Gradient Refractive

Gradient Refractive Index Anode for High Contrast OLEDs.517... 

FIGURE 6.26 Schematic diagram of a high contrast OLED using a gradient refractive index anode. 

Itoh and Eujishima reported a sensitivity factor for the optical signal of 20-40 for a multimode structure and approximately 150 for a single-mode waveguide [27, 28]. These sensitivity factors are consistent with the weak confinement provided by a gradient-refractive index waveguide. Another relevant work was... 

Poly(vinyl pyrrolidone) HEMA Gradient-refractive index Calderara et al., 1996... 

Rogozinski R., Producibility of the ion-exchange method in manufacturing gradient refractive index in glass, Bull. Acad. Pol. Sci. Biol. - Technical Sciences, 62 (4), 655-665 (2014). 

Isothermal frontal polymerization (IFP) is a self-sustaining, directional polymerization that can be used to produce gradient refractive index materials. Accurate detection of frontal properties has been difficult due to the concentration gradient that forms from the diffusion and subsequent polymerization of the monomer solution into the polymer seed. A laser technique that detects tiny differences in refractive indices has been modified to detect the various regions in propagating fronts. Propagation distances and gradient profiles have been determined both mathematically and experimentally at various initiator concentrations and cure temperatures for IFP systems of methyl methacrylate with poly(methyl methacrylate) seeds and wilh the thermal initiator 2,2 -azobisisobutryonitrile. 

Other areas of IPN application cover circuit boards (Tate and Vamell 1989 Takahashi et al. 1996) and, via gradient IPN technology, improved optical fibers (Bukhbinder and Kosjakov 1996). This last works by having a gradient refractive index firom the axis to the surface, curving the light back away from the surface and... 

Figure adapted from X. Li, L. Xue, Y. Han, Broadband antireflection of block copolymer/ homopolymer blend films with gradient refractive index structures. Journal of Materials Chemistry 21 (2011) 5817-5826. 

J. Li, S. Gauza, and S. T. Wu, High temperature-gradient refractive index liquid crystals. Opt. Express 12, 2002 (2004). 

As shown in Equation (12.5), the focal length of an LC lens depends on the lens radius, LC layer thickness, and its gradient refractive index. Normally, a lens can either have a positive or negative focal length. In this section, an LC microlens array whose focal length can be switched from positive to negative or vice versa by the appUed voltage is introduced. 

Hou H, Nieto A, Ma F, Freeman WR, Sailor MJ, Cheng L (2014) Tunable sustained intravitreal drug delivery system for daunorubicin using oxidized porous silicon. J Control Release 178 46-54 Hull R (1999) Properties of crystalline silicon, vol 20, EMIS datareview series. lEE Press, London Ilyas S, Gal M (2006) Gradient refractive index planar microlens in Si using porous silicon. Appl Phys Lett 89 211123... 

Lewis and Volpert continue the discussion of the isothermal form of frontal polymerization in Chapter 5. Isothermal frontal polymerization is also a localized reaction zone that propagates but because of the autoacceleration of the rate of free-radical polymerization with conversion. A seed of poly(methyl methacrylate) is placed in contact with a solution of a peroxide or nitrile initiator, and a front propagates from the seed. The monomer diffuses into the seed, creating a viscous zone in which the rate of polymerization is faster than in the bulk solution. The result is a front that propagates but not with a constant velocity because the reaction is proceeding in the bulk solution at a slower rate. This process is used to create gradient refractive index materials by adding the appropriate dopant. 

I I Monomer soiution (homogeneous refractive index) I I Viscous region (gradient refractive index)... 

The results shown in Table 1 and Fig. 7 prove the applicability of our model - a gradient refractive index layer, where the local refractive index is determined from the volume fraction of the constituents by the Lorentz-Lorenz formula, as the fitted layer thickness corresponded to the particle diameter (Table 1) - and the other results were also consistent with the expectations both about the behavior of the particles and the structure of the interfacial layer. 

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