Conformable supramolecular solids based on acid dihydrazide and 1-hydroxyethylidene-1,1-diphosphonic acid for dielectric gap filling and capacitive coupling enhancement in soft electronics

Achieving effective dielectric coupling across non-ideal, compliant interfaces remains a significant challenge in soft capacitive electronics, where surface roughness, mechanical mismatch, and parasitic air gaps can substantially reduce capacitance. Here, we report a supramolecular ADH–HEDP solid formed via thermal aqueous co-assembly of adipic acid dihydrazide (ADH) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) at a 1: 1 M ratio. Following solvent removal, the material forms a dense, clay-like, and conformable solid that can be readily processed as an interfacial layer. Raman and FTIR spectroscopy, supported by solution-state 31 P NMR, confirm the formation of a noncovalent supramolecular network driven by strong intermolecular interactions between hydrazide and phosphonic acid functionalities. Broadband impedance spectroscopy reveals a frequency-dependent electrical response characterized by electrode polarization and proton-mediated charge transport at low frequencies, a well-defined bulk resistance corresponding to a conductivity of ∼4 × 10 −6 S cm −1 , and a transition to dielectric-dominated behavior at higher frequencies, where the intrinsic relative permittivity approaches ∼9.4. The material further exhibits a thermal conductivity of 0.426 W m −1 K −1 and a strain-adaptive compressive response, showing initial compliance followed by pronounced strain-stiffening at higher deformation, enabling effective conformal contact under load. In a proof-of-concept parallel-plate capacitor configuration, replacing an air gap with the ADH–HEDP interlayer increases capacitance from 3.36 to 11.37 pF at 100 kHz under fixed electrode spacing, demonstrating enhanced capacitive coupling. These results establish ADH–HEDP supramolecular solids as a promising platform for compliant dielectric interface engineering, combining moderate ionic conductivity, dielectric functionality, and mechanical adaptability for soft electronic applications.