Diffusion coefficients during regenerated cellulose fibers formation using ionic liquids as solvents: Experimental investigation and molecular dynamics simulation

Regenerated cellulose fibers (RCFs) are an essential type of bio-based chemical fibers. The preparation of RCFs using ionic liquids (ILs) as solvents is an efficient utilization of ecological resources. Investigating the diffusion coefficients during RCFs formation using ILs as solvents is vital due to the potential impact of the interaction between ILs and coagulants on the morphology and properties of RCFs. The determination of diffusion coefficients during RCFs formation is challenging due to its instantaneous and simultaneous nature. For this research, the method and apparatus for measuring the diffusion coefficients during RCFs formation were established, and the diffusion coefficients of various IL and coagulant systems were also explored under different formation conditions. In addition, the relationship between the diffusion coefficient, the formation condition and the self-diffusion coefficient of ILs were investigated using numerical simulation and molecular dynamics simulation. The results demonstrated that the formation conditions, particularly the temperature and composition of coagulants, significantly impact the diffusion coefficient. Lowering the temperature of the coagulants and incorporating ethanol with lower polarity reduced the diffusion coefficient. The diffusion coefficient of 1-ethyl-3-methylimidazolium diethylphosphate ([Emim]DEP) in the ethanol coagulation bath was 0.79 x 10(-9) m(2)center dot s(-2)center dot s(-1) at 293 K, which was nearly twice as small as that in the water coagulation bath. These findings were validated by molecular dynamics simulations. Modifying the formation conditions can regulate the structure and properties of the RCFs by affecting the diffusion coefficients during RCFs formation.