Glass transition temperature ferroelectric polymers

In principle, liquid crystalline polymers can be applied in displays. Unfortunately, the response of them to the external fields isn t satisfactory because their viscosity is greater than the small molecular mass liquid crystals by a few orders of magnitude. In fact, only when the temperature is near the glass transition temperature, can the response be measured in seconds. Apparently, this is far from the real requirement. One may mix the liquid crystalline polymer with small molecular mass liquid crystal for such a purpose, but the mixture doesn t show an advantage over the small molecular mass liquid crystal displays. The ferroelectric liquid crystalline polymer is an exception. It works with a very fast effect and can achieve a display with a response time of a few milliseconds or a fewr tens of milliseconds. 

To summarize the ferroelectric and piezoelectric properties of the discussed polymers, some important ferroelectric and piezoelectric parameters are tabulated in Table 4. As discussed in the previous sections, the ferroelectric and piezoelectric properties of polymeric and polymeric composite systems depend on various factors, such as crystallinity, pohng conditions, glass transition temperature, and before and after electrical poling treatments (electrical, mechanical, and thermal treatments). In addition to the factors mentioned above, for composite systems, laminates or blends, fraction of constituents, and interfacial polarization are also important. Therefore, the... 

Side-chain polymers with polysiloxane backbones are known for their low viscosity and low glass transition temperatures. Those properties are favorable for applications of switchable ferroelectric IX polymers. The 6rsl examples exhibiting a Sc phase were reported by Hahn and Percec [IS] (polymers 4a and 4b, Fig. 7). The Sc mesophases were identified only by optical microscopy. Investigation of fenoelectric properties was not reported. 

In common with most polymers that are completely or partly amorphous, ferroelectric polymers experience a phase change at the glass transition temperature Tg. Below Tg, the polymers are hard, rigid glasses. At Tgand above, the polymers become flexible and elastomeric. Brittle, rigid polymers have a Tg above room temperature for example, polystyrene has Tg = 100 °C. Rubbery or elastomeric materials have a Tg below room temperature. This is the case for PVDF and the copolymers, which have a Tg in the region of — 40 °C. 

Assume a side chain liquid crystal polymer, consisting of a flexible backbone and mesogenic side groups, is able to form the Sc phase and its glass transition is below the ambient temperature, such a side chain liquid crystal polymer will be expected to show ferroelectricity. The side groups are packed in a way similar to small molecular mass ferroelectric liquid crystals. The backbone is suppressed between layers, occasionally penetrating into them. The conformation of the backbone is discus-like. 

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