Expansion coefficients, thermotropic liquid

Liquid crystal polymers (LCP) are polymers that exhibit liquid crystal characteristics either in solution (lyotropic liquid crystal) or in the melt (thermotropic liquid crystal) [Ballauf, 1989 Finkelmann, 1987 Morgan et al., 1987]. We need to define the liquid crystal state before proceeding. Crystalline solids have three-dimensional, long-range ordering of molecules. The molecules are said to be ordered or oriented with respect to their centers of mass and their molecular axes. The physical properties (e.g., refractive index, electrical conductivity, coefficient of thermal expansion) of a wide variety of crystalline substances vary in different directions. Such substances are referred to as anisotropic substances. Substances that have the same properties in all directions are referred to as isotropic substances. For example, liquids that possess no long-range molecular order in any dimension are described as isotropic. 

The interest in thermotropic liquid-crystalline polymers has grown in recent years due to the their inherently high stil ess and strength, high use temperatures, excellent chemical resistance, low melt viscosity and low coefficient of thermal expansion. 

Thermotropic liquid crystalline polymers (TLCPs) have gained increased commercial attention because of their unique properties. These include their low coefficients of thermal expansion, low viscosity, and high modulus, low permeability to gases, low dielectric constants, and chemical resistance. As the demand for these characteristics increases, it is anticipated that the use of TLCPs will grow, rising at a projected annual growth rate of 25 % from an estimated use of ten million pounds in recent years. In expanding the potential uses for TLCPs, it has been found that TLCP/TLCP blends can possess characteristics which are better than those of either individual TLCP (Utracki and Favis 1989). But the better result is only possible if the LCP fibrillation is prominent in the blend system. 

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