Polymers PDMS/silica compound

Figure 6.10 shows typical dynamic properties of vulcanized PDMS-silica systems, as investigated through strain sweep experiments at constant frequency and temperature. As can be seen, dynamic strain softening is observed in a qualitatively similar manner to other filled polymers. It follows that models, which successfully fit conventional filled rubbers (e.g., carbon black filled compounds), are expected to well suit such data. This is indeed the case, as shown by the curves in Figure 6.10, drawn by fitting the Kraus-Ulmer equations, i.e.. 

Unlike the other techniques, SPME has a considerable concentration capacity and is very simple because it does not require especial equipment. The principle involves exposing a silica fibre covered with a thin layer of adsorbent in the HS of the sample in order to trap the volatile components onto the fibre. The adsorbed compounds are desorbed by heating and introduced into the detection system A SPME sampler consists of a fused silica fiber that is coated by a suitable polymer (e.g. PDMS, PDMS/divinylbenzene, carboxen/PDMS) and housed inside a needle. The fiber is exposed to headspace volatile and after sampling is complete, it is retracted into the needle. Apart from the nature of the adsorbent deposited on the fiber, the main parameters to optimize are the equilibration time, the sample temperature and the duration of extraction. Compared with other sampling methods, SPME is simple to use and reasonably sensitive, so it is a user-friendly pre-concentration method. 

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