Combining optical microscopy, turbidimetry, and DSC to study structural transformations in the mixtures of semicrystalline polymers with low-molar-mass crystallizable substances

The phase behavior of low-density polyethylene mixtures with 1,2,4,5 – tetrachlorobenzene and camphor is investigated by optical methods and differential scanning calorimetry. The use of a photoconductive cell integrated into an optical microscope equipped with a heating stage, allows us, for the first time, to combine turbidimetry with visual observations to detect crystallization of a low-molar-mass substance from the amorphous regions of a semicrystalline polymer. Crystallization in the restrained conditions of an apparently solid polymer matrix leads to crystals much smaller than the low-molar-mass crystals formed in a mixture with the melted polymer. We discuss the details of reversible structural changes taking place to the binary mixtures of crystallizable components in the course of their heating and cooling. Constructed phase diagrams provide important information for developing technologies based on thermally induced phase separation in such systems.