scholarly journals Structuring of hydroxy-terminated polydimethylsiloxane filled by fumed silica

e-Polymers ◽  
2021 ◽  
Vol 21 (1) ◽  
pp. 131-139
Author(s):  
Zhengwei Peng ◽  
Yan Qin ◽  
Jiuqiang Song ◽  
Di Zhu ◽  
Shuisheng Chen ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Water Content ◽  
Silicone Rubber ◽  
Fumed Silica ◽  
Room Temperature ◽  
Adsorbed Water ◽  
Solvent Free ◽  
Dissolution Model ◽  
Different Temperatures ◽  
Initial Viscosity

Abstract The term “structuring” used in silicone rubber describes a phenomenon of the increase in the viscosity of polydimethylsiloxane filled with silica during storage, which limits the applications of the room temperature vulcanized (RTV) silicone rubber in the field of aerospace and military. In this pursuit, the present study was envisaged to solve the problem of structuring of the RTV. A solvent-free method was used to hydrophobize the hydrophilic silica with hexamethyldisilazane. An RTV composition prepared using eight parts of hydrophobic silica with 2.91% C content exhibited a viscosity of less than 100 Pa s, with no significant change in 21 days. In contrast, eight parts of the hydrophilic fumed silica showed an initial viscosity of RTV to be greater than 2,000 Pa s. Silica samples with different adsorbed water content were used to prepare the RTV compositions. It was found that the viscosity of the RTV prepared using the sufficiently dried silica was 5.6 times lower than that of the wet silica. The “dissolution” model of the silica–silica hydrogen bonds in water was proposed. Furthermore, the change in the viscosity of the RTV compositions at different temperatures in the range of −15°C to 30°C was studied. The viscosity of RTV stored at –15°C for 34 days did not change significantly, whereas that stored at room temperature increased from 100 to 1,710 Pa s within 21 days.

A polymorphism-dependent T1/2 shift of 100 K in a hysteretic spin-crossover complex related to differences in intermolecular weak CH⋯X hydrogen bonds (X = S vs. S and N)

2016 ◽  
Vol 52 (4) ◽  
pp. 815-818 ◽  
Author(s):  
Hiroaki Hagiwara ◽  
Shohei Okada
Keyword(s):  
Hydrogen Bonds ◽  
Room Temperature ◽  
Spin Crossover ◽  
Solvent Free

[FeIILMe(NCS)2] crystallizes in two solvent-free polymorphs and shows hysteretic spin crossover with polymorphism-dependent T1/2 shift of 100 K spanning room temperature.

scholarly journals Umur Simpan Saos Tomat Pada Berbagai Konsentrasi Bahan Pengental

2019 ◽  
Vol 2 (2) ◽  
pp. 113
Author(s):  
Catur Budi Handayani ◽  
A. Intan Niken Tari ◽  
Afriyanti Afriyanti
Keyword(s):  
Shelf Life ◽  
Water Content ◽  
Room Temperature ◽  
Fungal Growth ◽  
Tomato Sauce ◽  
Organoleptic Test ◽  
Calculation Results ◽  
Different Temperatures ◽  
Refrigerator Temperature

Research on the shelf life of tomato sauce at various coagulant concentrations uses local tomatoes from the Sukoharjo with a concentration of 5, 7.5 and 10% of maezena flour from tomatoes used. The shelf life calculation uses the Archenius method with storage for 4 weeks at 3 different temperatures namely refrigerator temperature (4 OC), room temperature (27 OC), and temperature of 50 OC. Calculations are based on changes in water content, fungal growth and organoleptic tests of taste. The calculation results show that the shortest shelf life of tomato sauce is 24 days for sauces with 5 and 7.5% coagulant and 47 days for sauces with 10% coagulant, which are calculated based on organoleptic test of taste.Keywords: tomato sauce, shelf life, coagulant

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

Preparation and Characterization of a Novel Room Temperature Dicationic Ionic Liquid and its Application in the Synthesis of Xanthenediones Under Solvent-Free Conditions

2018 ◽  
Vol 21 (8) ◽  
pp. 602-608 ◽  
Author(s):  
Zainab Ehsani-Nasab ◽  
Ali Ezabadi
Keyword(s):  
Ionic Liquid ◽  
Room Temperature ◽  
Reaction Times ◽  
Significant Loss ◽  
Solvent Free ◽  
Acidity Function ◽  
Efficient Catalyst ◽  
Solvent Free Conditions ◽  
Hammett Acidity Function ◽  
Dicationic Ionic Liquid

Aim and Objective: In the present work, 1, 1’-sulfinyldiethylammonium bis (hydrogen sulfate) as a novel room temperature dicationic ionic liquid was synthesized and used as a catalyst for xanthenediones synthesis. Material and Method: The dicationic ionic liquid has been synthesized using ethylamine and thionyl chloride as precursors. Then, by the reaction of [(EtNH2)2SO]Cl2 with H2SO4, [(EtNH2)2SO][HSO4]2 was prepared and after that, it was characterized by FT-IR, 1H NMR, 13C NMR as well as Hammett acidity function. This dicationic ionic liquid was used as a catalyst for the synthesis of xanthenediones via condensation of structurally diverse aldehydes and dimedone under solvent-free conditions. The progress of the reaction was monitored by thin layer chromatography (ethyl acetate/n-hexane = 3/7). Results: An efficient solvent-free method for the synthesis of xanthenediones has been developed in the presence of [(EtNH2)2SO][HSO4]2 as a powerful catalyst with high to excellent yields, and short reaction times. Additionally, recycling studies have demonstrated that the dicationic ionic liquid can be readily recovered and reused at least four times without significant loss of its catalytic activity. Conclusion: This new dicationic ionic liquid can act as a highly efficient catalyst for xanthenediones synthesis under solvent-free conditions.

Synthesis of Dihydropyrimidinones (DHPMs) and Hexahydro Xanthene Catalyzed by 1,4-Diazabicyclo [2.2.2] Octane Triflate Under Solvent-Free Condition

2019 ◽  
Vol 16 (5) ◽  
pp. 776-786 ◽  
Author(s):  
Deepa ◽  
Geeta D. Yadav ◽  
Mohd J. Aalam ◽  
Pooja Chaudhary ◽  
Surendra Singh
Keyword(s):  
Ethyl Acetoacetate ◽  
Biginelli Reaction ◽  
Solvent Free ◽  
Efficient Catalyst ◽  
Solvent Free Condition ◽  
Solvent Free Conditions ◽  
Xanthene Derivatives ◽  
Different Temperatures ◽  
Flash Column Chromatography ◽  
Biginelli Condensation

Objective:DABCO salts were evaluated as catalysts for the Biginelli reaction between 4- methoxybenzaldehyde, urea and ethyl acetoacetate under solvent-free conditions. 1,4-Diazabicyclo [2.2.2] octane triflate was found to be a simple, inexpensive, highly efficient catalyst for Biginelli reaction for a variety aromatic aldehyde with urea and ethyl acetoacetate at 80°C afforded corresponding 3,4-dihydropyrimidinones in 50-99% yields after 30-120 minutes. 1,3-Cyclohexadione was used in place of ethyl acetoacetate in the absence of urea this methodology is giving hexahydro xanthene derivatives in good to excellent yields after 3-4 hours.Methods:DABCO salt 4 (5 mol%), 4-methoxybenzaldehyde (0.73 mmol) and urea (0.73 mmol) were stirred for 10 minutes at 80°C, then ethyl acetoacetate (1.5 equiv.) was added and reaction mixture was stirred at 80°C for specified time. The resulting solution was stirred continuously and progress of the reaction was followed by TLC. The crude reaction mixture was purified by flash column chromatography on silica gel (hexane/ethyl acetate (1:2)) to give pure desired product.Results:Reaction conditions of the Biginelli reaction were optimized using 4-methoxybenzaldehyde (0.73 mmol), urea (0.73 mmol), and ethyl acetoacetate (5 equiv.) as model substrates catalyzed by 1,4-Diazabicyclo [2.2.2] octane triflate (5 mol%) in a different solvents, screening of different catalysts and different temperatures. Neat condition was found to be the best for the Biginelli condensation and corresponding 3,4- dihydropyrimidinones was obtained in good to excellent yields. When the reaction was carried out with benzaldehyde derivatives and cyclohexane-1,3-dione in place of ethyl acetoacetate in the absence of urea, solely corresponding hexahydro xanthene derivatives were obtained in 61-91% yields.Conclusion:In conclusion, we have applied salts of 1,4-Diaza-bicyclo [2.2.2] octane as catalysts in the Biginelli condensation and corresponding 3,4-dihydropyrimidinones were obtained in 50- 99% yields under solvent free conditions. This methodology is having advantages like simple work-up; low loading of catalyst and reaction was performed at moderate temperature under solvent-free conditions.

scholarly journals Properties of Silicone Rubber-Based Composites Reinforced with Few-Layer Graphene and Iron Oxide or Titanium Dioxide

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1550
Author(s):  
Vineet Kumar ◽  
Anuj Kumar ◽  
Minseok Song ◽  
Dong-Joo Lee ◽  
Sung-Soo Han ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Titanium Dioxide ◽  
Iron Oxide ◽  
Stress Relaxation ◽  
Silicone Rubber ◽  
Room Temperature ◽  
Relaxation Rates ◽  
Layer Graphene ◽  
Few Layer Graphene ◽  
Mechanical Actuation

The increasing demand for polymer composites with novel or improved properties requires novel fillers. To meet the challenges posed, nanofillers such as graphene, carbon nanotubes, and titanium dioxide (TiO2) have been used. In the present work, few-layer graphene (FLG) and iron oxide (Fe3O4) or TiO2 were used as fillers in a room-temperature-vulcanized (RTV) silicone rubber (SR) matrix. Composites were prepared by mixing RTV-SR with nanofillers and then kept for vulcanization at room temperature for 24 h. The RTV-SR composites obtained were characterized with respect to their mechanical, actuation, and magnetic properties. Fourier-transform infrared spectroscopy (FTIR) analysis was performed to investigate the composite raw materials and finished composites, and X-ray photoelectron spectroscopy (XPS) analysis was used to study composite surface elemental compositions. Results showed that mechanical properties were improved by adding fillers, and actuation displacements were dependent on the type of nanofiller used and the applied voltage. Magnetic stress-relaxation also increased with filler amount and stress-relaxation rates decreased when a magnetic field was applied parallel to the deformation axes. Thus, this study showed that the inclusion of iron oxide (Fe3O4) or TiO2 fillers in RTV-SR improves mechanical, actuation, and magnetic properties.

scholarly journals Temperature-Dependent Stimulated Emission Cross-Section in Nd3+:YLF Crystal

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 431
Author(s):  
Giorgio Turri ◽  
Scott Webster ◽  
Michael Bass ◽  
Alessandra Toncelli
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Room Temperature ◽  
Radiative Decay ◽  
Emission Cross Section ◽  
Spectroscopic Properties ◽  
Stimulated Emission ◽  
Different Temperatures ◽  
Stimulated Emission Cross Section ◽  
Semi Empirical

Spectroscopic properties of neodymium-doped yttrium lithium fluoride were measured at different temperatures from 35 K to 350 K in specimens with 1 at% Nd3+ concentration. The absorption spectrum was measured at room temperature from 400 to 900 nm. The decay dynamics of the 4F3/2 multiplet was investigated by measuring the fluorescence lifetime as a function of the sample temperature, and the radiative decay time was derived by extrapolation to 0 K. The stimulated-emission cross-sections of the transitions from the 4F3/2 to the 4I9/2, 4I11/2, and 4I13/2 levels were obtained from the fluorescence spectrum measured at different temperatures, using the Aull–Jenssen technique. The results show consistency with most results previously published at room temperature, extending them over a broader range of temperatures. A semi-empirical formula for the magnitude of the stimulated-emission cross-section as a function of temperature in the 250 K to 350 K temperature range, is presented for the most intense transitions to the 4I11/2 and 4I13/2 levels.

Proteinase and phospholipase activities and development at different temperatures of yeasts isolated from bovine milk

2011 ◽  
Vol 78 (4) ◽  
pp. 385-390 ◽  
Author(s):  
Priscilla A Melville ◽  
Nilson R Benites ◽  
Monica Ruz-Peres ◽  
Eugenio Yokoya
Keyword(s):  
Dairy Products ◽  
Room Temperature ◽  
Bovine Milk ◽  
Raw Milk ◽  
Pathogenic Potential ◽  
Proteinase Production ◽  
Different Temperatures ◽  
Quality Of Milk ◽  
Means Of Transmission

The presence of yeasts in milk may cause physical and chemical changes limiting the durability and compromising the quality of the product. Moreover, milk and dairy products contaminated by yeasts may be a potential means of transmission of these microorganisms to man and animals causing several kinds of infections. This study aimed to determine whether different species of yeasts isolated from bovine raw milk had the ability to develop at 37°C and/or under refrigeration temperature. Proteinase and phospholipase activities resulting from these yeasts were also monitored at different temperatures. Five genera of yeasts (Aureobasidium sp., Candida spp., Geotrichum spp., Trichosporon spp. and Rhodotorula spp.) isolated from bovine raw milk samples were evaluated. All strains showed one or a combination of characteristics: growth at 37°C (99·09% of the strains), psychrotrophic behaviour (50·9%), proteinase production (16·81% of the strains at 37°C and 4·09% under refrigeration) and phospholipase production (36·36% of the isolates at 37°C and 10·9% under refrigeration), and all these factors may compromise the quality of the product. Proteinase production was similar for strains incubated at 37°C (16·81% of the isolates) and room temperature (17·27%) but there was less amount of phospholipase-producing strains at room temperature (15·45% of the isolates were positive) when compared with incubation at 37°C (36·36%). Enzymes production at 37°C by yeasts isolated from milk confirmed their pathogenic potential. The refrigeration temperature was found to be most efficient to inhibit enzymes production and consequently ensure better quality of milk. The viability of yeasts and the activity of their enzymes at different temperatures are worrying because this can compromise the quality of dairy products at all stages of production and/or storage, and represent a risk to the consumer.

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