“Grafting to” Rubber Composite for Elastic Dielectric Material

Abstract

In addition to traditional rubber applications, 1,4-cis-polyisoprene (cis-PI) has been utilized in wearable electronics. While synthetic PI typically exhibits lower durability compared to natural rubber (NR), high-molecular-weight cis-PI compensates by offering improved mechanical properties and chemical resistance. The group proposes using a commercial cis-PI with high molecular weight of 250 000 g mol⁻¹ (PI_250K-C) grafted onto modified nanoparticle structures including silicon dioxide (mSiO₂), rutile titanium dioxide (mRTiO₂), and anatase titanium dioxide (mATiO₂) as an insulator in organic field effect transistors (OFETs) due to its naturally low dielectric constant. The nanoparticles are pretreated with a coupling agent to improve adhesion and prevent aggregation. Rubber composite films, designated X%-mY-PI_250K-C (where X = 10, 20, 30% and Y = mSiO₂, mRTiO₂, mATiO₂), are fabricated using sulfur vulcanization. The modified films demonstrate excellent mechanical stress (1.15 ± 0.1 MPa) and elasticity, enduring 50 loading–unloading cycles without residual strain. In contrast, rubber composites produced from simple blending show half the mechanical stress at 0.7 ± 0.3 MPa, which is attributed to nanoparticle agglomeration observed in SEM and EDX results. Additionally, mRTiO₂ nanoparticles significantly increase the dielectric constant of PI_250K-C from 2.12 to 12.93, enhancing electrical performance for TFT applications. This study underscores the effectiveness of the “grafting to” approach for producing robust rubber composites, highlighting the importance of nanoparticle selection and fabrication precision for stretchable organic electronics.