Dielectrics PMMA

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

Upadhyay et al. [98] used primarily correlated XPS and water contact angle measurements to study the surface degradation and recovery of amorphous films of a PMMA and a poly (aryl ether ether ketone) (PEEK). Surface modification of the films was carried out in a dielectric barrier discharge (DBD) unit, samples being treated with different dose levels of dielectric discharge. The modified (treated) samples were then stored for one month and re-examined. Figure 35 shows C(ls) and 0(1 s) XPS envelopes and their curve-fitting deconvolutions,... 

NHE OCP ONO OPS PCD PDS PL PLE PMMA PP PP PS PSG PSL PTFE PVC PVDF normal hydrogen electrode (= SHE) open circuit potential oxide-nitride-oxide dielectric oxidized porous silicon photoconductive decay photothermal displacement spectroscopy photoluminescence photoluminescence excitation spectroscopy polymethyl methacrylate passivation potential polypropylene porous silicon phosphosilicate glass porous silicon layer polytetrafluoroethylene polyvinyl chloride polyvinylidene fluoride... 

Banerjee S, Kumar A (2010) Dielectric behavior and charge transport in polyaniline nanofiber reinforced PMMA composites. J Phys Chem Solids 71 381... 

The last column of Table 2 lists the values of k calculated from Eq. (103). In the calculation, s at 1 MHz was used and Poisson s ratio m was assumed to be 0.35. Agreement between observed values and calculated ones is fairly good except for poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA), which exhibit a remarkable dielectric relaxation at room temperature. 

In contrast to polystyrene the observed intercepts for PMMA and PEMA in the glassy state remain high with values that are a substantial fraction of those observed in the equilibrium liquid state. Such a result should not be too surprising since it was shown above that a large part of the observed relaxation function above Tg was due to the secondary relaxation. The frequency of maximum dielectric or mechanical loss for the /9... 

Fig. 107 Temperature dependence of the dielectric loss, s"y for two different samples of PMMA at 1 Hz (from [75])...

A detailed analysis of the dielectric response of PMMA has been performed [75]. The frequency dependence of the dielectric loss, e"y at a few temperatures is shown in Fig. 108. An increase in temperature is associated with a shift towards higher frequency, as expected, but also with quite a significant increase in the height of the peak maximum. 

The chemical structure of PMMA makes assignment of the dielectric P transition easy. Indeed, the ester group O - C = O is planar and its dipole moment is represented in Fig. 110. 

Fig. Ill Relaxation map of PMMA derived from dielectric e" (, O) and mechanical E" ( ) data (from [75])...

The molecular motions underlying the dynamic mechanical and dielectric f3 transition in PMMA have been studied in detail [77] by using the 2D exchange NMR experiment. This detects slow reorientations that occur during a mixing time, fm, by measuring the angular-dependent NMR frequencies (expressed in ppm) before and after tm. The 2D frequency spectrum S( >i,... 

The 13 C powder NMR line shapes of the carboxyl group chemical shift tensor are shown Fig. 115 as a function of temperature. At 27 °C, a nearly regular powder spectrum is found, with o = 268 ppm, <722 = 150 ppm and (733 = 112 ppm. As temperature rises, increasingly pronounced line-shape changes are observed, which are indicative of large motions with rates exceeding 10 kHz. The motional rates estimated at the various temperatures fit quite well on the relaxation map of PMMA obtained from mechanical and dielectric measurements (Fig. 111). Thus, the motions of the carboxyl groups observed by NMR are directly related to the f3 transition. 

The quasi-static modelling of the dynamics of the ester group flip in an amorphous cell of atactic PMMA has yielded information complementary to that derived from dynamic mechanical analysis, dielectric relaxation and, mainly, multidimensional 13C and 2H solid-state NMR. The main results are ... 

The dielectric relaxation of CMIMx copolymers has been studied and compared to the PMMA dielectric behaviour [75]. Figure 129 shows the temperature dependence of the dielectric loss, e > at 1 Hz. 

It is interesting to point out the change in the relative heights of the and a peaks between PMMA and CMIM20 (Fig. 129). In the latter polymer, only a small part of the dielectric relaxation happens through the j3 motional processes. The cooperative motions involved in the a transition are required for achieving an important relaxation, whereas it is the opposite for PMMA. Such a behaviour is consistent with the hindrance of main-chain cooperativity by the rigid CMI units. 

Whereas for PMMA (Fig. 113) the two p peaks are quite well superposed, except in the p - a crossover region, in the case of the CMIM20 copolymer, the dielectric loss is weaker than the mechanical loss in the high-temperature part of the P transition. In contrast, in the p - a crossover region, the same behaviour is observed for the mechanical and dielectric responses, showing that, in CMIM20, the CMI units lead to a complete decoupling between the P and a transitions, which is not the case for PMMA. 

Such a behaviour is consistent with the weaker intensity, observed in the high-temperature part of the dielectric p peak, for CMIM20 compared to PMMA. 

The mean activation energy for CMIM20 is 53 kj mol-1, significantly smaller than that obtained for PMMA (58 kj mol x). Such a trend agrees with the dielectric data (Sect. 8.2.2), in spite of the larger change observed experimentally. 

Fig. 137 Internal rotation angle changes of the main-chain C C bonds associated with the ester group jr-flips activated in the dielectric relaxation of PMMA and CMIM20 at 50 °C. (from [78])...

The temperature dependence of the dielectric loss, e", at 1 Hz for CMIM20 and MGIM21 and PMMA, is shown in Fig. 148. It appears that the two imide groups have different effects on the dielectric response of PMMA. In the low-temperature region, the MGI unit leads to e" values lower than the CMI unit. However, the largest effect arises in the high-temperature part of the f3 transition. Indeed, whereas the CMI units strongly hinder the cooperativity of the... 

The mechanical loss modulus, and the dielectric loss modulus, m", at 1 Hz, are compared for the various MGIMx copolymers in Fig. 149, using the same scales which lead in PMMA to superposition of the low-temperature parts of the j3 transition (Fig. 112). In all cases, the mechanical loss, E , is higher than the dielectric loss, m", over the whole temperature range. 

A useful approach for comparing the effects of introducing MGI units within a PMMA chain is by taking as a reference the response expected from the MMA content in the MGIMx copolymers. This refers to Fig. 142 for the mechanics and Fig. 147 for the dielectric experiments. 

Calculations of the incident electron penetration depth into the dielectric layer is a well understood phenomenon [58,59] in recent years many Monte Carlo simulation tools were developed to study it. In our case it allowed an easy calculation of the photoresist layer thickness for different exposure parameters of the eb. For example if the eb exposure is done with Vo = 15 kV accelerating voltage and the dielectric layer is selected to be polymethylmethacrylate (pmma), we estimate the penetration depth by Kanaya and Okayama s [58] expression ... 

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