Self-Healing EPDM Rubbers with Highly Stable and Mechanically-Enhanced Urea-Formaldehyde (UF) Microcapsules Prepared by Multi-Step In Situ Polymerization.

The mechanically-enhanced urea-formaldehyde (UF) microcapsules are developed through a multi-step in situ polymerization method. Optical microscope (OM) and field emission scanning electron microscope (FE-SEM) prove that the microcapsules, 147.4 µm in diameter with a shell thickness of 600 nm, are well-formed. From 1H-nuclear magnetic resonance (1H-NMR) analysis, we found that dicyclopentadiene (DCPD), a self-healing agent encapsulated by the microcapsules, occupies ca. 40.3 %(v/v) of the internal volume of a single capsule. These microcapsules are mixed with EPDM (ethylene-propylene-diene-monomer) and Grubbs' catalyst via a solution mixing method, and universal testing machine (UTM) tests show that the composites with mechanically-enhanced microcapsules has ca. 47% higher toughness than the composites with conventionally prepared UF microcapsules, which is attributed to the improved mechanical stability of the microcapsule. When the EPDM/microcapsule rubber composites are notched, Fourier-transform infrared (FT-IR) spectroscopy shows that DCPD leaks from the broken microcapsule to the damaged site and flows to fill the notched valley, and self-heals as it is cured by Grubbs' catalyst. The self-healing efficiency depends on the capsule concentration in the EPDM matrix. However, the self-healed EPDM/microcapsule rubber composite with over 15 wt% microcapsule shows an almost full recovery of the mechanical strength and 100% healing efficiency.

Modeling and impedance matching for radio frequency driven plasma lamp considering cold and hot states.

A new dual-state impedance matching scheme for a microwave driven plasma lamp using a solid-state power amplifier (SSPA) is presented. The impedance of the plasma lamp depends on the amount of input radio frequency (RF) energy, and therefore has very different values for hot and cold states. First, a method for effectively modeling the electrical characteristics of a plasma lamp that depends on RF power has been proposed. Second, a new technique has been proposed to achieve dual-state impedance matching for two state impedances at two very close frequencies using a T-shaped matching network with two section shunt stub and additional transmission line. The proposed method can achieve dual state impedance matching in two frequency bands located very closely when compared to the conventional methods. The accuracy of the proposed model and the effectiveness of the proposed dual-state matching are verified via a plasma lamp system with a 2.45 GHz 300 W GaN SSPA.