Solidification, liquid between parallel

The second example is the solidification of liquid enclosed between parallel boundaries. Here it is necessary to deal with two fictitious bodies of constant dimensions, one representing the liquid and the other the solid. For the solid phase one deals not with an initially finite body whose dimensions are shrinking, but with a body whose dimensions increase from zero. For this reason an imaginary initial temperature turns out to be more appropriate than an imaginary heat input. 

The most common form is the nematic, a bimdle of parallel, long, rodlike molecules. Additional cooling to the primary transition temperature, T leads to solidification into a solid crystalline phase (small crystallites). In the region between Tj and T , a liquid of very low viscosity prevails, in contrast to the high melt viscosity. The aromatic polyesters have high heat distortion temperatures (HDT). Vectra, composed of para-hydroxy-benzoic acid (PHBA) and para-hydroxy-naphtoic acid (PHNA), has an HDT of 180 C-240 C. Xy-dar, composed of PHBA, tera-phthalic acid and biphenol, has an even higher HDT of 260 C-350 C. 

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