Effect of surfactants on sol–gel transition of silk fibroin

In this study, various surfactants were added to control the gelation time of silk fibroin (SF) aqueous solution. The gelation behaviors of SF aqueous solution in the presence of surfactant were investigated with attenuated total reflectance infrared, SEM, and a viscometer. When surfactants other than chitooligosaccharide were added into an SF aqueous solution, the gelation time of the solution was decreased under the fixed conditions. Particularly, anionic surfactant was found to be more effective than non-ionic and cationic surfactants in accelerating the gelation of SF. In addition, the conformational changes of SF hydrogel with or without surfactant were investigated in a time-resolved manner using infrared spectroscopy. Conformational transitions of SF nanofibers from random coil to β-sheet forms were strongly dependent on the inherent properties of surfactant, and on the different interactions between surfactant and SF molecules in aqueous solution. This approach to controlling the gelation of SF aqueous solution by the surfactant, and to monitoring their conformational changes on a real-time scale, may be critical in the design and tailoring of SF hydrogels useful for biomedical applications.     

Effect of copper addition on glass transition of silicate–phosphate glasses

Glass transformation effect of mixed SiO₂?CP₂O₅?CK₂O?CMgO?CCaO?CCuO glasses was studied by DSC, XRD, SEM, and Raman spectroscopy methods. The relationship between the parameters characterizing glass transformation effect and an amount of phosphorous and copper forming the glassy structure was discussed. It was shown that an increasing content of phosphorous increased solubility of copper in the structure of the studied glasses which was the result of P?CO?CCu bonds formation. Degree of changes of T _g, ?c _p, and time of relaxation values were higher in glasses with higher content of P₂O₅ and CuO. The observed relations were explained on the basis of the local atomic interactions in the structure of glass.     

Effect of Surfactants on Electrodeposition of the Sn–Ni Alloy from Oxalate Solutions

The effects of surfactants on the electrolytic deposition of tin–nickel alloys from oxalate–ammonium electrolytes were determined. The adsorption of the nonionic surfactant at the interface decreases the rate of charge transfer across the interface. As a result, the electrochemical stage of the electroreduction of metals slows down, and the alloy is deposited in the form of shiny finely crystalline coatings. The range of optimum surfactant concentrations in the oxalate–ammonium electrolyte was determined based on the simulation of the interface impedance obtained during the alloy deposition and the electron microscopy studies of the obtained coatings.     

Effect of cooling rate on the microstructure and solidification parameters of Mg–3Al–3Nd alloy

Journal of Thermal Analysis and Calorimetry - The effect of cooling rate on the microstructure and solidification parameters of Mg–3Al–3Nd alloy was investigated by thermal analysis....     

Thermal analysis of cadmium addition on the glass transition and crystallization kinetics of Se–Te–Sn glassy network

Journal of Thermal Analysis and Calorimetry - Calorimetric measurements have been performed in quaternary glassy system Se78−xTe20Sn2Cdx (x = 0, 2, 4, and 6) to study the...     

Effect of cooling rate and Al content on solidification behavior and microstructure evolution of as-cast Mg–Al–Ca–Sm alloys

Journal of Thermal Analysis and Calorimetry - In the present study, the Mg–xAl–2Ca–2Sm (x = 3, 5, 9 and 15) alloys were fabricated in sand mold with stepped type, and...     

Effect of the functionalizing of carbon nanotubes on the electrodeposited catalysts’ structure and catalytic properties

The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation and oxygen electroreduction reactions. When minor amounts (5–10 μg cm⁻²) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst is formed, with specific surface area up to 150–300 m² g⁻¹; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers.     

Effect of organic solvent on the crystal structure of Concanavalin A

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Effect of Sonochemical Treatment Modes on the Electrodeposition of Cu–Sn Alloy from Oxalic Acid Electrolyte

Methods of scanning electron microscopy, potentiodynamic polarization, and X-ray diffraction analysis were used to study the kinetic features of the electrodeposition process of the copper–tin alloy from an oxalic acid electrolyte and analyze the structure, composition, and luster of coatings formed under sonochemical treatment conditions at varied power of the ultrasonic field and current load. The ultrasonic treatment with power of 8–40 W dm^–3 makes it possible to 2–8 times intensify the cathodic process and obtain coatings containing 10–15 wt % tin with luster of 20–40%. The specific content of tin in a coating being formed is nearly independent of the ultrasound power and grows with increasing the cathodic current density.     

Effect of surfactant structure on catalysis of microemulsion for photoisomerization of trans-stilbene

In this study,the photoisomerization of trans-sfilbene was carried out in water in oil (W/O) microemulsions by using sodium dodecyl sulfate (SDS),dodecyl trimethyl ammonium bromide (DTAB) and cetyl trimethyl ammonium bromide (CTAB) as surfactant,respectively.The catalytic effect of microemulsion on this reaction is closely related to the structure of surfactant.When there is no photosensitizer 9,10-dicyanoanthracene (DCA),the surfactant with shorter hydrophobic chain is preferred,while in the presence of DCA,the surfactant with anionic polar group is preferred.     

Effect of preparation conditions on the composition,structure, and properties of iron–molybdenum catalyst

X-ray phase analysis, synchronous thermal analysis, and IR spectroscopy were used to study the process in which an iron-molybdenum catalyst for partial oxidation of methanol to formaldehyde is prepared. The influence exerted by the pH of the medium on the composition, structure, and properties of the oxide Fe–Mo catalyst was examined. It was found that the amount of the active component in a sample obtained at pH 2 is the largest, and the sample exhibits the best activity in the reaction of methanol oxidation to formaldehyde. The possibility was examined of the occurrence of side reactions in which carbon monoxide is converted. It was found that the conversion occurs only on samples obtained at pH > 2.     

Effect of addictives on polymorphic transition of ε-CL-20 in castable systems

In order to explore the law of polymorphic transformation in the process of preparing hexanitrohexaazaisowurtzitane (CL-20)-based composite explosives in cast-cured method, the polymorphic transition of CL-20 crystal under heat stimulation was investigated by X-ray diffraction and differential scanning calorimetric method, respectively, and the effects of different addictives (mainly involved in castable systems) on polymorphic transition of CL-20 were elaborately explored. The transition mechanism was systemically analyzed from the point of view of kinetic and thermodynamic. The experiment results showed that the polymorphic transition was closely related to temperature and ambient surroundings, and the influence of different additives was not consistent in the process of polymorphic transition. In addictives with higher dipole moment or solubility of CL-20, ε-form could easily be polarized and tend to transform into γ-form and the process occurred in fluid medium was much easier than that in solid matrix. The investigation contributes to comprehend the polymorphic transformation mechanism of CL-20 and provides guidance for effective control on the CL-20 polymorphs in preparing CL-20-based composite explosives.     

Effect of γ-irradiation on the molecular-topological structure of Viton® fluoroelastomers

The molecular–topological structure of a terpolymer based on vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene has been studied for the first time with the use of thermomechanical spectrometry. A five-block topologically amorphous and crystalline pseudo-network structure with crystallites, which have different initial melting temperatures, as branching points has been detected in the terpolymer at temperatures from–100 to 250°C. When γ-irradiated at a dose of 30 kGy, the crystalline blocks of high-temperature modifications assimilated into one cluster block with the formation of a pseudo-network with a 1.5fold increase in the block-average molecular weight and a decreased initial molecular flow temperature.     

Effect of pressure on the structure and dynamics of hydrogen bonds in ethylene glycol–water mixtures: Numerical simulation data

Water?ethylene glycol mixtures containing from 0.002 to 0.998 mole fractions of ethylene glycol at T = 298.15 K and P = 0.1 and 100 MPa are simulated by means of classical molecular dynamics. Such structural and dynamic characteristics of hydrogen bonds as the average number and lifetime, along with the distribution of molecules over the number of hydrogen bonds, are calculated; their changes are analyzed, depending on the mixture’s composition and pressure. It is shown that the components are characterized by a high degree of interpenetration and form a uniform infinite hydrogen-bonded cluster over the range of concentrations. It is found that the higher the concentration of ethylene glycol, the greater the stability of all hydrogen bonds. It is concluded that an increase in pressure lowers the number of hydrogen bonds, while the average lifetime of the remaining hydrogen bonds grows.     

Effect of Re addition on the crystallization,heat treatment and structure of the Cu–Ni–Si-Cr alloy

Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the Fe₆₇Nb₅B₂₈ metallic glasses prepared by melt-spinning method. DSC traces exhibit that the crystallization takes place through a single exothermic reaction, and it processes a good thermal stability in thermodynamics. The activation energies for nucleation and grain growth processes were calculated to be 536 ± 22 and 559 ± 20 kJ mol^?1 by Kissinger equation, respectively, and 551 ± 24 and 574 ± 20 kJ mol^?1 by Ozawa equation, respectively. It means that the grain growth process is more difficult than the nucleation process. The variation of local Avrami exponent n(x) with crystallized fraction x demonstrates that the crystallization mechanism varies at different stages. The n(x) is larger than 2.5 at the initial stage of 0 < x < 0.3, implying a mechanism of diffusion-controlled three-dimensional growth with increasing nucleation rate. The n(x) decreases from 2.5 to 1.5 in the range of 0.3 < x < 0.65, suggesting that the crystallization belongs to three-dimensional nucleation and grain growth with decreasing nucleation rate. And n(x) lies between 1.0 and 1.5 in the range of 0.65 < x < 0.95, indicating that the crystallization corresponds to the growth of particles with an appreciable initial volume. Low-temperature annealing corresponds to the precipitation of α-Fe, Fe₂B, and Fe₂₃B₆ phases, and further annealing leads to the formation of α-Fe, Fe₂B, and FeNbB phases. The magnetic properties in relation to microstructure change of the Fe₆₇Nb₅B₂₈ metallic glasses are discussed.     

Effect of chemical structure of hydroxyethyl imidazolines inhibitors on the CO2 corrosion in water–oil mixtures

The corrosion inhibition of oleic, coconut, and stearic acid modified hydroxyethyl imidazolines on 1018 carbon steel was evaluated by using potenthiodynamic polarization curves, linear polarization resistance, and electrochemical impedance spectroscopy techniques. Solutions included deaerated CO₂ saturated 3% NaCl with and without Diesel at 50 °C. Regardless of the presence of diesel, the corrosion rate was decreased with the addition of the inhibitors, but the time to reach a steady state was longer than when the oily part, i.e., diesel, was present. This was because the inhibitors are oil soluble, and with diesel, they are more easily transported towards the metal surface. With diesel, the formed film seems to be more stable and protective, not allowing the electrolyte to corrode the sample increasing the efficiency values up to 87 and 94%. The most efficient inhibitors were the coconut type fatty acid hidroxyethyl imidazoline because the formed film was much more stable from the beginning of the test, whereas the least efficient was the stearic acid modified hydroxyethyl imidazoline.     

Effect of gas-induced semisolid process on solidification parameters and dendrite coherency point of Al–4.3Cu alloy using thermal analysis

Journal of Thermal Analysis and Calorimetry - Semisolid processing of Al–4.3%Cu (A206) alloy was carried out using gas-induced semisolid (GISS) process in different conditions. The flow rate...     

Effect of alkanolamines on properties of epoxy–anhydride compounds

Hot-cured epoxy compound based on ED-20 resin and isomethyltetrahydrophthalic anhydride was modified with alkanolamines of different structures. The influence exerted by the structure of alkanolamines on the structure and operation characteristics of modified epoxy–anhydride compounds was examined. Introduction of alkanolamines decreases the gel and cure times and enhances the operation properties of cured epoxy–anhydride compounds. The best products were obtained with alkanolamines derived from ethylenediamine. Their introduction into epoxy–anhydride compounds enhances by a factor of 1.5–2 the elasticity, tensile strength at uniform extension, and impact resilience of the cured formulations.     

Effect of Sn content on the properties of passive film on PbSn alloy in sulfuric acid solution

The effect of Sn content on properties of anodic film formed on PbSn alloys in sulfuric acid solution was investigated using linear sweeping voltage (LSV), cyclic voltammetry (CV), and a.c. voltammetry (ACV), based on the Mott-Schottky analysis. The results revealed that the addition of Sn into lead alloys can promote the corrosion resistance property and could decrease the impedance of anodic film; these results were more remarkable with enhancing the Sn content. The over potential of oxygen evolution on lead alloys enhanced with the increase of Sn content. The Mott-Schottky analysis indicated that the passive film appeared an n-type semiconductor, and the donor density of passive film increased with increasing Sn content. The increased vacancies in the passive film with Sn content increasing could illustrate this trend.     

Effect of catalyst structure on the reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane

Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place. In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that leads to formation of long chain linear and cyclic siloxanes of general formula HMe₂Si(OSiMe₂) _n H and (-OSiMe₂-)m (n = 2–6, m = 3–7), respectively. Platinum catalysts promotes formation of linear siloxanes, while both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate metallocomplexes is studied.