Solvent spinning lines

Fig. 9.3 Cartoon of the fabrication of crosslinked layers. The functional unit (i. e. the semi-conductive unit) is shown in green, the reactive unit in red. The spacer between them is shown as a black line. The material is dissolved in a suitable solvent, spin coated on the top of the substrate, and finally cured to yield an insoluble polymer network (red line). Multiple-layer structures are obtained by repeated deposition and curing.

Wirtz formula (Eq. 14) in calculating D s when empirical values were not available. As can be seen from Table 10, the D vv values are nearly idential to the experimental values Dg p in hydrocarbon solvents. Spin-statistical factors calculated from the individual slopes in Fig. 12 are all very close to the expected value of Va (Table 11). Of the radicals in Table 10, only the /-propyl radical shows systematic deviations from the theoretical line (166). Since these deviations are outside of the estimated experimental uncertainty (166), and this behavior was not expected a priori, the results for the /-propyl radical are treated in detail below. 

Evaporation of solvent is a relatively slow process, slower than cooling in melt spinning. It is therefore essential that the spinning filaments are thin. The common approach is to use small spinning holes (50-100 gm) and apply a low draft in the spin-line. For example, both the extrusion speed from the holes and the exit speed from the dry-spinning column would be around 300 m min . Even a draft below 1 is possible, which means that the die swell effect is not completely undone. 

Solidification of the dry spinning filament is due to the evaporation of the solvent component from the spin line. There are three mechanisms in the solvent removal process ... 

The solvent diffuses from the spinning line (or filament) to the spinning line surface with diffusivity f>AP, and it is carried away by the flowing air in a convective mode. Air is flowing at a cross direction to the fiber movement, but due to the high speed of the fiber air is also entrained in the parallel direction. Consequently, the convective mass transfer is taking place in the r as well as in the z directions. Because the cross-flow velocity is four times the parallel-flow velocity, the mass transfer coefficient of the cross flow is 3.17 (= 0.52 x 4 /0.26) times that of the parallel flow. Consequently, the controlling mass transfer coefficient is that of parallel flow. 

Stabilizers, pigments, and other additives are milled in spinning solvent, normally along with small amounts of the urethane polymer to improve dispersion stabiUty this dispersion is then blended to the desired concentration with polymer solution after chain extension. Most producers combine prepolymerization, chain extension, and additive addition and blending into a single integrated continuous production line. 

Fig. 14. Dependence of the quantity (fito/gy l V )k where k is the rate constant for spin conversion on halkgT as calculated from the single-mode approximation Eq. (79) solid lines) and the full expression Eq. (77) for the value q = 0.3 of the solvent reorganization parameter dashed lines). Data are given for p = — 2.0, 0, -I- 2.0 and for the value of the coupling parameter S = 15. According to Ref. [117]...

The very high resolution for the ESR spectrum of cob(II)alamin in the enzyme system is undoubtedly due to the fact that all the coenzyme molecules are bound in an identical environment at the enzyme active site. This results in a homogeneous cobalt-benzimidazole geometry, because both identical binding sites, solvent, and solute molecules can no longer approach the Bia-molecule closely. In addition, the enzyme bound cob(II)alamin molecules are more isolated from one another and thus relaxation due to spin-spin interactions is less effective in broadening spectral lines. 

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