Surface Modification of Amorphous SiO2 Nanoparticles by Oxygen-Plasma and Nitrogen-Plasma Treatments

In this study, amorphous silica gels were synthesized and treated by oxygen plasma and nitrogen plasma at a radio frequency power of 60 W, at heating temperature of 300°C, and a treatment period of 400 s. The silica gels were characterized by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller, and thermal conductivity analyzers. The characterization results show that oxygen-plasma treatment has remarkably reduced the surface hydroxyl groups in silica gels, whereas nitrogen-plasma treatment has less effects. The reduction of the hydroxyl groups is a key factor contributing to reduced particle size from 30 nm to 15 nm, thus resulting in an increased specific surface area from 124 to 420 m²/g. In addition, the reduced particle size has drastically lowered the thermal conductivity of silica gels, from 0.14220 to 0.00014 W/mK. Therefore, oxygen-plasma treatment is a feasible method to enhance the thermal insulating properties of silica gels.     

Preparation of transparent pea protein gels: a comparison of isolation procedures

Two commercially viable procedures for the preparation of protein fractions from pea flour are described and discussed. These fractions form thermally induced transparent gels at acid pH and are composed of the globulins, vicilin and legumin, identified by electrophoresis and differential scanning calorimetry. The gels have clarities that allow their use as vegetarian substitutes for gelatin and additionally show thermal stabilities suitable for applications in hot products. The influence of other food ingredients (salt, sugar and vegetable oil) on gel clarity is also investigated.     

Flow and aggregation characteristics of thermo-responsive poly(N-isopropylacrylamide) spheres during the phase transition

To date, a great many researches were focused on improving stimuli-responsive and controlled-release properties of thermo-responsive hydrogel carriers, whereas for the research on flow characteristics during the phase transition, prior reports have not been found. In this paper, poly(N-isopropylacrylamide) (PNIPAM) spheres with thermo-responsive phase transition characteristics were prepared by cross-linked polymerization. In a transparent Pyrex glass pipe with hydrophilic inner wall, flow and aggregation characteristics of PNIPAM spheres during the phase transition from low temperature which was lower than the lower critical solution temperature (LCST) to high temperature (T>LCST) was studied for the first time. Many interesting phenomena about the flow and aggregation behaviors of PNIPAM spheres were found. The velocity of PNIPAM spheres in horizontal pipe decreased from 1.07 cm/s before the phase transition to 0.65 cm/s or even became zero after the phase transition, which is what targeting drug delivery systems desired. When the initial distance was about 5.5 mm at the entrance of testing pipe section, the PNIPAM spheres could aggregate together after the phase transition and subsequently roll forward; but when the initial distance was as large as 8.5 mm, the distance became close at first during the phase transition and then far after the phase transition. Similar results were also found as mentioned above in vertical pipe. When 10 spheres aggregated together, they stopped at a certain position just after the phase transition in horizontal pipe. If the flowrate was more than 40 ml/min, the aggregation configurations such as triangle, tetrahedron, hexahedron and octahedron which formed after the phase transition at flowrate of 20 ml/min disappeared. The results provided valuable information for future applications of thermo-responsive PNIPAM spheres.     

Study of sol–gel transition in calcium alginate system by population balance model

The growth of calcium alginate (Ca-alginate) clusters and its sol–gel transition phenomena were simulated with a population balance model. The classical statistical concept proposed by Flory–Stockmayer has been adopted and incorporated by the factor of cyclic structures formation into the model. Ca-alginate gelation was described as a random cross-linking of multifunctional monochains. The resulting discretized kinetic equations were solved numerically by parallel computation. After demonstrating the accuracy of this model, the effect of the cyclic structure, the reaction rate constants and the physical properties of the reactants (i.e., alginate and gelling agent of Ca²⁺ ions) were examined. The present work clarifies the mechanisms for forming ionotropic Ca-alginate gels and presents the concentration ranges where the transition between the sol state and the gel state occurs. The model allows for the estimation of the relative magnitude of stepwise reaction rate constants and the prediction of the sol–gel transition boundary. Finally, a reasonable agreement was obtained between the experimental results and model predictions.     

Combined microscopic and dynamic rheological methods for studying the structural breakdown properties of whey protein gels and emulsion filled gels

The microstructural and large deformation rheological properties of model food gels were studied by performing notch propagation tensile testing on the gels using a tensile stage and observing changes in the microstructure of the gels during tensile testing using confocal laser scanning microscopy (CLSM). Heat-set whey protein (WP) gels containing either added sodium caseinate (NaCN) or sunflower oil droplets emulsified with WP or NaCN as the emulsifier protein were prepared in 0 or 50 mM NaCl. The WP gel structure strengthened in the presence of added NaCl and NaCN. The rheological properties of WP gels containing sunflower oil droplets emulsified with WP or NaCN were influenced by the NaCl concentration, oil concentration and extent of oil droplet aggregation in the gel or by the type of emulsifier protein used. During tensile testing, the notch length in all gels increased above a certain critical stress, leading to fracture of the gels through the notch. Also, the microstructural changes in the oil phase of emulsion filled gels subjected to tensile testing were influenced by the structural properties of the WP gel matrix and the proximity of the oil droplet to the fracture path.     

How to Make Colorless Poly(ethylene terephthalate)(PET)

Abstract

The methods and flow charts used for the industrial preparation of PET are shown and briefly discussed. Then, the three classes of contaminants usually appearing in PET are described and their causes elucidated. The organic contaminants impart to the produced PET an undesired yellow-amber tinge while those containing metal ions or elemental metals impart to the polymer various undesirable colors. Other organic contaminants are crosslinked gels and flakes, and especially the latter may cause filament rupture and may lead to the disruption of melt spin-draw processes. Some remedies to eliminate or minimize the appearance of such contaminants are then suggested, followed by a brief discussion of non-antimony catalysts which eliminate the gray discoloration usually imparted to PET by antimony-containing catalysts.     

Geopolymerisation kinetics. 3. Effects of Cs and Sr salts

Alternating current impedance spectroscopy (ACIS) is used to monitor in situ the kinetics of geopolymer formation by alkali silicate activation of metakaolin at 40 °C. The evolution of conductivity and resistivity as a function of time are found to correlate very well with existing models of geopolymerisation kinetics. The dissolution of metakaolin gives a rapid increase in conductivity, with a subsequent decrease due to gelation and gel ageing. After a period of curing, the resistivity of the gel network is seen to be a sensitive probe of the development of a well-formed gel structure. This enables investigation of the changes in geopolymer formation kinetics and gel structure caused by addition of various salts of interest in nuclear waste management, in particular the nitrate, sulphate and hydroxide salts of caesium and strontium. Each of the six salts studied is shown to have specific effects on the kinetics of geopolymer formation and the pore structure of the final geopolymer gel. Caesium nitrate and caesium sulphate have very similar effects, with a slight retardation of gelation followed by significant disruption of gel structure while caesium hydroxide accelerates gel formation markedly. Strontium nitrate at high concentrations interferes significantly with the pore network development, while strontium sulphate is converted gradually to carbonate salts by atmospheric carbonation.     

A study of diffusion of dyes in model foods using a visual method

Many food processing operations involve mass transfer. The application of electric fields can influence the mass transfer properties of foods. A major limitation of infusion studies is the lack of successful measurement techniques to quantify the depth of penetration and localisation of infused material. Diffusion of two dyes (rhodamine 6G and methylene blue) in agar and alginate gels was visualised insitu for 10 min. The experiments were performed at three temperatures (30, 50, and 70 °C) and four voltage gradients (167, 333, 500, 667 V m⁻¹) plus a control (0 V m⁻¹). The effect of hydrocolloid concentration and electrical conductivity on diffusion and response to the electric field were tested. The limitations of Fickian analysis led to a new method of data analysis, the penetration model. The effect of the type of gel and the diffusing molecule charge and mass on the combined diffusion and electric field process is discussed.