Temperature-induced polymorphic phase transitions in gels and aerogels of nylon 11

Abstract

Understanding the Brill transition behavior in nylons is particularly important in processing, as the thermal and mechanical properties of these polymers are highly dependent on the structural transitions. In this work, we report the preparation of a thermoreversible gel of nylon 11, which was freeze-dried to obtain the nylon 11 aerogel. Both gel and aerogel samples crystallized predominantly into the γ form at room temperature. The temperature-induced structural transitions of the gel and aerogel samples were studied using wide-angle X-ray diffraction measurements. The gel samples showed a reverse Brill transition from γ to α form on heating and the transition temperature showed a linear dependency on the polymer concentration in gels. On the other hand, the nylon 11 aerogel samples showed a structural transition from γ to high-temperature pseudohexagonal form upon heating. Current results demonstrate that the solvent molecules within the gel samples trigger the chain conformation change from gauche to trans on heating to induce a reverse Brill transition behavior. By adjusting the gel concentration, nylon 11 aerogel samples with varying porosities were obtained, which in turn display low dielectric constant values that rely on density/porosity. Further, the aerogels are also found to be suitable for oil-water separation applications due to their highly hydrophobic nature.