Isotopic and Confinement Effects on the Phase Behavior and Molecular Dynamics of Protonated and Deuterated Terphenyls in Electrospun Fibers.

This work provides the first systematic analysis of isotopic effects on liquid crystal dynamics under two-dimensional polymer confinement. This study investigates the physicochemical properties and molecular dynamics of a partially fluorinated liquid-crystalline terphenyl and its deuterated analogue. Differential scanning calorimetry, polarized optical microscopy, and broadband dielectric spectroscopy are employed to characterize the mesomorphic behavior, thermal transitions, and relaxation dynamics of the compounds, both in bulk and confined within electrospun poly(ε-caprolactone) fibers. While both isotopologues exhibit similar mesophases, the deuterated compound uniquely undergoes cold crystallization, highlighting the effect of deuteration on crystallization dynamics. When embedded in polymer fibers, two distinct glass transition temperatures reveal a heterogeneous, microphase-separated morphology. The incorporation of liquid crystals disrupts the crystalline structure of the polymer, increases the free volume, and reduces the activation energy of the β-relaxation process, especially for the deuterated variant. These effects point to the formation of dynamic microdomains with differentiated segmental and local mobility. The findings provide insight into how molecular confinement and isotopic substitution influence hybrid fiber system thermal and dielectric behavior, offering a design strategy for tunable materials in soft electronics and smart textiles.