Preform Drawing

Fundamentals cf Plastic Optical Fibers, First Edition. Yasuhiro Koike. 

The fabrication methods of SI preforms are not discussed in this book. Literature on these methods is widely available but not in strong demand today, both in academia and industry, except for some specific applications. Several representative techniques for fabricating GI preforms are discussed in Section 5.2. 

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In 2012, the first PSt-based GI POP was reported [20]. The fiber was obtained by preform-drawing and rod-in-tube methods. Its attenuation spectrum is shown in Figure 4.6 alongside that of the PMMA-based GI POF. The wth overtones of the aliphatic and aromatic C-H bonds are labeled as v and v, respectively. The attenuation of the PSt-based GI POF is 166-193 dB/km at 670-680 nm, which is significantly lower than the attenuation of the PMMA-based GI POF in the same region ( 240-270 dB/km). 

The preform-drawing method is a batch process where a polymeric preform is fabricated first, which is then followed by thermal drawing of the preform into the fiber. A schematic diagram of the process is shown in Figure 5.1. In this method, a cylindrical polymer rod consisting of a core and cladding layers, usually prepared by radical polymerization in bulk under a clean environment, is positioned vertically in the middle of the furnace where its lower portion is heated locally to the drawing temperature. The furnace temperature appropriate for the preform is... 

While there are many reports on sol-gel-derived oxide glass fibers, few works have been done on fluoride glass fibers. Fiber drawing of multi-component precursor oxide gels and their fluorination appear to be much less viable. Heavy-metal fluoride glass fibers are usually produced by the preform drawing technique. 

Fig. 11. OVD process (a) soot deposition, (b) soot perform cross section, (c) preform sintering, and (d) fiber drawing.

Furthermore, the utilization of preformed films of polypyrrole functionalized by suitable monomeric ruthenium complexes allows the circumvention of problems due to the moderate stability of these complexes to aerial oxidation when free in solution. A similar CO/HCOO-selectivity with regards to the substitution of the V-pyrrole-bpy ligand by an electron-with-drawing group is retained in those composite materials.98 The related osmium-based redox-active polymer [Os°(bpy)(CO)2] was prepared, and is also an excellent electrocatalyst for the reduction of C02 in aqueous media.99 However, the selectivity toward CO vs. HCOO- production is lower. 

Figure 12-15 Schematic drawing of the active site of a cysteine protease of the papain family with a partial structure of an acyl-enzyme intermediate in green. The thiolate-imidazolium pair of Cys 25 His 159 lies deep in the substrate-binding cleft and bridges an interface between two major structural domains, just as the Ser His pair does in serine proteases (Fig. 12-10). This may facilitate small conformational changes during the catalytic cycle. Asn 175 provides a polarizable acceptor for positive charge, helping to stabilize the preformed ion pair, and allows easy transfer of an imidazolium proton to the product of substrate cleavage. The peptide NH of Cys 25 and the side chain of Gin 19 form an oxyanion hole.

From the wealth of observations on catalyst preformation and catalyst aging reported in the literature it is extremely difficult to draw definitive conclusions about the nature of the reactions which occur during this process step. Nevertheless, it is rather evident that contrary to metallocene catalysts, the majority of Nd-based catalyst systems do not exhibit the features of single site catalysts (SSC). As bimodal and multimodal MMDs are observed for Nd-based catalyst systems various active species (or active sites) are present... 

In latex saturation processes of preformed fiber webs, the predominant force responsible for drawing the rubber particles to fiber crossings and coagulating these particles into a coherent mass is the surface tension of the evaptxatittg water medium. Current trends are to develop latexes whose surface tension is close to water by ulibzing oligomeric emulsifiers (White, 1976) or emulsifiers polymerized into the polymer chain (Sweeney, 1958) to maximize the surface tension forces. 

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