A high-pressure x-ray study of Nylon 11

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Abstract
An x-ray diffraction study of Nylon 11 was carried out at high pressures and high temperatures. Careful measurements made on both wet and dry samples at atmospheric pressure indicated that the structure of Nylon 11 suggested by Slichter was not quite correct. Some distortion of the planar conformation causes a shortening of the c repeat distance from the value required for a fully extended conformation. The compressibility of the crystal lattice at higher pressures up to 20 kbar was studied and related to the anisotropic bonding present in the structure. A crystal transition at atmospheric pressure previously unreported was observed to occur at 95 °C, the triclinic structure (α phase) changing to a pseudohexagonal structure. The influence of pressure on this transition was studied. It was found that the increase in transition temperature with pressure dTt/dP (∼15 K/kbar) was greater than the melting temperature increase with pressure dTm/dP (∼9 K/kbar). A pressure-temperature phase diagram for Nylon 11 was obtained and a triple point was observed at 310 °C and 14.5 kbar. At pressures above 14.5 kbar the α phase is stable until melting.

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