Mechanical field effect, networks

Mechanical Field Effects on Liquid-Crystalline Networks... 

A question to be asked is whether the macro-mechanical deformation of liquid crystal elastomers or stress fields can produce effects similar to those observed in conventional liquid crystals under external fields. Studies using the stress optical properties, conoscope, and X-ray diffraction have shown that applied mechanical fields do have a profound effect on the arrangement of the mesogenic groups in LC network [26]. 

These networks exhibit a nematic mesophase. Clearly, the type of response to the mechanical field is extremely structure dependent. The effect of spacer length on elastomer behavior was examined [27]. The reported work showed that the coupling between the mechanical stress and polymer backbone can greatly influence the mesomorphic order. This effect can be enhanced by coupling the mesogenic group more tightly to the polymer backbone. 

For Sq elastomers, a mechanical field should cause orientation effects toward uniform alignment of the phase structure. Additionally, the piezoelectric behavior is expected to be similar to the piezoelectricity of solid-state material because the network structure prevents flow. The electro-mechanical behavior of smectic C networks was already addressed by Brand in 1989 [8]. In agreement with the monoclinic symmetry of these systems, he derived ten piezoconstants for the S networks. Furthermore, rotatoelectric effects are predicted. Due to the noncentrosymmetric character of the untwisted phase, further nonlinear optical effects like frequency doubling occur. 

The first and most often encountered separation mechanism in CE is based on mobility differences of the analytes in an electric field these differences are dependent on the size and charge-to-mass ratio of the analyte ion. Analyte ions are separated into distinct zones when the mobility of one analyte differs sufficiently from the mobility of the next. This mechanism is exemplified by capillary zone electrophoresis (CZE) which is the simplest CE mode. A number of other recognized CE modes are variations of CZE. These are micellar electrokinetic capillary chromatography (MECC), capillary gel electrophoresis (CGE), capillary electrochromatography (CEC), and chiral CE. In MECC the separation is similar to CZE, but an additional mechanism is in effect that is based on differences in the partition coefficients of the solutes between the buffer and micelles present in the buffer. In CGE the additional mechanism is based on solute size, as the capillary is filled with a gel or a polymer network that inhibits the passage of larger molecules. In chiral CE the additional separation mechanism is based on chiral selectivity. Finally, in CEC the capillary is packed with a stationary phase that can retain solutes on basis of the same distribution equilibria found in chromatography. 

Once the pore size and length I are given to the pore network, one can calculate the effective pressure field (by using iteration method), the temperature field through the network, and its effect on the vapor flux through the membrane. This model takes into account all molecular transport mechanisms based on the kinetic gas theory for a single cylindrical tube and could be applied to all forms of membrane distillation process [61]. 

Closure to debates appears to come through changes in wider social and institutional commitments. In effect, it takes a network of credible colleagues and institutional support to end a controversy. As we shall see, controversies over drug safety and efficacy often turned into disputes over testing methods themselves. Closure was reached by different mechanisms in the two countries in the United States, the FDA used its full regulatory authority to end disputes, while in Germany, physicians invoked professional norms and the credibility of their field in order to reach consensus. 

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