Large mass migration

Surface-relief grating (SRG, regular topological surface modification) formed via irradiation with an interference pattern of coherent light has been demonstrated only recently/ and is perhaps the most attractive target in the current research of azo polymers (Chapters 13 and 14 of this book focus on this subject). It is still unclear whether there are any common mechanisms involved between SRG formation and the photomechanical response observed in monolayers described in Section 15.4.1. Nevertheless, with regard to photoinduced motions in Az polymers, it is quite important to proceed with SRG experiments. 

14 Molecular structure of the materials used in photogenerated surface-relief formation. 

UV light treatment (circles) and without treatment (triangles). For the hybrid film with UV-light treatment, a sharp growth of diffraction efficiency was observed at an early exposure stage (circles). The diffraction efficiency reached a maximum of 1.1% in 250 mj cm , corresponding to ca. 5.0 s exposure at 50 mW cm . Further exposure reduced the efficiency to give a constant value around 0.5%. 

The surface undulation can be erased by nonpolarized UV-light irradiation at a very low light doses (200 mJ cm ) at room temperature. Ffeating at 100°C (isotropic phase of the hybrid film) for. 30 min also erased the surface structure. 

17 Diffraction efficiency (filled circles) and top-to-valley height (open circles) estimated by AFM as a function of the molar fraction (f) of 5CB. (From reference 66 copyright permission from Wiley-VCH.) 

16 Typical topological AFM image of surfece relief gratings. 

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The smaller Cw values are also connected with water deficiency in Steppe and Desert ecosystems. However, the concentration of various chemical species in rainwater of background regions is higher that that in the Forest ecosystem belt. The major reason is the wind deflation of the soil s surface owing to lack of tree species and only a lean protective layer of grasses and half-shrubs. A large mass of soil particles becomes entrained into the air migration. The most characteristic example is connected with the Yellow sand phenomenon (see Box 7). 

While the chemical hydrolysis of PLA has been widely studied other information concerning the chemical stability or resistance of PLA is rather limited. Stability and possible migration from polylactide to food simulants has been evaluated in a few studies (36). The stability in water, 3% acetic acid and isooctane has been shown to be adequate. However, large mass losses were reported in contact with alcoholic food stimulants such as 95% ethanol. Migrants... 

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