In situ Fourier transform infrared spectroscopic study of the conformational changes of nylon-10,12 during its Brill transition

Over the years, much research has been done on the nylon and its crystal transitions. In 1942, Brill first reported that during the heating process, nylon-6,6 undergoes a change from a triclinic to a pseudo-hexagonal crystal structure, which was termed as the Brill transition. Many efforts have been taken to explore the origin of this crystal-to-crystal transition. However, the mechanism of Brill transition is still under controversy. Three principal standpoints have been put forward to demonstrate the interesting phenomenon. Colclough believed that the anisotropy of heat expansion in nylon crystal leads to Brill transition. Other researchers thought that the solid transition was related to the change from two-dimensional hydrogen-bonded sheets present at room temperature to a three-dimensional H-bonded network at high temperature. Later investigations seemed to suggest that the appearance of Brill transition may be due to the local melting of methylene segments, whereas the integrity of the hydrogen-bonded sheet structure was maintained up to the melting point. Either way, there is not enough evidence to convince any of the preceding models. Although many groups accepted that Brill transition originated from local melting of the methylene chains, no one has circumstantiated it directly from experiments.