Interfacial-Gel Polymerization Technique

The interfacial-gel polymerization technique is particularly common in acrylic GI POP studies and enables the precise control of the refractive index profile, leading to a maximal bandwidth. However, this batch process requires many complicated procedures. Furthermore, the fiber length obtained at any one time is completely dependent on the preform size. This is a serious limitation in terms of fabrication costs. 

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It is well known that the dispersion in the optical fibers is divided into three parts, modal dispersion, material dispersion, and waveguide dispersion. In the case of the SI POF, the modal dispersion is so large that the other two dispersions can be approximated to be almost zero. However, the quadratic refractive-index distribution in the GI POF can dramatically decrease the modal dispersion. We have succeeded in controlling the refractive-index profile of the GI POF to be almost a quadratic distribution by the interfacial-gel polymerization technique (2). Therefore, in order to analyze the ultimate bandwidth characteristics of the GI POF in this paper the optimum refractive index profile is investigated by taking into account not only the modal dispersion but also the material dispersion. 

G1 preforms can also be fabricated by an interfacial-gel polymerization technique. The principle is basically the same as that of the photo-copolymerization method discussed above, except for the mechanism that forms the initial gel phase. In this method, the core solution (the monomer) is placed in a polymer tube rather than in a glass tube. The gel phase in the photo-copolymerization method is referred to as a prepolymer with a conversion of less than 100%, whereas in this method the gel phase comprises the polymer layer on the inner wall of the tube swollen by the core monomer. The reaction is carried out under UV irradiation or heating. 

Figure 5.11 Interfacial-gel polymerization technique using dopants.

Figure A.7 Formation process of Gl distribution by the interfacial-gel polymerization technique.

As far as GI-POFs are concerned, Ohtsuka and co-workers reported several GI-POFs with low losses. By using the interfacial-gel-polymerization technique, the GI-POF attenuation loss was reduced to nearly the same value as that of SI-POF. Single-mode POF was also reported by several researchers around 1992. ... 

As the main part of the GI-POFs is composed of PMMA, the loss spectrum is nearly the same as that of SI-POF with PMMA core. The attenuation loss of GI-POF with the gel-copolymerization technique at 652 nm is 134 dB/kra Koike s group, Keio University, has used an interfacial-gel-polymerization technique where bro-mobenzene or other chemicals are used as unreactive components instead of vinyl phenyl acetate or vinyl benzoate in the interfacial-gel-copolymerization method. An attenuation loss of 90 dB/km at 572 nm was obtained. MMA-dg was also used as a monomer instead of MMA, and the deuterated polymer core GI-POF was successfully fabricated. Fluorinated acrylate monomer was also used to fabricate moisture-resistant GI-POF. Attenuation losses of 113 and 155 dB/km at 780 nm wavelength were obtained for deuterated and fluorinated POFs, respectively. These POFs are Oj pected to serve as the signal transmission medium with high information capacities in local area network systems. However, this GI-POF has not been commercially available so far because of the fabrication difficulty of the technique in a mass production level with reasonable attenuation loss and fabrication cost. 

Figure 15 Differential mode attenuation of Gl POFs based on the PMMA-DPS systems prepared by the rod-in-tube method and the interfacial-gel polymerization technique. Adapted with permission from Noda, T. Koike, Y. Opt Exp. 2010, 18 3128, 2010 OSA.

Figire 16 Relationship between index profile coefficient gand -3 dB bandwidth for 100 m of PMMA-DPS-based GI POP at 650 nm wavelength. Solid lines are the calculated results. Closed circles are the measured bandwidths of GI POFs prepared by the interfacial-gel polymerization technique (spectral width is 3.0 nm). Adapted with permission from Koike, Y. Ishigure, T. J. Lightw. Technol. 2006,24,4541 2006 IEEE. 

Y. (1988) New interfacial-Gel Co-polymerization technique for steric grin polymer optical waveguides and lens arrays. Appl. Opt., 27, 486 491. 

Lee outlines three different physical methods that are commonly utilized for enzyme immobilization. Enzymes can be adsorbed physically onto a surface-active adsorbent, and adsorption is the simplest and easiest method. They can also be entrapped within a cross-linked polymer matrix. Even though the enzyme is not chemically modified during such entrapment, the enzyme can become deactivated during gel formation and enzyme leakage can be problematic. The microencapsulation technique immobilizes the enzyme within semipermeable membrane microcapsules by interfacial polymerization. All of these methods for immobilization facilitate the reuse of high-value enzymes, but they can also introduce external and internal mass-transfer resistances that must be accounted for in design and economic considerations. 

Microencapsulation techniques make use of sol-gel processes, coacervation, surface and in situ polymerization methods or, generally, interfacial reactions to produce soluble or insoluble and impermeable or permeable capsule walls. In addition to the coating and spray drying methods that were discussed previously, a growing number of other processes deposit particles onto cores or solid surfaces whereby the binding mechanisms of agglomeration are utilized [B.97] (Chapter 11). 

It has been indicated how interfacial morphology plays a crucial role in the transport properties of hybrid membranes, and conditions as close as possible to the ideal case must be achieved to ensure advanced separation performances. For this reason, several fabrication techniques have been developed to reduce as much as possible the influence of a nonideal interfacial morphology on the transport characteristics of the hybrid membranes. Among the most frequently used procedures there are solution blending, the sol-gel procedure, surface modification, and interfacial polymerization. In some cases a combination of these techniques is required to reach the best dispersion of the filler within the matrix. 

We have focused on hollow spheres to reveal the relation between structure of solid acid or catalyst and catalytic activity for hydrolysis of NH3BH3 [4, 6, 8, 9]. A number of efforts to find new methods have been devoted to generating colloids with the core-shell structure, such as template-assisted sol-gel process [4, 8-11], layer by layer (LBL) techniques [12, 13], microemulsion/interfacial polymerization strategies [14, 15]. 

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