Aqueous Nanoparticle Dispersions Research Articles

Efficacy of SiO2 nanofluids in a miniature plate heat exchanger with undulated surface

In a variety of applications, there is a clear need for an efficient and reliable heat management of high heat flux densities. In this study a miniature Plate Heat Exchanger (PHE) with modulated surface along with nanofluids used as working liquids is proposed aiming for a more compact and efficient cooling equipment for low-temperature applications. The suggested working fluid is a nanofluid, i.e. a 1% v/v aqueous dispersion of SiO2 nanoparticles, which we have proved that can enhance heat transfer rate up to 35% compared to water. Relevant CFD simulations, also conducted during this study, have shown that for a given operating temperature less cooling liquid and consequently less pumping power is needed when this nanofluid is used instead of water. As the SiO2 nanoparticles are relatively inexpensive and their nanofluids are easy to prepare, their use appears to be an attractive solution for mini-scale devices or low-power applications.

A Facile Approach to Monodisperse Au Nanoparticles on Fe3O4 Nanostructures with Surface Plasmon Resonance Amplification.

Composite magnetic nanoparticles, Fe3O4@Au, were synthesized in an aqueous phase via reducing gold chloride acid (HAuCl4) in-situ on (3-aminopropyl) triethoxysilane layer around Fe3O4 nanostructures. Connection between gold and Fe3O4 was confirmed by the magnetic separa- tion technique and X-ray diffraction (XRD). Transmission electron microscopy (TEM) observation revealed that the gold nanoparticles were dispersed on the surface of magnetic Fe3O4 nanoparticles. Significantly, aqueous dispersion of such composite nanoparticles exhibited surface plasmon of Au nanoparticles. The composite magnetic nanoparticles were then modified with 3-mercaptopropionic via an Au-S bond. These ligand-modified nanoparticles were facilely conjugated to anti-penicillin antibody. The resulting Fe3O4@Au-antibody conjugates were successfully used as a powerful sandwich element and an excellent amplification reagent for surface plasmon resonance based sandwich immunoassay. By the amplification effect of Fe3O4 @ Au-antibody conjugates, there was a nearly 30-fold increase in signal and penicillin in aqueous solution was detected at a lowest detection limit of 5 ng/ml. The biological properties of the Fe3O4@Au-antibody conjugates were investigated by Western Blotting. To our knowledge, this is the first report on the in-situ synthesis of monodisperse Au nanoparticles on Fe3O4 magnetic nanostructures in an aqueous solution with surface plasmon resonance amplification.

Synthesis and surface modification of cobalt nanoparticles and electromagnetic property of Co/PPy nanocomposites

In this work, cobalt nanoparticles were synthesized by chemical reduction procedure. After the hydrophilic functionalization, Co/polypyrrole (PPy) nanocomposites were prepared by in situ polymerization of pyrrole in aqueous dispersion of Co nanoparticles. The Co/PPy nanocomposites show good electromagnetic properties with both magnetic loss and dielectric loss to electromagnetic wave. The electromagnetic wave absorbing bandwidth (reflection loss <−10 dB) for Co/PPy (20 wt%) is above 5.5 GHz at a thickness of 2 mm, and with a maximum reflection loss (around −20.02 dB) at 14.77 GHz. This magnetic nanoparticles/conducting polymer nanocomposites are great potential candidates for electromagnetic wave absorbent, because of their wide-absorbing frequency, strong absorption, good compatibility, low density, and controllable absorbing properties.

Effect of structure of cationic comb copolymers on their adsorption and stabilization of titania nanoparticles.

Cationic linear polymer poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride) p(METAC), neutral brush polymer poly(poly(ethylene glycol) methyl ether methacrylate) p(PEO22MEMA), and cationic comb copolymers p(METAC-PEO(x)MEMA) were used for the stabilization of titania dispersions under neutral and alkaline conditions. Random comb copolymers p(METAC-PEO(x)MEMA) differing in charge density and length of PEO side chains were synthesized by RAFT. The adsorption of cationic polymers on titania nanoparticles was evaluated by thermogravimetric analysis; changes in surface potential, by measuring the zeta potential; and the stability of the treated TiO2 dispersions, by laser diffraction and DLS. Cationic linear and comb copolymers containing relatively short PEO side chains promoted the inversion of nanoparticle surface potential from strongly negative (-60 mV) to moderately positive (10-35 mV). Cationic comb copolymers containing longer PEO side chains increased the zeta potential of the treated nanoparticles but did not invert it to positive. Aqueous dispersions of titania nanoparticles stabilized by cationic comb copolymers under alkaline conditions (pH 10) were dispersed by high-energy planetary ball milling up to a primary particle size of 20 nm and were stable for at least 2 days.

Use of an exposure chamber to maintain aqueous phase nanoparticle dispersions for improved toxicity testing in fish.

A novel chamber for maintaining aqueous phase dispersions of nanoparticles (NPs) to enable improved toxicity testing in larval zebrafish was developed. Aqueous concentrations were within 80% of initial NP concentrations, and the 96-h median lethal concentration (LC50) values were highly reproducible (coefficient of variation <0.16, n = 3 tests). Significantly lower toxicity for each NP tested (Ag, Cu, and TiO2 NPs) in static beakers suggested that traditional acute toxicity tests may underestimate aqueous phase toxicity of NPs.

Feasibility of the development of reference materials for the detection of Ag nanoparticles in food: neat dispersions and spiked chicken meat

The feasibility of producing colloidal silver nanoparticle reference materials and silver nanoparticle spiked reference matrix materials was investigated. Two concentrations of PVP-coated silver nanoparticle dispersions were evaluated and used to spike chicken meat, with the aim of producing a set of reference materials to support the development of analytical methods for the detection and quantification of nanoparticles in food. Aqueous silver nanoparticle (AgNP) dispersions were evaluated for their homogeneity of mass fraction and particle size and found sufficiently homogeneous to be used as reference materials. Stability studies at 4 °C, 18 °C and 60 °C demonstrated sufficient short- and long-term stability, although particle size decreases in a linear fashion at 60 °C. The AgNP dispersions were characterized for total Ag mass fraction by ICP-OES, dissolved Ag content by ultrafiltration-ICP-MS, as well as AgNP particle size by dynamic light scattering, transmission electron microscopy (TEM) and gas-phase electrophoretic molecular mobility analysis. Chicken breasts were homogenized by cryo-milling and spiked with aqueous AgNP dispersions. Rapid freezing over liquid nitrogen resulted in homogeneous and stable materials. The spiked chicken materials were characterized for their total Ag mass fraction by neutron activation analysis and for the AgNP particle size by TEM and single-particle inductively coupled plasma mass spectrometry. The observed differences in particle sizes between the spiked chicken samples and the original silver dispersions indicate relevant matrix effects. The materials demonstrate that production and characterization of reference materials for the detection and quantification of silver nanoparticles in meat are feasible, but challenges especially in assessing stability and having sufficiently precise methods for assessment of homogeneity and stability remain.

Calcination-free micromolding in capillaries for nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets

We report calcination-free micromolding in capillaries for the nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets. We prepared Er3+- and Yb3+-codoped NaYF4 nanoparticles modified with a cationic polymer to improve dispersion stability of aqueous dispersion of the NaYF4 nanoparticles. We controlled the line width and density of nanoparticles in the NaYF4 nanoparticle films on flexible plastic sheets by adjusting the concentrations of the NaYF4 nanoparticle dispersion and the channel sizes of silicone stamps, resulting in the formation of nanopatterned NaYF4 nanoparticle films at the line width of the nanoparticle size (50nm). Visible upconversion luminescence and near-infrared fluorescence appeared from the NaYF4 nanoparticle films excited with a near-infrared laser beam. These results demonstrate that calcination free micromolding in capillaries using aqueous dispersion of NaYF4 nanoparticles modified with a cationic polymer allows for the nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets.

Cobalt/polypyrrole nanocomposites with controllable electromagnetic properties.

In this work, cobalt/polypyrrole (Co/PPy) nanocomposites were prepared via an in situ oxidation polymerization of pyrrole in an aqueous dispersion of Co nanoparticles (NPs). The Co/PPy nanocomposites showed good electromagnetic properties because of the coexistence of magnetic loss and dielectric loss to electromagnetic waves. The electromagnetic wave absorbing bandwidth (reflection loss < -10 dB) for Co/PPy (30 wt% in a paraffin matrix) was located at 11.7-16.47 GHz with a thickness of 2 mm, and with a maximum reflection loss (around -33 dB) at 13.6 GHz. More interestingly, the electromagnetic wave absorbing properties of the nanocomposites can be easily controlled by tuning the ratio of the two components in the composites. This improved electromagnetic wave absorption may be attributed to the excellent electromagnetic match at the corresponding resonance peaks for dielectric and magnetic loss. These magnetic nanoparticles/conducting polymer nanocomposites are great potential candidates for use as electromagnetic wave absorbents due to their excellent properties such as wide absorbing frequency, strong absorption, good compatibility, low density and controllable absorbing properties.

Reversible sol-gel transitions of aqueous dispersions of silica nanoparticles grafted with diblock copolymer brushes composed of a thermosensitive inner block and a charged outer block.

We report in this article that aqueous dispersions of thermosensitive diblock copolymer brush-grafted 17 nm silica nanoparticles (hairy NPs) can undergo in situ, reversible sol-gel transitions in response to temperature changes. The brushes consisted of a thermosensitive poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA) inner block and a charge-carrying, poly(DEGMMA-co-2-(methacryloyloxy)ethyltrimethylammonium iodide) outer block, which were prepared by a one-pot, surface-initiated atom transfer radical polymerization and subsequent quaternization of tertiary amine moieties in the second block with iodomethane. Above a critical concentration, the aqueous dispersion of hairy NPs with an appropriate block copolymer composition exhibited a reversible transition from a free flowing liquid to a free standing hydrogel upon cooling from elevated temperatures, which was driven by the lower critical solution temperature transition of the thermosensitive inner block of hairy NPs as confirmed by dynamic light scattering study. At the same concentration of hairy NPs, the sol-gel transition temperature was higher when the highly hydrated, charged outer block was longer. The transition temperature decreased with decreasing the concentration of hairy NPs in the dispersion; reversible gelation was achieved with a concentration of hairy NPs in water as low as 5.5 wt%. Interestingly, the LCST transition of the inner thermosensitive PDEGMMA block disappeared and no sol-gel transition was observed in the studied temperature range when the charged outer block was sufficiently long.

Changes in proteome profiles of rat liver microsomes induced by silicon dioxide nanoparticles

The effect of daily intragastric administration of an aqueous dispersion of silicon nanoparticles (NPs) (the dose range from 1.0 mg/kg to 100 mg/kg body weight for 28 days) to rats on the proteomic profile of liver microsomes has been investigated by 2D-electrophoresis followed by subsequent mass spectrometry identification. The liver microsomal fraction was isolated by differential centrifugation and its protein composition was analyzed by 2D-polyacrylamide gel electrophoresis. Identification of protein spots was carried out using MALDI-TOF mass spectrometric analysis. The mass spectrometry analysis revealed the protein GRP78 (78 kD glucose-regulated protein precursor), belonging to the family of heat shock proteins. This protein present in animals of the control group was not detected in NP-treated rats of group 2 (1 mg/kg body weight/day) and group 3 (10 mg/kg body weight/day). This protein predominantly localized in the liver cell endoplasmic reticulum and plasma membrane has the chaperone biological activity. Possible mechanisms of the effects of engineered nanoparticles on biosynthetic processes in the body are discussed.

Thermal-lens probing of the enhanced thermal diffusivity of gold nanofluid-ethylene glycol mixture

The thermal diffusivity values of mixtures comprising ethylene glycol and an aqueous dispersion of gold nanoparticles (50/50 volume ratio) is measured using dual-beam thermal-lens technique, as a function of concentration of gold nanoparticles, and the results are compared with the corresponding thermal diffusivity values of gold nanofluids alone. The results show that, in addition to the well-known effect of nanoparticle concentration, the host fluid also play a crucial role in determining the effective thermal diffusivity value of the mixture. The UV–Vis spectroscopic studies of nanoparticles, prepared via citrate reduction method, exhibit the surface plasmon resonance band peaking around 520 nm and the transmission electron microscopic studies reveal that the particles are well dispersed and are having an average size of 15 nm. The transmission electron microscopy images of the gold nanoparticles in the mixture clearly indicate the formation of chain-like aggregates due to dipole–dipole interaction. Such a chain-like structure allows easy transport of thermal energy, which results in enhancement of thermal diffusivity values of the mixture as compared to the gold nanofluids alone.

Single-step colloidal processing of stable aqueous dispersions of ferroelectric nanoparticles for biomedical imaging

The biomedical applications of ferroelectric nanoparticles rely on the production of stable aqueous colloids. We report an implementation of the high energy ball milling method to produce and disperse ultrafine BaTiO3 nanoparticles in an aqueous media in a single step. This technique is low-cost, environmentally friendly and has the capability to control nanoparticle size and functionality with milling parameters. As a result, ultrafine nanoparticles with sizes as small as 6 nm can be produced. These nanoparticles maintain ferroelectricity and can be used as second harmonic generating nanoprobes for biomedical imaging. This technique can be generalized to produce aqueous nanoparticle colloids of other imaging materials.

Preparation and characterization of zwitterionic phospholipid polymer-coated poly(lactic acid) nanoparticles

Poly(lactic acid) (PLA) nanoparticles (NPs) are the most promising polymer NPs for drug delivery and targeting. However, they are easily recognized as a foreign body and rapidly cleared from the body by the mononuclear phagocyte system. Cell membrane mimetic random copolymers, bearing both zwitterionic phosphorylcholine groups and hydrophobic butyl side chains (PMB) and additional cross-linkable trimethoxysilylpropyl side chains (PMBT), were synthesized and coated on PLA NPs. Effects of the zwitterionic copolymer coatings on the NP size distribution, dispersion stability, and drug release behavior were investigated. Furthermore, the effect of the coatings on phagocytosis was also investigated. Compared with conventional polyvinyl alcohol coating, the cell membrane mimetic copolymer coatings decreased the size and increased the stability of the PLA NPs aqueous dispersions. More importantly, doxorubicin (DOX) release was well controlled and NPs phagocytosis by mouse peritoneal macrophage was decreased to one-third when the nanoparticles were coated with PMBT. This simple and effective zwitterionic polymer coating strategy may serve as a new route to design and optimize long-circulating intravenously injectable nanoparticle drug carriers.

Lanthanum complex of a multifunctional water-soluble siloxane compound—Synthesis, surface activity and applications for nanoparticles stabilization

A tris(hydroxymethyl)aminomethane-modified polysiloxane has previously been investigated for surface properties and valuable practical applications have been proposed, including nanoparticle stabilization, complexing of 3d metals, micellar solubilization of drugs and water dispersion of metal oxide nanoparticles. In this article we show the ability of this multifunctional polymer to bind 4f metals. A polymeric lanthanum complex was obtained and characterized. The most probable structure was assigned based on ESI-MS and FT-IR, using data obtained with a homologous disiloxane model compound. The polymeric lanthanum complex shows surface activity, with a CMC value of 150mg/L. Self-assembling in water was also studied by DLS and TEM, which revealed formation of vesicles. The La complex was tested with very good results for polymer nanoparticle stabilization. Polycarolactone nanoparticles of ca. 150nm with long-term stability (Zeta potential=55mV) were obtained. The aqueous dispersion of organic-coated metal oxide nanoparticles was also successful.

Multiscale active layer morphologies for organic photovoltaics through self-assembly of nanospheres.

We address here the need for a general strategy to control molecular assembly over multiple length scales. Efficient organic photovoltaics require an active layer comprised of a mesoscale interconnected networks of nanoscale aggregates of semiconductors. We demonstrate a method, using principles of molecular self-assembly and geometric packing, for controlled assembly of semiconductors at the nanoscale and mesoscale. Nanoparticles of poly(3-hexylthiophene) (P3HT) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were fabricated with targeted sizes. Nanoparticles containing a blend of both P3HT and PCBM were also fabricated. The active layer morphology was tuned by the changing particle composition, particle radii, and the ratios of P3HT:PCBM particles. Photovoltaic devices were fabricated from these aqueous nanoparticle dispersions with comparable device performance to typical bulk-heterojunction devices. Our strategy opens a revolutionary pathway to study and tune the active layer morphology systematically while exercising control of the component assembly at multiple length scales.

Optically pumped distributed feedback dye lasing with slide-coated TiO₂ inverse-opal slab as Bragg reflector.

We demonstrate an optical amplification of organic dye within a TiO2 inverse-opal (IO) distributed feedback (DFB) reflector prepared by a slide-coating method. Highly reflective TiO2 IO film was fabricated by slide coating the binary aqueous dispersions of polystyrene microspheres and charge-stabilized TiO2 nanoparticles on a glass slide and subsequently removing the polymer-opal template. TiO2 IO film was infiltrated, in turn, with the solutions of DCM, a fluorescent dye in various solvents with different indices of refraction. Optical pumping by frequency-doubled Nd:YAG laser resulted in amplified spontaneous emission in each dye solution. In accordance with the semi-empirical simulation by the FDTD method, DCM in ethanol showed the best emission/stopband matching for the TiO2 IO film used in this study. Therefore, photo excitation of a DCM/ethanol cavity showed a single-mode DFB lasing at 640 nm wavelength at moderate pump energy.

Poly(phosphonate)s via Olefin Metathesis: Adjusting Hydrophobicity and Morphology

Olefin metathesis step-growth (acyclic diene metathesis (ADMET)) and chain-growth (ring-opening metathesis) polymerization was used to prepare linear poly(phosphonate)s with variable hydrophilicity. The first phosphonate monomer, i.e., di(undec-10-en-1-yl) methylphosphonate, for ADMET polymerization was developed, and potentially degradable and biocompatible, unsaturated poly(phosphonate)s were prepared with molecular weights up to 23 000 g mol–1 with molecular weight dispersities Đ < 2. These polymers were studied with respect to their interaction with a calcium phosphate bone substitute material from an aqueous nanoparticle dispersion that was prepared by a solvent evaporation miniemulsion protocol. Ring-opening metathesis polymerization (ROMP) was employed to synthesize more hydrophilic amorphous polyphosphonates from a novel seven-membered cyclic phosphonate monomer, i.e., 2-methyl-4,7-dihydro-1,3,2-dioxaphosphepine 2-oxide, as well as hydrophobic crystalline copolymers with cis-cyclooctene. ROMP yiel...

Sustained release of PTX-incorporated nanoparticles synergized by burst release of DOX⋅HCl from thermosensitive modified PEG/PCL hydrogel to improve anti-tumor efficiency

As drug therapies become increasingly sophisticated, the synergistic benefits of two or more drugs are often required. In this study, we aimed at improving anti-tumor efficiency of paclitaxel (PTX)-incorporated thermo-sensitive injectable hydrogel by the synergy of burst release of doxorubicin hydrochloride (DOX⋅HCl). Thermosensitive injectable hydrogel composed of nanoparticles assembled from amphiphilic copolymer poly(ε-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone)-poly(ethylene glycol)-poly(ε-caprolaone-co-1,4,8-trioxa[4.6]spiro-9-undecanone) (PECT) was fabricated. Hydrophobic PTX and hydrophilic DOX⋅HCl were loaded simultaneously in the thermo-sensitive injectable hydrogel by a two-stage entrapment. Thermosensitive gelling behaviors of drug-loading PECT nanoparticle aqueous dispersions were studied. In vitro release profiles of PTX and DOX⋅HCl and in vivo anti-tumor effect by dual drugs from PECT hydrogel were investigated. The results showed that hydrophilic and hydrophobic drugs could be successfully entrapped in PECT hydrogel simultaneously without affecting its thermo-sensitive behavior. In vitro release profiles demonstrated the burst release of DOX⋅HCl and the sustained release of PTX. Anti-tumor effect was improved by a fast and tense attack caused by the burst release of hydrophilic DOX⋅HCl from hydrogel, which was continued by the sequent sustained release of PTX-incorporated nanoparticles and remnant DOX⋅HCl. Unintentionally, entrapped in PECT hydrogel, hydrophilic DOX⋅HCl was observed to have a sustained releasing pattern in vitro and in vivo.

Magneto-responsive hybrid materials based on cellulose nanocrystals

We fabricated self-standing films of cellulose nanocrystals (CNC) and electrospun composite fibers with CNC and polyvinyl alcohol both with magnetic properties arising from cobalt iron oxide nanoparticles in the CNC matrix. Aqueous dispersions of cobalt-iron oxide nanoparticles (10–80 nm diameter) and CNCs (ca. 150 nm length) were used as precursor systems for the films and composite fibers. The properties of the hybrid material were determined by electron and atomic force microscopy, X-ray diffraction, thermogravimetry and magnetometry. The CNC-inorganic system was ferromagnetic, with a saturation magnetization of ca. 20 emu g−1 of the magnetic phase. We demonstrate potential applications of the precursor dispersions, including magnetic fluid hyperthermia and highlight possible uses of the CNC-based magneto-responsive systems in biomedical and magneto-optical components.

Aqueous dispersions of organogel nanoparticles - potential systems for cosmetic and dermo-cosmetic applications.

The preparation and physicochemical characterization of organogel nanoparticles dispersed in water have been developed. These systems could be employed as nanocarrier for cosmetic applications or as hydrophobic reservoirs for drug delivery. Gelled particles of organic liquid and 12-hydroxystearic acid (organogelator) were obtained by hot emulsification (T>Tgel), with a surfactant (acetylated glycol stearate) and polymers (sodium hyaluronate and polyvinyl alcohol) as stabilizing agents, and cooling at room temperature (T<Tgel). An organic UVB sunscreen molecule, obtained by microwave activation, was used as a hydrophobic model molecule. The physicochemical properties of the starting organogel (gelation tests; rheological study) and the dispersed gelled particles (rheological study; particle mean size, size distribution, zeta-potential measurements; physical stability evaluation; UVB absorption and water resistance ability) were studied. The synthesis of sunscreen compound using microwave activation was also described. According to the gelation test results, organogels were obtained with various organic liquids. Vaseline and almond oils were selected as organic medium for the gelled nanoparticle preparation. A preliminary formulation study was carried out in order to determine the optimal experimental conditions to obtain stable nanoparticle dispersions. Gelled nanoparticles contained the sunscreen model molecule, with mean size of 450nm, polydispersity index of 0.18 and zeta-potential value above -30mV, were obtained by ultrasound probe homogenization method. A comparative study of their dispersion ageing showed a greatly enhanced stability after gelation. According to the UVB absorption evaluation, gelled particles improved the photoprotective ability and the photostability of immobilized UVB blocker. They showed a high water resistance (~83%) even after 40min of immersion. The obtained results demonstrate the interest of these gelled nanoparticles and their aqueous dispersion for the preparation of new formulations for cosmetic and dermo-cosmetic applications.