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Mechanisms of Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
The theory of electrostatic stabilization of particles is called the Deryaguin-Landau-Verwey-Overbeek (DLVO) theory [81] after the scientists who developed it. The DLVO theory relies on the consideration of both electrostatic forces and van der Waals forces. The principle of electrostatic stabilization is the presence of a net electric charge at the surface of the particles dispersed in a polar medium (Fig. 2.15). Around these charges, a well-defined layer (Stern layer) of ions of opposite sign to that of the surface ions (counter ions) is formed. In addition, as a result of electrostatic interactions and thermal motion of the molecules, a non-uniform diffuse second layer develops around the particles, which is composed mainly of counter ions, but may contain also ions of the same sign as the surface (co-ions). This layer, called the diffuse electrical layer, can be described mathematically by the Poisson-Boltzmann equation [82].
2 nanoparticles for potential applications in membranes
Published in Alberto Figoli, Jan Hoinkis, Sacide Alsoy Altinkaya, Jochen Bundschuh, Application of Nanotechnology in Membranes for Water Treatment, 2017
Tiziana Marino, Marcel Boerrigter, Mirko Faccini, Christiane Chaumette, Lawrence Arockiasamy, Jochen Bundschuh, Alberto Figoli
The dispersion and stabilization of TiO2 powders in liquid media are still a big problem, since numerous properties of the final solution depend strongly on the colloidal stability of particles and their distribution in certain volumes. The sedimentation behavior is often seen as the crucial stability criterion. According to the Derjaguin, Landau, Verwey and Overbeek theory (DLVO theory), there are two basic forces controlling the stability of colloidal suspensions: van der Waals and the electrostatic forces (Hunter et al., 1981). Van der Waals forces are a weak attractive force between atoms or non-polar molecules caused by a temporary change in dipole moment arising from a brief shift of orbital electrons to one side of one atom or molecule, creating a similar shift in adjacent atoms or molecules. The electrostatic forces are related to the particle charge. The ζ potential is often used to measure these forces. For most suspensions, high values of this parameter indicate high stability, while low values imply coagulation (Fadda et al., 2009; Veronovski et al., 2010). Therefore, the stability of the suspension strongly depends on: Choice of solvents and additives (surfactants).Concentrations and particle size of TiO2 nanoparticle.
Colloidal Systems
Published in K.S. Birdi, Surface Chemistry and Geochemistry of Hydraulic Fracturing, 2016
The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory describes that the stability of a colloidal suspension is mainly dependent on the distance between the particles (Adamson and Gast, 1997; Bockris et al., 1981; Birdi, 2003, 2016; Somasundaran, 2015). DLVO theory has been modified in later years and different versions are found in the current literature. Electrostatic forces will give rise to repulsion at large distances (Figure 6.4). This arises from the fact that the electrical charge–charge interactions take place at a large distance of separation. The resultant curve is shown (schematic) in Figure 6.4. The barrier height determines the stability with respect to the quantity k T, the kinetic energy. DLVO theory predicts, in most simple terms, that if the repulsion potential (Figure 6.4) exceeds the attraction potential by a value () W≫kT
The effect of contaminated particle sphericity and size on membrane fouling in cross flow ultrafiltration
Published in Environmental Technology, 2018
Amira Abdelrasoul, Huu Doan, Ali Lohi, Chil-Hung Cheng
The extent of the interaction between attraction and repulsion forces has the potential to significantly influence the attachment of the colloidal particles to the membrane’s surface. The DLVO theory is the most commonly accepted explanation of the stability of colloids in suspension. In particular, the DLVO theory takes into account the balance between van der Waals attraction force and electrostatic repulsion force so as to effectively rationalize the propensity of particle attachments [20]. Figure 1(a) showcases the van der Waals interaction forces between macroscopic particles that occur through a third medium. The electrostatic repulsion force becomes significant when two particles approach each other and their double layers begin to interfere with one another. In most cases, as shown in Figure 1(b), the strength of the forces acting on each particle depends on the separation distance between the centers of two particles (r). The smaller the separation distance between the centers of two particles, the greater the strength of the forces acting on the particle. This dynamic can be attributed to the fact that van der Waals attractive force is inversely proportion to the seventh power of the separation distance between the centers of the particles affecting each other [21]. As a result, large particles generally have a large separation distance between them, thus causing a lower attraction force. This correlation indicates that the effect of particle size plays an essential role in their spatial configuration or arrangement in agglomerates.
A novel zwitterionic quaternary copolymer as a fluid-loss additive for water-based drilling fluids
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Xiaofeng Chang, Jinsheng Sun, Fan Zhang, Kaihe Lv, Xinyu Zhou, Jintang Wang, Jianwei Zhao
According to DLVO theory, the stability of colloids depends on the attraction and repulsion between the particles (Di Marco et al. 2007). When colloidal particles collide in Brownian motion, if the attraction is greater than the repulsion, colloidal particles coalesce. On the contrary, the particles remain dispersed (Lemaire et al. 2001). Therefore, the stability of the colloidal system is determined by the attraction and repulsion of the sol particles in the system. The repulsion force comes from the electrostatic repulsion force and the hydration film repulsion force, and the electrostatic repulsion force between the two colloidal particles is proportional to the square of Zeta potential (Li et al. 2008). Therefore, the Zeta potential can truly reflect the repulsion force between colloidal particles, thus reflecting the colloidal stability of WBDFs system (Yang et al. 2017). Figure 8 reveals that the Zeta potential of clay particles in WBDFs increases gradually (absolute value) with the increase of PDANV dosage. PDANV adsorbed clay particles effectively, made the diffusion electric double layer of bentonite thicker, zeta potential increased, the repulsion force between clay particles increased, and clay particles remained dispersed, so the appearance of filter cake was compact and the filtration loss was reduced. The zeta potential of PDANV/WBDFs showed a downward trend after hot rolling at 260°C for 16 h due to thermal degradation of PDANV adsorbing groups and reduction of adsorbing capacity on clay particles. Additionally, the coalescence passivation of clay particles also leaded to a decrease in potential under ultra-high temperature.
The stability and surface activity of environmentally responsive surface-modified silica nanoparticles: the importance of hydrophobicity
Published in Journal of Dispersion Science and Technology, 2020
Vahid Rajabi Ghaleh, Aliasghar Mohammadi
The images recorded during four days from our nanofluids are shown in Figure 2. The unmodified-silica nanofluid exhibits stability up to, at least, four days in double-distilled water. In the presence of salts, the stability of the nanofluid is lost through a coagulation process, lasting two days. The stability depends on interparticle forces, classically described by the DLVO theory for bare (unmodified) nanoparticles. Based on the DLVO theory, the interaction comprises attractive van der Waals and repulsive electrostatic forces. The competition between van der Waals and electrostatic forces controls the stability of the colloidal suspensions.