Silicones dielectric loss

For the dielectric loss measurement by a bridge (Ando Co. TR-10C),metal-PPE-metal sandwich specimens were prepared on the silicon dioxide substrate (Corning 7059). Evaporated aluminum was used as a metal electrode. The PPE film for the use of dielectric measurement was formed with the discharge electrode whose surface area was 26 cm2 and the remainder of the electrode was covered by the Teflon plate. Two kinds of samples were prepared for this experiment. One of them was formed at 5 KHz, 0.5 torr, 20 cm3STP/min and 5 watts. The other was formed at 13.56 MHz, 0.5 torr, 40 cm3STP/min and 25 watts. 

Additions of BN powder to epoxies, urethanes, silicones, and other polymers are ideal for potting compounds. BN increases the thermal conductivity and reduces thermal expansion and makes the composites electrically insulating while not abrading delicate electronic parts and interconnections. BN additions reduce surface and dynamic friction of rubber parts. In epoxy resins, or generally resins, it is used to adjust the electrical conductivity, dielectric loss behavior, and thermal conductivity, to create ideal thermal and electrical behavior of the materials [146]. 

Of considerable interest is the use of silicone rubbers for insulation in electrotechnical equipment. This is accounted for by superior heat resistance of elastomers and their good dielectric properties. E.g., the dielectric permeability of polyorganosiloxane elastomers at 500 V and 60 Hz is 3.5-5.5, their electric strength at 60 Hz is 15-20 KV/mm, and the dielectric loss tangent, which characterises the losses of electric energy in insulation, at 500 V and 60 Hz amounts only to 0.001. It is very important that these characteristics are preserved in a much wider temperature range than in the case of natural and synthetic organic elastomers. 

The methyl silicone oils also are insoluble in natural and synthetic rubber and hence do not swell rubber compositions. Electrically they are found to have very low dielectric losses the power factor of a typical sample was found to be about 0.0001 at 12 megacycles and to be quite constant with frequency and with temperature. Some related methyl phenyl, ethyl phenyl, and ethylsiloxane liquid polymers are recommended as dielectric media for transformers and capacitors.16... 

The susceptor materials used in high-temperature processing include zirconia, boron nitride, graphite, carbon black, sodium-beta alumina, zinc oxide, and silicon carbide. While each of these susceptor materials has relatively high dielectric losses at room temperature, silicon carbide is also refractory with a relatively good resistance to oxidation at temperatures up to roughly 1500°C.t ° ... 

Figure 5 - Micro-dielectric (loss factor) Measurement of Silicone Gel Cure Study.

A number of approaches have been explored for increasing the dielectric constant of elastomers for DEs. The most common approach involves the addition of high dielectric constant filler materials to an elastomer host. Silicone is of particular interest for this type of approach as it possesses good actuation properties to begin with, is readily available in gel form, and has a low dielectric constant. Results thus far do not appear particularly promising increases in dielectric constant have been met with concomitant increases in dielectric loss and reductions in dielectric breakdown strength [184—186]. It has also been shown that the elastic modulus is affected by the addition of filler [187]. 

Figure 28 The shear stresses of oxidized polyacrylonitrile (OP) and aluminosilicate (AS)/silicone oil suspensions obtained at 0.5 kV/mm against the dielectric loss tangent of dispersed particle obtained at 1000 Hz. The particle volume fraction is 35 vol%. Reproduced with permission from T. Hao, Z. Xu, Y. Xu, J. Colloid Interface Sci. 190 (1997) 334.

Figure 4 The dielectric loss of two emulsions made of chlorinated paraffins dispersed into silicone oil vs. frequency. The chlorinated paraffin concentration of those two emulsions arc 10 wt%. Reproduced with permission from L. Rejon, B. Ortiz-Aguilar, H. de Alba, and O. Manero, Colloids Surf. A, 232(2004)87.

Figure 5 The dielectric constant and dielectric loss vs. frequency for the polyaniline-coatcd (O ) or uncoatcd ( ) silica dispersed in silicone oil. Reproduced with permission from A. Lengalova, V. Pavlnek, P. Saha, J. Stcjskal, T. Kitano, O. Quadrat, Physica A, 321(2003)411.

Figure 6 Fhe dielectric loss e" vs. frequency for polyaniline(PA) coaled poly(methyl methacty late)(PMMA) dispersed in silicone oil. The particle volume fraction is 10 vol%. The weight ratio of PA to PMMA is 0.2. The primary PMMA particle diameters of the PA coated PAPMMA20-20, PAPMMA 20-45, PAPMMA 20-90 are 2, 4.5, and 9 pm, respectively. Reproduced with permission from M.S. Cho, Y.H. Cho, H.J. Choi, and M.S. Jhon, Langmuir, 19(2003)5875.

Figure 2 The dielectric loss of the sulplionated poIy(styrene-co-di vinyl benzene) particles (SSD) of different diameter diameters (5,15, and 50 jim) dispersed in silicone oil vs. frequency. The particle volume fraction is 6.8 vol% and water content is 2.8 wt%. Reproduced with permission from F. Ikazaki, A. Kawai, T. Kawakami, K. Edamura, K. Sakurai, H. Anzai, and Y. Asako, J. Appl. Phys. D, 31(1998)336...

Figure 4 The dielectric loss tangent of the liquid crystalline polymer of the polysiloxane main chain (the number of silicon is 31) and 4-cyanophenyl-4-propyloxy benzoate side chain (the number is 14, this polymer is named LCPP) dissolved in phenyl-substituted polydimethylsiloxane (Ph-PDMS, 15% phenyl content) as a function of frequency obtained at 20-60 "C. Reproduced with permission from T. Hao, A. Kawai, and F.lkazaki, J. Colloid and Interface Sci., 239(2001)106...

However, ifp is of a negative value, then the yield stress will decrease as increases, which is unable to be explained by the polarization model but was experimentally observed, rhe parameter p only becomes positive when the dielectric loss tangent of the dispersed solid material is larger than 0.1, as we demonstrated before both experimentally and theoretically. Eq. (69) and (70) incorporates the dielectric criteria proposed earlier. Figure 13 shows the calculated yield stress using Eq.(69) as the function of the particle volume fraction at the particle-to-oil dielectric ratio 10, ds JdT =-2.4x 10 C experimentally determined for the silicone oil, and dc JdT -0,4 C as dc JdJ should be larger than zero for the ER... 

Besides dielectric constant, the dielectric loss also increases with the applied electric field strength substantially for polyurethane particle/silicone oil ER suspension [67]. 

Madsen et al. (2014) recently developed a toolbox for obtaining homogenously functionalized sihcone elastomers by the use of a clickable chain extender (Fig. 3), which greatly facilitates the targeted formulation of silicone elastomers in modular fashion, as illustrated in Fig. 4. The chloro-functional intermediate in scheme X furthermore was shown to simultaneously increase the dielectric permittivity and decrease the dielectric loss of the resulting silicone elastomers. These initial results indicate that a sensitive balance of certain properties such as elastic moduli, permittivity, dielectric loss, conductivity, and electrical breakdown is required to optimize the electromechanical response for DBAs. However, with the recent developments reported for silicone elastomers, an increasing number of DBA-targeted properties can be more fully developed. 

SijN4 is primarily used in structural apphcations however, it possesses low dielectric loss, thermal expansion match to silicon, and high thermal conductivity, making it an exceptional candidate for substrate applications. The relatively high fabrication costs and difficulty of fabrication, sintering, or hot pressing above 1700°C hmit its potential. 

---