Colloids drag forces

The characterization and control of electrostatic forces are of particular interest. Electrostatic forces depend on the electric charge and potential at the particle surfaces. When subjected to a uniform, unidirectional electric field E. charged colloidal particles accelerate until the electric body force balances the hydrodynamic drag force, so that the particles move at a constant average velocity v. This motion is known as electrophoresis, and v is the electrophoretic velocity. 

In colloidal systems the sedimentation principle uses the fact that particles of different mass have different velocities in a fluid at rest when the inertial force acting on the particle is equal to the difference between its weight minus buoyancy and the drag force of the medium ... 

In the presence of non-uniform AC electric field, colloidal particles suspended in an aqueous medium experience electrokinetic forces including electrophoresis (EP), dielectrophoresis (DEP), and hydrodynamic drag force due... 

Of particular interest in water treatment is the permeability of aggregates. When a regates deposit on a membrane, flux is determined by the resistance of the formed cake. Furthermore, the drag force on the colloid is determined by the aggregate porosity. Veerapaneni and Wiesner (1997) predicted the resistance to fluid flow as a function of fractal dimension. They determined that fluid flow through the aggregates decreased with increasing fractal dimension. 

From fluid mechanical calculations, if the velocity field around the collector in the absence of the colloidal particles is known, then Vp, the velocity field of the particles, can also be found, at least to a good approximation. Moreover, the particle diffusion coefficient becomes position dependent since the Stokes drag force used to derive Equation 3.72 is modified by the presence of the nearby collector surface. The conservation equations (Equations 3.75 and 3.77) must therefore be replaced with the appropriate one ... 

C. Binder, M.A.J. Haitig, W. Peukert, Structural dependent drag force and orientation prediction for small fractal aggregates. J. Colloid Interface Sci. 331(1), 243-250 (2009). doi 10.1016/j. jcis.2008.11.021... 

Sedimentation (MICROSCOPIC PROCESS) motion of particles in viscous media due to gravitation or centrifugal fields (also settling), the term refers frequently to the state in which the field forces are counterbalanced by the drag force this state is almost instantaneously achieved in the case of colloidal suspensions the sedimentation of an individual particle depends on its size, the density contrast, the rheological fluid properties, the field strength, and the viscous interactions with other particles. 

One difference between dry fine powders and colloids in liquids is that the low viscosity of air (and other gases) make hydrodynamic drag forces minimal for dry powders in many instances, except when the particles have very low density (such as dust and smoke) or the gas velocity is very high. However, fine particles in liquids are strongly influenced by hydrodynamic drag forces as described in Chapter 2 because the viscosity of liquids is much greater than that of gases. 

Second, the dynamic equations for polymer motion and for colloid motion are qualitatively the same, namely they are generalized Langevin (e.g., Mori-Zwanzig) equations, including direct and hydrodynamic forces on each colloid particle or polymer segment, hydrodynamic drag forces, and random thermal forces due to solvent motion, all leading to coupled diffusive motion. 

There are three forces that are acting on the falling ball gravity, the viscous drag of the solvent, and the entropic force that is due to the disturbed microstructure of the colloidal particles. A force balance on the falling ball gives... 

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