Phase Transformation of Polymeric Materials in High Magnetic Field

Abstract

A model to describe a non-rotation type magnetic alignment of crystalline polymers during crystallization from melts is presented. The model is based on the presence of mesophase existing between the melt phase and the crystalline phase, with an extremely small transformation enthalpy and a resultant large shift of melting point in the presence of a magnetic field. A calculation of the magnetic effect on the nucleation and growth rates of mesophase is carried out. It is shown that these rates are enhanced for the mesophase with a specific orientation with respect to the applied field, resulting in alignment.

Magnetic-Field-Induced Liquid Phase Transformation of an Ionic Liquid N,N,N-Trimethyl-N-propylammonium Bis(trifluoromethanesulfonyl)imide

“…Because magnetic fields will change the Gibbs energy of materials, various magnetic field effects on phase transition were reported, such as the melting point of water, the crystallization temperature of polymers, the gelation temperature of agarose gel, the volume phase transition of NIPA gel, and the structural transformation of metals and alloys . The phenomena, however, have never been explained quantitatively from the viewpoint of magnetic energy Δ E mag = [(1/2)­μ 0 ]­Δχ B 2 (Δχ: change in the magnetic susceptibility of a phase; μ 0 : magnetic permeability of vacuum) − because such a magnetic energy is too small. The phase transition can be detected sensitively by the electric potential generated between the two phases. − The freezing potential (FP) is the electric potential that arises from the charge separation between an ice and aqueous dilute salt solution during solidification .…”

“…The freezing point, determined by the FP, DSC, and superconducting quantum interference device (SQUID) measurements, remained unchanged with magnetic fields. This is plausible because the magnetic energy is on the order of μJ mol –1 for diamagnetic materials and thus may be too small to induce the temperature shift in T f , although several papers reported a little shift in the phase transition temperature. − On the other hand, the MFI phase transformation was induced by magnetic fields larger than B th , which was detected by various in situ methods: electric potential, magnetic moment, and Raman intensity. The B th line was determined by the least-square method.…”