Molecular Dynamics Simulation in the Interlayer of Mixed-Layer Clays Due to Hydration and Swelling Mechanism

The swelling behavior of clay minerals is widely known for its importance in soil and environmental sciences and its detrimental effects in engineering fields. Although more than 70 percent of all clays are of mixed-layer types, the vast majority of the previous experiments and simulations are focused on pure clays, which cause the swelling mechanism of the widespread mixed-layer clay (MLC) and its role in soils are little understood, especially the most common illite-montmorillonite (I-M) mixed-layer clay (MLC). This paper reports on a molecular dynamics (MD) study of the differences in swelling behavior between I-M MLCs containing K+ and Na+ and Na-montmorillonite (MMT). It captures the evolution of quantitative properties such as basal spacing d, interaction energy, and many hydrogen bonds in the clay interlayer, increasing hydration for the first time through the scripts. It is found that MLCs have smaller swellings than Na-MMT due to the asymmetric interlayer charges and mixed counterions in the I-M interlayer. However, in terms of the interaction energy for the in-depth reason of swelling, it is found that the clay-clay interaction energy and the clay-ion interaction energy drop, while the clay-water interaction energy increases with increasing hydration. In addition, the attractive interaction of clay-bound water seriously promotes swelling, and it is mainly composed of Coulomb interaction and Van der Waals interaction. The higher the K+ concentration, the more noticeable these phenomena are. Besides, it is also reported that the number and distribution mechanism of hydrogen bonds in MLCs are very different from that of pure clay. This work provides insight into the molecular mechanism for initial swelling and clay-bound water interaction in widespread MLCs. This will help to decipher its specific role in soils and minimize clay swelling.

Characterization of a lignin-based gel responsive to aqueous binary solvents and pH

A lignin-based gel (AL-PE gel) was obtained from hardwood acetic acid lignin (AL) and poly(ethylene glycol) diglycidyl ether (PE) as a cross-linker at a high AL concentration, while the reaction at a lower AL concentration yielded an amphipathic derivative (am-AL-PE). The gel has been reported to swell in aqueous ethanol but shrink in pure water and ethanol. In the present work, swelling behaviors in other aqueous binary solvents and the swelling mechanism were investigated to explore novel lignin-based functional materials, such as stimuli-and/or environment-responsive gels. The AL-PE gel swelled in aqueous methanol, isopropanol, acetone, and tetrahydrofuran, and the order of swelling in the solvents was consistent with that of the am-AL-PE. Spin-spin relaxation time (T 2 ) measurements with 1H NMR analysis of the gel in aqueous acetone revealed that gel swelling was closely related to an increasing T 2 of acetone bound to the gel network. The nature of the lignin moiety in the gel also enabled a pH response, and the amphipathic nature of the gel provided it with a function as an absorbent for cationic surfactants. The results of this study can contribute to the valorization of lignin as a main component for solvent sensors and environmental purification materials.

Hydrogels as Controlled Drug Delivery System: A Brief Review of Properties Classification and Synthesis

Hyrogels are cariers of novel drug delievry system and these polymeric network have ability to hold large amount of water but they do not dissolve in water .These polymeric network may be crosslinked either through chemical or physical crosslinking method. Without changing their three dimensional structure hydrogels undergo the swelling mechanism Hydrogels are used as drug delivery carriers because of their distinctive properties. They have three dimensional configurations and have water soluble cross linked network of polymers .Hydrogels have porous structure and by changing the cross linker concentration we can modify their affinity for water. Because of their unique properties these are used for various medical purposes like cellular immobilization , tissue engineering ,diagnostics and regenerative medicines.

Efecto de la descomposición de gas de amoniaco (NH3) sobre el hinchamiento de óxidos de hierro durante reducción

Con el objeto de estudiar la relación y efecto del gas nitrógeno en los gases reductores utilizados en los ensayos de reducibilidad de óxidos de hierro, en condiciones isotérmicas, se ejecutó un esquema de ensayos utilizando gas amoniaco, tal que la descomposición del gas en el reactor produjera un gas de H2 y N2. Además, se planifico la adición de 6% de NH3 en una corriente de gas 28% H2 y 68% N2 para obtener una composición de gas de 70% N2 y 30% H2. Esto permitiría la reinterpretación de los datos de laboratorio para comparar las curvas d reducibilidad entre ambas condiciones, asumiendo que la posible diferencia entre ambas condiciones a comparar los cambios de volumen de las muestras reducidas. La diferencia a estudiar se basará en la estimación y comparación de la velocidad de formación de hierro metálico en las etapas de reducción de hematita/magnetita/wustita (FeO), así como los efectos del nitrógeno absorbido por el hierro metálico fresco producido, partir de la mezcla de gas reductor, sobre el cambio de volumen de las muestras. Así mismo se comparan empíricamente los cambios catastróficos de volumen causados por el nitrógeno comparando fuentes de este gas en reductores carbonosos sólidos. Palabras clave: reducción gaseosa, hierro de reducción directa (HRD), catálisis, catalizador de hierro, amoniaco, hinchamiento, absorción, nitruración. ensayos isotérmicos, nitrógeno en carbón. Referencias [1]O.G. Dam . The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction. Univ. of London. PhD Thesis 1983. [2]J.D Bogde.- Thermoelectric Power Measurements in Wustite. Univ. of Michigan. 1976. [3]O.G. Dam y J. Jeffes. Model for the Assessment of Chemical Composition of reduced iron ores from single measurements. Ironmaking and Steelmaking. 1987. Vol. 14, N`5. [4]M. Yang. Nitriding-Fundamentals, modelling and process optimization. Tesis PhD. Worcester PolytechInstitute. 2012. [5]T. EL Kasabgy y W-K. LU. (1980). The Influence of Calcia and Magnesia in Wustite on the Kinetics of Metallization and Iron Whisker Formation. Metallurgical 1980 American Society for Metals and the Metallurgical Society of AIME Volume 11b, September 1980, pp. 410-414. [6]Srikar Potnuru Studies nn the Physical Properties and Reduction Swelling Behavior of Fired Haematite Iton ore Pellets. MSc Thesis. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2012. [7]R.S Agarwal y S.S. Hembram. To Study the Reduction and Swelling Behavior Iron Ore Pellets. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2013. [8]C.E. Seaton y J.S. Foster. and Velasco. Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char. Transactions ISIJ, Vol. 23, 1983, pp. [10]C. Bozco. et.al. Interaction of Nitrogen with Iron Surfaces. Journal of Catalysis 49. 1977. [11]L.S. Darken y R.W. Gurry, Physical Chemistry of Metals. Mc Graw hIll . 1953. [12]H. A. Weirdt, y Z .Zwell. Trans. AIME. 229. 142. 1969. [13]J.J.S.Schulten. et al. Trans. Soc. Faraday. 53, 1363, 1957. [14]E.G.Barret y C.F. Wood. Bureau of Mines R-I 3229. 1934.