Polymer irradiation time, effect

Fig. 12 (a) Image of PMAA-protected fluorescent silver clusters prepared with increasing initial ratio Ag+ MAA from 0.5 1 to 12 1 and equal irradiation time, (b) Absorption spectra of the same samples as in (a), (c) Variation of absorption maxima of some of the samples in (a) with molar ratio. Black arrows indicate how the absorption band shifts to the blue with the addition of extra polymer to a fluorescent cluster solution explaining the transfer effect of silver clusters among PMAA chains [20]... 

The effect of ultraviolet irradiation in air on the wettability of thin films of amorphous polymers has been studied. With poly(vinyl chloride), poly(methyl methacrylate), poly(n-butyl methacrylate), poly (ethylene terephthalate), and polystyrene the changes in contact angles for various liquids with irradiation time are a function of the nature of the polymer. A detailed study of polystyrene by this technique and attenuated total reflectance spectra, both of which are sensitive to changes in the surface layers, indicates that the contact angle method is one of the most sensitive tools for the study of polymer photooxidation in its early stages. The method is useful in following specific processes and in indicating solvents to be used in the separation and isolation of photooxidation products. 

It has been known for a long time that gas is formed during irradiation of PMMA. When the internal pressure of the gas formed in the reaction is sufficient to overcome the viscosity of the irradiated polymer, bubbling occurs. By suitable control of the irradiation dose and subsequent heating of the polymer, this bubbling effect can transform PMMA into a foamed material. Data on the volatile products formed at room temperature has been given by many workers [392—396]. The results are shown in Table 29. The yields seem to depend on the purity of the polymer sample. This problem will be discussed below in relation to the yield of chain scission. 

Oxidation and photo-oxidation preferentially occur at the surface of the films and little oxidation takes place in the bulk of the sample even on prolonged exposure. After a given irradiation time the amounts of the hydroperoxide and the carbonyl oxidation products decrease with the increasing effective depth of the reflected beam penetration. Examples of this decrease are illustrated in Fig. 10, which shows the variation of C=0 absorption across the cross-section of a film during two periods of photo-oxidation [126, 127]. The dependence of the oxidation rate on sample thickness confirms the view that oxidation and photo-oxidation of polymers occurs preferentially close to the surface [628, 673]. The... 

As can be seen in Figure 9.9b, the temperature dependence of (3 for PVA is similar to that of polyethylene (Matsuo et al. 2002). It can be seen that increases as a function of temperature up to -10°C. The increase in has been proved to be due to the positron irradiation effect on a polymer at low temperature. The secondary electrons that escape from the positron spur could be easily trapped in shallow potentials formed between the polymer chains when the motions of the molecular chains and groups are frozen at low temperature. Due to the positron irradiation time (experimental time), the probability of formation would become larger. As can be seen in this figure, becomes a maximum at around -10°C, and begins to decrease with increasing temperature. (3 attains a minimum at ca. 75°C and increases again beyond ca. 75°C. This is due to an apparent increase in the number of holes detected by positron annihilation, because of the thermal expansion of the holes at... 

Fig. 5.13 Effects of UV lamp irradiation time and NO type on NO purification performance of photocatalytic polymer-modified paste or slurry coating...

The effect of UV radiation in air on the wettability of thin films of polyvinyl chloride (Fig. 10.106) poly(methyl methacrylate), poly(n-butyl methacrylate), poly(ethylene terephthalate) and polystyrene (Fig. 10.107) show that the changes in contact angle for various liquids with irradiation time are a function of the nature of the polymer [667]. 

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