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Monomers adsorbed

The transition shows up in many other characteristics the fraction of adsorbed monomers (Fig. 5(a)), and the average orientation of bonds. [Pg.572]

FIG. 5 (a) Fraction of adsorbed monomers (i.e., those with z-coordinate less than 6) vs ejk T for four different chain lengths, (b) The same for the second Legendre polynomial P2 cosd). (c) Scaling plot of and P2 cos9) vs distance from the adsorption threshold, using = —1.9 [13]. [Pg.572]

At a specific density pi of adsorbed monomers, a capture time can be defined as... [Pg.885]

Fig. 32 a-d. Phase transition a from the extended coil b to a globule state as found by scaling analysis [83] c the transition is caused by lowering the surface pressure below a certain critical value TTc at which the fraction of adsorbed monomers 3=N2d/N undergo discrete changes d hereby, the depends critically on the side chain length... [Pg.165]

Propagation occurs by reaction of adsorbed monomer at the active sites at a rate given by... [Pg.662]

Primary free radicals can also be formed on the surface of the deposited polymer through the dissociation of adsorbed monomer caused by the energy released... [Pg.50]

At the polymer surface, propagation can occur by the reaction of surface free radicals with either gas phase or adsorbed monomer. The rates for these processes can be expressed as... [Pg.52]

The role of ions in initiating polymerization was further elaborated by Poll et al.. For frequencies below f. they proposed that the impact of ions with the growing polymer film produced free radicals via reactions 1 and 2. New polymer would then form by the reaction of surface free radicals with adsorbed monomer. It was also proposed that the concentration of surface free radicals is proportional to the current density striking the growing polymer surface and, hence, that the rate of polymerization is given by... [Pg.56]

The rest of the mechanism proposed by Tibbitt et al. " is also shown in Table 6. Two assumptions were introduced to simplify the mechanism. The first is that the extent of gas phase termination is very small and consequently, that essentially all of the radicals formed in the gas phase are adsorbed on the polymer surface. The second assumption is that the concentrations of adsorbed monomer and free radical are proportional to the gas phase concentrations of these species. These relationships are expressed by... [Pg.60]

Cosmic ray particles can work as a trigger of the chain of polymerization of formaldehyde adsorbed (e.g., at the surface of interstellar silicate dust). However, the triggering of the polymerization chain is a necessary but still not sufficient condition for obtaining the interstellar polymers. If the addition of any new link of the chain would require a hit of adsorbed monomer layer by another cosmic ray particle (i.e., if there is no spontaneous growth of chains after they are started by some external factor), the formation of polymers in interstellar space would be highly improbable. Therefore the spontaneous growth of polymer chains near absolute... [Pg.246]

Fig. 12 Schematic representation of the CDSD copolymerization process in the cases when one of the comonomers is selectively absorbed by a polymer globule (top) or adsorbed on a surface (bottom), a Growing chains diming the copolymerization (reaction zone around the growing chain end is marked with a dashed line) resulting copolymers in b globular (adsorbed) and c coil-like states. Regions where absorbed (adsorbed) monomers dominate are shown in gray... Fig. 12 Schematic representation of the CDSD copolymerization process in the cases when one of the comonomers is selectively absorbed by a polymer globule (top) or adsorbed on a surface (bottom), a Growing chains diming the copolymerization (reaction zone around the growing chain end is marked with a dashed line) resulting copolymers in b globular (adsorbed) and c coil-like states. Regions where absorbed (adsorbed) monomers dominate are shown in gray...
In a previous publication (4) it was shown that at pressures above 500 p.s.i.g., the rate of reaction ultimately levels out, approaching zero order. This behavior offers evidence that polymerization occurs by reaction of an adsorbed monomer molecule with an adjacently adsorbed monomer molecule or growing polymer chain (Langmuir-Hinshelwood mechanism). If polymerization occurred by reaction of monomer in the gas phase with adsorbed monomer or adsorbed growing polymer chains (Rideal mechanism), the reaction rate should increase without limit as pressure is increased. [Pg.407]

Therefore the process is best described as a polymerization in an adsorbed monomer layer created and stabilized as a miniemulsion ( ad-miniemulsion polymerization ). The process is schematically shown in Fig. 16. [Pg.107]

In a second step we minimize the free energy F with respect to n, taking Into account the adsorption energy E per adsorbed monomer, and the above value of d ... [Pg.323]

In discussions of the mechanism of plasma polymerization appearing in the literature, polymerization, particularly the growth mechanism of polymer formation, is dealt with in a somewhat vague manner without any clear distinction between mechanism of polymerization and mechanism of polymer deposition. For instance, the hypothesis that plasma polymerization occurs via the polymerization of adsorbed monomer on the surface invokes the location of polymer formation rather than mechanism of polymerization that is, the mechanism of polymerization, whatever that would be, is intuitively or a priori assumed. Nevertheless, such a hypothesis constitutes an important school of thought in dealing with the polymerization mechanism. [Pg.57]

This curling can be attributed to an internal stress arising in the plasma polymer during polymer deposition. It is important to recognize that the internal stress in the plasma polymer (in the as-polymerized state) is an expansive stress and that this is in marked contrast to what would be expected if the adsorbed monomer were polymerized at the surface of the substrate, which would create, with very few exceptions, contractive stress due to the contraction of volume on the polymerization of a monomer. [Pg.222]

As shown in Figure 12.7, an initial deposition rate that is roughly four times greater than the steady-state deposition rate is observed with styrene, which is an easily condensable vapor (high adsorption onto the surface), by method A. The gaseous monomer acetylene, on the other hand, shows an initial deposition rate identical to the steady state is obtained immediately on the inception of discharge, as shown in Figure 12.8. Whether the adsorbed monomer polymerizes at the surface or... [Pg.254]

As no completely satisfactory representation of the formation and nature of active species in heterogeneous catalysts has yet been devised this may be an over-simplification. Clearly the first order dependence of rate on monomer concentration is indicative of comparable solvent and monomer adsorption, even with what might be considered more strongly adsorbed monomers, such as butadiene, in comparison with mono-olefins or aliphatic hydrocarbons. The role of the more strongly adsorbed metal alkyl is more difficult to assess. The proportion of active alkylated transition metal atom sites will obviously increase with increase in [A] up to a limiting value. [Pg.152]

The subscripts A and H correspond to sites with alkyl (polymer) and hydride groupings and the superscripts M and N to adsorbed monomer and nitrogen. The coefficients f, b> f, b refer to adsorption and desorption of monomer and nitrogen respectively while /e, k , kfr and kp are the rate coefficients of termination, re-initiation, transfer and propagation. This leads to a rate relationship (G, constant total no. of active sites)... [Pg.186]


See other pages where Monomers adsorbed is mentioned: [Pg.237]    [Pg.570]    [Pg.571]    [Pg.55]    [Pg.174]    [Pg.215]    [Pg.162]    [Pg.70]    [Pg.546]    [Pg.51]    [Pg.53]    [Pg.56]    [Pg.56]    [Pg.31]    [Pg.92]    [Pg.187]    [Pg.305]    [Pg.237]    [Pg.145]    [Pg.52]    [Pg.164]    [Pg.409]    [Pg.412]    [Pg.196]    [Pg.246]    [Pg.254]    [Pg.67]    [Pg.58]    [Pg.255]    [Pg.460]    [Pg.620]    [Pg.626]   
See also in sourсe #XX -- [ Pg.91 ]




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