Particle charged radicals

In the case of more water-soluble monomers and (amphiphilic) macromonomers, the Smith-Ewart [16] expression does not satisfactorily describe the particle nucleation. The HUFT [9,10] theory, however, satisfactorily describes the polymerization behavior or the particle nucleation of such unsaturated hydrophilic and amphiphilic monomers. The HUFT approach implies that primary particles are formed in the aqueous phase by precipitation of oligomer radicals above a critical chain length. The basic principals of the HUFT theory is that formation of primary particles will take place up to a point where the rate of formation of radicals in the aqueous phase is equal to the rate of disappearance of radicals by capture of radicals by particles already formed. Stabilization of primary particles in emulsifier-free emulsion polymerization may be achieved if the monomer (or macromonomer) contains surface active groups. Besides, the charged radical fragments of initiator increases the colloidal stability of the polymer particles. 

Another important problem that has been debated for a long time is whether or not the electric charges and the emulsifier layers on the surfaces of the polymer particles affect the radical entry rate of a charged radical (p). It is now con-... 

The term e in the expression for l/F is said to take into account the feet that the charged radical at the outside surface of the particle is brought up to a higher energy level, expressed by the Boltzmann fector e. However,... 

Thus far, in Sect. 9.6 we have considered the electronic structure and the singleparticle excitations of (Fa)2PF6 crystals as examples of radical-cation salts. For single-particle charge transport at T < T, a thermal activation of the charge carriers across the energy gap is necessary. It corresponds to a frequency of = 4.4 10 Hz, thus an excitation in the infrared spectral range. 

Dozens of reactions of free radicals (SiCla, SiClsO, Cl, OCl, H, OH, HO, =Si, =SiO, etc.), charged particles, ion-radicals, O atoms, molecules and proto-particles in the flame with SiCU, O2, H2 and related compounds on synthesis of fumed silica are worthy of special attention, since variations in synthesis conditions allow one to prepare materials strongly different in their morphological (primary and secondary particle size distributions, type of contacts between adjacent particles) and surface (concentrations of silanols and intact water) properties. These problems as well as structural and adsorptive characteristics of different silicas were analyzed in details by Mironyuk and coworkers in a series of publications [36]. 

Fitch and Shih [8S] elaborated Garden s calculation of the rate at which radicals generated in the aqueous phase would collide with latex particles. They found that the electrostatic barrier between a latex particle stabilized only by ionic end-groups and a similarly charged radical was negligible. But experimental results indicated that the rate of radical entry was not proportional to the cross-section of the particles as required by the collision theory instead it was proportional to particle radius as predicted for diffusional entry. 

Another component of the entry rate coefficient can be from re-entry of radicals which have exited (desorbed) from another particle. Desorbed radicals will have arisen from some transfer reaction inside a particle, and are thus unlikely to be charged, and hence will be lipophilic. Hence once a desorbed radical in the aqueous phase meets the surface of a particle, it is likely to penetrate immediately into the interior of the particle its probability of entry into a monomer-rich region is unity. Denoting these radicals as E, one has... 

Luminescence can arise from two mechanisms (1) recombination of charged particles or radicals (2) mechanical excitation of units in the polymer chain. Thus, luminescence depends on the nature of the polymer, the presence of additives, and temperature. As luminescence has been found to be absent on grinding in vacuum or in an inert atmosphere, it has thus been suggested that the afterglow is a result of recombination of peroxy radicals [43]. Chemiluminescence intensity thus depends on the kind and pressure of the surrounding gas [44]. 

For the flow of energy to take place, either a moist conductor or an electrolyte must be present An electrolyte is an electricity-conducting solution containing ions, which are atomic particles or radicals bearing an electrical charge. Charged ions are present in solutions of acids, alkalis, and salts. The presence of an electrolyte is necessary for corrosion to occur. Water, especially salt water, is an excellent electrolyte. 

Radicals generated from water-soluble initiator might not enter a micelle (14) because of differences in surface-charge density. It is postulated that radical entry is preceded by some polymerization of the monomer in the aqueous phase. The very short oligomer chains are less soluble in the aqueous phase and readily enter the micelles. Other theories exist to explain how water-soluble radicals enter micelles (15). The micelles are presumed to be the principal locus of particle nucleation (16) because of the large surface area of micelles relative to the monomer droplets. 

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