Flow towards a Stagnation Region of a Curved Surface in a Hybrid Nanofluid with Buoyancy Effects

This paper examines the impact of hybrid nanoparticles on the stagnation point flow towards a curved surface. Silica (SiO2) and alumina (Al2O3) nanoparticles are added into water to form SiO2-Al2O3/water hybrid nanofluid. Both buoyancy-opposing and -assisting flows are considered. The governing partial differential equations are reduced to a set of ordinary differential equations, before being coded in MATLAB software to obtain the numerical solutions. Findings show that the solutions are not unique, where two solutions are obtained, for both buoyancy-assisting and -opposing flow cases. The local Nusselt number increases in the presence of the hybrid nanoparticles. The temporal stability analysis shows that only one of the solutions is stable over time.

Influence of Fillers and Ionic Liquids on the Crosslinking and Performance of Natural Rubber Biocomposites

This work concerns the effect of fillers and ionic liquids on the cure characteristics of natural rubber (NR) compounds, as well as the mechanical and thermal properties of the vulcanizates. Three types of white filler were applied, such as cellulose, nanosized silica and hydrotalcite, to modify the performance of NR composites. Additionally, ionic liquids (ILs) with bromide anion and different cations, i.e., 1-butyl-3-methylimidazolium (Bmi) and 1-butyl-3-methylpyrrolidinium (Bmpyr), were used to improve the cure characteristics of NR compounds and functional properties of the vulcanizates. The type of filler and the structure of ILs were proved to affect the rheometric properties and cure characteristics of NR compounds as well as the performance of the NR vulcanizates. Owing to the adsorption of curatives onto the surface, silica reduced the activity of the crosslinking system, prolonging the optimal vulcanization time of NR compounds and reducing the crosslinking degree of the elastomer. However, silica-filled NR exhibited the highest thermal stability. Hydrotalcite increased the crosslink density and, consequently, the mechanical properties of the vulcanizates, but deteriorated their thermal stability. ILs beneficially influenced the cure characteristics of NR compounds, as well as the crosslink density and mechanical performance of the vulcanizates, particularly those filled with silica. Cellulose did not significantly affect the vulcanization of NR compounds and crosslink density of the vulcanizates compared to the unfilled elastomer, but deteriorated their tensile strength. On the other hand, cellulose improved the thermal stability and did not considerably alter the damping properties of the vulcanizates.

How Surface Properties of Silica Nanoparticles Influence Structural, Microstructural and Biological Properties of Polymer Nanocomposites

The aim of this work was to study effect of the type of silica nanoparticles on the properties of nanocomposites for application in the guided bone regeneration (GBR). Two types of nanometric silica particles with different size, morphology and specific surface area (SSA) i.e., high specific surface silica (hss-SiO2) and low specific surface silica (lss-SiO2), were used as nano-fillers for a resorbable polymer matrix: poly(L-lactide-co-D,L-lactide), called PLDLA. It was shown that higher surface specific area and morphology (including pore size distribution) recorded for hss-SiO2 influences chemical activity of the nanoparticle; in addition, hydroxyl groups appeared on the surface. The nanoparticle with 10 times lower specific surface area (lss-SiO2) characterized lower chemical action. In addition, a lack of hydroxyl groups on the surface obstructed apatite nucleation (reduced zeta potential in comparison to hss-SiO2), where an apatite layer appeared already after 48 h of incubation in the simulated body fluid (SBF), and no significant changes in crystallinity of PLDLA/lss-SiO2 nanocomposite material in comparison to neat PLDLA foil were observed. The presence and type of inorganic particles in the PLDLA matrix influenced various physicochemical properties such as the wettability, and the roughness parameter note for PLDLA/lss-SiO2 increased. The results of biological investigation show that the bioactive nanocomposites with hss-SiO2 may stimulate osteoblast and fibroblast cells’proliferation and secretion of collagen type I. Additionally, both nanocomposites with the nanometric silica inducted differentiation of mesenchymal cells into osteoblasts at a proliferation stage in in vitro conditions. A higher concentration of alkaline phosphatase (ALP) was observed on the material modified with hss-SiO2 silica.

DEVELOPMENT OF MODIFIED SORBENT FOR INCREASE IN EFFICIENCY OF ADSORPTIVE PURIFICATION OF CORN OIL

Проведена модификация сорбента, повышающего эффективность адсорбционной очистки кукурузного масла. Для получения сорбента использовали силикагель с поверхностью 300 м2/г, в качестве модификатора – гамма-аминопропилтриэтоксисилан из расчета 4 аминогруппы на 1 нм2поверхности. Силикагель (СГ) перед модификацией высушивали до постоянной массы. Навеску СГ диспергировали в разных органических растворителях – н-гексане, хлороформе и хлористом метилене – и вносили модификатор. Реакцию проводили при перемешивании реакционной смеси в ротационном вакуумном испарителе. Далее растворитель отделяли декантированием и промывали осадок. Остатки растворителя отгоняли под вакуумом. Полученный модифицированный СГ высушивали при заданной температуре. Для подтверждения модификации применяли метод ИК-спектроскопии с преобразованием Фурье на спектрометре FSM-1201. Для первичной обработки спектров использовали программное обеспечение F-Spec, для отнесения полос поглощения – IR Pal версии 2.0. С целью проверки способности синтезированного сорбента к сорбции карбонильных соединений использовали кукурузное масло, полученное в производственных условиях, после отбелки, с высоким значением анизидинового числа (около 8). Установлено, что использование модифицированного СГ значительно повышает эффективность адсорбционной очистки кукурузного масла: анизидиновое число масла, обработанного модифицированным сорбентом, снижается до 8 раз по сравнению с аналогичным показателем масла, обработанного немодифицированным СГ; на величину изменения анизидинового числа влияет дозировка модифицированного сорбента; свойства растворителя, в котором проводилась модификация, не оказывают существенного влияния на активность сорбента. Modification of the sorbent, which increases the efficiency of adsorption purification of corn oil, was carried out. Silica gel with a surface 300 m2/g was used to produce a sorbent, as a modifier – gamma-aminopropyltriethoxysilane at the rate of 4 amino groups per 1 nm2 surface. Silica gel (SG) before modification was dried to a constant mass. The sample of SG is dispersed in different organic solvents – n-hexane, chloroform and methylene chloride – and the modifier was introduced. Further, the solvent was separated by decanting, and the precipitate was washed. Residues of solvent are removed under vacuum. The obtaining modified SG was dried at a given temperature. Method of IR-spectroscopy with transform Fourier on the FSM-1201 spectrometer is used to confirm the modification. Software F-Spec is used for primary processing of spectra, IR Pal version 2.0 – for assignment of absorption bands. Corn oil obtained in production conditions, after bleaching, with a high anisidine number (about 8) was used to test the ability of the synthesized sorbent to sorption of carbonyl compounds. It was found that the use of modified SG significantly increases the efficiency of adsorption purification of corn oil: the anisidine number of oil treated with a modified sorbent is reduced to 8 times compared to the same indicator of oil treated with unmodified SG; the dosage of the modified sorbent affects the amount of change in the anisidine number; the properties of the solvent, in which the modification was carried out, do not have a significant effect on the activity of the sorbent.