Formation and relaxation kinetics of starch-particle complexes

© The Royal Society of Chemistry.The formation and relaxation kinetics of starch-particle complexes were investigated in this study. The combination of cationic nanoparticles in suspension and anionic starch in solution gave rise to aggregate formation which was studied by dynamic light scattering, revealing the initial adsorption of the starch molecules on the particle surface. By examining the stability ratio, W, it was found that even in the most destabilized state, i.e. at charge neutralization, the starch chains had induced steric stabilization to the system. At higher particle and starch concentrations relaxation of the aggregates could be seen, as monitored by a decrease in turbidity with time. This relaxation was evaluated by fitting the data to the Kohlrausch-Williams-Watts function. It was found that irrespective of the starch to particle charge ratio the relaxation time was similar. Moreover, a molecular weight dependence on the relaxation time was found, as well as a more pronounced initial aggregated state for the higher molecular weight starch. This initial aggregate state could be due to bridging flocculation. With time, as the starch chains have relaxed into a final conformation on the particle surface, bridging will be less important and is gradually replaced by patches that will cause patchwise flocculation. After an equilibration time no molecular weight dependence on aggregation could be seen, which confirms the patchwise flocculation mechanism

Application of Replica Ornstein-Zernike equations in studies of the adsorption of electrolyte mixtures in disordered matrices of charged particles

The Replica Ornstein-Zernike (ROZ) equations were used to study the adsorption of ions from electrolyte mixtures. The adsorbent was represented as a quenched primitive model +1:-1 size symmetric electrolyte, while the mobile particles were ions differing in charge and/or size. The ROZ equations in hypernetted-chain (HNC) approximation were tested against new Monte Carlo results in the grand canonical ensemble; good agreement between the two methods was obtained. The ROZ/HNC theory was then used to study the exclusion coefficients as a function of size and/or charge asymmetry of the annealed ions.Реплiчне рiвняння Орнштейна-Цернiке (РОЦ) застосоване для вивчення адсорбцiї iонiв iз сумiшей електролiтiв. Адсорбент розглядається у виглядi замороженої примiтивної +1:-1 моделi розмiрно симетричного електролiту, тодi як рухомi частинки – це iони, що вiдрiзняються зарядом та/або роз- мiрами. Данi, що отриманi з рiвняння РОЦ у гiперланцюжковому наближеннi (ГЛН), порiвняно з но- вими результатами Монте-Карло моделювання у великому канонiчному ансамблi i виявлено хороше узгодження мiж обома методами. Теорiю РОЦ/ГЛН далi було використано для вивчення коефiцiєнтiв виключення, в залежностi вiд параметрiв розмiрної та/або зарядової асиметрiй нерухомих iонiв

Natural coagulates for wastewater treatment; a review for application and mechanism

The increase of water demand and wastewater generation is among the global concerns in the world. The less effective management of water sources leads to serious consequences, the direct disposal of untreated wastewater is associated with the environmental pollution, elimination of aquatic life and the spread of deadly epidemics. The flocculation process is one of the most important stages in water and wastewater treatment plants, wherein this phase the plankton, colloidal particles, and pollutants are precipitated and removed. Two major types of coagulants are used in the flocculation process included the chemical and natural coagulants. Many studies have been performed to optimize the flocculation process while most of these studies have confirmed the hazardous effects of chemical coagulants utilization on the ecosystem. This chapter reviews a summary of the coagulation/flocculation processes using natural coagulants as well as reviews one of the most effective natural methods of water and wastewater treatment

A Voronoi-diagram analysis of the microstructures in bulk-molding compounds and its correlation with the mechanical properties

Voronoi analysis is implemented to assess the influence of fiber content on the microstructure and mechanical properties of bulk-molding compounds containing different weight fractions of E-glass fibers (EGF) (5–20 wt%). The fiber distribution in the polymer matrix is analyzed by scanning electron microscopy followed by the Voronoi tessellations, radial distribution function and statistical calculations. The experimental results are compared to modelled microstructures. The derived microstructural descriptors allow us to correlate the fiber weight content and the degree of fiber distribution homogeneity with the mechanical properties of EGF-reinforced composites. The distribution of fibers in composites with 10 and 15 wt% of fibers could be considered as the most homogeneous. This is in a good agreement with the results of the flexural strength and dynamic mechanical analyses, which confirmed that the latter samples exhibit the highest level of reinforcement

Evaluation of the homogeneity in Pb(Zr,Ti)O3–zirconia composites prepared by the hetero-agglomeration of precursors using the Voronoi-diagram approach

Hetero-agglomeration of precursor particles was employed to achieve a homogeneous distribution of tetragonal zirconia (TZ) grains within a lead zirconate titanate (PZT) ceramic matrix. The surface charge of the zirconia particles in the aqueous suspension was modified by the addition of citric acid. At pH 5, the citric-acid-modified TZ particles were negatively charged, while the PZT particles were positively charged, which led to the agglomeration of the two types of particles. The homogeneity of the TZ distribution in the PZT–TZ ceramic composites prepared from the hetero-agglomerated particles was evaluated using Voronoi-diagram analyses. The results showed that the homogeneity of the composites prepared using the citric-acid-modified TZ particles was higher than in the case where the TZ particles were not modified. The curves for the crack-growth resistance were also determined in order to investigate the impact of particle homogeneity on the fracture behavior

Structural and electrical properties of Pb(Sc0.5Nb0.5)O3 and 0.57Pb(Sc0.5Nb0.5)O3-0.43PbTiO3 ceramics prepared by mechanochemical activation

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