Single-polymer layer

FIGURE 5.90 Schematic presentation of two extremes of composite structures that can be obtained by polymer melt intercalation of layered silicates. The rectangular bars represent individual silicate layers (1 nm thick), (a) Single polymer layers intercalated in the silicate galleries, (b) Delamination (exfoliation) of layered silicates and dispersion in a continuous polymer matrix. (After Giannelis, E. R 1996. Adv. Mater., 8(1), 29. With permission.)... 

Perhaps the obvious advantage of using polymer multilayers in biosensor design is that they offer a solution for enzyme immobilization when it is otherwise not feasible in a single-polymer layer, as is the case with polyaniline biosensors whose electropolymerization conditions in acid media tend to significantly compromise the activity of immobilized enzymes [155]. 

This device gave an incident-photon-to-collected-electron efl ciency of 12.1% and a power conversion efl ciency of 0.8% under monochromatic irradiation [279]. Single-polymer-layer photovoltaic devices using polybithiophene (PBT) thin films and fluorine-doped tin oxide substrate have also been constructed (Fig. 7.22). As well as the difference in the work functions of the electrodes, the high organization of the molecular dipoles in PBT yielded an open-circuit potential of 2 V when an aluminum top contact was used [279]. 

Several different materials can be used as transparent electrodes, most of them as anode material ITO [113,194,195,200], pofyaniline and polyaniline blends [206, 207, 209, 210], TO [201, 202,204], and F-doped TO [112,205]. The use of transparent material as a cathode has also been reported [202]. In the case of PPV and several of its derivatives, the effective mobility of the electrons is lower than that of the holes, implying a reduction in the extent of the recombination zone in the electroluminescent polymer layer, as observed in PPP LEDs [164]. Further, the values of polymer electroaffinity and ionization potential make the injection and transport of holes etisier than that of electrons in single-polymer-layer devices. The injection dynamics also depends on the injected carrier that remains in the polymer (space charge), modifying the electric field distribution in the device [217]. For these reasons, different materials are tested as cathode and anode and, in several cases, intermediate layers are also introduced in order to improve the injection of a specific charge carrier type or to block its transport through the device [212,213,218-220]. 

The film tube is collapsed within a V-shaped frame of rollers and is nipped at the end of the frame to trap the air within the bubble. The nip roUs also draw the film away from the die. The draw rate is controlled to balance the physical properties with the transverse properties achieved by the blow draw ratio. The tube may be wound as such or may be sHt and wound as a single-film layer onto one or more roUs. The tube may also be direcdy processed into bags. The blown film method is used principally to produce polyethylene film. It has occasionally been used for polypropylene, poly(ethylene terephthalate), vinyls, nylon, and other polymers. 

Frozen Polymer Layer Figure 1. Single die hole. 

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