Physical Properties Changing And Its Mechanism Of Polyacrylonitrile/dimerthyl Solfoxide Solution During Physical Aging

The nature of the polyacrylonitrile?PAN?solution directly affects the structure and properties of PAN-based carbon fibers precursors.Usually,the fresh PAN solution is a process which changes from thermodynamic non-equilibrium to equilibrium.Although some techniques have been used to investigate the aging mechanism of PAN homopolymer in some previous reports,the aging mechanism of the PAN solution are still not satisfied.Such as the change of the conformation of PAN in solution,the influence of additives?electrolytes,water,etc?on the properties of the solution.Now,most attention was paid to the interaction of PAN and the interaction between PAN and solvents in the literatures,whereas little attention was paid to the property change of solvents during physical aging.In the present work,the primary contribution is to provide some insights into the mechanism of the physical aging of PAN/DMSO solutions at the molecular level.In order to understand the effects of temperature,time and water on PAN/DMSO solution,as well as the change of DMSO itself during the physical aging process of the solution.?1?It was studies that the relationship between the properties of DMSO and temperature.The dissociation of DMSO dimer occurred in the solvent during the heating process,and free DMSO is formed.It is important to explore the effect of water on DMSO,because of the extremely strong moisture absorption of DMSO.the interaction between DMSO and water molecules is stronger than the interaction of the self-association DMSO.So the water destroys the DMSO dimer,and then associate with free DMSO by hydrogen bonding.?2?Physical properties of PAN/DMSO solution were investigated in detail during the aging process.Macroscopically,it can be determined by the color change of PAN solution that physical aging phenomenon was occurred during the heating or time extension.Microscopically,the[?]of the solution indicates the hydrodynamic volume of the polymer coil,and its change demonstrates that physical aging of the solution always occurs.The PAN/DMSO solution possesses lower critical solution characteristics.The fresh solution of PAN/DMSO is not a thermodynamic stable system,and the solution can reach a thermodynamic equilibrium state after a long period of physical aging.On the one hand,the conformational entropy of PAN coil molecule is increasing,and the entanglement between molecular chains increases.On the other hand,the Brownian motion of the solvent molecules was enhanced,and a part of the PAN molecular happened desolvation.The above reasons led that the enhanced shrinkage of PAN molecular coil,higher entanglement between CN groups and more uneven distribution of molecular segment in space.?3?Physical properties of PAN/DMSO/H₂O solution were investigated in detail during the aging process.The aging mechanism of PAN/DMSO/H₂O solution is similar to that of PAN/DMSO solution.The presence of water enhanced the decrease of PAN coils,the degree of PAN molecular coils shrinkage enhances with increasing water content.The desolvation of DMSO molecules by Brownian motion and PAN molecules is more intense,and and the interaction between CN groups is closer.When the water was added to the solution,H₂O molecules were preferred to capture DMSO molecules associated with CN and to form hydrogen bond with DMSO,the rest are present in free form.