Solvent-dependent conformational transitions of poly- and oligo-oxyethylene under strong electric fields: Insights from molecular dynamics simulations

Abstract

During the fabrication of nonwoven nanotextiles by electrospinning, polymer solutions are subjected to intense external electric fields, especially near the tip of the Taylor cone, where electric field lines concentrate. Under such conditions, significant conformational changes in polymers can occur, influencing the properties of the resulting nanofibers. This study investigates the restructuring of oligo- and poly-oxyethylene chains of different lengths – from 1 to 32 monomer units – in response to strong electric fields in two solvents – water and methanol – using molecular dynamics simulations. The findings reveal that very short chains tend to arrange themselves perpendicularly to the applied electric field. However, as chain length increases, solvent-specific effects emerge, resulting in distinct behaviors in water versus methanol. In methanol, polymer coils are compressed in the direction of the electric field, whereas in water they are elongated parallel to the field leading to a prolate shape. We attribute this behavior to the disruption of multiple hydrogen bonds in the region where the polymer coils come into contact with the solvent. This disruption leads to an excess of donor sites from solvent molecules. In water, where there are relatively few unoccupied acceptor sites available, the donor centers remain unbound, prompting the solvent to favor prolate coil conformations with minimal hydrogen bond disruption. Conversely, in methanol, the excess donor centers readily bind to free acceptor sites on oxygen atoms, resulting in the conservation of the oblate shape of the polymer coil.