Ab initio study of mixed clusters of water and N,N′-dimethylethyleneurea

Intermolecular interactions between a single water and two N,N′-dimethylethyleneurea (DMEU) molecules have been investigated using local and density-fitting approximations of the standard Moller-Plesset perturbation theory (DF-LMP2) with the aug-ccpVTZ basis set. Six stable configurations have been found. In the first three, the water molecule intercalates between two DMEU molecules. In the next three configurations, the water molecule is attached to a stacked DMEU dimer, and these structures are more stable than the first three. These results support the view that DMEU molecules can form contact pairs in dilute aqueous solutions. © 2011

Investigation of silica - PVA xerogel microstructure evolution during thermal treatment by SANS experiment

The purpose of the study was to investigate the appearance of certain microstructures developing in the SiO2/PVA nanocomposite xerogels at different temperatures by small-angle neutron scattering (SANS). The samples were prepared by the alcoxide route of the sol-gel method. The SANS measurements were performed over a q (scattering vector) range from 0.05 to 3.7 nm-1, providing structural information at length scales (2π/q) between approximately 1 and 100 nm. The measured small-angle scattering intensities of silica and silica/PVA samples aged at 60°C and heat-treated at different temperatures, are presented in log-log plots. It is shown that both the molecular mass of organic and the temperature of thermal treatment have strong influence on transition tendency from mass fractal toward surface fractal structures

Formation of unilamellar dipalmitoylphosphatidylcholine vesicles promoted by Ca2+ ions: A small-angle neutron scattering study

Dipalmitoylphosphatidylcholine (DPPC) was hydrated in 0.2-60 mM solution of CaCl 2 in heavy water and thoroughly homogenized by freezing-thawing process. Small-angle neutron scattering (SANS) shows formation of unilamellar vesicles in the range 1-60 mM of CaCl 2. From the Kratky-Porod plot ln[I(Q)Q 2] vs. Q 2 of SANS intensity I(Q) in the range of scattering vectors Q corresponding to the interval 0.001 Å -2≤Q 2≤0.006 Å -2, the vesicle bilayer radius of gyration R g and the bilayer thickness parameter d g were obtained. The structure of the bilayer displays different behavior for the gel phase and the liquid-crystalline phase: In the gel phase (at 20°C), the values of d g indicate nonlinear changes in the lipid bilayer thickness, with a maximum at ∼5 mM CaCl 2. In the liquid-crystalline phase (at 60°C), the parameter of the lipid bilayer thickness d g=43.2±0.3 Å is constant within the concentration range 1≤c Ca≤40 mM. Vesicles prepared at 60 mM CaCl 2 show within experimental error, the same values of d g as pure DPPC unilamellar vesicles prepared by extrusion using polycarbonate filter with pores of diameter 500 Å

Mesoporous silica matrices derived from sol-gel process assisted by low power ultrasonic activation

The present work contributes to elucidating the differences between silica gels obtained by low doses ultrason- ic activation, and those obtained by the conventional method, termed as classical sol gel. Silica matrices were produced by sol-gel synthesis process, assisted and non-assisted by an ultrasonic field, and subsequently char- acterized by various methods. Nitrogen adsorption and small-angle neutron scattering (SANS) measurements provided texture and microstructure of the dried gels. The adsorption results show that the sample sonicated for 2 hours presents the most ordered microstructure, characterized by pore shape close to spherical and the narrowest size distribution – about 90 % of the pores for this sample fall into the mesopore range (2–50 nm). SANS data reveal the formation of primary structural units of sizes around 1.5–2 nm which are small linear or branched polymeric species of roughly spherical shape and with rough surface. They are generated in the very early stage of sol gel process, as a result of hydrolysis and condensation reactions. The aggregated primary units form the secondary porous structure which can be described as a rough surface with fractal dimension above 2. The best porosity characteristics were obtained for the sample activated for 2 hours, indicating the optimal doses of sonication in the present conditions. Our results demonstrate the possibility of tailoring the pore size distribution using a low power ultrasonic bath

Study on the Microstructure of Polyester Polyurethane Irradiated in Air and Water

The gamma irradiation induced aging of thermoplastic polymer Estane 5703 in air and water environments was studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and X-ray diffraction (XRD). The degree of phase mixing was increased after irradiation, accompanied by the increase of domain distance and decrease of domain size. The hard domain distance increased from 9.8 to 11.2 nm and 14.4 nm for the samples irradiated in air and water with a dose up to 500 kGy, respectively. The GPC results indicated progressive formation of larger linked structures with very high molar mass with increasing absorbed doses. The samples irradiated in water exhibited a stronger aging effect than those irradiated in air. The FTIR results suggested that the cross-linking occurred among the secondary alkyl radicals, and the interactions in hard domains weakened because of the loss of inter-urethane H-bonds. The volume fraction of well-ordered soft segments in Estane increased upon irradiation

Структура амилоидных агрегатов лизоцима по данным малоуглового рассеяния рентгеновских лучей

Методом малоуглового рассеяния рентгеновских лучей исследована структура филаментных амилоидных агрегатов лизоцима яичного белка в воде. Для описания экспериментальных данных использованы различные цилиндрические модели, среди которых лучшее соответствие показывает модель длинной спирали. При сравнении полученных результатов с данными малоуглового рассеяния нейтронов обнаружено влияние тяжелого компонента растворителя (смеси H2O/D2O) на структуру филаментов

Ultrasonic preparation of mesoporous silica using pyridinium ionic liquid

Mesoporous silica matrices have been prepared via classic acid catalyzed and sono-catalyzed sol-gel routes. Tetramethoxysilan (TMOS) and methyl-trimethoxysilane (MTMS) were used as silica precursors, and N-butyl-3-methylpyridinium tetrafluoroborate ([bmPy][BF4]) was employed as co-solvent and pore template. The ionic liquid (IL) to silica mole ratio was varied between 0.007 and 0.07. Nitrogen adsorption-desorption and small-angle neutron scattering measurements were used to characterize the obtained materials. The ionic liquid played the role of catalyst that affected the formation of the primary xerogel particles, and changed the porosity of the materials. Ultrasound treatment resulted in microstructure change on the level of the colloid particle aggregates. In comparison with IL containing xerogels, the IL containing sonogels show increased pore diameter, bigger pore volumes and diminished surface areas

Исследование мезоструктуры биоактивных покрытий для каменных материалов на основе эпоксидно-силоксановых золей, модифицированных наноалмазами, методом малоуглового рассеяния нейтронов

Методом малоуглового рассеяния нейтронов (МУРН) исследовано структурообразование синтезирован- ных золь-гель-методом эпоксидно-силоксановых композиций с разным соотношением основных прекурсоров (RTEOS/EPONEX1510 = 16/38, 27/27, 38/16mass%), а также с разной концентрацией наноалмаза детонационного синтеза (cDNA = 0.05, 0.1, 0.2mass%). На основе данных МУРН выявлено, что синтезированные эпоксидно-силоксановые ксерогели представ- ляют собой системы с двухуровневой фрактальной структурой, в образовании которой доминирующая роль принадлежит силоксановой составляющей. Обнаружено, что как фрактальная размерность Dm2, так и радиус гирации Rg2 кластеров в эпоксидно-силоксановых композициях снижаются с ростом содержания силоксановой составляющей. Установлено, что введение в эпоксидно-силоксановую композицию с равным соотношением основных прекурсоров RTEOS/EPONEX1510 = 27/27mass% малых добавок детонационного нано- алмаза (менее 1mass%) приводит к переходу от двухуровневой к трехуровневой структурной организации и влияет на фрактальную размерность Dm и радиус гирации Rg формируемых кластеров