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Light Scattering Techniques for Characterization of NANPs and Their Formulations
Published in Peixuan Guo, Kirill A. Afonin, RNA Nanotechnology and Therapeutics, 2022
Lewis A. Rolband, Joanna K. Krueger
Often thought of as a partner technique of DLS, phase-analysis light scattering (PALS) or electrophoretic light scattering (ELS) serves to investigate the surface charges of macromolecules and nanoparticles. This is accomplished by applying an oscillating electric field to a solution of nanoparticles and observing the phase difference in the scattered light and of a reference beam. The difference in the phase is due to the Doppler shift that occurs as the light is scattered from a moving particle. The magnitude of this difference is proportional to the velocity of the particle as it moves in response to the electric field. In turn, the velocity of the particle as it translates through the solution is dependent on the solvent’s dielectric constant, the solution’s viscosity, and the zeta potential, ζ, of the particle, as given by the Smoluchowski equation [6, 10]. It is an important distinction that the ζ of a particle is not the same as its surface charge, as ζ is the charge at the slipping plane of the electrical double layer formed in solution. The zeta potential can serve as an important parameter for assessing colloidal stability, with values closer to neutral being more likely to aggregate [5–7, 10].
Effect of Potential Drop in Migration Testing of Chloride Diffusivity in Concrete
Published in J. Mietz, B. Elsener, R. Polder, Corrosion of Reinforcement in Concrete — Monitoring, Prevention and Rehabilitation, 2020
The intrinsic potential drop ΔUin is determined by the physical-chemical properties of the system. In a system for migration testing of chloride diffusivity in concrete, this potential drop is mainly due to the polarisation of the electrodes induced by the d.c. current and the formation of an electrical double layer both at the interface between the solutions and the specimen and between the solutions and the electrodes. According to the theory of electrical double layer, the formation of an electrical double layer is the result of a selective adsorption of ions from the solution on the electrode surface. Thus, in such a system this potential drop is determined by the properties of the electrodes, the concrete as well as the solution. Since the solutions in the upstream and down-stream cells usually are different, the potential drops at the cathode and the anode will also be different [5]. The reversible dissociation potential of water can also be considered as being part of the intrinsic potential drop. At pH = 13 and 25°C, this potential makes up a value of 0.463 V.
Recent Advances in Polymer Nanocomposite Coatings for Corrosion Protection
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Subramanyam Kasisomayajula, Niteen Jadhav, Victoria Johnston Gelling
A phenomenon called electrical double layer occurs at the metal-electrolyte interface as a result of the interactions between ions present in both metal and electrolyte. While Figure 2(a) depicts the basic model, Figure 2(b) is the complex model of electrical double layer, the Bockris-Devanathan-Muller (BDM) model, which is the modified version of previous models, the Stern and the Gouy-Champan models. According to the BDM model, if a positive charge develops on metal surface, it will be neutralized by the combination of negatively charged anions and water molecules with oxygen side (negative side of dipole) facing toward metal surface. The layer containing adsorbed negatively charged ions in simple model (Figure 2(a)) or the layer containing both adsorbed negatively charged ions and adsorbed water molecules in the BDM model (Figure 2(b)) is known as Stern layer or Inner Helmholtz plane. Since this layer is formed right at the interface as a result of attraction from positive ions of metal substrate, it creates a very high field of strength up to 1 × 107 V/cm. In the subsequent layer, negatively charged ions adsorbed to metal surface in Stern layer are counterbalanced by opposite ions and these counter-ions are further counterbalanced by their opposite ions in electrolyte solution. This second layer continues to exist in the solution and diminishes gradually with increase in distance away from surface of substrate. This layer is called the Gouy-Chapman diffuse layer.
Cycling stability depends closely on scan rate: the case of polyaniline supercapacitor electrodes
Published in Soft Materials, 2021
Liya Hou, Haihan Zhou, Hua-Jin Zhai
As one type of energy storage devices, supercapacitors (SCs) have attracted a great deal of attention because they have higher power output and better cycling performance than secondary batteries, as well as larger energy output than traditional capacitors.[1,2] Thus, SCs have been applied in an array of fields, like electric vehicles, portable/wearable electronics, and digital communication.[3,4] The charges in SCs can be stored in two forms. One is through reversible adsorption of positive and negative ions at the interface of electrolyte and electrode materials, which is called electrical double-layer capacitance. The other is by fast and reversible redox reactions at the surface or near-surface of electrode materials, called pseudo-capacitance.[5,6] Electrode materials, therefore, play a critical role in the charge storage for SCs, which traditionally include carbon materials, transition metal oxides, and conducting polymers.[7,8]
On the Volta potential measured by SKPFM – fundamental and practical aspects with relevance to corrosion science
Published in Corrosion Engineering, Science and Technology, 2019
Cem Örnek, Christofer Leygraf, Jinshan Pan
More work is required to move the charge further towards or through the ‘surface’. This is the region where short-range forces prevail and where the charge gets induced and chemical variations occur [36,37]. The surface of an electrically conducting phase, in general, is composed of an electrical double layer. Metals form usually a negative ‘layer’ or ‘cloud’ of electrons above the surface, whereas the positive counter layer is formed directly underneath [14,15,38,39]. This is different to the electrochemical double-layer concept, where the metal is usually negatively charged and the electrolyte above is positively charged [14,15,38,39]. The change in charge distribution due to the interaction with the electrolyte leads to a change of the Volta potential, which explains why the corrosion potential (depending on both the electrode and electrolyte) does not always correlate with the Volta potential [1]. The sum of charge of the entire metal surface is zero but there is still work needed to move charge from the bulk interior through the surface layer, and vice versa. The change of the electrostatic potential associated with this bipolar surface layer is hearkened back to the so-called Surface potential [14,15,36,37].
Identifying critical parameters in the settling of African kimberlites
Published in Mineral Processing and Extractive Metallurgy Review, 2018
E. T. Boshoff, J. Morkel, N. Naude
The zeta potential (ζ) is defined as the electrical potential at the plane of shear of the diffuse electric double layer and is the only experimentally possible measurement of particle charge. The zeta potential is dependent on the surface charge of the particles and on the concentration and charge of the counter-ions in solution, according to Wills (1997). Derjaguin and Landau (1941) and Verwey and Overbeek (1948) used the double layer compression concept to develop the DLVO theory for particle-particle interaction. This theory states that when two particles in solution move closer to one another, the electric double layers will overlap, and the residual attraction energy can be predicted by adding the double layer repulsion and van der Waal’s attractive energies. In a solution with high ionic strength, the electric double layer will be compressed, resulting in a lowering of the strength of the repulsive forces surrounding the clay particles. This allows particle interaction to occur, which leads to more effective dewatering.