In-situ growth of porous Cu3(BTC)2 on cellulose nanofibrils for ultra-low dielectric films with high flexibility

Abstract

The design of flexible polymeric films with internal porous structures has received increasing attention in low dielectric applications. The highly porous metal-organic frameworks (MOFs) of [Cu3(BTC)2]n (BTC=benzene-1,3,5-tricarboxylate) were introduced into aramid nanofibers (ANF) matrix by using carboxylated cellulose nanofibrils (CNF) as carriers to obtain strong, flexible, and ultra-low dielectric films. The well-dispersed “flowers-branch” like [email protected] through in-situ growth of CuBTC on CNF surface endowed the ANF/[email protected] films with excellent thermal stability, mechanical integrity and low dielectric properties. Besides, the flexible dielectric films exhibited superior ultraviolet (UV) resistance, lower coefficient of thermal expansion (4.28×10−5 °C − 1) and increased water contact angle (83.81°). More interestingly, the removal of guest molecules from the ANF/[email protected] films according to the vacuum heat treatment (VHT) process significantly improved their dielectric response. The specific surface areas of the composite films after VHT increased obviously, and the dielectric constant and dielectric loss tangent decreased to the expected 1.8–2.2 and 0.001–0.03 at 100 MHz, respectively. Consequently, such designable ultra-low dielectric films with high flexibility play an incredible significance in applications of microelectronics under large deformation conditions, especially in flexible/wearable devices at the arrival of 5 G era.