SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Journal of colloid and interface science

28

ZnO nanorods were grown on microfibers of Polyethylene terephthalate (PET) fabric by seeding method to develop hierarchical roughness structure. XRD and XPS analysis show the presence of crystalline ZnO and chemical Zn species at the fiber surface at each stage of the process. Five series of samples with different seed concentrations have been realized, and their surface morphology and topography were characterized by AFM and SEM. Increasing seed concentrations lead to samples with superhydrophilic properties. Not only the water contact angle at fabric surface tends to zero but also the water capillary diffusion inside fabric is faster. Nanostructuration affects the structure inside the fabric, and further experiments with decane liquid have been made to get a better understanding of this effect. To study the superhydrophobicity, nanorods treated samples were modified with octadecyltrimethoxysilane (ODS) by two method; solution deposition and vapor deposition. The superhydrophobicity was characterized by measuring the water contact angle and water sliding angle with 5μl water droplet. The samples modified with ODS by vapor deposition showed higher water contact angles and low water sliding angle than the ones modified with solution method. The lotus effect has been well correlated with the surface morphology of the nanorods structured fibers. The application of the Cassie-Baxter equation is discussed.

Concepts: Chemistry, Zinc, Liquid, Surface tension, Angle, Zinc oxide, Polyester, Contact angle

28

A model for the limiting surface tension of surfactant solutions (surface tension at and above the critical micelle concentration, cmc) was developed. This model takes advantage of the equilibrium between the surfactant molecules on the liquid/vacuum surface and in micelles in the bulk at the cmc. An approximate analytical equation for the surface tension at the cmc was obtained. The derived equation contains two parameters, which characterize the intermolecular interactions in the micelles, and the third parameter, which is the surface area per surfactant molecule at the interface. These parameters were calculated using a new atomistic modeling approach. The performed calculations of the limiting surface tension for four simple surfactants show good agreement with experimental data (∼30% accuracy). The developed model provides the guidance for design of surfactants with low surface tension values.

Concepts: Chemistry, Surface tension, Surfactant, Micelle, Quaternary ammonium cation, Solution, Macromolecule, Colloidal chemistry

28

Well-aligned CdS nanorod arrays (CdS NRs) with ∼100nm in diameter and ∼700nm in length were fabricated on FTO (fluorine-doped tin oxide) substrate by using glutathione as capping agents. The growth of CdS NRs was studied in details by exploring the roles of each active binding group in glutathione. The thiol group in glutathione plays an important role in forming a compact CdS nanocrystal film, upon which the nanorods grow subsequently via the synergetic effect of thiol and dicarboxyl groups in glutathione. The influence of surface passivation with glutathione on the photoelectrical property of CdS NRs was also tested. The results revealed that glutathione ligands encapsulated in the surfaces of CdS NRs act as insulating barriers between CdS NRs and solution, hindering charge transport. Hybrid photovoltaic cells of FTO/CdS NRs/P3HT (poly(3-hexylthiophene))/Au were then assembled. The performance of the photovoltaic devices was increased with increasing the length of the as-prepared CdS nanorods and further enhanced to the highest efficiency of 0.373% after the thermal sulfuration treatment.

Concepts: Zinc, Disulfide bond, Sulfur, Cadmium, Photovoltaics, Cysteine, Thiol, Cadmium sulfide

28

The structure of solubilized water in water-in-n-heptane aggregates stabilized by mixtures of single- and double-tail quaternary ammonium surfactants, namely didodecyldimethylammonium chloride/dodecyltrimethylammonium chloride (DDAC/DTAC) or didodecyldimethylammonium bromide/dodecyltrimethylammonium bromide (DDAB/DTAB) was studied by two noninvasive techniques, (1)H NMR and FT-IR. In the former, the chemical shift data, δ(obs), were used to calculate the so-called deuterium/protium fractionation factor, φ(M), of the aggregate-solubilized water and were found to be unity. In the FT-IR study, upon increasing water/surfactant molar ratio, W, the frequency, ν(OD), of the HOD species decreases, while its full width at half height and its area increase. The results obtained from both techniques indicate that the water appears to be present as a single nano-phase and the structure varies continuously as a result of increasing W. In addition, the effect of changing the counter-ion (Br(-) or Cl(-)) on (1)H NMR and FT-IR results was investigated. In spite of the known difference in the dissociation of these counter-ions from micellar aggregates, this was found not to affect the state of solubilized water. This report gives further insight into the contradictory scientific debates on the structure of water in the polar nano-cores of microemulsions.

Concepts: Nuclear magnetic resonance, Addition, Emulsion, Surfactant, Micelle, Quaternary ammonium cation, Cocamidopropyl betaine, Fabric softener

28

The overarching goal of this feature article is to review the recent developments in the field of drug delivery specifically involving colloidal lyotropic liquid crystalline dispersions. The development of advanced particles for drug delivery applications is regarded as the next necessary step in the advancement of nanomedicine. An outline of the state of the art in preparation and application of self-assembled nanoparticles to drug delivery and medical imaging is presented. The basic concepts for controlling the nature of the internal structure of particles by tuning the self-assembly properties of small molecule amphiphiles is covered. Theranostics is an exciting emerging area for this colloidal material class, and the types of therapeutic compounds and medical imaging agents that can be incorporated as well as their methods of preparation are described. The stabilisation and biocompatibility of the colloidal dispersions are also discussed. Finally an overview of lesion-specific active and passive targeting is presented. Exploiting such a multi-functional drug delivery platform is essential to not only the next generation delivery of bioactive molecules but also in the creation of new diagnostic tools.

Concepts: Medicine, Molecule, Chemistry, Nanotechnology, Colloid, Liquid crystal, Lyotropic liquid crystal

28

TiO(2) nanospheres with diameters mostly in the range of 20-200nm are prepared by using cathodic plasma electrolysis at low voltage of 70V. It is found that the low voltage could efficiently depress the particle sizes and their distribution, and result in more anatase phases. The nanospheres have an excellent optical absorption from 240nm to 2600nm.

Concepts: Electron, Photon, Magnesium, Solar cell, Titanium dioxide, Chlorine, High voltage, Rutile

28

The time-evolutions of nanoparticle hydrodynamic radius and aggregate fractal dimension during the aggregation of fullerene (C(60)) nanoparticles (FNPs) were measured via simultaneous multiangle static and dynamic light scattering. The FNP aggregation behavior was determined as a function of monovalent (NaCl) and divalent (CaCl(2)) electrolyte concentration, and the impact of addition of dissolved natural organic matter (humic acid) to the solution was also investigated. In the absence of humic acid, the fractal dimension decreased over time with monovalent and divalent salts, suggesting that aggregates become slightly more open and less compact as they grow. Although the aggregates become slightly more open, the magnitude of the fractal dimension suggests intermediate aggregation between the diffusion- and reaction-limited regimes. We observed different aggregation behavior with monovalent and divalent salts upon the addition of humic acid to the solution. For NaCl-induced aggregation, the introduction of humic acid significantly suppressed the aggregation rate of FNPs at NaCl concentrations lower than 150mM. In this case, the aggregation was intermediate or reaction-limited even at NaCl concentrations as high as 500mM, giving rise to aggregates with a fractal dimension of 2.0. For CaCl(2)-induced aggregation, the introduction of humic acid enhanced the aggregation of FNPs at CaCl(2) concentrations greater than about 5mM due to calcium complexation and bridging effects. Humic acid also had an impact on the FNP aggregate structure in the presence of CaCl(2), resulting in a fractal dimension of 1.6 for the diffusion-limited aggregation regime. Our results with CaCl(2) indicate that in the presence of humic acid, FNP aggregates have a more open and loose structure than in the absence of humic acid. The aggregation results presented in this paper have important implications for the transport, chemical reactivity, and toxicity of engineered nanoparticles in aquatic environments.

Concepts: Chemistry, Soil, Aggregate, Aggregate data, Light scattering, Humus, Natural organic matter, Fractal

28

Uric acid, the major component in many kinds of kidney stones, as well as its sodium, ammonium, calcium, and barium salts were successfully prepared as uniform dispersions by precipitation in basic aqueous solutions. The effects of the reactant concentrations, pH, and the stabilizers were evaluated in detail. Except for the platelets of the pure acid, all prepared compounds appeared as needles or their aggregates. The electron micrographs showed that kidney stones consisted of such aggregates although less regular in size and morphology. All prepared urate salts had a 1:1 cation/uric acid ratio, regardless of the valence of the cation. The electrokinetic measurements showed all these particles to have negative ζ-potentials over the pH range 3-9. The precipitated salt particles were chemically and morphologically unstable at low pH values by decomposing into ill-defined aggregates of the pure uric acid.

Concepts: Ammonia, Water, Chemistry, Nitrogen, PH, Sodium, Uric acid, Kidney stone

28

The concept of hydrophilic/CO(2)-philic balance (HCB) was extended to describe stabilization of carbon dioxide-in-water (C/W) foams (also called emulsions) with silica nanoparticles adsorbed at the CO(2)-water interface. Opaque, white C/W foams (bubble diameter <100 μm) were generated with either PEG-coated silica or methylsilyl modified silica nanoparticles in a beadpack with CO(2) densities between 0.2 and 0.9 g mL(-1). For methylsilyl modified silica nanoparticles, 50% SiOH modification provided an optimal HCB for generation and stabilization of viscous C/W foams with high stability. The apparent viscosity measured with a capillary tube viscometer reached 120-fold that of a CO(2)-water mixture without nanoparticles, a consequence of the small bubble size and the energy required to deform a high density of aqueous lamellae between CO(2) bubbles. Air-in-water (A/W) foams stabilized with nanoparticles were used to gain insight into the relationship between nanoparticle surface properties and adsorption of the nanoparticles at various types of interfaces. With suitable nanoparticles, A/W foams were stable for at least 7 days and C/W foams were stable for at least 23 h. The ability to achieve long term stability for nanoparticle stabilized C/W foams could offer an alternative to conventional surfactants, which are known to have much lower adsorption energies.

Concepts: Nanoparticle, Water, Colloid, Silicon, Viscosity, Liquid, Surface tension, Non-Newtonian fluid

28

A high resolution interferometric technique was used to determine swelling behavior of weakly charged polyacrylamide hydrogels in the presence of oppositely charged surfactants and subsequent exposure to cyclodextrins. Hydrogels of copolymerized acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid (0.22, 0.44, 0.88 mol%) crosslinked with bisacrylamide (3, 6, 12 mol%) were employed. The equilibrium swelling and swelling kinetics of the hydrogels were determined with 2nm resolution of the optical length and sampled at approximately 1 Hz. These properties were determined for the hydrogels exposed to cationic surfactants dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB) at concentrations from 10(-7) up to 2×10(-3)M. The distribution of surfactant within one AAM-co-AMPSA hydrogel equilibrated in CTAB/perylene solution was investigated by confocal laser scanning microscopy. Hydrogels equilibrated at selected surfactant concentrations were subsequently exposed to cyclodextrins (α-CD, β-CD, methyl-β-CD and γ-CD) forming inclusion complexes with the surfactants. The results show different types of behavior for the two surfactants used, arising from the difference in the length of surfactant hydrophobic tail. The changes in the surfactant induced swelling of the hydrogels are suggested to arise from the net effect of electrostatic screening of sulfonic acid-amide group interactions and surfactant micellization. Hydrogels with the largest charge density and the lowest crosslink density yielded the most pronounced changes in swelling properties on exposure to DTAB or CTAB. The hydrogels displayed swelling kinetics on stepwise changes in surfactant concentrations that depended on the surfactant concentration range. The high resolution monitoring of hydrogel swelling associated with supramolecular complex formation in three-component systems hydrogel-amphiphilic molecule-cyclodextrin provides more details on the swelling behavior than previously disclosed.

Concepts: Electric charge, Supramolecular chemistry, Surfactant, Micelle, Solution, Pulmonary surfactant