Optical film coating technique

This study represents the first systemmatic application of the optical waveguide technique to the study of the response of polymer film coatings to condensed vapor molecules. These results indicate that the technique is useful for surveying rapidly potential polymeric films as possible vapor sensor coatings. Moreover, this work has further substantiated that the vapor pressure is an important physical property to be taken into account when employing polymeric films as surface coatings. 

Solid-phase extraction devices and applications are evolving rapidly, and novel techniques that stretch the classical definition of SPE are becoming routine. Pawliszyn introduced solid-phase micro extraction (SPME) in 1989,5,14 and a commercial apparatus is available from Supelco (Bellefonte, PA). The SPME apparatus is merely a modified syringe that houses a fused silica optical fiber coated with an immobilized polymer film. The fiber can be exposed for extraction and then retracted for insertion or removal from the sample vial or instrument. Both manual and autosampler devices are available and each can be adjusted for proper fiber depth. Several coatings are available with varying thickness including polydimethylsiloxane, polyacrylate, polydimethylsiloxane/divinylbenzene, and carbowax/divinylben-zene. In contrast to SPE, which is an exhaustive extraction approach, SPME will extract only a fraction of an available analyte, hence it is not suitable for the isolation of impurities and degradants in most applications.15... 

A distinguishing feature of the materials is that they were produced by the mixing of water-alcohol solutions of azobenzene derivatives and the polyelectrolytes. The materials were readily processed into films by conventional film preparation techniques, such as spin coating and casting. If the complex was precipitated, the product was separated and dissolved in another solvent. Otherwise the complexes were sufficiently soluble in water-alcohol mixture to form films of good optical quality with thicknesses in the range from 100 nm to a few micrometers directly from the solutions. 

The PVA/ZnO nanocomposite was prepared by adding ZnO powder into PVA solution in distilled water and the mixture was stirred for two hours and then sonicated for five minutes. Highly transparent and homogeneous thin films of the nanocomposite were prepared on ultrasonically cleaned and optically flat glass substrates using spin-coating technique (Spin 150). ZnO/PVA nanocomposite thin films were obtained with both pristine and OA modified ZnO for 1 wt%, 2 wt% and 3 wt% of ZnO nanopowder. 

The polysilanes represent another class of polymers that has been extensively studied for nonlinear optical applications [62- ]. These polymers have a molecular structure (R,—Si—R2) that is a long catenated a-bonded silicon backbone with two side groups R, and R2, usually carbon based, attached to each Si atom in the backbone chain. They are soluble in most hydrocarbon solvents and thin films of excellent optical quality can be fabricated with conventional spinning and coating techniques. In spite of the o--bonded nature of the backbone, the poly silanes show extensive electronic delocalization, resulting in strong transitions for excitations polarized parallel to the backbone [65]. They are unique in that they are transparent through the visible to the infrared in contrast to the 7r-electron polymers. 

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