Diffusion of protons in silica hydrogel

The effect of preparation pH of silica hydrogel on the effective diffusion coefficient of protons in silica hydrogel (D _e , m²/s), on surface area of silica gel (S, m²/s) and on particle size of silica gel (D _p , mm) was studied. Silica hydrosols were obtained by adding water glass to sulfuric acid. The effective diffusion coefficient of proton in silica hydrogel was determined by the method of diffusion from silica hydrogel plane sheet to a stirred solution of a limited volume. A numerical solution was obtained for the diffusion equation using the Regula Falsi method. Regression analyses of experimental data were conducted.Diffusion of protons in silica hydrogel is a complicated process due to a decelerating effect of the porous structure of silica hydrogel and to the accelerating effects of slow ions such as Na⁺ and surface diffusion. The effective diffusion coefficient increased with surface area of silica gel, indicating the diffusion of protons on the surface of the silica particles.     

Diffusion energies of oxygen diffusing into polystyrene (PS)/poly (N‐isopropylacrylamide) composites

Diffusion coefficient of oxygen penetrating into polystyrene (PS) latex/poly (N‐isopropylacrylamide) (PNIPAM) microgel composite films were measured using Fluorescence technique. Three different (5, 15, and 40 wt%) PS content films were prepared from PS/PNIPAM mixtures. Diffusivity of PS/PNIPAM composite films were studied by diffusion measurements which were performed over the temperature range of 24–70°C. Pyrene was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined using the Stern–Volmer fluorescence quenching method combined with Fickian transport and were computed as a function of temperature for each PS content film. The results showed that D values were strongly dependent on both temperature and PS content in the film. Diffusion energies were measured and found to be dependent on the composition of the composite films. Copyright © 2011 John Wiley & Sons, Ltd.     

Fluorescence Enhancement of IgG-FITC Based on Surface Plasmon Resonance of Ag@SiO2 Nanoparticles as Application of Biomarker

Ag@SiO₂ nanoparticles with the core-shell structure have been prepared, of which the silver core was about 50 nm and the thickness of silica shell was approximately 10 nm. In slightly alkaline aqueous solution (pH = 8), through electrostatic force between cationic polymer PDDA (i.e., poly-diallyldimethylammonium chloride) and the obtained Ag@SiO₂ nanoparticles, PDDA molecules were fixed on the surface of Ag@SiO₂ nanoparticles. The prepared Ag@SiO₂/PDDA nanoparticles have both rich positive surface charges and rich micro-holes of silica shell. Based on micro-hole adsorption, the small molecule FITC (i.e., fluorescein isothiocyanate) marking on IgG (i.e., immunoglobulin) was adsorbed into the rich microholes of silica shell; at the same time, the negatively charge macromolecule IgG marked by FITC was firmly fixed on the rich positive charges surface of Ag@SiO₂/PDDA nanoparticles by electrostatic interaction. And then, Ag@SiO₂/PDDA/IgG-FITC fluorescent nanoparticles with the SPR fluorescence enhancement were prepared. The shell-type SiO₂/PDDA/IgG-FITC nanoparticles were obtained by dissolving the silver core in the prepared core-shell Ag@SiO₂/PDDA/IgG-FITC nanoparticles by using H₂O₂. Compared with the shell-type nanoparticles, the fluorescence intensity of Ag@SiO₂/PDDA/IgG-FITC was enhanced 1.7 times. The prepared Ag@SiO₂/PDDA/IgG-FITC nanoparticles have both SPR-based fluorescence enhancement ability and the surface distributing IgG–based obvious advantages including good biocompatibility and easy marking with other biomolecules.     

Glucose diffusivity and porosity in silica hydrogel based on organofunctional silanes

The silica hydrogels prepared at physiological conditions were characterized with respect to the glucose diffusion properties and the porosity by employing various approaches. A diffusion coefficient of glucose in silica hydrogel in the range of 2 × 10⁻¹⁰ m² s⁻¹ was determined by two complementary techniques based on the glucose ingress and egress, respectively. The confocal laser scanning microscopy in a time-lapse imaging mode was employed to measure the ingress of fluorescently labeled glucose analogue inside the hydrogel. In addition, a method for direct glucose release from the hydrogel was established. The simple diffusion model based on the Fickian diffusion and Ritger–Peppas theory were employed for evaluation of diffusion coefficients, respectively. The BET analysis and permeation of fluorescently labeled dextrans of various molecular weights were used to characterize the porosity of silica hydrogel. The radius of pores accessible for diffusion of dextran molecules in prepared silica hydrogel ranges between 1 and 6 nm.     

Control of Semiconductor Particle Size in Sol-Gel Thin Films

Thin silica and silica-titania films containing CdS and PbS quantum size particles were obtained by separate preparation of the matrix and the colloidal sols and successive mixing. Sulfide particles were obtained by reaction of metal acetates with thioacetamide and control of particle size was achieved by surface capping agents. Powders and thin films deposited on soda-lime slides were prepared and characterized by XRD. Absorption spectra were recorded on films. The nonlinear refractive index was measured by anm-line technique on a CdS-doped sample. The nonlinear effect was found to be reversible and an ₂ value of −3 10⁻⁹ cm²/kW was measured.     

Influence of some amino acids on the dynamic swelling behavior of radiation-induced acrylamide hydrogel

The influence of some amino acids—alanine, glycine, valine, glutamine, histidine, phenylalanine, and tryptophan—on the swelling behavior of acrylamide (AAm) hydrogel prepared by γ-radiation was investigated. Swelling experiments of AAm hydrogel were made in the universal buffer solutions and the amino acid solutions at certain pHs at 37°C. These selected pH values were pK₁, pK₂ and isoelectric point (pI) values such as ionization of α-carboxyl groups, ionization of α-amino groups, and the pIs of the amino acids, respectively. The swelling of AAm hydrogel increased when pH values of solutions were increased. The value of equilibrium swelling of AAm hydrogel in the solution of universal buffer was 880% at pH 10.0, whereas it was 670% at pH 2.0. The values of equilibrium swelling of AAm hydrogel in amino acid solutions were between 830 and 965% at pH 10.0, whereas they were between 635 and 775% at pH 2.0. The rate constant of swelling, initial swelling rate, theoretical maximum swelling, diffusional exponent, network parameter, and diffusion coefficient were calculated by swelling kinetics. Diffusions of the amino acid solutions into the hydrogel were generally found as non-Fickian in character. The diffusion coefficients of the hydrogel were between 0.91 × 10⁻⁶ and 2.41 × 10⁻⁶ cm²/s.     

Evolution of an iron passive film in a borate buffer solution (pH 8.4)

The evolution under open-circuit conditions of iron passive films formed at 0.8 V_SCE in a borate buffer solution at pH 8.4 was investigated with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composition of the freshly formed passive film as determined by X-ray photoelectron spectroscopy (XPS) was found to be in agreement with a bilayer model, where the inner layer is composed mainly of iron oxide and the outer layer consists of a hydrated material. Results of XPS measurements also showed that the open-circuit breakdown of passive films was consistent with a reductive dissolution mechanism. When the iron electrode reached an intermediate stage in the open-circuit potential decay (approximately −0.3 V_SCE), the oxide film, containing both Fe(II) and Fe(III), was still protective. The impedance response in this stage exhibited a mixed control by charge transfer at the metal/film and film/solution interfaces and diffusion of point defects through the film. At the final stage of the open-circuit potential decay (approximately −0.7 V_SCE), the oxide film was very thin, and the ratio of Fe³⁺/Fe²⁺ and O²⁻/OH⁻ had decreased significantly. The impedance response also exhibited a mixed charge-transfer–diffusion control, but the diffusion process was related to transport of species in the electrolyte solution resulting from dissolution of the oxide film.     

Diffusion of99TcO4 - in compacted bentonite: Effect of pH, concentration, density and contact time

In order to assess radionuclide diffusion and transport properties in compacted bentonite, the “in-diffusion” method based on bentonite filled capillaries is used. The effect of ⁹⁹TcO₄ ^- concentration and pH value of the solution, the contact time and the dry density of compacted bentonite on the apparent diffusion coefficient (D _a) and on the distribution coefficient (K _d) values obtained from the capillary test was studied. The D _a and K _d values decrease with increasing of the bulk dry density of compacted bentonite. Ion exclusion influences the diffusion of ⁹⁹TcO₄ ^- in the same substance. As compared to literature data, the K _d values obtained from capillary tests are in most cases lower than those from batch tests, the difference between the two K _d values is a strong function of dry density of the compacted bentonite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction between lactose and cadmium chloride in aqueous solutions as seen by diffusion coefficients measurements

Diffusion coefficients of an aqueous system containing cadmium chloride 0.100 mol · dm⁻³ and lactose at different concentrations at 25 °C have been measured, using a conductimetric cell and an automatic apparatus to follow diffusion. The cell relies on an open-ended capillary method and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times. From these results and by ab initio calculations, it was possible to obtain a better understanding of the effect of lactose on transport of cadmium chloride in aqueous solutions.     

Preparation of amino-functionalized mesoporous silica thin films with highly ordered large pore structures

Highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of triblock copolymer Pluronic P123 surfactant species under acidic conditions by sol-gel dip-coating. The effect of the sol aging on thin films organization is systematically studied, and the optimal sol aging time is obtained. The amino-functionalized mesoporous silica thin films exhibit a long-range ordering of 2D hexagonal (p6mm) mesostructure with a large pore size of 8.3 nm, a large Brunauer–Emmett–Teller (BET) specific surface area of 680 m² g⁻¹ and a large pore volume of 1.06 cm³ g⁻¹ following surfactant extraction as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM), and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for the amino-functionalized mesoporous silica thin films is calculated to be 3.2 amino-groups per nm². Moreover, the functionalized thin films display improved properties for immobilization of cytochrome c in comparison with pure-silica mesoporous thin films.     

Silver containing sol–gel derived silica thin films: effect of aluminum incorporation on optical,microstructural and bactericidal properties

Silver containing silica (Ag–SiO₂) thin films with and without aluminum (Al) were prepared on soda-lime-silica glass by spin coating of aqueous sols. The coating sol was formed through mixing tetraethyl orthosilicate [Si(OC₂H₅)₄]/ethanol solution with aqueous silver nitrate (AgNO₃) and aluminum nitrate nonahydrate [(AlNO₃)₃·9H₂O] solutions. The deposited films were calcined in air at 100, 300 and 500 °C for 2 h and characterized using x-ray diffraction, UV-visible and x-ray photoelectron spectroscopy. The effect of Al incorporation and calcination treatment on microstructure and durability of the films, and chemical/physical state of silver in the silica thin film have been reported. The bactericidal activity of the films was also determined against Staphylococcus aureus via disk diffusion assay studies before and after chemical durability tests. The investigations revealed that the optical, bactericidal properties and chemical durability of Ag–SiO₂ films can be improved by Al addition. The Al-modified Ag–SiO₂ thin films do not exhibit any coloring after calcination in the range of 100–500 °C, illustrating that silver is incorporated within the silica gel network in ionic form (Ag⁺). Al incorporation also improved the overall durability and antibacterial endurance of Ag–SiO₂ thin films.     

Swelling Kinetics of Microgels Embedded in a Polyacrylamide Hydrogel Matrix

Composite hydrogels—macroscopic hydrogels with embedded microgel particles—are expected to respond to external stimuli quickly because microgels swell much faster than bulky gels. In this work, the kinetics of the pH‐induced swelling of a composite hydrogel are studied using turbidity measurements. The embedded microgel is a pH‐ and thermosensitive poly(N‐isopropylacrylamide‐co‐acrylic acid) microgel and the hydrogel matrix is polyacrylamide. A rapid pH‐induced swelling of the embedded microgel particles is observed, confirming that composite hydrogels respond faster than ordinary hydrogels. However, compared with the free microgels, the swelling of the embedded microgel is much slower. Diffusion of OH^? into the composite hydrogel film is identified as the main reason for the slow swelling of the embedded microgel particles, as the time of the pH‐induced swelling of this film is comparable to that of OH^? diffusion into the film. The composition of the hydrogel matrix does not significantly change the characteristic swelling time of the composite hydrogel film. However, the swelling pattern of the film changes with composition of the hydrogel matrix.     

Dual crosslinked pH‐ and temperature‐sensitive hydrogel beads for intestine‐targeted controlled release

Novel drug‐loaded hydrogel beads for intestine‐targeted controlled release were developed by using pH‐ and temperature‐sensitive carboxymethyl chitosan‐graft‐poly(N,N‐diethylacrylamide) (CMCTS‐g‐PDEA) hydrogel as carriers and vitamin B₂ (VB₂) as a model drug. The hydrogel beads were prepared based on Ca²⁺ ionic crosslinking in acidic solution and formed dual crosslinked network structure. The structure of hydrogel and morphology of drug‐loaded beads were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The study about swelling characteristics of hydrogel beads indicated that the beads had obvious pH‐ and temperature‐sensitivity. In vitro release studies of drug‐loaded beads were carried out in pH 1.2 HCl buffer solution and pH 7.4 phosphate buffer solution at 37°C, respectively. The results indicated that the dual crosslinked method could effectively control the drug release rate under gastrointestinal tract (GIT) conditions, which was superior to traditional single crosslinked beads. In addition, the effects of grafting percentage, pH value, and temperature on the release behavior of the VB₂ were investigated. The drug release mechanism of CMCTS‐g‐PDEA drug‐loaded beads was analyzed by Peppa's potential equation. According to this study, the dual crosslinked hydrogel beads based on CMCTS‐g‐PDEA could serve as suitable candidate for drug site‐specific carrier in intestine. Copyright © 2009 John Wiley & Sons, Ltd.     

Binary gaseous diffusion coefficients,III: Sulfur hexafluoride with cyclohexane,methylcyclohexane and toluene at 1 atm pressure and 10–70°C

The binary gaseous diffusion coefficients at 1 atm pressure of sulfur hexafluoride with cyclohexane, methylcyclohexane, benzene, and toluene were measured at 10, 25, 40, 55 and 70°C by the capillary tube method ofStefan ¹. Diffusion coefficients were calculated (a) by usingLennard-Jones (6, 12) pair potential parameters in conjunction with theHudson-McCoubrey combining rule², and (b) with a semiempirical method somewhat similar to that suggested bychen andOthmer ³. Diffusion coefficients calculated via method (b) were in much better agreement with experiment than those obtained via method (a).     

Characterization of physical structure of silica nanoparticles encapsulated in polymeric structure of polyamide films

Polyamide nanocomposite films were prepared from nanometer sized silica particles and trimesoyl chloride–m-phenylene diamine based polyamides. The type of silica nanoparticles used is commercial LUDOX^® HS-40 and the particle size characterized by the radius of gyration (R_g) is about 66 Å. The immediately prepared films were easily broken into particles to form colloidal-like dilute suspension of the silica–polyamide composite particles in D₂O–H₂O solutions for SANS measurements, that in this dilute system SANS data the complication of scattering data from the interacting particles is minimized. At about 60% D₂O of the sample solution, the silica is contrasted out, therefore the SANS profiles are predominantly from the organic polyamide scattering. The SANS profile of the sample solutions measured at 90% D₂O clearly indicates scattering from both silica and polymer. The scattering heterogeneities for two-phase system were evident from the validity of the Debye–Bueche expression in case of the nanocomposite with high silica loading. At limited silica loading of the nanocomposite, interaction between the silica and polymer chains forming core–shell morphology was observed. The transport properties of the membranes made from the nanocomposite films were measured on a batch type test kit with an aqueous solution of 500 ppm dioxane concentration at pressures ranging from 50 to 200 psig, and correlated to their composite structure.     

Barrier and semiconducting properties of thin anodic films on chromium in an acid solution

The study of barrier and semiconducting properties of anodically formed oxide films on chromium in an acid solution was carried out using the Cr-quartz crystal electrode. The oxide film formation and growth occur through an anion vacancies transport via a low-field-assisted mechanism (H = 10⁶ V cm⁻¹). The anion diffusion coefficient, which quantitatively describes the transport of point defects within the growing film, was calculated from capacitance data using the Nernst-Planck equation for low-field limit approximation and Mott-Schottky analysis. The depletion region in the passive film, close to the film|electrolyte interface, dominates the semiconducting properties. The passive film on Cr in an acid solution behaves as an n-type semiconductor. An energy-band structure model of the passive film is given.     

Diffusion of polymer molecules into polymer networks: Effect of stresses and contraints

Fine threads of cis-1, 4-polyisoprene, diameter ca. 50 μm, were prepared by drawing from solution and drying. They were crosslinked by reaction with H₂S and SO₂ and then swollen with linear cis-polyisoprene liquids of varied molecular weight M_s, from 1,000 to 24,000 g/mol. Diffusion coefficients were determined from the initial rate of uptake, for both unrestrained and stretched threads. They were found to be in good agreement for stretches of up to about 300%. On the other hand, the equilibrium uptake increased markedly (> 100%) over this range of strain, similar to the increase in swelling observed with low-molecular-weight liquids. Values of diffusion coefficient were also obtained from the rate of deswelling upon release of swollen threads from tension, and from the rate of uptake of polymer liquids by a thin coating of crosslinked polymer, bonded onto glass fibers. Satisfactory agreement was obtained in all cases. A number of simple experiments thus give similar values for the diffusion coefficient of polymer liquids in lightly crosslinked polymer networks, in the range 10^?13?10^?16 m²/s, depending upon the molecular weight M_s of the polymer liquid approximately weight as M^?2_s. The amount of liquid absorbed was strongly dependent on its molecular weight, M_s, the degree of crosslinking of the host material, and applied stresses or constraints.     

Gamma-radiolysis of quinoline in 2-propanol solution

In the last twenty years the ionizing effects on matter of⁶⁰Co γ-rays have been widely discussed. However, regarding organic compounds, mainly aromatic ones, results are scarce, particularly those obtained in alcoholic solution. γ-Radiation is used mainly in industry and medicine, particularly for sterilization of surgical materials. In this work we studied the chemical and radiolytic stability of products by radiation from quinoline in isopropanol solution. Doses were from 2×10⁴ to 3×10⁵ Gy and the samples concentration was 1∶1 by volume. We have observed significant effects for high radiation doses. Lower doses effected the solvent with the production of long polymeric hydrocarbons. Products formed were characterized by capillary gas chromatography coupled to a mass-selective detector (GC/MSD). We have used a fused silica capillary column 25 m long, 0.2 mm in internal diameter, covered by a 0.33 μm thick film of crosslinked 5% phenyl methyl silicone.     

New ionic liquid for inorganic cations analysis by capillary electrophoresis: 2-hydroxy- N , N , N -trimethyl-1-phenylethanaminium bis(trifluoromethylsulfonyl)imide (phenylcholine NTf2)

The potentialities of new ionic liquids (ILs) based on choline were evaluated as an electrophoretic medium in capillary electrophoresis for the analysis of alkaline and alkaline earth cations (Li⁺, K⁺, Na⁺, Cs⁺, Mg²⁺, Ba²⁺, Ca²⁺, and Sr²⁺) with indirect UV detection. Two types of capillaries were tested: an untreated fused silica and fused silica coated with a film of polyvinylalcohol. The coated capillary proved to be the best adapted for the metal ions studied. Moreover, it appeared that the nature of the ionic liquid anion influenced the baseline stability, and the bis(trifluoromethylsulfonyl) imide (NTf₂ ⁻) anion seemed to be the most efficient. These preliminary studies led us to synthesize a new ionic liquid, 2-hydroxy-N,N,N-trimethyl-1-phenylethanaminium NTf₂ (phenylcholine NTf₂). This liquid was able to act as the running electrolyte and probe, generating the background signal in indirect UV light and consequently simplifying the electrophoretic medium. Excellent baseline stability, good reproducibility, as well as good sensitivity of detection were obtained with this new ionic liquid. Thus, 510,000 plates/meter for Li⁺ with 40 mM IL were successfully obtained. The optimal concentration of IL was 20 mM with a detection limit ranging from 28 μg L⁻¹ for Li⁺ to 1,000 μg L⁻¹ for Cs⁺. This method (phenylcholine NTf₂ with polyvinylalcohol capillary) was applied to analyze different commercial source and mineral waters. Finally, the potentiality of this ionic liquid in nonaqueous capillary electrophoresis was explored. The use of phenylcholine NTf₂ with a fused silica capillary, in pure methanol medium and in the presence of acetic acid, made it possible to obtain separation selectivity different from that obtained in aqueous medium.     

Preparation of a piezoelectric immunosensor for the detection of Salmonella paratyphi A by immobilization of antibodies on electropolymerized films

 To obtain new coatings for the preparation of piezoelectric immunosensors, the anodic polymerization of o-aminophenol (oAP), o-phenylenediamine (oPD) and m-phenylenediamine (mPD) onto a gold-plated crystal has been studied. The possibility of immobilizing an antibody (anti-S. paratyphi A) onto the crystal via the electropolymerized films was investigated. The poly-mPD film gave the best results for immobilizing the antibody. With antibodies crosslinked on the poly-mPD film, a piezoelectric immuno-assay for the detection of S. paratyphi A was proposed. The shift (ΔF=F_20s−F_400s, Hz) between the frequency at 20 s after the addition of sample (F_20s), and that of 400 s (F_400s) was used to construct a calibration graph, and shortening of the assay time was achieved. The S. paratyphi A concentration in the range of 10^5–10⁹ cells/ml can be measured by this method. Received: 9 May 1996/Revised: 6 September 1996/Accepted: 19 September 1996