Absorption spectra polymer films

In order to follow progress of elimination, reactions were also performed on thin films in a special sealed glass cell which permitted in situ monitoring of the electronic or infrared spectra at room temperature (23°C). Typically, the infrared or electronic spectrum of the pristine precursor polymer film was obtained and then bromide vapor was introduced into the reaction vessel. In situ FTIR spectra in the 250-4000 cm-- - region were recorded every 90 sec with a Digilab Model FTS-14 spectrometer and optical absorption spectra in the 185-3200 nm (0.39-6.70 eV) range were recorded every 15 min with a Perkin-Elmer Model Lambda 9 UV-vis-NIR spectrophotometer. The reactions were continued until no visible changes were detected in the spectra. 

Figure 9 shows the electronic absorption spectrum of a PTTB film which has undergone extensive but incomplete reaction with bromine in a non-in-situ experiment. The absorption spectrum is that expected for a one-dimensional conjugated polymer. The sharpest absorption edge is at about 1490 nm (o.83 eV) and the absorption maximum is located at 1240 nm (1.0 eV). Thus, this material has a bandgap of about 0.83 eV. Note that two small... 

The ground states of the TIN and TINS stabilizers respond to the influence of the molecular environment in polymer films in almost the same manner as they do in solution. The absorption spectra of TIN in PMMA film (Figure 9) and TIN in PS film are similar to those observed for TIN in low polarity, non hydrogen-bonding solvents. A linear combination of the TIN planar) and TIN(non-planar) component spectra from the PCOMP analysis was used to fit the absorption spectrum of TIN in PMMA. 

The spectrum of TIN in PS is red-shifted compared to its spectrum in PMMA and so the relative proportion of each form could not be calculated using this method. However, the similarity between these two spectra suggests that a comparable proportion of TIN molecules in PS assume a non-planar conformation. The absorption spectrum of MeTIN in a PMMA film consists of a single absorption band (see Figure 9). This band is similar to that observed for MeTIN in solution suggesting that MeTIN exists almost entirely in a non-planar conformation in this polymer. 

It was found from the absorption spectrum that 1.1 % of the incident photons were absorbed at 2537 A by a PMMA film of 0.5 ym thickness (Fig. 5). The molecular weight distribution and the average molecular weight of the coated polymer which was irradiated for the least irradiation time required for the dissolution of polymer coating in the developer were measured by gel-permeation chromatography (Fig. 7). 

Figure 6. Changes in absorption spectrum of neural polymer film on exposure to Br2 vapor (I) no Brt (II, III) after increasing exposure times...

An important point is that the electrochemically driven charge transport in these polymeric materials is not dependent on the presence of mixed valence interactions which are well known to give rise to electronic conductivity — in a number of cation radical crystalline salts. This is clearly seen from the absorption spectrum of the electrochemically oxidized pyrazoline films (Figure 8) which show no evidence for the mixed valence states that are the structural electronic prerequisites for electrical conductivity in the crystalline salts. A more definitive confirmation of this point is provided by the absorption spectrum (Figure 10) of electrochemically oxidized TTF polymer films which shows... 

Amorphous polymers characteristically possess excellent optical properties. Unlike all the other commercially available fluoropolymers, which are semicrystalline, Teflon AF is quite clear and has optical transmission greater than 90% throughout most of the UV, visible, and near-IR spectrum. A spectrum of a 2.77-mm-thick slab of AF-1600 is shown in Figure 2.5. Note the absence of any absorption peak. Thin films of Teflon AF have UV transmission greater Ilian 95% at 200 mm and are unaffected by radiation from UV lasers. The refractive indexes of Teflon AF copolymers are shown in Figure 2.6 and decrease with increasing FDD content. These are the lowest refractive indexes of any polymer family. It should be noted that the abscissa could also be labeled as glass transition temperature, Tg, since Tg is a function of the FDD content of the AF copolymer. Abbe numbers are low 92 and 113 for AF-1600 and AF-2400. 

The changes in the optical absorption spectra of conducting polymers can be monitored using optoelectrochemical techniques. The optical spectrum of a thin polymer film, mounted on a transparent electrode, such as indium tin oxide (ITO) coated glass, is recorded. The cell is fitted with a counter and reference electrode so that the potential at the polymer-coated electrode can be controlled electrochemically. The absorption spectrum is recorded as a function of electrode potential, and the evolution of the polymers band structure can be observed as it changes from insulating to conducting (11). 

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