Fundamentals in Colloid Science

Abstract

Preparation and handling of colloidal suspension or even their characterisation is not possible without a basic understanding of the physical effects that prevail on the microscopic level. Some of these effects are directly related to the fineness of the particles because it coincides with a large specific surface area (which corresponds, e.g., to a high adsorption capacity), a considerably curvature of the particle surface (which i. a. promotes dissolution), a high number concentration (i.e. significant osmotic pressure and large collision frequencies), small interparticle distances (i.e. strong interactions between scattered waves), low particle mass (i.e. low weight and inertia), or with the fact that the wavelength of light is larger than particle size (i.e. weak optical scattering). A further effect of the small size of colloidal particles is that their diffusive motion is much faster than for micrometre particles. Moreover, the interactions between colloidal particles are decisive for the macroscopic behaviour of the whole suspension (e.g. with regard to rheology or coagulation). These interactions may be attractive and/or repulsive and depend on the chemical nature and the material properties of the particles. Most of all, they are affected by the interfacial properties which reflect the physico-chemical interaction between the particulate phase, the solvent, and the solutes (e.g. hydrophobicity, adsorption, surface charging).This chapter provides a brief introduction to the fundamentals in colloid science. It addresses the physico-chemical properties of single colloidal particles as well as the processes at the interface and the structure of the interfacial layer. It further examines the non-viscous interactions that occur among colloidal particles. For detailed explanation, the reader is referred to the textbooks of Adamson and Gast

Efficient Method for the Electrodynamics Langevin-Dynamics Simulation of Multiple Nanoparticles Based on the Coupling Theory of Quasinormal Mode

“…In LD simulations, we treat the possible collisions between two particles as elastic collisions and take into account the electrostatic double-layer force between two particles with a small spacing. The electrostatic double layer on the particle surface will generate a repulsive force between two metallic nanoparticles, , which can be obtained by differentiating the electrostatic double-layer potential U DL with respect to the surface separation d , i.e., F DL = (−∂ U DL /∂ d ) u , where u is a unit vector pointing from the center of the particle that exerts the force to the center of the particle that experiences the force. For the electrostatic double-layer force between two identical particles, there is , U DL = 2 π ε ψ 0 2 a false[ 2 a / false( 2 a + d false) false] exp false( prefix− κ d false) where d is the distance between the surfaces of the two particles, a is the particle radius, ε is the permittivity of the ambient medium, ψ 0 is the surface potential of the particles, and κ –1 is the Debye screening length.…”

“…The electrostatic double layer on the particle surface will generate a repulsive force between two metallic nanoparticles, , which can be obtained by differentiating the electrostatic double-layer potential U DL with respect to the surface separation d , i.e., F DL = (−∂ U DL /∂ d ) u , where u is a unit vector pointing from the center of the particle that exerts the force to the center of the particle that experiences the force. For the electrostatic double-layer force between two identical particles, there is , U DL = 2 π ε ψ 0 2 a false[ 2 a / false( 2 a + d false) false] exp false( prefix− κ d false) where d is the distance between the surfaces of the two particles, a is the particle radius, ε is the permittivity of the ambient medium, ψ 0 is the surface potential of the particles, and κ –1 is the Debye screening length. For a symmetric electrolyte (i.e., z-z electrolyte), there is κ=[ε k B T /(2 z v 2 e 2 N A I )] −1/2 , where e is the electron charge, k B is the Boltzmann constant, N A is the Avogadro constant, I is the ionic concentration, and z v is the valency of ions.…”

“…Besides, in the LD equation, we take into account not only the optical force, viscous resistance, and the Brownian motion of nanoparticles that are routinely considered in previous ED-LD simulations, 8,[17][18][19]23 but also the electrostatic double-layer force that generally exists between two particles in solution with a small spacing. 30,31 This method is generally applicable to any incident light beam, as well as nanoparticles with irregular shapes or inhomogeneous materials. Compared with the ED-LD method based on full-wave FEM for calculating optical force (abbreviated as FEM-ED-LD), our method can reduce the computation time by at least 2 orders of magnitude.…”

“…In this method (abbreviated as QNM-ED-LD), by exploiting the method proposed in based on the QNM-coupling theory for an efficient electrodynamics (ED) calculation of optical force of multiple nanoparticles, we achieve a fast solving of the Langevin dynamics (LD) equation that governs the motion of multiple nanoparticles. Besides, in the LD equation, we take into account not only the optical force, viscous resistance, and the Brownian motion of nanoparticles that are routinely considered in previous ED-LD simulations, ,− , but also the electrostatic double-layer force that generally exists between two particles in solution with a small spacing. , This method is generally applicable to any incident light beam, as well as nanoparticles with irregular shapes or inhomogeneous materials. Compared with the ED-LD method based on full-wave FEM for calculating optical force (abbreviated as FEM-ED-LD), our method can reduce the computation time by at least 2 orders of magnitude.…”

Ultrasonic Based Device to Monitor Oil Separation from Oily Water Discharges

“…Thus the wave propagation regime is shortwave, which is dominated by scattering losses, while the contribution of other terms is negligible. [17,18] The expression for scattering losses given below shows that for a given liquid (1) and solid phase (2), the losses are proportional to (k 1 r) 3 : [20,21] a sc ¼ wk 1 k 1 r ð Þ 3 1 6 Thus, for a given particle size, losses can be reduced by selecting a lower frequency transducer, thus reducing k 1 r. Based on these observations, further tests for device development were conducted with a 1 MHz transducer. The estimated loss coefficient can also be used to calculate initial signal amplitude for a desired received signal using Equations (6) or (7).…”