Space materials fluoride polymers

METHYL-l-PHENYL-ETHENE (98-83-9) Forms explosive mixture with air (flash point 129°F/54°C). Violent reaction with strong oxidizers, butyl lithium, oleum, xenon tetra-fluoride. Unless inhibited, forms unstable peroxides. Incompatible with acids. Reacts with heat and/or lack of appropriate inhibitor concentration, and/or contact with catalysts for vinyl or ionic polymerization, such as aluminum, iron chloride, or 2,5-dimethyl-2,5-di(rert-butylperoxy)hexane. The uninhibited monomer vapor may block vents and confined spaces by forming a solid polymer material. 

VINYLIDINE FLUORIDE (75-38-7) Flammable gas (flash point <-85°F/ < —65°C). Violent reaction with oxidizers, barium, sodium, or potassium. Reacts with aluminum chloride. Incompatible with hydrogen chloride. May form explosive compounds with light metals and metallic azides. Capable of forming unstable peroxides may cause explosive polymerization. Undergoes thermal decomposition when exposed to flame or red-hot surfaces. May accumulate static electricity, and cause ignition of its vapors. The uninhibited monomer vapor may block vents and confined spaces by forming a solid polymer material. 

Capacitive sensors can be used to detect displacement from the fact that capacitance between two parallel metal plates, C = eoEt A/x, where eo = dielectric constant of free space, Cf = relative dielectric constant of media. Displacement can be measured by changing aU these three parameters. A good example is the capacitance microphone that is responding to displacement by sound pressure. Piezoelectric sensors are used to measure physiological displacement and record heart sounds. These sensors are fabricated from piezoelectric ceramics and piezoelectric polymers. For flexible wearable sensors, fiber or film form of polymer piezoelectric materials such as polyvinyli-dene fluoride (PVDF) are desirable. 

Ferroelectric materials are a subclass of pyro- and piezoelectric materials (Fig. 1) (see Piezoelectric Polymers). They are very rarely foimd in crystalline organic or polymeric materials because ferroelectric hysteresis requires enough molecular mobility to reorient molecular dipoles in space. So semicrystalline poly(vinylidene fluoride) (PVDF) is nearly the only known compoimd (1). On the contrary, ferroelectric behavior is very often observed in chiral liquid crystalline materials, both low molar mass and poljuneric. For an overview of ferroelectric liquid crystals, see Reference 2. Tilted smectic liquid crystals that are made from chiral molecules lack the symmetry plane perpendicular to the smectic layer structure (Fig. 2). Therefore, they develop a spontaneous electric polarization, which is oriented perpendicular to the layer normal and perpendicular to the tilt direction. Because of the liquid-like structure inside the smectic layers, the direction of the tilt and thns the polar axis can be easily switched in external electric fields (see Figs. 2 and 3). 

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