动态光散射法研究海藻酸钠凝胶松弛行为

在前文的基础上，用相关函数轮廓分析的方法剖析了运动模型模式的复杂性。通过海藻酸钠水溶液在０．１ｍｏｌ／ＬＣａＣｌ２水溶液透析凝胶化过程中交联网络的松弛时间谱表明它不是单一的峰，有两上特征运动模式，并随透析向更慢的运动模式发展，这很慢的运动模式估计与区域的结构的生成有关。     

In situ polyurethane/silica composite formation via a sol‐gel process

Polyurethane acrylate anionomer (PUAA)/silica composite gels were prepared by the sol‐gel reaction of tetraethoxysilane (TEOS) and methacryloxypropyl trimethoxysilane (MPTS) incorporated to PUAA gels by using a swelling method. The formation and structure of composites were confirmed by FTIR, X‐ray diffraction, and SEM. As a result, we found that silica components in composites are located within the ionic domains of their gels and interacted with PUAA via hydrogen bonding. This drastically enhanced the mechanical properties of the composites. Mechanical properties are also improved by MPTS, because MPTS improves the dispersibility and adhesion of silica components in PUAA/silica composite gels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2327–2334, 2002     

Hybrids of cellulose acetate and sol–gel silica: Morphology,thermomechanical properties,water permeability,and biodegradation evaluation

Hybrids based on cellulose acetate (CA) and SiO₂ were prepared by hydrolysis of tetraethoxysilane (TEOS). More rigid films were obtained with an inorganic phase incorporation. The thermal stability of the hybrids was similar to pure CA. Composite membranes were prepared by casting of CA/TEOS mixtures onto a poly(vinylidene fluoride) support. The water permeation decreased with the incorporation of the inorganic phase. Hybrid membranes were able to retain solutes with a molar mass of ?9000 g/mol (?98% retention). Hybrids were submitted to biodegradation tests. The presence of the inorganic phase did not inhibit the growth of Thricoderma harzianum fungi. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2196–2205, 2002     

Effect of oxygen flow rate on the structural and electrochemical properties of lithium nickel oxides synthesized by the sol–gel method

The structural and electrochemical properties of LiNiO₂ powders were investigated as a function of the oxygen flow rate employed in the preparation of lithium nickel oxide. It was found that oxygen played an important role in the synthesis of highly crystallized LiNiO₂(R3¯m). In the crystallization process of LiNiO₂, a deficiency of oxygen in the calcination reactor induced the formation of impurities and cubic rock-salt structure (Fm3m) in LiNiO₂ powders. For LiNiO₂ prepared at higher oxygen flow rates, the electrode delivered high discharge capacities with relatively good retention rates. But very low electrode capacity was obtained from LiNiO₂ prepared at lower oxygen flow rates.     

Rich photoluminescence emission of SnO2–SiO2 composite aerogels prepared with a co-fed precursor sol–gel process

Tin oxide–silica composite aerogels were successfully prepared with a co-fed precursor sol–gel process. The crystallinity of the tin oxide nanoparticles, embedded in the mesoporous SiO₂ network, was improved with increasing the post-reaction thermal treatment temperature. The composite aerogels exhibited a rich photoluminescence (PL) emission contributed by both SnO₂ and SiO₂. The PL peak of 346 nm was from the near band edge emission of the tin oxide nanoparticles, and the ones located at 310 and 476 nm were attributable to the oxygen deficiencies of the silica network. Three more emission peaks, 387, 432, and 522 nm, were observed, with the 387 nm peak contributed by the oxygen vacancies V_O⁺⁺, the 432 nm peak by the Sn interstitials, and the 522 nm peak by the oxygen vacancies V_O⁺, respectively, of the tin oxide nanoparticles. The intensities of these three defect level emissions were found decreased, as compared to that of the near band edge emission, with increasing the post-reaction thermal treatment temperature as the tin oxide crystallinity improved.     

Application d'une méthodologie expérimentale à l'étude du diagramme ternaire d'un gel

Nous avons montré sur l'exemple d'un gel, mélange de trois constituants (C12–C15 Alcohols Benzoate, Cyclomethicone et Ethylene Vinyl Acetate Copolymer) qu'il est possible d'optimiser une formulation en un nombre preécis d'essais en faisant appel à une stratégic expérimentale optimale. Le gel avait déjàétéétudié par Chang,¹ mais par approches successives.
Nous avons utlisé les matrices d'expériences développées dans le cas des mélanges par Scheffe sous le nom de 'reseaux-simplex'. Prévoyant des intéractions de 2éme ordre entre les constituants nous avons retenu le modéle appelé'cubique réduit'. Cette approche permet l'exploration systémique de tout le domaine.
Les réponses étudiées sont la compatibilité (gel homogène ou non), la consistance, la blancheur et le coût. Le meilleur gel étant celui qui se rapproche le plus de la vaseline.
A partir des résultats, nous avons tracé des courbes d'isoréponse en blancheur, consistance et coût. La superposition des diagrammes conduit à la détermination d'une zone où les réponses sont optimales.
En ajoutant la réponse supplémentaire: 'facilité d'étalement sur la peau'on arrive au meilleur gel avec un nombre réduit d'essais.
La même méthode s'appliquerait à des mélanges de plus de trois constituants.
Study of a ternary diagram gel according to a methodology of experimental research     

Restoration of the red colour of photo-bleached carthamine in calcium-alginate gel membranes

The restoration of the red colour of carthamine (photo-bleached in polymeric heterosaccharide gels) was investigated using sodium salts, potassium salts, and alkali. Ca-alginate gel was stained with carthamine, and the red-dish membranes were exposed to fluorescent light for 2·5, 4·0 and 20 h (at 28°C). The resulting orange-yellow gel membranes were treated with Na- or K-citrate solution and the restoration of the red colouration was followed spectrophoto-metrically. The results indicate that the red colour of carthamine can be retained within the gel membranes, while yellow-coloured compounds were removed and/or transformed by the alkaline salt solutions.     

Sunflower Head Residue Pectin Extraction as Affected by Physical Conditions

Effects of extraction pH, temperature, and time on yield and quality of pectin from sunflower heads (Interstate cultivar) were investigated. The low-methoxyl pectin was extracted, using 0.75% sodium hexametaphosphate at pH 3, 4, and 5 and at 75, 85, and 95°for 20, 40, and 60 min, respectively. Yield, molecular mass, and firmness of jellies of the pectins were determined. Three-way statistical analysis on yield, molecular mass and gel firmness showed strong interactions among pH, temperature and time. Highest yields were obtained at pH 5, 95°for 20 min and pH 4, 85°for 40 min. Pectin extracted for 40 min at pH 3 and 4 and at 85°and 75°C, respectively, had the highest molecular mass. Gel firmness of sunflower pectin prepared at pH 5.4 was higher than that of a commercial citrus pectin.     

Photoelectrochemical properties of sol–gel-derived Ti1−xVxO2 solid solution film photoelectrodes

Ti_1−xV_xO₂ solid solution film photoelectrodes were prepared by the dip-coating sol–gel method. X-ray diffraction and X-ray photoelectron spectroscopy were employed to ensure the formation of the solid solution and their composition. Obvious photoresponses were observed in the visible region for the solid solution film electrodes with x0.05 and the red shift of the photoresponse was enhanced with increasing x. Moreover, the solid solution film electrodes were found to be photoelectrochemically stable. However, the onset potential of photocurrent shifted positively with increasing x. Band model of the solid solution was suggested to explain the effects of the vanadium incorporation on the photoelectrochemical properties.     

Nanocrystalline orthoferrite powders: Synthesis and magnetic properties

Nanocrystalline orthoferrite powders were synthesised at low temperatures by employing an aqueous sol–gel process. Colloidal sols and water re-dispersible gels of orthoferrite precursors were prepared by room-temperature processing of inexpensive metal salts. The average diameter (Z_av) of the precursor particles was in the size range from 4 to 7 nm; the diameters had a narrow size distribution. Water re-dispersible translucent gel monoliths were obtained by concentrating the aqueous sols followed by drying them under reduced pressure (10⁻² Torr) at room temperature. The sol–gel transition was found to be completely reversible. Nanocrystalline fine powders of orthoferrites of general formula, LnFeO₃ (Ln = La, Sm, Gd, Dy, Er, Yb and Y) having a crystallite size of about 25 nm were prepared by heating the gel precursors at 650–700 °C in air. Powder X-ray diffraction and thermogravimetry, respectively, were employed to identify perovskite phase formation and delineate thermal events that lead to gel to crystallite conversion. Magnetic measurements were carried out on the resultant powders at room temperature and down to 40 K. Nanocrystalline orthoferrite powders exhibited weak ferromagnetic behaviour, and reduced magnetic moments.