Spontaneous birefringence

It is interesting to observe that rod-shaped molecules such as tobacco mosaic virus or flat plate particles such as bentonite show the so-called coacervation at rather low concentrations at which the second phase solution shows a spontaneous birefringence. Oparin discussed the possible connection of such a phenomenon with the origin of life (25). 

In solutions of normally encountered randomly coiled macromolecules the formation of spontaneously birefringent phases is not expected. (Phase separation does occur when the interaction between solute molecules is strong.) Here, we have investigated solutions of the polyelectrolyte sodium carboxymethylcellulose in water, which are rubberlike at high concentrations 12). (Materials that form such solutions are commonly called gums.)... 

Relatively high dichroic ratio up to 2.3 due to geometry of the molecule (high aspect ratio of Direct Red 80) has been achieved (Advincula et al., 2003). To manufacture these films with PD ADM AC of ca. 100-nm thickness, 100 layers were necessary. Less effective photoorientation of spin-coated and LbL films with other polyelectrolyte (PAH, PEI) was attributed to specific formation of J-aggregates in LbL films. In the LbL films produced from chitosan and Sunset Yellow (dos Santos et al., 2002), spontaneous birefringence of 0.04 for the film of 300-nm thickness was observed however, the value was not affected by the light. This fact underlines the importance of selection of dye and polyelectrolyte. 

By substituting Eq. 9 into Eq. 8, we find that the spontaneous birefringence in the absence of an electric field is proportional to the square of Ps, so it results only in a spontaneous Kerr effect (see Table 7.1.4). 

Ferroelectric domains are those regions where the spontaneous polarization is aligned on a certain direction. Usually, a single crystal includes many domains, and forms a polydomain structure. The ferroelectric domains were first demonstrated in a study of spontaneous birefringence (Elatmer et al. Batthias et al., 1948). There are some methods to observe ferroelectric domains, as follows ... 

Preliminary polarizing microscope studies on poly(/ -phenylethyl isocyanide) show the spontaneous reversible formation of a highly birefringent mesophase in concentrated solutions. These observations suggest that small differences in conformations due to concentration changes give rise to the occurrence of a phase separation and molecular ordering. 

The selective reflection of circularly polarized light on radiation of normal light is also exhibited by the cholesteric polymers. Like the 1-l.c. systems, the Grandjean-texture is formed spontaneously, if the polymer is sandwiched between glass plates as shown in Fig. 23. The measurements of indicate no difference to low molar mass systems. In Fig. 24 VHT) is shown for the induced cholesteric polymers, whose birefringence was discussed above (refer to Table 8, copolymers No. 4, m = 6). The different curves refer to different mole fractions of the chiral comonomer. With... 

The model predicts that for the typical elastic parameters the polarization splay is small, just a few degrees. This was also confirmed experimentally as only a small change of birefringence under the electric field is detected for the Blrev phase. The electric field eliminates the spontaneous splay by aligning the dipole moments along the electric field direction. 

Refractive index data are very useful for the quantitation of isotropic (liquid and cubic liquid crystal) phases, and for the calibration of cell thickness and nonflatness. Hovever, the analysis of birefringent phases using refractive index data has been found to be unreliable (9). A problem arises from the fact that the orientation of such phases relative to the direction of the light path, as veil as the system variables, influence refractive indices. In order to use refractive index data for quantitation, a phase must spontaneously orient in a reproducible fashion. Such orientation does occur in the case of fluid lamellar phases (as in short chain polyoxyethylene nonionic systems (7)), but viscous lamellar phases, hexagonal phases, and crystal phases do not orient to a sufficient degree. 

This expression leads to a temperature dependence for Q that is distinctly different from that implicit in Equation (5) above. For small values of h, Q decays steeply near the critical temperature and then levels off, creating a characteristic defect tail (Fig. 8). These defect tails are commonly observed in the temperature evolution of properties in impure solids that are proportional to the square of the order parameter, such as birefringence and spontaneous strain. To the extent that the sudden strengthening in the dependence of Q with temperature near Tc diverges from the dependence at lower temperatures, two transition temperatures must be differentiated the critical temperature extrapolated from lower temperatures (r ), and the observed f as measured experimentally ff"). 

Figure 3 The experimental setup. A type II Spontaneous parametric down-conversion is used both to produce the ancilla pair (in the spatial modes <23 and a4) and to produce the two input qubits (in the spatial modes ai and 0,2). In this case initial entanglement polarization is not desired, and it is destroyed by making the photons go through polarization filters which prepare the required input state. Half-wave plates have been placed in the photon paths in order to rotate the polarization compensators are able to nullify the birefringence effects of the non-linear crystal and of the polarizing beam splitters. Overlap of the wavepackets at the PBSs is assured through spatial and spectral filtering.

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