High-Temperature Mechanical Behavior and Phase Morphology of Poly(Tetrafluoroethylene)/Siloxane Nanocomposites Used as U
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HIGH-TEMPERATURE MECHANICAL BEHAVIOR AND PHASE MORPHOLOGY OF POLY(TETRAFLUOROETHYLENE)/SILOXANE NANOCOMPOSITES USED AS ULTRA LOW-k DIELECTRICS PING XU 1, SHICHUN QU 2, TOM ROSENMAYER 2 AND MIN Y. LIN 3 W. L. Gore & Associates, Inc., 2401 Singerly Road, Elkton, MD 21921 2 W. L. Gore & Associates, Inc., 1414 West Hamilton Avenue, Eau Claire, WI 54703 3 National Institute of Standards and Technology, React E 151, Gaithersburg, MD 20899 1
ABSTRACT Poly(tetrafluoroethylene) (PTFE)/siloxane nanocomposites have been prepared as ultra low-k dielectrics. These new nanocomposites show excellent high-temperature mechanical properties compared to unfilled PTFE while their dielectric constant almost remains unchanged. Specifically, the data from the dynamic mechanical study indicates that these nanocomposites have the mechanical behavior similar to that of crosslinked polymers. Small-angle neutron scattering (SANS) has been carried out to characterize the phase morphology of the PTFE/siloxane nanocomposites and the size of the inorganic networks. It has been shown that no phase separations or orientations appear in these nanocomposites in the range of 12 to 469 nm. These SANS results suggest that these materials are single-phase nanocomposites that are very homogeneous and isotropic. They are basically PTFE-based molecular composites. INTRODUCTION It is well known that PTFE is an excellent electrical insulator. Its physical and chemical properties have been well documented.1 Because of its excellent electrical property, this material has been widely used as a dielectric material. To further improve its high-temperature mechanical strength, PTFE/siloxane nanocomposites have been developed. SpeedfilmTM BX known as an ultra low-k dielectric developed by Gore is a new material.2,3 This material is a hybrid nanocomposite of PTFE and siloxane, and has a dielectric constant of 2.1. Since this material is an organic-inorganic nanocomposite, several issues need to be studied, for example, inorganic domain sizes, phase separations and orientations, etc. Any submicron-scale inhomogeneity will influence material performance in the microchip application. This study was carried out to investigate the two issues as to whether PTFE/siloxane nanocomposites have improved high-temperature mechanical strength, and contain any submicron-scale phase separations and orientations. EXPERIMENTAL PTFE/siloxane nanocomposites were prepared by mixing a PTFE nanoemulsion and a siloxane as described previously.2 Mixtures were first dried and then heated at 400 oC for 2 hours in air. The same PTFE nanoemulsion sample without a siloxane was treated under the same condition and used as reference. Dynamic mechanical analysis (DMA) measurements were made on an ARES rheometer (Rheometric Scientific) in a parallel-plate geometry. Samples were first pressed into 25-mm
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diameter disks of about 0.8-mm thickness and then loaded under air. Dynamic rheology measurements were carried out in a temperature sweep mode at a fixed frequency of 10 rad/second at temperat
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