Glass transition of one-dimensional molecular chains of p-nitroaniline confined in AlPO4-5 nanopores revealed by dielectric spectroscopy

Abstract

The dynamics of molecular chains of hydrogen-bonded p-nitroaniline (pNA), confined in the one-dimensional pore system of AlPO 4 -5, was studied by broadband dielectricspectroscopy (10 −2 –10 6 Hz). Two relaxation processes were observed. A fast process (the α process) shows above 72 ° C a Vogel–Fulcher–Tammann behavior typical of glass-forming materials, indicating cooperative dynamics of the “condensed” pNA chains. Below the glass temperature the α -relaxation peak broadens significantly and obeys an Arrhenius law. Both observations imply a change in length scale of cooperativity ξ from a temperature-controlled to a chain-length-dependent one. The second relaxation process is tentatively assigned to structuralrelaxations of the AlPO 4 -5 host lattice itself, since it is also present in calcined (empty) crystals.