Large-Scale Nanofiber Manufacturing| Dimethyl Sulfoxide and Sodium Chloride Modulate theCrystal Structure in PMlA to Enhance Dyeing Performance:Moecular Dynamics Simulation and Experimentanvestigations

 Jiangnan University Adv. Sci.: DMSO/NaCl Synergistically Modulates Meta-Aramid Crystal Structure to Achieve Breakthrough in Fiber Dyeing Performance

Meta-aramid fiber (PMIA), with its excellent high-temperature resistance, chemical stability and mechanical properties, is widely used in aerospace, protective clothing and other fields. However, its high crystallinity and tight molecular structure result in poor dyeing performance. This study employs the synergistic effect of DMSO and NaCl, combining experiments with molecular dynamics simulations to reveal the regulatory mechanism of the DMSO/NaCl system on PMIA fiber structure, providing a green and efficient solution for dyeing technology of high-performance fibers.

In this work, Prof. Zhu Bo's team at Jiangnan University discovered through experimental characterization and molecular dynamics simulations that DMSO significantly increases the free volume and chain mobility of PMIA fibers by disrupting intermolecular hydrogen bonds, while NaCl reduces electrostatic repulsion between dyes and fibers by neutralizing surface charges. Under their synergistic effect, the dyeing depth (K/S value) of PMIA fibers increased from 2.6 to 16.0, and the dye uptake rate jumped from 20.4% to 73.2%, while maintaining excellent color fastness and mechanical properties. Simulation results further validated the synergistic regulatory effect of the DMSO/NaCl system on fiber microstructure, providing theoretical support for functional modification of high-performance fibers.The research was published online in Advanced Science under the title "Dimethyl Sulfoxide and Sodium Chloride Modulate the Crystal Structure in PMIA to Enhance Dyeing Performance: Molecular Dynamics Simulation and Experimental Investigations." Master's student Zhuo Yan and Ph.D. candidate Wang Kuang from Jiangnan University Textile Research Institute are co-first authors.

图1 Schematic representation of DMSO/NaCl-induced PMIA fiber structural modulations  and enhanced dye adsorption pathways.

图2 Modeling process of PMIA amorphous region under DMSO/NaCl solution system.

Construction process of molecular dynamics simulation model for the amorphous region of meta-aramid fiber in DMSO/NaCl solution. 

图3 a Surface morphology of dyed PMIA fibers. b Elemental content of PMA fiber surface. c Curve-fitted C1s of PMIA fibers.

SEM, EDS, and XPS analyses revealed that DMSO/NaCl treatment significantly altered the surface structure and elemental distribution of PMIA fibers: The dyed meta-aramid fiber showed markedly increased surface grooves and cracks due to DMSO-induced swelling, along with enhanced surface roughness. EDS results indicated a significant increase in nitrogen (N) and sulfur (S) elements on the surface of dyed meta-aramid fibers, suggesting enhanced adsorption of cationic dye B-159. XPS C1s peak fitting demonstrated an increased proportion of C─N groups and a decreased proportion of C─C groups, indicating greater exposure of C─N groups from the dye structure. Simultaneously, DMSO treatment opened up the PMIA molecular chain structure, exposing more amide groups (C═O), which synergistically promoted the embedding and adsorption of dye molecules.

图4.a) FT-IR spectra. b) Intensity ratio of hydrogen bonds. c,d) XRD of different samples. e,f) Crystallinity of different samples.

The synergistic effect of DMSO and NaCl impacted the hydrogen bonds and crystallinity of PMIA fibers: Experimental results showed a redshift in the N-H vibration peak (3279 cm⁻¹) and an increased hydrogen bond strength ratio (C=O...H/C-C peak), indicating reorganization and strengthening of PMIA's hydrogen bond network. XRD analysis confirmed that PMIA's crystal structure remained intact, as DMSO/NaCl induced molecular chain rearrangement under heating conditions, promoting expansion of crystalline regions while dye molecules filled amorphous voids, further reinforcing the hydrogen bond network.

图5 a b K/S values of different samples. c, d Dye uptake of different samples.

图6 Cross-section and surface photographs of dyed PMIA fabrics.

Experimental results demonstrated that DMSO/NaCl synergistic treatment significantly improved the dyeing performance of PMIA fibers: The K/S value and dye uptake rate of dyed meta-aramid fibers increased to 15.0 and 71.9%, respectively. Levelness tests showed that the synergistic effect of DMSO and NaCl significantly reduced the standard deviation of K/S values in dyed meta-aramid fabrics, with markedly improved dyeing uniformity across fiber cross-sections. Color fastness tests confirmed that DMSO and NaCl maintained excellent color fastness while enhancing dyeing depth, reflecting their synergistic balance between optimizing dyeing performance and fastness.

图7a, d change in the number of hydrogen bonds. b, e Average number of a, d) change in the number of hydrogen bonds. b, e) Average number of hydrogen bonds within PMIA. c, f) RDF curves for H(N─H) to O(O═C) in PMIA.

Molecular dynamics simulations revealed that the DMSO/NaCl system regulated dyeing performance by disrupting the hydrogen bond network in PMIA's amorphous regions: The S═O groups of DMSO interacted with N-H or C═O groups of PMIA, breaking the original hydrogen bond network. Simulations showed that as DMSO concentration increased, the number of hydrogen bonds in PMIA's amorphous regions significantly decreased (e.g., from an initial 134 to 106.27 in the D-50% group), enhancing molecular chain mobility and increasing free volume to provide more adsorption sites for dyes. Radial distribution function (RDF) analysis indicated that DMSO caused hydrogen bond peaks to shift rightward, forming longer and weaker hydrogen bonds that improved fiber flexibility and dye penetration. In contrast, NaCl weakened hydrogen bonds at low concentrations through ionic effects but promoted stronger hydrogen bond formation at high concentrations, explaining the maintenance of mechanical properties observed in experiments. This dynamic balance demonstrated the microscopic mechanism by which DMSO/NaCl synergistically disrupted and rebuilt hydrogen bond networks to enhance dyeing performance while preserving fiber structural stability.

图8 a, c MSD values of different models. b, d values of different models. e, f FFV of different models. g Schematic of the free volume of the model.

Mean square displacement (MSD) and free volume results showed that DMSO and NaCl cooperatively regulated PMIA molecular chain mobility and free volume to influence dyeing performance: Increasing DMSO concentration significantly enhanced MSD and diffusion coefficients (D) of PMIA molecular chains. Beyond a specific threshold, chain segment mobility stabilized while free volume fraction (FFV) substantially increased from initial values, providing more space for dye diffusion. NaCl exhibited bidirectional regulation—at low concentrations, it enhanced chain segment mobility and expanded free volume by neutralizing fiber surface charges, whereas high concentrations restricted segment mobility and reduced free volume due to excessive ionic strength. Optimal synergistic effects occurred at moderate concentrations. These microstructural changes explained the molecular mechanism by which the DMSO/NaCl system improved PMIA dyeing uniformity and depth while maintaining fiber structural stability through hydrogen bond network disruption, increased free volume, and optimized charge distribution.

图9 a, d) Change in cohesion energy value. b, e) Mean value of cohesion energy. c, f) Solubility parameters for different models.

Cohesive energy density (CED) and solubility parameters (δ) elucidated DMSO/NaCl's regulatory mechanism on PMIA fiber structure: DMSO reduced PMIA's CED by breaking hydrogen bond networks, weakening intermolecular forces, whereas NaCl increased CED by promoting hydrogen bond reconstruction. Their synergistic effect balanced fiber swelling and structural stability. Solubility parameter theory indicated that when the δ value of the DMSO/NaCl system most closely matched PMIA's δ (e.g., in the D-50% group), solvent-fiber compatibility was optimal, yielding the best swelling effect. This was attributed to more efficient penetration of solvent molecules into the polymer network. NaCl maintained good compatibility at moderate concentrations in DMSO solution but caused compatibility degradation when excessive, explaining why optimal dyeing performance in experiments was achieved by regulating intermolecular forces and solvent-polymer interactions to improve dyeability while preserving structural integrity.

This study combined experiments and molecular dynamics simulations to reveal the mechanism by which DMSO/NaCl synergistically regulates PMIA fiber dyeing performance: Under their cooperative action, PMIA achieved significantly enhanced dyeing depth and uptake rates while maintaining excellent mechanical properties and color fastness. Both experimental and simulation results demonstrated that DMSO promotes dye penetration by disrupting hydrogen bond networks to induce fiber swelling, while NaCl further enhances dye adsorption by modulating the electrolyte environment. Their synergy outperformed individual components. This system provides an efficient dyeing solution for PMIA, with future potential for extension to acid/disperse dye systems and exploration in other high-performance fibers like para-aramid and PBO. Moreover, the integrated experimental-simulation approach establishes a new paradigm for regulating complex fiber structures.