Processing of polymers in high magnetic fields

Abstract

Many organic molecules and polymers have an anisotropic diamagnetic susceptibility, and thus can be aligned in high magnetic fields. The presence of liquid crystallinity allows cooperative motions of the individual molecules, and thus the magnetic energy becomes greater than the thermal energy at experimentally obtainable field strengths. Our work has determined the effect of magnetic field alignment on the thermal expansion and mechanical properties of liquid crystalline thermosets in the laboratory. Further advances in magnet design are needed to make magnetic field alignment a commercially viable approach to polymer processing.

Negative Diamagnetic Anisotropy and Birefringence of Cellulose Nanocrystals

“…It is well established that polymer chains may be aligned by magnetic fields, and as a consequence, the use of magnets in polymer processing may lead to polymer materials with enhanced properties. , Well-documented cases of magnetic field-induced alignment include polymers organized in liquid crystalline order, especially in the nematic or chiral nematic states. − For such ordered systems, because of the strong coupling of molecular orientation due to liquid crystalline organization, moderate magnetic fields are sufficient to produce very strong macroscopic alignment. Liquid crystalline epoxy polymers are examples where the processing under magnetic field has led to significant improvements of physical properties. , Polymer crystallization is another area where magnetic fields have been shown to induce substantial morphological modifications that could lead to a number of advanced materials. − In that case, it is believed that it is the transient mesophase − in the polymer melt prior to crystallization, which is responsible for the orientation by magnetic field.…”