Photosensitive multilayers

Other sensitive PEMs have been described which respond to different stimuli. Photosensitive multilayers were prepared using polyelectrolytes functionalized with photoisomerizable azobenzene chromophores. Barrett et al. have prepared sensors, the mechanical properties of which change under Hght irradiation [22]. Solvent-responsive polymer brushes have been prepared by anchoring two types of polymers (one hydrophobic and one hydrophilic) on a wafer surface. As a function... 

Multilayer and heterogeneous systems allow us to increase our understanding of photogeneration and charge transfer processes and obtain the high photosensitivity needed for practical applications. Carrier injection into PVC of... 

Maximum photosensitivity was obtained for two layer system containing a thin PVC-TNF layer covered by thick PVC layer [73] (Fig. 14). Here CT complex realizers photogeneration function and PVC the transport one. Memory effects, p-n transitions, and others may be obtained for multilayers and polydispersed systems. The photosensitivity of the last ones strongly depend from the incapsulation velocity of the inorganic photoconductors in polymer matrixes [79-81]. 

It was pointed out earlier that photosensitivity may be realized not only by the inclusion of dyes in a polymer matrix, but also by means of multilayered system production. For TPA dispersed in a polycarbonate, sensitized by a thin layer of vacuum-deposited amorphous selenium, the quantum yield was equal to 0.7 at the electric field strength 6 x 10s V cm-1 [308]. The photoinjection efficiency of holes into polymer was equal to the efficiency in pure selenium. The spectra of the quantum efficiency is shown in Fig. 54. 

A recording medium was developed in which photosensitive films (urethane-urea copolymer), nonphotosensitive (polyvinyl alcohol, PVA and poly( methyl methacrylate), PMMA) films, were coated on a glass substrate. Figure 16.13 shows the structure of the multilayered recording medium. 

FIG. 16.13 Multilayered recording medium in whidi photosensitive films and nonphotosensttive transparent PVA and PMMA films are stacked alternately. 

Another way to achieve the reading data with RCM is to use the multilayered recording medium in which photosensitive thin films and nonphotosensitive transparent films are alternately stacked. Since the photosensitive films are thinner than the depth of focus of the recording beam, the spatial-frequency distribution of the recorded-bit data is extended in the axial direction. The extended distribution overlaps the coherent optical transfer function of the RCM. 

The readout result with RCM optics is shown in Figure 16.15. The four recording layers are clearly detected. As a result, it has been determined that the reflection type confocal microscope configuration can be used as a readout system of multilayered optical memory by using the recording medium in which the photosensitive thin films and transparent films are piled up alternately. 

Figure 3.88. Composition of a multilayer optical data storage medium photosensitive layer of about 1-p.m thickness (1), nonphotoactive polymer as separating layer of 30-pm thickness (2), and glass substrate (3) [244],...

Alternatively, the container may contain an opacifying agent, e.g., titanium dioxide. The use of multilayered bags was demonstrated to inhibit photochemical decomposition of vitamin E in TPN fat emulsions (Allwood and Martin, 2000). PVC films discolor on irradiative exposure due to photochemical degradation of the polymer (Hollande and Laurent, 1997). Plastic containers for parenteral use may contain several additives, e.g., antioxidants, stabilizers, plasticizers, lubricants, impact modifiers, and coloring matter when justified and authorized. In an appendix, the European Pharmacopoeia presents a list of plastic additives that may be used (European Pharmacopoeia, 2002). The additives should not be extracted by the contents in such quantities as to alter efficacy or stability of the product or to present any risk of toxicity (European Pharmacopoeia, 2002). However, organic additives extracted in concentrations below the detection limits of the analytical methods authorized by the European Pharmacopoeia may be sufficient to initiate photosensitized reactions in the formulation. 

For systems that are naturally and reversibly photosensitive such as the carbon monoxide complexes of heme proteins [18,. 30, 31], initiation by a light pulse is possible. By preparation of inert but photoactivable reactant or cofactor precursors such as caged ATP [32-34], photosensitivity may be conferred on otherwise photoinert systems [21], thus extending the generality of this approach. This approach was first combined with x-ray monitoring by Blasie [35, 36], in studies of oriented multilayers containing the Ca2+-ATPase from sarcoplasmic reticulum. 

Complex formation occurs in MeN02 solution and the solution is then applied to the surface to be coated. Washing with water removes the Lewis acid leaving a thin film of the photosensitive pigment. The Lewis acid pigment solubilization (LAPS) technique has been used to fabricate multilayer photoconductors and appears to have a promising technological future. 

Ning, L., Kommireddy, D.S., Lvov, Y., Liebenberg, W., Tiedt, L.R., De Villiers, M.M. Nanoparticle multilayers Surface modification of photosensitive drug microparticles for increased stability and in vitro bioavailability. J. Nanosci. Nanotechol. 2006, 6 (9-10), 3252-3260. 

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