Esters, dielectric behavior

Great attention has been focussed on lower threshold materials and their threshold/temperature characteristics. A comparison of more recent liquid crystal materials for multiplexing has been given by Raynes. 9 Examples of mixtures using biphenyls, PCH s, PCH esters are shown in Fig. 35. These three mixtures may be adequate for up to 1 in 5 duty cycle. The biphenyl mixture is characterized by a sharp threshold while the PCH-ester systems have low temperature-threshold dependence. The exact reason for large differences in threshold/temperature characteristics between the various classes of materials is little understood, e.g., biphenyls are poor and azoxy compounds are excellent. A comparison of threshold sharpness between the materials shows that some progress can be made and the answer appears to be in mixtures of materials of different classes. Such mixtures appear to offer promising results in terms of dielectric behavior and elastic constants, both of which are a key to threshold sharpness. 

Very few studies have considered the behavior of ionomers in relatively polar solvents, i.e., solvents with high dielectric constants, e. Schade and Gartner(8) compared the solution behavior of ionomers derived from copolymers of styrene with acrylic acid, methacrylic acid, or half esters of maleic anhydride in tetra-hydrofuran (THF), a relatively non-polar solvent (e 7.6), and dimethyl formamide (DMF), a polar solvent (e = 36.7). They ob-... 

This study compared methacrylate and acrylate polymers to structural analogs with fluorinated ester groups. Two types of relaxations were characterized, the primary relaxation associated with the glass transition and secondary relaxations associated with side group motion and localized segmental motion. Dielectric analysis was used to characterize the response of dipoles to an electric field as a fimction of temperature. Mechanical properties were analyzed via dynamic mechanical analysis and stress relaxation measurements. Relaxation behavior was interpreted in terms of intermolecular and intramolecular mechanisms. 

A tenside with a relatively strong lipophilic group and weak hydrophilic group is mainly soluble in oil and preferentially stabilizes a w/o emulsion, and vice versa. This fact led to the development of a standard with which the relative strength or activity of the hydrophilic and lipophilic groups of emulsifiers can be evaluated. It is called the HLB value (hydrophilic-lipophilic balance). It can be determined, e. g., from dielectric constants or from the chromatographic behavior of the surface-active substance. The HLB value of the fatty acid esters of polyhydroxy alcohols can also be calculated as follows (SV =... 

The secondary or B relaxation, assigned to motions of the ester side group is a minor feature dielectrically in contrast to the behavior of the poly(alkylmethacrylates). 

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