Micellar theory

The kinetic mechanism of emulsion polymerization was developed by Smith and Ewart [10]. The quantitative treatment of this mechanism was made by using Har-kin s Micellar Theory [18,19]. By means of quantitative treatment, the researchers obtained an expression in which the particle number was expressed as a function of emulsifier concentration, initiation, and polymerization rates. This expression was derived for the systems including the monomers with low water solubility and partly solubilized within the micelles formed by emulsifiers having low critical micelle concentration (CMC) values [10]. 

The spatial configurations proposed by Kratky [38] and Mark [39] repeat in principle the basic idea of the fringe micellar theory, according to which long cellulose chains lie lengthwise through the crystal and amorphous phases form the fibre (Fig. 80). 

Micellar theory has developed in a somewhat uncertain fashion and is still in many respects open to discussion. Possible micelle structures include the spherical, laminar and cylindrical arrangements illustrated schematically in Figure 4.14. Living cells can be considered as micellar-type arrangements with a vesicular structure. 

Although the problem of the gross structure of cellulose is outside the scope of this review, it is of interest that Lieser32 has interpreted the behavior of cellulose with cuprammonium in support of a micellar theory of cellulose structure Staudinger,33 of a long chain theory Compton,34 of a particulate theory Hess,35 of a theory of secondary valence association between CsHioOs units and Pacsu,36 of a theory of acetal linkages in equidistant open-chain units and the laminated chain structure of cellulose. 

Since polymers cannot be completely crystalline (i.e. cannot have a perfectly regular crystal lattice) the concept "crystallinity" has been introduced. The meaning of this concept is still disputed (see Chap. 2). According to the original micellar theory of polymer crystallisation the polymeric material consists of numerous small crystallites (ordered regions) randomly distributed and linked by intervening amorphous areas. The polymeric molecules are part of several crystallites and of amorphous regions. 

AU discussions of particle nudeation start with the Smith-Ewart theory in which Smith and Ewart (1948) in a quantitative treatment of Harkins micellar theory (Harkins, 1947, 1950) managed to obtain an equation for the particle number as a function of emulsifier concentration and initiation and polymerization rates. This equation was developed mainly for systems of monomers with low water solubility (e.g., styrene), partly solubilized in micelles of an emulsifier with low critical micelle concentration (CMC) and rseeited to work well for such systems (Gerrens, 1963). Other authors have, however, argued against the Smith-Ewart theory on the grounds that (i) particles are formed even if no micelles are present, (ii) the equation for the... 

One main objection to the micellar theory has been that even if the particle number determined 1 polymerization of sparingly water-soluble monomers like styrene or octyl acrylate changes steeply at or directly below the CMC, this is not the case for more water-soluble monomers (Siitterlin... 

Earlier concepts about the fine structure of microfibrils have been reviewed by several authors - " and will be only briefly mentioned here as background for the description of later developments. In 1858, Nageli - - proposed the micellar theory this assumed the presence of separate, brick-like, crystalline micelles within the cellulose fibers (see Fig. 6) to explain the birefringence observed with a polarized... 

Fig, 6.—The Brick-like Structure of Cellulose Fibers, According to the Original Micellar Theory... 

Fig. 7.—Arrangement of Cellulose Molecules in (a) Continuous and (b) Fringed-Micellar Theories. ...

The micellar theory in its essential features was supported by numerous authors at the time of the vivid revival of colloid science in 1910 and after, e. g., by Zsigmondy (1911), Bachmann (1912), Arisz (1915), Bradford (1918) and others. This theory may be classified as the solid-liquid theory of gel structure. 

Anisotropy of swelling can already be explained on the basis of the ancient micellar theory of Von NaGELi Let us consider a fibre with uniaxial orientation consisting of rodlet shaped particles (Fig. 93). If the fibre is allowed to swell, and equal layers of a liquid are inserted between the particles, the change in diameter will surpass the change in length, since in the direction perpendicular to the fibre axis more intersticies per unit length occur than in the direction parallel to the fibre axis. 

Fig. 93. The explanation of anisotropical swelling on basis of the ancient micellar theory.

According to the micellar theory [6, 7] the rate of polymerization (in the stationary interval 2) is proportional to the 0.4 power of the concentration of initiator and the 0.6 power of the concentration of emulsifier [4]. It was later shown by Roe [23], Fitch [22,25, 67] and Hansen and Ugelstad [18] that this behavior is also consistent with homogeneous nucleation. Indeed, identical exponents can be predicted by virtually any mechanism which assumes that (1) coagulation does not occur, (2) nucleation ceases when the surface area of the latex particles is equal to the total surface area capable of being occupied by the emulsifier molecules, and (3) the rate of production of free radicals is uniform. Here, determination of exponents for [I] and [E] fails to discriminate between competing micellar and homogeneous nucleation theories. 

Peggion et al. [76], however, concluded that the strong deviations from the micellar theory cannot be ascribed to the solution polymerization which competes with the micellar polymerization and suggest the following reaction mechanism The radicals produced by decomposition of the initiator react with the monomer dissolved in water. The polymer radicals separate from the... 

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