA), polyvinylpyrrolidone (PVP) and poly(styrene-butadiene-styrene) (SBS) based micro and nanoparticles with an average size of about 200 nm and encapsulating B(III) compounds have been prepared via the reprecipitation method by using tetrahydrofuran as the oil phase and water. The compounds are highly hydrophobic, but their encapsulation into a polymer matrix allows obtaining stable colloidal dispersions in water (3.39 µM) that maintain the photophysical behavior of these dyes. Although thermally activated non-radiative processes occur by increasing temperature from 25 to 80 °C, the colloidal suspension of the B(III) particles continues to emit greenish light (λ = 509 nm) at high temperatures. When samples are cooling back to room temperature, the emission is restored, being reversible. A probe of concept drug delivery study was conducted using coumarin 6 as a prototype of a hydrophobic drug.

Triphenylphosphine-Functionalized Core-Cross-Linked Micelles and Nanogels with a Polycationic Outer Shell: Synthesis and Application in Rhodium-Catalyzed Biphasic Hydrogenations.

Unimolecular amphiphilic nanoreactors with a poly(4-vinyl-N-methylpyridinium iodide) (P4VPMe+ I- ) polycationic outer shell and two different architectures (core-cross-linked micelles, CCM, and nanogels, NG), with narrow size distributions around 130-150 nm in diameter, were synthesized by RAFT polymerization from an R0 -4VPMe+ I- 140 -b-S50 -SC(S)SPr macroRAFT agent by either chain extension with a long (300 monomer units) hydrophobic polystyrene-based block followed by cross-linking with diethylene glycol dimethacrylate (DEGDMA) for the CCM particles, or by simultaneous chain extension and cross-linking for the NG particles. A core-anchored triphenylphosphine (TPP) ligand functionality was introduced by using 4-diphenylphosphinostyrene (DPPS) as a comonomer (5-20 % mol mol-1 ) in the chain extension (for CCM) or chain extension/cross-linking (for NG) step. The products were directly obtained as stable colloidal dispersions in water (latexes). After loading with [RhCl(COD)]2 to yield [RhCl(COD)(TPP@CCM)] or [RhCl(COD)(TPP@NG)], respectively, the polymers were used as polymeric nanoreactors in Rh-catalyzed aqueous biphasic hydrogenation of the model substrates styrene and 1-octene, either neat (for styrene) or in an organic solvent (toluene or 1-nonanol). All hydrogenations were rapid (TOF up to 300 h-1 ) at 25 °C and 20 bar of H2 pressure, the biphasic mixture rapidly decanted at the end of the reaction (<2 min), the Rh loss was negligible (<0.1 ppm in the recovered organic phase), and the catalyst phase could be recycled 10 times without significant loss of catalytic activity.

Elaboration of PCBM Coated P3HT Nanoparticles: Understanding the Shell Formation

Solvent displacement, or nanoprecipitation, is a well-known process to develop colloidal dispersions in water. Using two successive and selective nanoprecipitation steps, we developed a method to generate [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) shell on poly(3-hexylthiophene) (P3HT) core nanoparticles (P3HT@PCBM). We report herein on the understanding of the shell formation during this process. Using several techniques (dynamic light scattering, zeta-potential, photoluminescence), we evidenced that after the first solvent displacement with dimethyl sulfoxide (DMSO), the PCBM molecules still dissolved in the medium are already in close interaction with the P3HT nanoparticles (NP). Such proximity of the P3HT core with PCBM molecules in the DMSO dispersion explains why PCBM aggregates around the nanoparticles during the second solvent displacement with water. A fast electron transfer from P3HT to PCBM was identified by transient absorption spectroscopy, confirming the core-shell morphology even for low PCBM concentration. This study opens the route for the development of well-defined nano-objects dispersed in water for fabrication of organic photovoltaic devices with eco-friendly processes.

Superposition of Acid Concentration and Temperature at Production of Nanocrystalline Cellulose Particles

Relationship between concentration of sulfuric acid (C) and temperature (T) required for the cellulose hydrolysis to prepare nanocrystalline cellulose particles (NCP has been studied in this paper. The experiments showed that there is a linear C and T superposition exists, namely: C= Co – n T. The higher the acid concentration, the lower the hydrolysis temperature should be used, and vice versa. The minimum level of acid concentration that can be used for production of CNP is 40 wt. % at optimal temperature of 80o C. If temperature or acid concentration is lower, there is a tendency to form of microparticles. On the other hand, at higher hydrolysis temperatures, carbonized CNP with decreased yield are obtained. The rod-like crystalline nanoparticles of cellulose produced at optimal hydrolysis conditions (C=40 wt. %, T=80o C) have average sizes of 150 x 15 nm, degree of crystallinity of 75-77% and degree of polymerization of 130-150. The nanoparticles form stable colloidal dispersions in water due to Brownian motion and negativeZeta potential imparting to these particles the mutual electrostatic repulsion. Estimated calculations have also shown that decrease in the concentration of sulfuric acid from 60 to 40 wt. % at production of CNP is economically advantageous despite increase in hydrolysis temperature from 45 to 80o C.

The Effect of Electronic Medical Record Adaptation on Reported Medication Errors in Peripartum Care Areas

Relationship between concentration of sulfuric acid (C) and temperature (T) required for the cellulose hydrolysis to prepare nanocrystalline cellulose particles (NCP has been studied in this paper. The experiments showed that there is a linear C and T superposition exists, namely: C= Co - n T. The higher the acid concentration, the lower the hydrolysis temperature should be used, and vice versa. The minimum level of acid concentration that can be used for production of CNP is 40 wt. % at optimal temperature of 80o C. If temperature or acid concentration is lower, there is a tendency to form of microparticles. On the other hand, at higher hydrolysis temperatures, carbonized CNP with decreased yield are obtained. The rod-like crystalline nanoparticles of cellulose produced at optimal hydrolysis conditions (C=40 wt. %, T=80o C) have average sizes of 150 x 15 nm, degree of crystallinity of 75- 77% and degree of polymerization of 130-150. The nanoparticles form stable colloidal dispersions in water due to Brownian motion and negative Zeta potential imparting to these particles the mutual electrostatic repulsion. Estimated calculations have also shown that decrease in the concentration of sulfuric acid from 60 to 40 wt. % at production of CNP is economically advantageous despite increase in hydrolysis temperature from 45 to 80o C.

Nonaqueous Sol-Gel Synthesis of Anatase Nanoparticles and Their Electrophoretic Deposition in Porous Alumina.

Titanium dioxide (TiO2) nanoparticles were synthesized by nonaqueous sol-gel route using titanium tetrachloride and benzyl alcohol as the solvent. The obtained 4 nm-sized anatase nanocrystals were readily dispersible in various polar solvents allowing for simple preparation of colloidal dispersions in water, isopropyl alcohol, dimethyl sulfoxide, and ethanol. Results showed that dispersed nanoparticles have acidic properties and exhibit positive zeta-potential which is suitable for their deposition by cathodic electrophoresis. Aluminum substrates were anodized in phosphoric acid in order to produce porous anodic oxide layers with pores ranging from 160 to 320 nm. The resulting nanopores were then filled with TiO2 nanoparticles by electrophoretic deposition. The influence of the solvent, the electric field, and the morphological characteristics of the alumina layer (i.e., barrier layer and porosity) were studied.

Fractals of graphene quantum dots in photoluminescence of shungite

Viewing shungite as loosely packed fractal nets of graphene-based (reduced graphene oxide, rGO) quantum dots (GQDs), we consider photoluminescence of the latter as a convincing proof of the structural concept as well as of the GQD attribution to individual rGO fragments. We study emission from shungite GQDs for colloidal dispersions in water, carbon tetrachloride, and toluene at both room and low temperatures. As expected, the photoluminescence of the GQD aqueous dispersions is quite similar to that of synthetic GQDs of the rGO origin. The morphological study of shungite dispersions shows a steady trend of GQDs to form fractals and to drastically change the colloid fractal structure caused by the solvent exchange. Spectral study reveals a dual character of the emitting centers: individual GQDs are responsible for the spectra position while the fractal structure of GQD colloids ensures high broadening of the spectra due to structural inhomogeneity, thus causing a peculiar dependence of the photoluminescence spectra on the excitation wavelength. For the first time, photoluminescence spectra of individual GQDs were observed in frozen toluene dispersions, which paves the way for a theoretical treatment of the GQD photonics.

Surface potential of diamond and gold nanoparticles can be locally switched by surrounding materials or applied voltage

Properties of nanoparticles in contact with other surfaces are crucial for various applications. Here, we show that electrical potential of individual nanoparticles or their aggregates (sizes 5–50 nm) can be locally switched between negative and positive via work functions of surrounding materials (Si, Au, and Pt). We employed novel methodology of Kelvin probe force microscopy (KPFM) to characterize surface potentials of hydrogenated, thermally oxidized, and partially graphitized detonation diamond nanoparticles (5 nm), as well as gold nanoparticles (20 nm) deposited on the substrates (Si, Au) from colloidal dispersions in water or methanol. We present a comprehensive model of the observed effect based on work functions of the involved materials and charge trapping in or on the nanoparticles. The model is further confirmed by modification of nanoparticle charges after intentional application of up to ±4 V through the KPFM tip. The observed effects may impact other physical properties such as electron emission and photoluminescence of the nanoparticles.

Preparation and characterization of aqueous dispersions of poly(3,4‐ethylenedithiathiophene‐co‐3,4‐ethylenedioxythiophene)/ poly(styrene sulfonate) and their conducting films

AbstractThe chemical oxidative copolymerization of 3,4‐ethylenedithiathiophene (EDTT) with 3,4‐ethylenedioxythiophene (EDOT) and 2′‐hydroxymethyl‐3,4‐ethylenedioxythiophene in a poly(styrene sulfonic acid) aqueous solution was successfully carried out to form stable, dark blue colloidal dispersions in water. Coating these dispersions onto polypropylene substrates led to the formation of free‐standing copolymer films. The mechanical, electrical, and thermoelectrical properties of these films were investigated; the films showed superior properties in comparison with those of poly(3,4‐ethylenedithiathiophene) (PEDTT)/poly(styrene sulfonate) (PSS). The copolymer film based on EDTT and EDOT achieved a high electrical conductivity (8.2 × 10−2 S cm−1) at 298 K; this could be improved about 10 times through the addition of dimethyl sulfoxide (DMSO) or DMSO/isopropyl alcohol into the polymer dispersion with almost constant Seebeck coefficients of about 9 μV K−1. On the contrary, these additives had almost no effect on the conductivity of PEDTT/PSS. The structure and morphology of the polymer films were studied by X‐ray diffraction and SEM analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Fabrication of palladium/graphene oxide composite by plasma reduction at room temperature

Pd nanoparticles were fabricated on graphene oxide (GO) using a deposition-precipitation method with a glow discharge plasma reduction at room temperature. Argon was employed as the plasma-generating gas. The novel plasma method selectively reduces the metal ions. The graphene oxide has no change with this plasma reduction according to the Fourier transform infrared analysis. The Pd nanoparticles on the GO were uniformly distributed with an average diameter of 1.6 nm. The functional groups on the GO not only prevent Pd nanoparticles from further aggregation but also provide a strong hydrophilic property to the Pd/GO composite, which can form stable colloidal dispersions in water.

Laminar flow and heat transfer characteristics of nanoparticle colloidal dispersions in water

Numerical analysis is performed to examine axisymmetric laminar flow and heat transfer characteristics of colloidal dispersions of nanoparticles in water (nanofluids). Effect of volume fraction on flow and heat transfer characteristics is investigated. Eight different materials, alumina, copper, copper oxide, diamond, gold, graphite, silver, and zirconia are considered. Heat transfer and property measurements were conducted previously for Alumina nanofluid and the results have shown that nanofluids behave as homogeneous mixtures. It is found that oxide-based nanofluids offer the least heat transfer enhancement compared to elements-based nanofluids. For a given volume flow rate, all nanofluids exhibited linear increase in heat transfer enhancement with increasing colloids volume fraction, up to 0.05. Furthermore, it is found that in the thermal entrance region, a hydrodynamically developing flow exhibits significantly higher heat transfer enhancement than fully-developed conditions.

Supercritical water: a fascinating medium for soft matter.

Properties of water change dramatically at high temperatures and high pressures near and/or above the critical point ( = 374 °C, = 22.1 MPa). The dielectric constant, for example, decreases from 78 at 25 °C and 0.1 MPa to 6 at the critical point, the value of which is comparable to that of 1-dodecanol. As fascinating characteristics of soft matter rely on unique properties of ambient liquid water, the change should have significant impacts on soft matter. However, our knowledge of soft matter under such extreme conditions is virtually nonexistent. In this article, properties of colloidal dispersions in water at high temperatures and high pressures are described. Implications of the findings for geological processes in deep-subsurface are also discussed.

Flow of Dilute Colloidal Dispersions in Water through a Small Orifice

Fluctuation of flows through a small orifice has been measured for water and two kinds of colloidal dispersions including fine particles about 100 nm in diameter with 1 % volume fraction in water. In this volume fraction, a surface potential of the particles is composed of an electrostatic repulsion and a van der Waals attraction and it affects flow properties. Experiments clarify that a specific flow instability occurs for water at the Reynolds number about 60, and the dispersion of polystyrene particles having strong repulsion increases the specific flow instability in low salt concentrations(LSC) but makes it disappear in high salt concentrations(HSC). Meanwhile, it is found that the dispersion of silica particles having strong attraction is stable in flows except the specific flow instability in LSC but it suppresses the specific flow instability in HSC as in the case of polystyrene particles. Criterion whether the orifice flow is stable or not is predicted by comparison of the second minimum location of the surface potential and the mean surfaces distance of the particles.

Long‐term stability of an ambient self‐curable latex based on colloidal dispersions in water of two reactive polymers

AbstractAn ambient self‐curable latex (ASCL) was prepared via the blending of colloidal dispersions in water of a chloromethylstyrene‐functionalized copolymer and a tertiary‐amine‐functionalized copolymer. Upon casting and drying under ambient conditions, the ASCL could generate crosslinked continuous polymer films. The crosslinking occurred via the Menschutkin reaction (quaternization) between the two types of functional groups. Because this reaction was reversible at high temperatures, the films could be decrosslinked and hence were self‐curable. The prepared ASCL exhibited excellent colloidal and chemical stability during long‐term storage: no significant changes in the colloidal properties, such as the particle size, electrophoretic mobility, and crosslinking reactivity, were observed after 48 months of storage. The electrophoretic measurements indicated that the electrostatic repulsion between the negatively charged particles of the ASCL was responsible for the excellent stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2598–2605, 2005

An ambient self-curable latex based on colloidal dispersions in water of two functionalized polymers and the thermally reversible crosslinked films generated

An ambient self-curable latex (ASCL) was prepared by mixing colloidal dispersions in water of a chloromethylstyrene (CMS)-functionalized polymer and a tertiary-amine-functionalized polymer. The two dispersions were obtained via the conventional emulsion copolymerization of CMS and 2-(dimethylamino)ethylacrylate (DMAEA), respectively, with styrene (St), butyl acrylate (BA), or both. No visible coagulation was observed either in the blends after 6 months of storage or after the latexes were introduced into aqueous media with pHs in the range of 3–11. Continuous, transparent, crosslinked elastic films with smooth surfaces were obtained via casting and drying the ASCL at room temperature, when one or both of the two functional polymer particles contained BA monomeric units. Thermocompression cycles; swelling experiments; solubility tests; and 1H NMR, IR, DSC, and transmission electron microscopy tests were carried out to investigate the crosslinking and morphology of the films. The following observations were made: (1) the crosslinks in the films were generated via the Menschutkin reaction (quaternization) between the CH2-Cl groups of the CMS containing particles and the amine groups of the DMAEA containing particles; (2) the crosslinked films were thermally remoldable due to reversible decrosslinking (dequaternization) on heating and recrosslinking (requaternization) on cooling; and (3) phase separation in the films was observed when one of the functional polymers (for instance, the nonpolar CMS-St copolymer) was incompatible with the other one (for instance, the polar BA-DMAEA copolymer). The present ASCL might be useful in producing water-borne coatings and adhesives, elastic films, and functional membranes. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 389–397, 2001

Stabilization of Hydrophobic Colloidal Dispersions in Water with Amphiphilic Polymers: Application to Integral Membrane Proteins

Stabilization of aqueous dispersions of highly hydrophobic colloidal particleshere three integral membrane proteins of nanometric dimensionswere obtained by substituting the classical protective layer of surfactant with low molecular weight amphiphilic polymers (“amphipols”). These polymers, derived from poly(acrylic acid), adsorb onto the particle despite the presence of residual surfactant from the initial stock solutions of proteins. Unbound amphipols and surfactants can be subsequently removed without dissociation of the complex or precipitation. As a consequence of multipoint attachment between the partners, complexation appears irreversible on the time scale of a few hours to a few days. Protein/amphipol complexes contain a much lower number of alkyl groups per particle as compared with classical protein/surfactant complexes. The density of coverage (≈100−200 alkyl groups per particle) increases with the salt concentration of the medium but is not sensitive to pH.

Swelling Equilibrium of Small Polymer Colloids: Influence of Surface Structure and a Size-Dependent Depletion Correction

Small polymer latex particles in the size range 15 nm < R < 100 nm with different types of covalently bound surface stabilizing groups are made via emulsion polymerization using diverse functionalization techniques like incorporation of polar comonomers, surface-active initiators, or polymerizable surfactants. These colloidal dispersions in water are swollen with toluene in the absense of free surfactants until equilibrium swelling is reached. The equilibrium size of the swollen latices is determined by combining densitometry and dynamic light scattering. For all surface groups, we observe a pronounced dependence of the swelling ratio on particle size where absolute values of swelling are much lower than described by classical theories. A modified description is presented which considers size-relevant effects (such as the Kelvin pressure and depletion) by an additional osmotic pressure term which increases with the inverse of the particle size. Other classical effects of colloids such as a size dependence of the thermodynamic interaction parameter or the interface energy can be excluded by quantitative considerations. The presented modified swelling equation describes the experimental data well and is expected to have some broader relevance for swelling phenomena of all colloidal systems. Charge stabilization as compared to steric stabilization results in higher swelling ratios and significant lower values for the interface energy. This underlines the importance of coulombic repulsion between fixed charges on the same particle for the swelling process as well as the existence of a “surface anchoring” effect, both of which are not considered in current concepts of the swelling process, too.