Charging of particles

The long-range interactions between a pair of molecules are detemiined by electric multipole moments and polarizabilities of the individual molecules. MuJtipoJe moments are measures that describe the non-sphericity of the charge distribution of a molecule. The zeroth-order moment is the total charge of the molecule Q = Yfi- where q- is the charge of particle and the sum is over all electrons and nuclei in tlie molecule. The first-order moment is the dipole moment vector with Cartesian components given by... 

The development of electrostatic precipitators was based mostly on empirical work, and it has produced more than 1000 patents covering all aspects of electrostatic air cleaning. From the theoretical point of view, important milestones were papers published by Deutsch as well as White.These papers deal with the collection efficiency of the electrostatic precipitator. The most important early papers dealing with the electrical charging of particles are the ones published by Arendt and Kallmann, Pautheniet and Moreau-Hanot, and White. ... 

The electrostatic force is directly proportional to the net charge of an aerosol particle. Therefore, effective charging of the particles is of great importance. Airborne particles are normally charged either due to their birth processes or due to charge transfer from gas ions to particles. The natural charging of particles is normally so weak that it has no practical importance for electrostatic air cleaning. 

There are, however, also similarities between the two discharge types. Positive ions drifting toward the opposite electrode form a space charge that affects the electric field and the corona current principally in the same way as in a negative corona discharge. Also, the charging of particles takes place almost in the same way for both types of corona discharge. 

Maurer, B., Discharges due to electrostatic charging of particles in large storage silos Ger. Chem. Engrg., 2 189-195 (1979)... 

B. Maurer, Discharges Due to Electrostatic Charging of Particles in Large Storage Silos, German Chemical Engineering (1979), 3 189-195. 

Based on calculations and comparisons two principles of adding spatial-energy criterions depending upon wave properties of P-parameter and systemic character of interactions and charges of particles were substantiated ... 

Electrostatic phenomena are a function of particle properties as well as particle charge. Of particle properties, the one most important and subject to the widest variation is particle size.3 Consequently, it would be most con-... 

Photoemission is unlikely to be a significant contributor to the charging of particles. Field emission, however, could be involved in some of the intensive electrostatic atomization processes where very fine highly charged particles are produced. Because of the dubious current applicability, no effort has been made to review the literature in these cases. 

Dissolved polymer molecules can be adsorbed by polymer particles via electrostatic attractive force or hydrophobic interaction. When polyelectrolyte is adsorbed on an opposite-charge particle, the polymer molecules usually have a loop-and-tail conformation and, as a result, inversion of charge occurs. For example, sulfatecarrying particles behave as cationic ones after they adsorb poly(lysine). Then poly(-styrene sulfonate) can be adsorbed on such cationic particles and reinvert the charge of particles to anionic (14). Okubo et al. pointed out that the alternate adsorption of cationic and anionic polymers formed a piled layer of polyelectrolytes on the particle, but the increment of adsorbed layer thickness was much less than expected. This was attributed to synchronized piling of two oppositely charged polyelectrolytes (15). 

The diffusion charging of particles in the presence of an external electric field is available in Murphy (1956) and Liu and Yeh (1968). 

It is noted that the particle-wall interaction in the boundary layer and the electrostatic effect due to the electrostatic charge carried by the particles may strongly affect particle collection and reentrainment in the cyclone and, consequently, affect the collection efficiency. In the presence of electrostatic charges of particles and an external electric field, the collection efficiency of a tangential inlet cyclone with a steep cone is given by [Soo, 1989]... 

In the presence of electrostatic charges of particles and an external electric field, the cut-off size of a tangential inlet cyclone with a steep cone is given from Eq. (7.30) as... 

Theoretical and experimental studying of the tunnel electrons transfer in relation to the size distribution of nanoparticles in a film and to mutual charging of particles of various sizes. 

The surface charge of particles in a liquid medium can also be adjusted through the selective use of surfactants. Whether through the use of pH adjustment or surfactants, one must always ensure that the solubility of the powder does not increase, thereby dissolving the particles. Commercial instruments are readily available for this technique. The same apparatus often performs particle size measurements using photon correlation spectroscopy, which is discussed in a following section. 

The electric charge of particles may be indicated by adding the superscript +, —, or 0 e.g. p+, n°, e , etc. If the symbols p and e are used without a charge, they refer to the positive proton and negative electron respectively. 

Fernandez-Urrusuno et al. [30] reported on development of a freeze-dried formulation of CT/TPP nanoparticles loaded with insulin. They tested various cry-protective agents for their ability to maintain the original size/charge of particles upon reconstitution. The best medium appeared to be 5 % trehalose or sucrose. This was confirmed with unloaded nanoparticles from System 2 (Fig. 16). The original suspension, without the trehalose addition, exhibited a size of 185 nm (SD 25 nm). 

---