Thermo-Viscoelastic residual stress behavior of fluorinated polyimide based on fluid Instability-Driven shear exfoliated graphenic nanosheet

Hwang, Yun Chan; Khim, Seongjun; Nam, Ki-Ho

doi:10.1016/j.cej.2022.140888

Cited by 1 publication

(1 citation statement)

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“…According to the Clausius–Mosotti equation, the D k of a PI decreases with the decrease in the dipole strength and the increase in the free volume of a material . The representative chemical modification of PI, such as fluorination, can reduce its D k because of the low dipole moment and low polarizability of the C–F bonds. − However, the bulky fluorine substituents reduce the glass transition temperature ( T g ) of macromolecular chains by forming nonlinear/noncoplanar conformations and suppressing dense chain packing. , Moreover, the D k is approximately 2.4–3.0 even in fluorinated PIs, , which remains a challenge.…”

Section: Introductionmentioning

confidence: 99%

Temperature-Invariant Large Broadband Polyimide Dielectrics with Multimodal Porous Networks

Khim

Hwang

Choi

et al. 2023

ACS Appl. Polym. Mater.

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Herein, we describe sponge-like polymeric materials with multimodal porous networks with stable ultralow dielectric properties over broad frequency and temperature ranges. A hierarchically porous polyimide (PI) film was prepared via nonsolventinduced phase separation (NIPS), followed by stepwise thermal imidization. Through the swelling and the subsequent liquid−liquid phase separation, highly insulating interconnected pores of the internal layer and the water-vapor impermeable, closed-cell skin of the outer layer were directly formed on the PI film. The grafting of porous PI onto amino-functionalized mesoporous silica (AMS) to further adjust the overall thermal stability and dielectric constant has become a valid strategy. The porous PI-grafted-AMS (PPI-g-AMS) exhibited uniform micropores, which were regularly shaped with an average diameter of 16.3 ± 0.6 μm. The glass transition temperature (T g ) of PPI-g-AMS increased considerably from 367 °C to as high as 398 °C because of the formation of interchain cross-linking bridges in the AMS. Outstanding dielectric constant (D k ) and dissipation factor (D f ) of 1.84 and 0.0018 at a frequency of 1 MHz, respectively, were achieved for PPI-g-AMS-1 with the addition of AMS with 1% wt. Moreover, stable and ultralow D k (∼1.84 at 1 MHz) and D f (∼0.001 at 1 MHz) values were achieved over a broad temperature range from −20 to 200 °C. These findings indicate the broad application potential of polymeric materials as interlevel insulation materials in the next-generation 5G/ 6G infrastructure.

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