Dielectric constant water uptake

Laminate T °C GTE below ppm/°C Water uptake, MIL-P-13949F, mg Dielectric constant at IMH2 Dissipation factor at 1 MH2 Tensde strength, MPa " Modulus of elasticity, GPa Thermal conductivity, W/(m-K)... 

A correlation between the dielectric constant of the plasticizer used in a polymer and its water uptake might be expected. However, according to the table below17 (Table 19), no predictions can be made. 

Plasticizer Lipophilicity of plasticizer (log P) Dielectric constant ofplasticizer Water uptake after one week with PVC/plasticizer = 1 2... 

Very low moisture absorption. Typically, Avatrel polymers absorb less than 0.1 wt.% water, while polyimides typically range from 2 to 3 wt.%. Water uptake increases the dielectric constant of the medium and can facilitate conductor corrosion. 

Table I lists the experimentally measured dielectric constants at 0% and 40% RH, polymer densities, and the weight uptake of water per 100 g film at 40% RH for all the samples investigated. The polarizability of the absorbed water in the films was calculated using the Clausius-Mossotti equation (Equation 1) which relates macroscopic dielectric constant to molecular polarizability as follows ...

Among various strategies that have been used to synthesize polyimides with lower dielectric constants, the most common approach is to incorporate fluorene, in the form of trifluoromethyl groups, into diamine and dianhydride units that minimize polarizability and increase the free volume [46]. It is well-known that fluorene atom has unique characteristics such as high electronegativity and low electric polarity. These properties give fluorinated polymers (e.g., poly[tetrafluoroethylene]) attractive features such as low water uptake, water and oil repellency, low permittivity, low refractive indices, resistance to wear and abrasion, and thermal and chemical stability. Fluorination is also known to enhance solubility and optical transparency and to lower the moisture absorption of polyimides. Therefore, it is expected that fluorinated polyimides will be widely applied in the electro-optical and semiconductor industries. The polymer series studied was essentially limited mainly to 6F dianhydride because it proved to be the only dianhydride with which many of the fluorinated diamines would form polymer films suitable for physical characterization. 

The absorption of water by polymers is especially suited to the development of a capacitive humidity sensor based on the high dielectric constant of water, since capacitance depends on the area, the thickness, and the dielectric constant of a dielectric. Uptake of water causes an increase in the dielectric constant followed by an increase in capacitance. Polyimide is a suitable sensitive material, but so are certain inorganic ceramics such as AI2O3 [142] and low-density Ta205, which change their capacitance with the formation of water dipoles. Low-density Ta20s layers can be formed by anodic oxidation of sputtered tantalum films, whereas polyimide films are deposited by spin coating and subsequent polymerization. 

Other properties of Pis were also improved by the diimide additives [135]. The dielectric constant, e of PI from BDSDA and 2,2 -bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) reduced appreciably by additives shown in Fig. 44. The results are as listed in Table 5. Furthermore, the addition of 10 wt% AN-BDSDA-AN into BDSDA-ODA m-PDA polyimide caused a decrease in the saturation moisture content from 1.52% for the neat PI to 1.27%. Positron annihilation spectroscopy proved that a decreased free volume is responsible for the reduced water uptake. Also, a slightly increased in modulus and a decreased CTE were caused by the 5% addition of AN-6FDA-A into LARC-TPI in both the undrawn and drawn states. 

Densely cross-linked PCN networks, synthesized by polymerization, via cy-clotrimerization reaction, of dicyanic ester of bisphenol A [159-161], consist of rigid triazine heterocycles as junctions connected with bisphenol A remainders (see a scheme in Fig. 26). At the total conversion of cyanate groups (Xcn pcn 1). PCN exhibits high Tg 300°C and rigidity, good adhesion to different substrates and chemical resistance, as well as low values of dielectric constant and water uptake. This allowed in particular its application as the matrix for glass- and aramid fiber-reinforced plastics in the electronics and aerospace industries. 

Equations 2.43 and 2.44 describe the water uptake phenomenon for a single pore in equilibrium with an external gas phase. The value of r]c can be related to the relative humidity, P /P through Equation 2.30. Equations 2.43 and 2.44, thus, establish the relation between environmental conditions (T, P", P ) and r]c. Parameters that control the water uptake by the pore are the charge density, cto,c, the dielectric constant of water, e, and the shear modulus of polymer walls, G. 

Extensive studies on the influence of the nature of the oil phase on the phase behaviour of the Brij 96-oil-water systems have been reported [34, 35]. The considerable influence of the oil phase on the aspect of the phase diagram is apparent from Fig. 2.16 which shows the phase behaviour for nine different oils. In Fig. 2.17a the percentage uptake of water into different isotropic L2 phases containing 50 per cent Brij 96 is plotted against the dielectric constant e of the oil... 

Figure 2.17(a) Water uptake in the isotropic oil phase, L2, as a function of the solvent dielectric constant, e. (b) Uptake of solubilisate molecules in the aqueous neat (G) phase of Brij 96 as a function of the dielectric constant of , aliphatic/alicyclic molecules, and A, aromatic molecules, (c) Uptake in the middle (Mj) phase at a concentration of surfactant of 50% as a function of the dielectric constant, e, of the solubilisate. o, Aliphatics/alicyclics , aromatics. From Lo et al. [35] with permission. 

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