China
Africa
Explore chapters and articles related to this topic
Physicochemical Aggregation and Deposition in Aquatic Environments
Published in Jacques Buffle, Herman P. van Leeuwen, Environmental Particles, 2018
Charles R. O’Melia, Christine L. Tiller
For submicron particles, Brownian diffusion controls particle transport, and hydrodynamic interactions are less significant than for larger particles. Light scattering techniques can be used to determine aggregation rates. Some recent results by Liang57 are presented in Figure 8. Results are reported in terms of the Fuchs stability factor, and range from slightly more than 1 up to 1000. Corresponding values of αa are slightly less than 1 to 0.001. These experiments were conducted at near neutral pH, where hematite is positively charged in the absence of specific adsorption of soluble species. Two polyelectrolytes were used, poly aspartic acid with a molecular weight of about 15,000 and NOM, a humic acid isolated from the Suwannee River. Both polyelectrolytes contain carboxyl groups and are negatively charged at neutral pH.
Stabilization of Dispersed Systems (in Particular Nanoparticles) by Polymers
Published in Victor M. Starov, Nanoscience, 2010
As a measure of aggregation (instability) a wide variety of parameters has been used, such as optical density, light scattering or light transmittance, Doppler or electroacoustic effects (i.e., monitoring the property of the whole system), rate of sedimentation or filtration, volume of sediment (characterizing the aggregates themselves), optical properties, electrical conductivity, or dielectric constant (i.e., properties of the supernatant above the aggregates). It is usual to compare the measured parameters after some arbitrarily chosen time. The most precise characteristics of aggregation can be obtained from kinetic data, that is, continuous measurements of some parameter, best of all number of particles, as a function of time. Particle counting methods like optical and electron microscopy, flow ultramicroscopy are capable of giving absolute rate constants. Comparative rate constants can also be obtained from some of the other methods mentioned, in particular light scattering [1].
The wettability of minerals and coal by magnetizable fluids
Published in Vladimír Strakoš, Vladimír Kebo, Radim Farana, Lubomír Smutný, Mine Planning and Equipment Selection 1997, 2020
M. Lovás, Š. Jakabský, A. Mockovčiaková, S. Hredzák
Ferrofluid is composed of 3 basic components: basic liquid, solid magnetic material and the stabilizing agent. The carry liquid is an arbitrary liquid, magnetic properties of that can be improved, for example water, kerosene, oil, etc. The carrier of magnetic properties of ferrofluids are single-domain magnetic particles of size 10−8 – 10−9 m. The role of the stabilizing agent is to prevent the colloidal particles from aggregation.
Organo-soluble dendritic zinc phthalocyanine: photoluminescence and fluorescence properties
Published in Inorganic and Nano-Metal Chemistry, 2022
Ebru Yabaş, Safacan Kölemen, Emre Biçer, Toghrul Almammadov, Pınar Başer, Mehmet Kul
Phthalocyanine aggregation generally defines as a coplanar association of structures from monomer to dimer and toward more phthalocyanine molecules by no bonded attractive interaction.[50] UV-Vis spectroscopy can be used to characterize the aggregation of the phthalocyanine molecules. Aggregation is dependent on the concentration of solution, species of metal ions, nature of the solvent, nature of substituents and temperature. In many cases, the spectra in the Q-band region show the effects of aggregation, typically by a blue shift and broadening of the maximum absorbance. Aggregation of phthalocyanines is not wanted as it reduces energy efficiency in applications.[51–53] In this study, the aggregation behavior of compound 2 was investigated in solution (Figure 3). Compound 2 did not show an aggregation in THF, DMF and DMSO. The aggregation behavior of compound 2 was also investigated at different concentrations (from 10.10−5 to 10.10−6 mol dm−3) in THF. No aggregation observed for compound 2.
Synthesis, characterization, and optical studies of pentoxy-substituted tetrakis(pentafluorobenzyloxy)phthalocyanines
Published in Journal of Coordination Chemistry, 2018
Mukaddes Özçeşmeci, Idris Sorar, Ibrahim Özçeşmeci, Esin Hamuryudan
Pcs are usually strongly aggregating because the planar molecular geometry causes significant π–π* interactions between the Pc molecules. Spectroscopic techniques can be used to analyze the nature and degree of aggregation. In general, the aggregation peak is blue-shifted with respect to the monomer peak. Quantitative study can be used using the molecular exciton approximation. This approximation is compromised by the presence of the strong π–π* interactions, but the general trends remain stable [38]. Aggregation behavior of 2 was examined by UV–vis spectroscopy in different concentrations ranging from 1 × 10−5 to 1 × 10−6 M. As shown in Figure 2, the appearance of the Q-band absorption maxima remained unchanged as the concentration increases as well as its apparent molar extinction coefficient remains almost constant for studied Pcs (1–3), indicating purely monomeric form which obeyed the Beer–Lambert Law [39].
Polyethylenimine-based nanocarriers in co-delivery of drug and gene: a developing horizon
Published in Nano Reviews & Experiments, 2018
Abbas Zakeri, Mohammad Amin Jadidi Kouhbanani, Nasrin Beheshtkhoo, Vahid Beigi, Seyyed Mojtaba Mousavi, Seyyed Ali Reza Hashemi, Ayoob Karimi Zade, Ali Mohammad Amani, Amir Savardashtaki, Esmail Mirzaei, Sara Jahandideh, Ahmad Movahedpour
The transfusion efficiency is closely related to the PEI binding with DNA and the ability to overcome a specific barrier [38]. Trafficking and destruction of vectors in lysosomes is one of the main barriers to cellular gene transfer. Akinc et al., have used quantitative methods to study the mechanism of polyethylenimine-mediated DNA transfection. The results are in complete agreement with the proton sponge hypothesis and show that PEI-mediated transfection is effective in avoiding lysosomal trafficking [39]. Polymer/DNA, using a number of possible mechanisms that include DNA protection from enzymatic degradation, faciliting cellular absorption, promoting endolysosomal escape, DNA unpacking in the cytosol, the nucleus and escorting nuclear translocation of DNA or nanoparticles [40]. The excess PEI significantly improves the efficiency of transfection of amounts of polyplex [38]. The transfection process can be affected by many unknown factors. However, several studies have linked the transfection efficiency and cytotoxicity of PEI preparations to the physicochemical properties, the molecular weight and the branching ratio of polymer [41,42], the amount of DNA, the DNA ratio to the PEI, the timing and the solution conditions for complex formation, the transfection medium and cell density at time of transfer [43,44]. In addition, many factors, including temperature, surfactant, complex concentration, ionic strength, viscosity, pH, can significantly affect the aggregation process. Random reduction of particles, increasing electrostatic explosion, preventing particle accumulation and reducing hydrophobicity can make the complex stable [44,45]. Particle size can be mentioned as the important factors affecting the cellular absorption of particles within the cytoplasmic membrane [44,46]. Particle aggregation results from colloidal instability and particle swelling due to charge screening, are two factors contributing to increasing particle size. Salt ions increase the size of PEI-DNA complex and the transfer efficiency, and the longer incubation period has the opposite effect [40,44]. In 2004, Grosse et al., found that cytotoxic effects of PEI could be due to its ability to eliminate endosomes. In fact, this ‘proton sponge effect’ causes high gene transfer capacity. They showed that lactosylated PEI retains the ‘proton sponge effect’ of the polymer unchanged, which is essential for the efficient gene delivery [47].