Gel Nanoparticles Research Articles

Molecularly imprinted sol–gel nanoparticles for mass-sensitive engine oil degradation sensing

Titanate sol-gel layers imprinted with midchain carbonic acids have proven highly useful for detecting engine oil degradation processes owing to selective incorporation of oxidised base oil components. Synthesising the material from TiCl(4) in CCl(4) and precipitating with water leads to imprinted TiO(2) nanoparticles with a diameter of 200-300 nm. Replacing the water by a 1 M ammonium hydroxide solution reduces the average particle size to 50-100 nm with retention of the interaction capabilities. Experiments with the latter solution revealed that the 100-nm particles take up substantially more analyte, indicating a size-dependent phenomenon. As the number of interaction sites within each material is the same, this cannot be a consequence of thermodynamics but must be one of accessibility. The sensor characteristic of water-precipitated particles towards engine oil degradation products shows substantially increased sensitivity and dynamic range compared with the corresponding thin films. Coating quartz crystal microbalances with such nanoparticle materials leads to engine oil degradation sensors owing to incorporation of acidic base oil oxidation products. Interaction studies over a large range of layer thicknesses revealed that both the absolute signal and the steepness of the correlation between the sensor signal and the layer height is 2 times higher for the particles.

A fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer/silica gel nanocomposite with no weight loss even at 800 °C equal to an original silica gel

Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)n-RF]/silica gel nanocomposite, which was prepared by reaction of the corresponding fluorinated oligomer with tetraethoxysilane and silica gel nanoparticles under alkaline conditions, exhibited no weight loss even at 800 °C equal to the original silica gel, although the corresponding parent RF-(DOBAA)n-RF oligomer was completely degraded at 600 °C. Thermogravimetric analyses/mass spectra of fluorinated nanocomposite showed that this nanocomposite decomposed around 280 °C to afford CO2 and H2O as the major evolved gaseous products including some minor fluoro- and hydrocarbons. X-ray photoelectron spectroscopy analyses also showed that the contents of C, F, and Si atoms in RF-(DOBAA)n-RF/SiO2 nanocomposite after the calcination at 800 °C were similar to those before the calcination. These findings suggest that the evolved gaseous products should be encapsulated quantitatively into nanometer-size-controlled silica matrices to give the fluorinated silica gel nanocomposite with no weight loss even at 800 °C equal to the original silica gel.

Polymer-bridged gels of nanoparticles in solutions of adsorbing polymers

We use a combination of polymer mean field theory and Monte Carlo simulations to study the polymer-bridged gelation, clustering behavior, and elastic moduli of polymer-nanoparticle mixtures. Polymer self-consistent field theory is first numerically implemented to quantify both the polymer induced interparticle interaction potentials and the conformational statistics of polymer chains between two spherical particles. Subsequently, the formation and structure of polymer-bridged nanoparticle gels are examined using Monte Carlo simulations. Our results indicate a universality in the fractal structure for the polymer-bridged networks over a wide range of parametric conditions. Explicitly, near the gelation transition, the fractal dimension d(f) ranges between 2.2 and 2.5, and above the gelation thresholds, the elastic moduli are found to follow a universal power law G(') proportional, variant(eta-eta(c))(nu(eta) ) with a critical exponent nu(eta) approximately 1.82. The latter suggests strong similarities between polymer-bridging induced percolation and classical elastic resistor network percolation. Our results show a very good agreement with the experimental results for polymer-particle mixtures and suggest a possible framework for experimentally distinguishing the origins of gelation phenomena observed in polymer-particle mixtures.

Sol–gel synthesis at neutral pH in W/O microemulsion: A method for enzyme nanoencapsulation in silica gel nanoparticles

The classical sol–gel synthesis of silica gels has been adapted to a W/O (micro)emulsion process under conditions that minimize denaturing effects on encapsulated enzymes. We have in particular focused on optimizing the purification procedures with the aim to produce water nanoparticles dispersions from W/O emulsions without the use of precipitation/sedimentation steps.A proof of principle of encapsulation has been conducted using horseradish peroxidase (HRP).

Ketoprofen nanoparticle gels formed by evaporative precipitation into aqueous solution

AbstractAqueous nanoparticle gels of a poorly‐water soluble drug, ketoprofen, were produced by evaporative precipitation into aqueous solution (EPAS). Liquid droplets of surfactant stabilized ketoprofen containing residual solvent were dispersed in water from 60 to 90°C below the melting point of pure ketoprofen. The carboxylic acid group in ketoprofen dissociates in pure water, providing electrostatic stabilization of the droplets to complement steric stabilization. Stable amorphous ketoprofen particles with a mean size of 135 nm, measured by dynamic light scattering, were formed with only 0.1% w/v poloxamer 407, resulting in an exceptionally high drug‐to‐surfactant ratio of 10:1. For 5% w/v poloxamer 407, interactions with ketoprofen produced a bluish, transparent gel composed of ∼50 nm particles. In 2 min, 98% of the ketoprofen in the gel nanoparticles dissolved. The favorable interactions between the ketoprofen and poloxamer 407, along with the electrostatic and steric stabilization, lead to gelation, which further stabilizes the unusually small particles. The rapidly dissolving wet gels with extremely small particle sizes, one month stability, and relatively low viscosities, are of interest in transdermal and parenteral delivery; furthermore, the gels may be dried for oral delivery. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Three-dimensional motion and transformation of a photoelectrochemical actuator

A new "photoelectrochemical actuator" consisting of poly(acrylic acid)/copper gel and TiO2 nanoparticles has been developed, which undergoes reversible expansion/contraction upon UV light irradiation/termination, likely due to dissociation/formation of carboxylic group/Cu2+ binding.

Sol?Gel Derived Rh/TiO2/SiO2 Nanocomposite Membranes

A porous borosilicate substrate has been coated with base catalysed SiO2 sol–gel nanoparticles. Onto these were deposited the vapour of titanium isopropoxide, where it reacted with the surface OH groups to give a TiO2-overcoat. This nanocomposite sol–gel derived TiO2/SiO2 membrane was then doped with 1%Rh giving Rh/TiO2/SiO2 membranes. These are shown to be coherent and crack-free, to have good permeability and activity in the isomerisation of butanes. It appears that sol–gel chemistry will allow such membranes to be totally engineered at a nm level.

First-order isotropic-smectic-A transition in liquid-crystal-aerosil gels.

The short-range order which remains when the isotropic to smectic- A transition is perturbed by a gel of silica nanoparticles (aerosils) has been studied using high-resolution synchrotron x-ray diffraction. The gels have been created in situ in decylcyanobiphenyl, which has a strongly first-order isotropic to smectic- A transition. The effects are determined by detailed analysis of the temperature and gel density dependence of the smectic structure factor. In previous studies of the continuous nematic to smectic- A transition in a variety of thermotropic liquid crystals the aerosil gel appeared to pin, at random, the phase of the smectic density modulation. For the isotropic to smectic- A transition the same gel perturbation yields different results. The smectic correlation length decreases more slowly with increasing random-field variance in good quantitative agreement with the effect of a random pinning field at a transition from a uniform phase directly to a phase with one-dimensional translational order. We thus compare the influence of random fields on a freezing transition with and without an intervening orientationally ordered phase.

Nanostructured polymer gels

AbstractA brief review of our recent work on polymer gel opals is given in memory of late Professor Tanaka. The central idea is to first synthesize monodisperse polymer gel nanoparticles, then self‐assemble them into a 3D network, and eventually covalently bond them. The covalent bonding contributes to the structural stability, while self‐assembly provides them with crystal structures that diffract light, resulting in colors. N‐isopropylacrylamide (NIPA) gel has been used as a model system for this study. The nanostructured NIPA gel, which contain up to 97 wt% water, displays a striking iridescence like precious opal but are soft and flexible like gelatin.

Hybrid Proton-Carrier Polymer Composites for High-Temperature FCPEM Applications

AbstractHybrid proton-carrier polymer composites were fabricated in an effort to develop high-performance high-temperature proton exchange membranes (PEMs) for fuel cell applications in the 100°–200°C range. The solution-cast hybrid membranes comprise a polymer host and a SiO2-based proton-carrier composite that was synthesized via sol gel approach using a functional silane and tetraethoxysilane (TEOS) in acidic conditions. The primary H+-carrying component was either a heteropoly silicotungstic acid (STA) or a sulfonic acid (SFA) that was thermooxidatively converted from a mercapto (-SH) group. The embedding level of STA on the silane-modified SiO2 sol gel composites was strongly affected by the presence and the functional group of the silane. Ion exchange capacity (IEC) of the water-washed, SiO2-based STA and SFA proton-carrier composite powders is in the range of 1.8–3.5 mmol/g, two to three times higher than that for Nafion 117 (0.9 meq/mol). A glycidylmethacrylate-type copolymer, PEMAGMA, which is stable up to ∼225°C, was able to produce mechanically robust and flexible hybrid membranes. Upon curing, the PEMAGMA composite membranes showed a ∼75% gel under the present formulation and retained the "free" STA effectively with slight loss when extracted in an 85°C water. The W12-STA-containing PEMAGMA membranes followed the weight loss trends of water from STA and the SiO2-based sol gel composite, showing a 10 wt% loss at 150°C and a 15 wt% loss at 225°C. Fuel cell performance tests of the preliminary films gave a Voc in the 0.85–0.93 V range, but a low current density of <4 mA/cm2. The resistive characteristics were attributed to inhomogeneous distribution of the sol gel nanoparticles in the PEMAGMA matrix, a result of phase separation and particulate agglomeration during film forming.

A New Route to Alumoxane Gel: A Versatile Precursor to γ‐Alumina and Alumina‐Based Ceramic Oxides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Biodegradable magnetic gel: synthesis and characterization

Biodegradable polymer-based magnetic gels have been synthesized using hydroxypropyl cellulose and maghemite. These magnetic gels have a network of nanoparticles of hydroxypropyl cellulose (30–100 nm) and a homogeneous distribution of nanosized maghemite (~7 nm). This has been observed in a STEM micrograph. The surface structure of the gels has been observed by atomic force microscopy, while transmission electron microscopy has shown the distribution of iron oxide in HPC gel nanoparticles. These gels have magneto-elastic properties. The magnetic susceptibility and magnetization of these gels are measured by a superconducting quantum interference device magnetometer.

A new route to alumoxane gel: a versatile precursor to gamma-alumina and alumina-based ceramic oxides.

We present a new route for the preparation of gamma-alumina and YAG nanoparticles. Metal salts of ethylhexanoic acids provide good solubility in hydrocarbon solvents and allow efficient ultrasonication. The sonication product is an alumioxane gel, which can reversibly collapse and reform, depending on the solvent used. The dried gel nanoparticles are calcined at temperatures significantly lower than those used in conventional syntheses, resulting in gamma-alumina nanoparticles. This is due to the complete mixing of elements at the atomic level and the small size of the formed nanoparticles.

The skin barrier and use of moisturizers in atopic dermatitis

Deficiency or altered composition of stratum corneum (SC) lipids such as ceramides (CERs), causing skin barrier dysfunction and skin dryness, have been associated with skin diseases such as atopic dermatitis and psoriasis, and ageing. Replenishing the depleted native CERs with exogenous CERs has also been shown to have beneficial effects in restoring the skin barrier. Phyto-derived CERs such as oat CERs were shown to be potential for skin barrier reinforcement. To effect this, however, the oat CERs should overcome the SC barrier and delivered deep into the lipid matrix using the various novel formulations. In an attempt to demonstrate the potential use of oat CERs, lecithin-based microemulsions (MEs) and starch-based nanoparticles (NPs) were formulated and characterized. Besides, ME gel and NP gel were also prepared using Carbopol®980 as a gelling agent. The in vitro release and penetration (using artificial four-layer membrane system) and ex vivo permeation (using excised human skin) of oat CERs from the various formulations were investigated. The results revealed ME enhanced the in vitro release and penetration oat CERs compared to the other formulations. On the other hand, the NPs retarded the release of oat CERs and small quantities of oat CERs incorporated into NP gel penetrated into the deeper layers of the multilayer membranes. The penetration-enhancing effect of ME was also observed in the ex vivo permeation studies where significant quantities of oat CERs were found in the acceptor compartment. Compared to the ME, the ME gel exhibited reduced depth and extent of oat CERs permeation. As compared to NP gel, ME gel enhanced the degree of permeation of oat CERs into the deeper layer of the skin. Generally the gel formulations were effective in concentrating oat CERs in the SC where they are needed to be.

Dynamics of concentrated colloidal suspensions: diffusion, aggregation and gelation

We show that diffusing wave spectroscopy (DWS) permits the characterization of dynamic properties of concentrated colloidal suspensions on a large range of time– and length–scales ranging from a few angstroms to tens of nanometres. We focus in particular on the study of the aggregation and sol–gel transition in concentrated colloidal suspensions. We present a new technique to overcome the problem of nonergodicity in DWS of solid–like systems. Using this technique we obtain quantitative information about the microscopic dynamics all the way from an aggregating suspension to the final gel, thereby covering the whole sol–gel transition. At the gel point a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. We combine DWS with small–angle neutron scattering and demonstrate that we can obtain an in situ characterization of the changes in the microstructure and the local particle dynamics as the system undergoes a sol–gel transition.

Novel Electrochemical Interfaces with a Tunable Kinetic Barrier by Self-Assembling Organically Modified Silica Gel and Gold Nanoparticles

A simple strategy is presented for the construction of an electrochemical interface with a tunable kinetic barrier by self-assembling organically modified silica gel and gold nanoparticles. Self-assembly of an organically modified silica layer is carried out from the hydrolyzed sol of the precursor mercaptopropyltrimethoxysilane. The kinetic barrier of this self-assembled silicate film is modified by gold nanoparticles that are self-assembled into the silicate network. The electrochemistry of ferricyanide redox reaction is used as a marker to probe the interface.

Layered Nanocomposite of Close-Packed Gold Nanoparticles and TiO2 Gel Layers

Nanocomposite films of gold nanoparticles and TiO2 gel have been successfully prepared by combination of a surface sol−gel technique and layer-by-layer assembly. Thanks to surface hydroxyl groups of gold nanoperticles, gold particles were deposited as close-packed monolayers on TiO2 gel layers. The resulting nanocomposite contained ca. 50 wt % of gold. Multilayer films were successfully prepared by alternate assembly of TiO2 gel and gold nanoparticles.