A new surface modification method to improve the dispersity of nano-silica in organic solvents

Different surface modification methods to improve the dispersity of nano-silica in organic solvents by γ-methacryloxypropyltrimethoxy silane (MOPTMS) anhydrous alcohol solution were investigated. The possible principles of these methods improving the dispersity of nano-silica in organic solvents were proposed. The optimum modification method was that nano-silica powders were chemically modified by γ-methacryloxypropyltrimethoxy silane anhydrous alcohol solution and γ-methacryloxypropyltrimethoxy silane anhydrous alcohol solution was dropwise added at 3 mL/min. The transparency of the optimum modified nano-silica powder anhydrous alcohol solution (0.1 wt. %) was 85.9%. The ²⁹Si cross polarization and magic-angle spinning nuclear magnetic resonance spectra suggested that nano-silica was chemically modified by γ-methacryloxypropyltrimethoxy silane anhydrous alcohol solution. The transmission electron microscopy images suggested that the optimum modified nano-silica was well dispersed. The dispersity of nano-silica in anhydrous alcohol, CH₂Cl₂, CCl₄, cyclohexane, and liquid paraffin increased from 0, 0, 0, 0, and 0.1 to 9.4, 9.6, 9.8, 9.8, and 10.0 g/100 mL after surface modification.     

Liquid-liquid phase-transfer of magnetic nanoparticles in organic solvents

We report a novel route for the preparation of well-defined colloidal dispersions of magnetic nanoparticles stabilized by steric repulsion in organic solvents. The usual methods standardly lead to the surfaction of multiparticle aggregates, incompatible with our long-term aim of studying and modeling the influence of magnetic dipolar interactions in colloidal dispersions which are free of aggregates, all other interactions being perfectly defined. A new and reproducible method based on a surfactant-mediated liquid-liquid phase transfer of individually dispersed gamma-Fe(2)O(3) nanoparticles from an aqueous colloidal dispersion to an organic phase is developed. The choice of the reagent and the preparation techniques is discussed. Among several solvent/surfactant pairs, the cyclohexane/dimethyldidodecylammonium bromide (DDAB) system is found to fulfill the colloidal stability criterion: aggregation does not appear, even upon aging. A complete transfer of isolated particles is observed above a threshold in DDAB concentration. The nanoparticle surface is then fully covered with adsorbed DDAB molecules, each surfactant head occupying a surface of 0.57+/-0.05 nm(2). The volume fraction of the cyclohexane-based organosols is easily tunable up to a volume fraction of 12% by modifying the volume ratio of the organic and of the aqueous phases during the liquid-liquid phase transfer.     

Layer-by-layer growth of oriented metal organic polymers on a functionalized organic surface

A metal-organic coordination polymer based on benzenetricarboxylic acid ligands and Zn(II) ions was grown on a COOH-terminated organic surface in a stepwise fashion. The deposited films were characterized using a number of surface analysis techniques, including X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. IR measurements show that the metal-organic coordination polymer grows in a layer-by-layer fashion and can be reversibly loaded with NH3. The deposition is very selective and occurs only on COOH-terminated regions of an organic surface, as demonstrated by AFM measurements.     

Nickel nanoparticles and solids using organic solvents

Nickel colloids were prepared by codeposition of the metal with several organic solvents: acetone, ethanol, 2-propanol, 2-methoxyethanol and 1,2-dimethoxyethane at 77 K. The stabilities of the colloids and fine powders were measured. The metallic films and active solids were obtained by evaporation under vacuum at room temperature. The Ni-2-methoxyethanol colloids are stable over three months at room temperature, and the UV-VIS absorption spectra of the most stable colloids were obtained. A chemical characterization of Ni solids was carried out by several techniques such as elemental analysis, FT-IR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry (TGA). The IR studies show the presence of the solvent in the solids, which was confirmed by microanalysis. From TGA, DSC, and TGA-FTIR the metal-solvent was studied. From TGA, the kinetic parameters of decomposition reaction were calculated using the Freeman and Carroll equations. Received: 6 June 2000 Accepted: 6 September 2000     

Laser ablation synthesis of gold nanoparticles in organic solvents

Free and functionalized gold nanoparticles are synthesized by laser ablation of a gold metal plate immersed in dimethyl sulfoxide, acetonitrile, and tetrahydrofuran. Functionalized gold nanoparticles are synthesized in a one-step process thanks to the solubility of the ligands in these solvents. It is possible to have significant control of the concentration, aggregation, and size of the particles by varying a few parameters. UV-vis spectroscopy and transmission electron microscopy are used for the characterization of the nanoparticles. The Mie model for spherical particles and the Gans model for spheroids allow a fast and reliable interpretation of experimental UV-vis spectra.     

Colloidal dispersion of fullerene C60 free of organic solvents

A new procedure for preparing aqueous colloidal dispersion of C₆₀ in water was developed.     

Surface modification of poly(dimethylsiloxane) for retarding swelling in organic solvents

A method of alleviating swelling problems of poly(dimethysiloxane) (PDMS) molds in organic solvents is developed that allows repeated use of the molds without deleterious solvent effects. The method involves surface modification of PDMS surface with poly(urethaneacrylate) that results in a partially modified PDMS surface. This modification leads to a significant reduction in the rate of solvent absorption into PDMS such that the swelling can be controlled.     

Colloidal stability of oleic- and ricinoleic-acid-coated magnetic nanoparticles in organic solvents

Polyacrylic acid (PAA) and polyacrylamide (PAAm) double network (DN) hydrogels with high mechanical strength (about 1.5 MPa) are obtained when two kinds of monomer solutions of 4M AA with 5 mol% crosslinker and 4M AAm with 0.1 mol% crosslinker are used for the optimal preparation. Their high mechanical strength can be maintained even at high water content (above 50%) and at external stimuli (solvent and pH). This optimized DN hydrogel is used to develop the PAA/PAAm inverse opal hydrogel with DN structure by twice infiltration-polymerization and colloidal templating. Its photonic stop band can be tuned by controlling the solvent and pH. It first shows a small red-shift (about 20 nm), and then a large blue-shift (about 180 nm) with the increased ethanol content. For pH response, the DN inverse opal hydrogel has a large stop-band shift of about 140 nm when the pH increases from 1.2 to 5.6. Moreover, the DN inverse opal hydrogel also shows rapid recovery ability without hysteresis phenomenon in strong acidic environment, good reproducibility and durability. The interaction between the independently crosslinked PAA network and PAAm network plays a significant role in determining the response performance.     

Preparation of magnetically doped multilayered functional silica particles via surface modification with organic polymer

Magnetically modified functional particles are emerging as one of the most promising candidate in numerous multidisciplinary applications. In this research, a simple process has been developed to prepare magnetically modified aminated silica (SiO₂) particles. Herein, submicron‐sized SiO₂ particles were modified with poly(methylmethacrylate‐methacrylic acid) by seeded polymerization without any stabilizer. The carboxyl groups localized near the particles surface were then covalently linked with ethylene diamine to prepare aminated composite particles. Iron ions were then precipitated on the surface of aminated composite particles to obtain magnetically doped functional SiO₂ particles. The preparation of such particles was confirmed by scanning electron microscopy, Fourier transform infrared, ¹H NMR, X‐ray photoelectron spectroscopy and thermogravemetric analyses. Relative measurement of adsorption study of different biomolecules suggested that magnetically doped functional silica particles are comparatively hydrophobic. Copyright © 2012 John Wiley & Sons, Ltd.     

Measurements of binary diffusion coefficients for metal complexes in organic solvents by the Taylor dispersion method

Infinite dilution binary diffusion coefficients, D₁₂, of ferrocene, 1,1′-dimethylferrocene and ethylferrocene in hexane, cyclohexane and ethanol at 313.2 K and pressures from 0.2 to 19 MPa, in acetonitrile at 298.2–333.2 K and 0.2 MPa, and various metallic acetylacetonate, acac, complexes such as Co(acac)₃, Ru(acac)₃, Rh(acac)₃, Pd(acac)₂ and Pt(acac)₂ mainly in ethanol at 313.2 K and 0.2 MPa were measured by the Taylor dispersion method. The D₁₂ values in m² s⁻¹ for the three ferrocenes in the present study and those of ferrocene and 1,1′-dimethylferrocene in supercritical carbon dioxide in our previous studies were represented by the modified hydrodynamic equation over a wide range of viscosity: M^0.5D₁₂/T = 1.435 × 10⁻¹³η^−0.8446 with average absolute relative deviation of 2.40% for 316 data points, where M is the solute molecular weight, T is the temperature in K, η is the solvent viscosity in Pa s. Although the D₁₂ values for the acac complexes were roughly represented by the above hydrodynamic equation, the accuracies were lower because they were dependent on not solute molecular weight but the number of acac ligand in the complex molecules.     

Interacting nanoparticles with functional surface groups

Functionalized nanoparticles with ionizable groups have generated a large variety of structures with important potential applications in technology. The nature of their interactions is crucial to determining their solubility and to exploring assemblies with diverse symmetries. Here, we use a molecular theory to describe the interactions between two nanoparticles coated with short polymer chains that contain ionizable (functional) end‐groups immersed in aqueous salt solution. It is shown here that the fraction of ionized functional groups in the system depends on factors such as the ionic strength and pH of solution, grafting density of polymer chains, the chain length, as well as the separation distance between the nanoparticles. The interactions between two neighboring nanoparticles influence the charge regulation of the end‐groups, which consequently induces an asymmetric distribution of these charged end‐groups on the nanoparticles, and thus confers a preferred directionality in nanoparticle–nanoparticle interactions. We show that the charge regulating system is less repulsive than an equivalent system with a fixed charge distribution. This is due to a decrease in the charge density of the weak acid end‐groups, to avoid a local increase in counterion confinement (condensation) in the region between neighboring nanoparticles, when their separation decreases. The anisotropic degree of ionization found in our results can be used to design aggregates of nanoparticles with reduced symmetries. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Heterodimers of nanoparticles: formation at a liquid-liquid interface and particle-specific surface modification by functional molecules

On the basis of a fundamental property of nanoparticles, the self-assembling at a liquid-liquid interface to form "colloidosomes", a heterogeneous reaction takes place on the exposed surface of the nanoparticles to produce the heterodimers of two distinct nanospheres, which can be modified by two different functional molecules in a particle-specific manner.     

Organic surface modification and analysis of titania nanoparticles for self-assembly in multiple layers

The characteristics of TiO₂ coatings can greatly influence their final performance in large-scale applications. In the present study, self-assembly of TiO₂ nanoparticles (NPs) in multiple layers was selected as a deposition procedure on various substrates. For this, the main prerequisite constitutes the surface modification of both NPs and substrate with, for example, silane coupling agents. A set of functionalized TiO₂ NPs has been produced by reaction with either (3-aminopropyl)triethoxysilane (APTES) or (3-aminopropyl)phosphonic acid (APPA) to functionalize the NP surface with free amino-groups. Then, the complementary functionalized NP set can be obtained from an aliquot of the first one, through the conversion of free surface amino groups to aldehydes by reaction with glutaraldehyde (GA). Several types of TiO₂ NPs differing in size, shape, and specific surface area have been functionalized. Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), SEM/ energy-dispersive X-ray spectroscopy (EDS), XPS, Auger electron spectroscopy (AES), and Time-of-Flight (ToF)-SIMS analyses have been carried out to evaluate the degree of functionalization, all the analytical methods employed demonstrating successful functionalization of TiO₂ NP surface with APTES or APPA and GA.     

Effect of particle size on surface modification of silica nanoparticles by using silane coupling agents and their dispersion stability in methylethylketone

The effect of particle size on the reactivity of hexyltrimethoxysilane (C6S) with the particle surface was studied by using silica nanoparticles (SNPs) with different diameters (30 or 200 nm). In case of 30-nm SNPs, a large amount of isolated silanol was observed. On the other hand, in the case of 200-nm SNPs, the amount of hydrogen bonded silanol and hydrogen bonded water molecules at the surface of the SNPs increased. Since the hydrogen bonded silanol and the hydrogen bonded water enhanced the reaction of C6S with SNPs, the chemisorbed C6S on 200-nm SNPs was larger than that on 30-nm SNPs. Furthermore, the effects of surface modification on the dispersion stability in MEK were studied using viscosity measurements and surface force measurements by the AFM colloid probe method. The viscosity of the dilute SNPs/MEK suspension did not change by the chemisorptions of C6S; however, the viscosity of dense suspension reduced effectively by surface modification. It was estimated that the suspension viscosity reduced effectively when the mean particle surface distance in the suspension was near to the distance where the repulsive force appeared by the surface force measurements using the colloid probe AFM.     

Superparamagnetism of magnetite nanoparticles: dependence on surface modification

Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (Au), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravimetric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of M?ssbauer spectroscopy as a function of an external magnetic field Hext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under Hext, and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to M?ssbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.     

Multifunctional surface modification of gold-stabilized nanoparticles by bioorthogonal reactions

Nanocarriers that combine multiple properties in an all-in-one system hold great promise for drug delivery. The absence of technology to assemble highly functionalized devices has, however, hindered progress in nanomedicine. To address this deficiency, we have chemically synthesized poly(ethylene oxide)-β-poly(ε-caprolactone) (PEO-b-PCL) block polymers modified at the apolar PCL terminus with thioctic acid and at the polar PEO terminus with an acylhydrazide, amine, or azide moiety. The resulting block polymers were employed to prepare nanoparticles that have a gold core, an apolar polyester layer for drug loading, a polar PEO corona to provide biocompatibility, and three different types of surface reactive groups for surface functionalization. The acylhydrazide, amine, or azide moieties of the resulting nanoparticles could be reacted with high efficiencies with modules having a ketone, isocyanate, or active ester and alkyne function, respectively. To demonstrate proof of principle of the potential of multisurface functionalization, we prepared nanoparticles that have various combinations of an oligo-arginine peptide to facilitate cellular uptake, a histidine-rich peptide to escape from lysosomes, and an Alexa Fluor 488 tag for imaging purposes. It has been shown that uptake and subcellular localization of the nanoparticles can be controlled by multisurface modification. It is to be expected that the modular synthetic methodology provides unique opportunities to establish optimal configurations of nanocarriers for disease-specific drug delivery.     

Phase transfer of large gold nanoparticles to organic solvents with increased stability

In this paper, we describe a new procedure to phase transfer large gold nanoparticles (diameters > 45 nm) from aqueous solution to organic solvents. This is accomplished using a covalent amide coupling reaction that incorporates dicyclohexylamine (DCHA) headgroups on the surface of mercaptoacetic acid (MAA) functionalized gold nanoparticles. Gold nanoparticles are first synthesized in aqueous solution by the citrate-reduction method, and nanoparticle size is controlled by the molar ratio of the reducing agent (sodium citrate) and the gold precursor (KAuCl4). MAA is then adsorbed to the surface of the gold nanoparticles followed by an amide-coupling reaction to covalently attach DCHA to the surface-immobilized MAA. The bulky dicyclohexyl groups entropically stabilize gold nanoparticles in organic solvents. This procedure was used to reliably transfer gold nanoparticles with diameters between 45 and 100 nm from aqueous solution to organic solvents such as dimethyl sulfoxide and chloroform.     

Dissociation and degradation of thiol-modified DNA on gold nanoparticles in aqueous and organic solvents

Gold nanoparticles functionalized with thiol-modified DNA have been widely used in making various nanostructures, colorimetric biosensors, and drug delivery vehicles. Over the past 15 years, significant progress has been made to improve the stability of such functionalized nanoparticles. The stability of the gold-thiol bond in this system, however, has not been studied in a systematic manner. Most information on the gold-thiol bond was obtained from the study of self-assembled monolayers (SAMs). In this study, we employed two fluorophore-labeled and thiol-modified DNAs. The long-term stability of the thiol-gold bond as a function of time, salt, temperature, pH, and organic solvent has been studied. We found that the bond spontaneously dissociated under all tested conditions. The dissociation was favored at high salt, high pH, and high temperature, and little DNA degradation was observed in our system. Most organic solvents showed a moderate protection effect on the gold-thiol bond. The stability of the gold-thiol bond in the DNA system was also compared with that in SAMs. While there are many similarities, we also observed opposite trends for the salt and ethanol effect. This study suggests that the purified DNA-functionalized gold nanoparticles should be freshly prepared and used in a day or two. Long-term storage should be carried out at relatively low temperature in low salt and slightly acidic buffers.     

Self-assembly of gold nanoparticles on functional organic molecular crystals

The utilization of metal nanoparticles (NPs) to fabricate metal electrodes under mild conditions is one of the most studied topic in recent years. In this work, colloidal Au NPs were deposited on two isostructural molecular crystals, namely 1,2,3,4-tetrafluoro-7-thiomethyl-acridine (MeSAcr) and 1,2,3,4-tetrafluoro-7-methoxy-acridine (MeOAcr), exposing S atoms and O atoms, respectively, at their largest crystal faces. The depositions were carried out mainly by drop casting under ambient conditions, increasing the contact time from 1 to 120 min, and the samples were then analyzed by atomic force microscopy (AFM) to evaluate the coverage. Thanks to the affinity between S and Au atoms, Au NPs are observed to adhere on the MeSAcr surface within 1-min contact time, whereas at least 1h is required to find NPs on the MeOAcr surface. NP adsorption is also affected by the substrate surface morphology; indeed, step edges represent preferential adsorption sites even in the absence of Au-S interaction. Experiments under different conditions were performed to maximize the coverage on MeSAcr, reaching values up to 13%. AFM equipped with fluid cell was also employed to simultaneously depositing and imaging NPs, achieving a better understanding of the adsorption mechanism.