Stable Colloidal Dispersions Research Articles

Synthesis and Characterizations of Highly Efficient Copper Nanoparticles and their Use in Ultra Fast Catalytic Degradation of Organic Dyes

The present study describes synthesis of highly active copper nanoparticles by a green and economically viable approach. The highly stable colloidal dispersions of copper nanoparticles ( Cu NPs) were prepared via modified sodium borohydride reduction route with controlled morphology in a aqueous phase using anionic surfactant, Sodium dodecyl sulfate (SDS), as directing agent and vitamin-C as a Quenching agent. The characterization studies like optimization of various parameters for preparation of nanoscale copper NPs, surface binding interactions, size and morphology of the fabricated Cu NPs were carried out using UV-Visible Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, X-Ray Diffraction (XRD) Analysis and Tunneling Electron Microscopy (TEM). The results of study revealed that CuNPs has ultra fast catalytic activity for the degradation of some frequently used organic dyes such as methylene blue (MB) and rose bengal (RB).

Preparation of a Pseudolatex-Membrane for Ketoprofen Transdermal Drug Delivery Systems

Ethyl cellulose (EC) and deproteinized natural rubber latex (DNRL) were used to prepare a pseudolatex-base as a matrix membrane for ketoprofen patches. The pseudolatex-base was prepared using a homogenization and solvent removal method. Either polyvinyl alcohol or polysorbate 80 was used as surfactant and emulsifier. Polyvinyl pyrrolidone, glycerine, isopropyl palmitate, and dibutyl phthalate were used as a channeling agent, skin humectant, enhancer, and plasticizer, respectively. Ketoprofen was incorporated into the pseudolatex-base. All pseudolatex formulations were homogeneous and smooth in texture and elegant in appearance. The pH of pseudolatex formulations was 5–7, and the particle size was 487–787 nm. The viscosity and spreadability test showed the good characteristics of membrane. Stable colloidal dispersion was formed with a zeta potential of −35.18 to −51.55 mV. All pseudolatex formulations were formed into in situ membranes by solvent evaporation in a hot air oven at 70 ± 2 °C. The mechanical test and moisture uptake were characterized, which significantly depended on ingredient. The in vitro release and skin permeation of ketoprofen from the pseudolatex-membrane were evaluated. The suitable pseudolatex-membrane was produced from a EC:DNRL ratio of 1:1 and provided a controlled release and suitable permeation patterns of the ketoprofen. Thus, these systems are essentially based on a matrix membrane made from polymeric pseudolatex systems.

Self-assembly of poly(ethylene glycol)-block-polypyridine copolymer into micelles and at silica surface: effect of molecular architecture on silica dispersion

We have newly synthesized amphiphilic block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic pyridine segments (PEG-b-Py). Chain transfer agent-terminated PEG was subsequently chain-extended with 3-(4-pyridyl)-propyl acrylate to obtain PEG-b-Py by reversible additional-fragmentation chain transfer polymerization. Particularly, the effect of varying molecular weight (Mn) of PEG (Mn = 2,000 and 5,000) and Py in the block copolymers was investigated in terms of critical micelle concentration, pyrene solubilization, micelle size distribution, and association number per micelle. Based on the amphiphilic balance, PEG-b-Pys formed core-shell type polymer micelle. The association number of PEG2k-b-Py was higher than that of PEG5k-b-Py, suggesting the degree of phase separation strongly depended on PEG Mn. Furthermore, the adsorption of PEG-b-Py copolymer onto silica nanoparticles as dispersant was studied to estimate the effect of PEG Mn in the copolymers and their solubility in the medium on the adsorption. Adsorbed density of PEG2k-b-Py copolymer onto silica nanoparticle was higher than that of PEG5k-b-Py, which was significantly correlated with the degree of phase separation. Furthermore, the adsorbed amount of copolymer increased with the increase in ionic strength due to the reduced solubility of PEG in the buffer solution. The resultant dispersion stability was highly correlated with the graft density of copolymer onto silica surface. However, the stability of PEG2k-b-Py coated particles was lower than that with PEG5k-b-Py, this is attributed to the relatively thin layer of PEG at the silica surface, which cannot provide the system with sufficient steric stabilization as the salt concentration increases. These fundamental investigations for the surface modification of the nanoparticle provide the insight into the highly stable colloidal dispersion, particularly in the physiological condition with high ionic strength.

Surfactant-free synthesis of graphene-functionalized carbon nanotube film as a catalytic counter electrode in dye-sensitized solar cells

We use graphene oxide (GO) as a “surfactant” to obtain stable colloidal dispersion of carbon nanotubes (CNTs). CNT films are subsequently synthesized successfully without the addition of any traditional surfactants. Dye-sensitized solar cells assembled using the resulting CNT film as a counter electrode deliver a power conversion efficiency up to 5.29%. More importantly, the additional reduced graphene oxide significantly increases the electrical conductivity and the catalytic activity of the CNT film. The cell performance using a CNT film counter electrode (5.29%) reaches 68.70% of that of cells prepared using a platinum film counter electrode (7.70%).

Conductive, Monodisperse Polyaniline Nanofibers of Controlled Length Using Well‐Defined Cylindrical Block Copolymer Micelles as Templates

Stable colloidal dispersions of polyaniline (PAni) nanofibers with controlled lengths from about 200 nm-1.1 μm and narrow length distributions (Lw/Ln < 1.04; Lw = weight average micelle length, Ln = number average micelle length) were prepared through the template-directed synthesis of PAni using monodisperse, solution-self-assembled, cylindrical, block copolymer micelles as nanoscale templates. These micelles were prepared through a crystallization-driven living self-assembly method from a poly(ferrocenyldimethylsilane)-b-poly(2-vinylpyridine) block copolymer (PFS25 -b-P2VP425). This material was initially self-assembled in iPrOH to form cylindrical micelles with a crystalline PFS core and a P2VP corona and lengths of up to several micrometers. Sonication of this sample then yielded short cylinders with average lengths of 90 nm and a broad length distribution (Lw/Ln = 1.32). Cylindrical micelles of PFS25 -b-P2VP425 with controlled lengths and narrow length distributions (Lw/Ln < 1.04) were subsequently prepared using thermal treatment at specific temperatures between 83.5 and 92.0 °C using a 1D self-seeding process. These samples were then employed in the template-directed synthesis of PAni nanofibers through a two-step procedure, where the micellar template was initially stabilised by deposition of an oligoaniline coating followed by addition of a polymeric acid dopant, resulting in PAni nanofibers in the emeraldine salt (ES) state. The ES-PAni nanofibers were shown to be conductive by scanning conductance microscopy, whereas the precursor PFS25-b-P2VP425 micelle templates were found to be dielectric in character.

Stable colloidal dispersion of functionalized reduced graphene oxide in aqueous medium for transparent conductive film

We prepared stable colloidal suspension graphene in aqueous medium by surface modification of graphene with 4-benzenediazonium sulfonate. The sulfonate group on graphene surface interacts with water, exhibits well dispersibility and which prevents the aggregation even at neutral pH. This dispersion shows stability for three months and facile to produce films. Using such a modified graphene dispersion, transparent conductive film (TCF) has been fabricated on glass substrate by spin coating method. At appropriate concentration, the film exhibits an excellent optoelectrical property with resistivity of 1.1kΩ with the transparency of 89% at the wavelength of 550nm. Further, we also demonstrated the mechanical, thermal, and optoelectrical properties of prepared films.

Hydrophobic agglomeration of colloidal kaolinite in aqueous suspensions with dodecylamine

The stability of colloidal kaolinite dispersions in the presence of dodecylamine (DDA) has been studied in this work through the measurements of aggregation degree, zeta potential and adsorption. The experimental results show that DDA can induce a strong aggregation of colloidal kaolinite in aqueous suspensions even though the particles are highly negatively charged. This aggregation closely correlated to the adsorption of DDA cation on kaolinite surfaces and the hydrophobicity, so that it should belong to hydrophobic agglomeration. The adsorption isotherm of DDA on kaolinite surfaces showed two regions in which the adsorption density sharply increased, which might correspond to the hemi-micelle and bilayer adsorption of DDA cation on the surfaces. In addition, the hydrophobic agglomeration could be weakened by the addition of NaCl, which was due to the decrease of DDA adsorption on kaolinite surfaces.

Dispersion Stability and Electrokinetic Properties of Intrinsic Plutonium Colloids: Implications for Subsurface Transport

Subsurface transport of plutonium (Pu) may be facilitated by the formation of intrinsic Pu colloids. While this colloid-facilitated transport is largely governed by the electrokinetic properties and dispersion stability (resistance to aggregation) of the colloids, reported experimental data is scarce. Here, we quantify the dependence of ζ-potential of intrinsic Pu(IV) colloids on pH and their aggregation rate on ionic strength. Results indicate an isoelectric point of pH 8.6 and a critical coagulation concentration of 0.1 M of 1:1 electrolyte at pH 11.4. The ζ-potential/pH dependence of the Pu(IV) colloids is similar to that of goethite and hematite colloids. Colloid interaction energy calculations using these values reveal an effective Hamaker constant of the intrinsic Pu(IV) colloids in water of 1.85 × 10(-19) J, corresponding to a relative permittivity of 6.21 and refractive index of 2.33, in agreement with first principles calculations. This relatively high Hamaker constant combined with the positive charge of Pu(IV) colloids under typical groundwater aquifer conditions led to two contradicting hypotheses: (a) the Pu(IV) colloids will exhibit significant aggregation and deposition, leading to a negligible subsurface transport or (b) the Pu(IV) colloids will associate with the relatively stable native groundwater colloids, leading to a considerable subsurface transport. Packed column transport experiments supported the second hypothesis.

Facile synthesis of reduced graphene oxide nanosheets by a sodium diphenylamine sulfonate reduction process and its electrochemical property

We report a new method to convert graphene oxide (GO) to stable colloidal dispersion of reduced graphene oxide nanosheets (RGONS) using sodium diphenylamine sulfonate (SDAS) as a reductant, as well as itself and its redox product as the stabilizer. The as-prepared RGONS have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, thermo-gravimetric analysis, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and Raman spectroscopy. The results indicate that the bulk of oxygen-containing functional groups from GO have been removed. Based on the cyclic voltammogram (CV) analyses, it is found that the RGONS-based material exhibits better electrochemical activity in sensing ascorbic acid than GO. The simple method provides a new efficient route for the synthesis of water-soluble RGONS on a large scale and novel composites.

Influence of emulsifiers on the characteristics of polyurethane structures used as drug carrier

BackgroundEmulsifiers have a significant role in the emulsion polymerization by reducing the interfacial tension thus increasing the stability of colloidal dispersions of polymer nanostructures. This study evaluates the impact of four emulsifiers on the characteristics of polyurethane hollow structures used as drug delivery system.ResultsPolyurethane (PU) structures with high stability and sizes ranging from nano- to micro-scale were obtained by interfacial polyaddition combined with spontaneous emulsification. The pH of PU aqueous solutions (0.1% w/w) was slightly acidic, which is acceptable for products intended to be used on human skin. Agglomerated structures with irregular shapes were observed by scanning electron microscopy. The synthesized structures have melting points between 245-265°C and reveal promising results in different evaluations (TEWL, mexametry) on murine skin.ConclusionsIn this study hollow PU structures of reduced noxiousness were synthesized, their size and stability being influenced by emulsifiers. Such structures could be used in the pharmaceutical field as future drug delivery systems.

Size- and Shape-Controlled Syntheses of Colloidal Sn, Te, and Bi Nanocrystals

Abstract We report the synthesis of monodisperse spherical Sn nanocrystals 9.0 nm in size by reduction of SnCl2 using tetrabutylammonium borohydride (TBBH, N(C4H9)4BH4) in a one-pot synthesis using a mixed solvent of oleylamine (OA, C18H35NH2) as a capping agent and tetrahydrofuran (THF). The size and shape of the Sn nanocrystals were found to be influenced by both the amount of OA and THF used and the synthetic temperature. The particle sizes varied from 9 to 83 nm. Spherical nanocrystals were formed at a particular initial concentration of OA, while rod-shaped nanocrystals were formed at reduced initial concentrations of OA. The Sn nanocrystals are used as a bonding material by mixing Cu nanocrystals. The shear strength of Cu plates bonded by the mixture of Cu and Sn nanocrystals at higher than 300 °C is significantly increased, compared with that bonded by Cu nanocrystals without addition of the Sn nanocrystals. The synthetic method was also applied to the synthesis of Te and Bi nanocrystals. The shapes of the Te and Bi nanocrystals were similarly controlled by the amount of OA used and the synthetic temperature. All of the samples were obtained as stable colloidal dispersions.

Aqueous Dispersible Graphene/Pt Nanohybrids by Green Chemistry: Application as Cathodes for Dye-Sensitized Solar Cells

Aqueous dispersible nanohybrids (NHBs) of graphene nanosheets (GNSs) and Pt nanoparticles (Pt-NPs) were synthesized through the one-pot reduction of their precursors using an environmentally benign chemical, vitamin C. The concurrent reduction of the precursors, which includes graphene oxide (GO) to GNS and H2PtCl6 to Pt(0), was facile and efficient to yield GNS/Pt-NHBs in which face-centered cubic (fcc) crystalline Pt-NPs with average diameters of ~5 nm were robustly attached on the surface of the GNSs. The conversion yield during Pt reduction was fairly high (∼90%) and the Pt content within the NHBs was easily controllable. The resulting stable aqueous colloidal dispersion of GNS/Pt-NHBs was successfully fabricated as thin films without using any binder by the electro-spray method at room temperature, and the fabricated samples were used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The electrocatalytic activity of the NHBs for I(-)/I3(-) redox couples in conventional DSSCs was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis. Doping of GNSs with small amounts of Pt-NPs (<10 wt %) could dramatically enhance the redox kinetics. The enhanced electrocatalytic activity of the GNS/Pt-NHBs was reflected in the performance of the DSSCs. The power conversion efficiency of optimized DSSCs using the NHB-CEs was 8.91% (VOC: 830 mV, JSC: 15.56 mAcm(-2), and FF: 69%), which is comparable to that of devices using the state-of-the-art Pt-based CEs (8.85%).

Chitosan-graft-β-cyclodextrin nanoparticles as a carrier for controlled drug release

Chitosan (CS) grafted with β-cyclodextrin (CD-g-CS) nanoparticles as a new carrier for poorly water-soluble drugs has been developed. The CD-g-CS polymer is readily synthesized from chitosan and mono-6-deoxy-6-(p-toluenesulfonyl)-β-cyclodextrin. Three different degrees of substitution (DS) of β-cyclodextrin (β-CD) on CD-g-CS (9.6, 14.0 and 20.0%) are designed and evaluated by controlling the mole ratio of β-CD to chitosan. Then CD-g-CS nanoparticles are prepared by an ionic gelation method, with the controlled size of 202.0-589.0 nm. Stable colloidal dispersion of the nanoparticles has been formed with the zeta potential of +23.0 to +43.0 mV. In vitro stability test indicates that CD-g-CS nanoparticles are more stable in phosphate-buffered saline compared with CS nanoparticles. Finally, the poorly water-soluble drug, ketoprofen (KTP), is used as a model drug to evaluate the efficiency of the new drug delivery carrier. It is found that the encapsulation efficiency of KTP in the nanoparticles with 20% DS of CD is as high as 1.36-fold than that of CS nanoparticles. Moreover, notably KTP is released from the nanoparticles in a controlled-release manner and is pH-responsive on DS of CD. In summary, these results suggest that the CD-g-CS nanoparticles, as a general promising drug delivery system, can be used as a potential biodegradable nano-drug delivery system for controlled release of poorly water-soluble drugs with pH-responsive capability.

Stable colloidal boron nitride nanosheet dispersion and its potential application in catalysis

Hexagonal boron nitride (h-BN) nanosheets, a promising layered material, have drawn more and more attention in recent years. In this study, a simple method has been developed to prepare stable colloidal h-BN nanosheet dispersion with high concentration in ethylene glycol based on the matching of the surface energies of h-BN and the surface tension of the solvent. It is found that bulk h-BN can be directly exfoliated and dispersed in ethylene glycol solvent with the assistance of sonication to form stable h-BN nanosheets with a few layers. Furthermore, the stable colloidal h-BN nanosheets have been demonstrated to be good carriers to support and disperse noble metal nanoparticles such as Ag, Au, and Pt with high catalytic activity for the reduction of p-nitrophenol. Our results suggest that stable colloidal h-BN dispersion with high concentration in ethylene glycol could open the way to a range of important applications of h-BN based materials.

Controlled reshaping and plasmon tuning mechanism of gold nanostars

Anisotropic multi-branched gold nanoparticles exhibit intense localized electromagnetic fields at their tips/edges and hence have attracted significant attention in surface enhanced Raman scattering (SERS), as well as in bio-sensing applications. Our quest for such complex hyper-branching in gold nanostructures has revealed that even the addition of a simple base (like NaOH) to the precursor reaction mixture enhances the fine tuning/reshaping of the 3D star/flower-like gold nanostars with controlled precision right from the nucleation stage. With increasing the basicity of the reaction mixture, the two strongly localized surface plasmon resonance (LSPR) peaks of the gold nanostars essentially merge into a broad singular peak, effectively indicating the steady transition from (non)planar structures to conventional spheroidal nanostructures, as confirmed by the transmission electron microscopy (TEM) measurements. Such pH induced size/shape transitions of gold nanostructures were monitored kinetically in detail through correlated molecular spectroscopic measurements nuclear magnetic resonance, fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy (NMR, FTIR and XPS), for the first time to the best of our knowledge, which ascertains a rational paradigm in better understanding the complex polyvinylpyrrolidone (PVP) functionality for its simultaneous reducing, as well as stabilizing action, in precisely controlling the anisotropic gold nanostructure growth mechanism and further exploiting this functionality in utilizing these as-formed extremely stable colloidal gold dispersions for various specific plasmonic applications.

Formation of one-dimensional Ag–Au solid solution colloids with Au nanorods as seeds, their alloying mechanisms, and surface plasmon resonances

In this work, one dimensional (1D) Ag-Au solid solution nanoalloys were synthesized by rapidly diffusing Ag into the preformed Au nanorod (AuNR) seeds at ambient temperature in aqueous solution. By varying the molar ratio of AgCl/AuNR (in gold atoms), two kinds of 1D Ag-Au alloy nanostructures with a narrow size distribution--AgAu nanowires and Ag(33)Au(67) nanorods--could be obtained in high yields when NaCl and polyvinylpyrrolidone (PVP) were used as an additive and capping reagent, respectively. Based on HRTEM imaging combined with a series of control experiments, it is conceivable that vacancy/defect-motivated interdiffusion of Ag and Au atoms coupled with oxidative etching is a crucial stage in the mechanism responsible for this room-temperature alloying process, and the subsequent conjugation of the fused Ag-Au alloyed nanostructures is associated with the formation of the AgAu nanowires. The resulting 1D Ag-Au nanoalloys form stable colloidal dispersions and show unique localized surface plasmon resonance (LSPR) peaks in the ensemble extinction spectra.

Facile synthesis of pyridopyrimidine and coumarin fused pyridine libraries over a Lewis base-surfactant-combined catalyst TEOA in aqueous medium

A highly convergent and efficient protocol, for the facile synthesis of a library of coumarin fused pyridine and pyridopyrimidine derivatives, has been developed by applying a Lewis base-surfactant-combined catalyst (LBSC) triethanolamine (TEOA). The method described has the benefits of operational simplicity and excellent yields of the targeted molecule. The LBSCs were found to form stable colloidal dispersions rapidly in the presence of reaction substrates in water, even when the substrates are solid. In light of the increased demand for reduction of organic solvents in industry, the surfactant aided Lewis base catalysis described here may have immense practical consequences in organic synthesis. This work may not only lead to environmentally benign systems but also will provide a newer aspect of organic chemistry in water.

Dynamic Light Scattering Based Microelectrophoresis: Main Prospects and Limitations

Microelectrophoresis based on the dynamic light scattering (DLS) effect has been a major tool for assessing and controlling the conditions for stability of colloidal systems. However, both the DLS methods for characterization of the hydrodynamic size of dispersed submicron particles and the theory behind the electrokinetic phenomena are associated with fundamental and practical approximations that limit their sensitivity and information output. Some of these fundamental limitations, including the spherical approximation of DLS measurements and an inability of microelectrophoretic analyses of colloidal systems to detect discrete charges and differ between differently charged particle surfaces due to rotational diffusion and particle orientation averaging, are revisited in this work. Along with that, the main prospects of these two analytical methods are mentioned. A detailed review of the role of zeta potential in processes of biochemical nature is given too. It is argued that although zeta potential has been used as one of the main parameters in controlling the stability of colloidal dispersions, its application potentials are much broader. Manipulating surface charges of interacting species in designing complex soft matter morphologies using the concept of zeta potential, intensively investigated recently, is given as one of the examples. Branching out from the field of colloid chemistry, DLS and zeta potential analyses are now increasingly finding application in drug delivery, biotechnologies, physical chemistry of nanoscale phenomena and other research fields that stand on the frontier of the contemporary science. Coupling the DLS-based microelectrophoretic systems with complementary characterization methods is mentioned as one of the prosperous paths for increasing the information output of these two analytical techniques.

Evaluation of particle interactions by in situ visualization of separation behaviour

Dispersion based products have applications in every area of life. During formulation of new products the dispersion properties have to be adjusted to obtain the desired stability, textural and rheological properties. Most often stable colloidal dispersions are required, sometime however, weak flocculation is purposely induced to adjust structural properties. In other cases strong flocculation is helpful for dispersion separation. From this it is evident that classification of the state of a dispersion regarding flocculation (net attractive particle interaction) and quantification of its degree are necessary and routine tasks in every day formulation and optimization work. Zeta potential is commonly used to predict the stability of virtually all colloidal dispersions. This neglects that the Zeta potential concept is limited to classical electrostatically stabilized dispersions. It has to be emphasized, however, that nowadays new dispersion products are stabilized by different approaches (e.g. by steric or rheological stabilization).Sedimentation analysis by multisample analytical centrifugation with photometric detection is a rather simple but powerful and high throughput method to characterize the dispersed state/degree of particle interaction. Visualization of in situ separation behaviour allows for the classification and differentiation between the various instability phenomena such as swarm sedimentation (stable dispersion) and zone sedimentation (flocculation, agglomeration). Even more, complex systems with subfractions of particles exhibiting a different behaviour can also be analyzed.Sedimentation behaviour of different dispersions made from plain or decorated nanoparticles as a function of pH of the continuous phase is presented and analyzed in terms of the degree and type of flocculation and compared with predictions based on Zeta potential data. Results demonstrate that contrary to measured Zeta potential the colloidal stability of the dispersed particles and the degree of particle flocculation/agglomeration were always well predicted by the sedimentation behaviour. This new approach can also be applied for soft particles and dispersion media regardless of their polarity.

Use of TX100-dangled epoxy as a reactive noncovalent dispersant of vapor-grown carbon nanofibers in an aqueous solution

The dispersion of carbon nanotubes (CNTs) into individual particles or small bundles has remained a vexing problem that limits the use of the excellent properties of CNTs in composite applications. Noncovalent functionalization is an attractive option for changing the interfacial properties of nanotubes because it does not destroy the nanotube grapheme structure. In this study, a new reactive copolymer, epoxy-toluene diisocyanate-Triton X-100 (EP-TDI-TX100) was successfully synthesized, which is shown to be highly effective in dispersing vapor-grown carbon nanofibers (VGCNFs) into individual or small bundles, as evidenced by transmission electron microscopy (TEM) and UV–vis absorption spectra. The strong π–π interaction between VGCNFs and EP-TDI-TX100 was revealed by Raman spectra and the covalent reaction between curing agent was confirmed via Fourier transform infrared spectroscopy. For an effective dispersion, the optimum weight ratio of EP-TDI-TX100 to VGCNFs is 2:1. The maximum VGCNF concentration that can be homogeneously dispersed in an aqueous solution is approximately 0.64mg/mL. The EP-TDI-TX100 molecules are adsorbed on the VGCNF surface and prevent reaggregation of VGCNFs, so that a colloidal stability of VGCNF dispersion can be maintained for 6months.