Intermittent growth

This intermittent growth model was further elaborated [334-341], and ethylene polymerisation systems were devised to involve consecutive equilibria appearing to convert alkylaluminium halide and metallocene first into donor-acceptor complexes [scheme (61)] equivalent to contact (inner) ion pairs and then into separated (dissociated) ion pairs [scheme (62)] [297,338] ... 

In polymerizations where desorption is very high, all micelles grow simultaneously. This is because radical absorption is followed almost iimiediately by desorption with only a brief micellar growth period. As a result, all micelles experience an equal but intermittant growth. The number of latex particles is determined solely by the number of micelles initially present. The number of micelles, m, is given by the expression... 

Waxman, D.J., P.A. Ram, N.A. Pampori, and B.H. Shapiro (1995). Growth hormone regulation of male-specific rat liver P450s 2A2 and 3A2 Induction by intermittent growth hormone pulses in male but not female rats rendered growth hormone deficient by neonatal monosodium glutamate. Mol. Pharmacol. 48, 790-797. 

Fig. 7 Left-. Reaction scheme of the successive equilibria for the formation of the polymerization active species C. Right. Intermittent growth model involving equilibria between polymerbearing, but inactive, primary complexes CP and active catalyst species C P ...

On the other hand, low QD density is desirable for some devices that use individual QDs, such as single-photon sources. However, precise control of low-density QDs is difficult because the growth mode transition from 2D to 3D occurs rapidly. To realize low-density growth, the surface concentration of adatoms should be suppressed, and the supply amount of growth materials should be precisely controlled. In Sect. 3.5.2, an intermittent growth method is presented for the controlled formation of low-density InAs/GaAs QD. 

Intermittent Growth of Low-Density InAs/GaAs Quantum Dots... 

Fig. 3.30 RHEED patterns and RHEED diffraction-beam intensity as a function of intermittent growth cycle number At each growth cycle. In flux was supplied for 16 s. For more than sixth cycle, diffraction-beam intensity slightly increased during the In supply, and then the intensity was almost kept constant during the growth interruption...

Fig. 3.32 AFM images of low-density InAs QDs with 5.5x10 cm , grown by the intermittent growth...

Following an established procedure (Anderson 2004), mode I fracture toughness Gjc was evaluated from load/unloaded data under the sequential intermittent growth of a central crack along the midplane of a symmetrically edge-loaded HI00 foam sample shown in Fig. 8.17. The sample, of dimensions 25 x 25 x 200 mm, was precracked at its loaded end and symmetrically notched along its entire midplane to channel the fracture direction. 

The funetions in the alkylaluminum aetivated metalloeene eatalyst systems have been deseribed by Reiehert and eoworkers [117 119]. The eoneeptualized point is that eaeh metal-polymer speeies appears to alternate between a dormant and aetive state in whieh the polymer ehain grows. This intermittent-growth model (Fig. 59) was further elaborated by Fink [120, 121] and Eiseh [122, 123] and their eoworkers in extensive kinetie and reaetivity studies (Fig. 59). Conseeutive equilibria appear to eonvert alkyl aluminum and (alkyl) metalloeene halides first into Lewis aeid-base adduets equivalent to an irmer (or contact) ion pair and then into a dissociated (or separated) ion pair. In these dynamic equilibria, only the cation of a separated ion pair appears to be capable of interacting with an olefin molecule and thus to dominate in these equilibria, and can then be termed dormant in this regard [124]. 

EIG. 59 Intermittent-growth model involving equilibria between polymer-bearing, but inactive, primary complexes (C-Pm) and active catalyst species (C -Pn), generated by excess alkyl aluminum halide. 

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