Probing Dielectric Relaxation in Green-Synthesized Fluoro-Nitrato Energetic Plasticizers via Self-Referenced THz Reflection Spectroscopy

We report the application of terahertz time-domain spectroscopy (THz-TDS) to investigate the dielectric relaxation dynamics and optical properties of newly synthesized fluoro-nitrato energetic plasticizers (ACR ENP series) and their polymer blends. The study was conducted over the frequency range of 0.1–2.5 THz. The ACR ENP-1 blends exhibit relaxation times in the range of 0.127–0.168 ps (corresponding to loss maxima of ∼0.95–1.25 THz), which are nearly an order of magnitude shorter than that of bulk water (∼8 ps), highlighting their exceptionally rapid dipolar reorientation. Among them, the random copolymer blend exhibits the shortest relaxation time (0.127 ps) and the highest static permittivity (ε s ≈ 5.1), whereas the ACR ENP-1 + Poly TFGE blend shows slower relaxation (0.168 ps) with a reduced ε s, indicating restricted dipolar motion. ACR ENP-2 composites display weaker dispersion in the neat state (ε s ≈ 2.0) but exhibit a pronounced increase in dielectric strength upon polymer incorporation, with Poly NIMMO composites showing ε s ≈ 6.8 and τ ≈ 0.187 ps. Across all samples, the high-frequency permittivity remains nearly constant (ε ∞ ≈ 4.45), confirming that the observed variations arise predominantly from dipolar relaxation rather than electronic contributions. Comparative analysis further reveals that ACR ENP-3 systems relax approximately 50–63 times faster than water, with dynamics governed by localized, ultrafast segmental reorientations rather than collective hydrogen-bond network motions. These findings demonstrate that structural modification and polymer blending provide an effective strategy for tuning dielectric relaxation behavior in energetic polymers, offering a promising pathway toward advanced THz-responsive materials for sensing and defense applications.