Birefringent solution

At c > 4 mM, the birefringent solution of Pn-2 becomes a self-supporting birefringent gel (Figure 4g). Gelation is associated with onset of fiber... 

Robinson as cholesteric. When viewed between crossed polars, these birefringent solutions present an image very reminiscent of a fingerprint. The spacing between the alternating bright and dark retardation lines is equal to one-half of the pitch of the cholesteric structure (Fig. 1, liquid). 

The steady-state dichroic ratio of liquid crystalline solutions of PBLG (Fig. 3) increases with external field strength and the a mptotic value is 4.5—4.7, regardless of the polymer concentration for completely birefringent solutions 23). It may be safe to say that all the polymer molecules are parallel or neady parallel within molecular aggregates 31). Therefore, the value of 7 for the particle is tentatively assumed... 

A theory of this kind neglects viscoelasticity, viscosity or birefringence. Solutions of these equations can be found [12] which connect states of small strain (e < to states of large strain (e > C2) across moving interfaces. These solutions have abrupt changes of strain across the interface, and the interface can come to rest, given proper boundary conditions at the ends of the fiber. 

Many ceUulosic derivatives form anisotropic, ie, Hquid crystalline, solutions, and cellulose acetate and triacetate are no exception. Various cellulose acetate anisotropic solutions have been made using a variety of solvents (56,57). The nature of the polymer—solvent interaction determines the concentration at which hquid crystalline behavior is initiated. The better the interaction, the lower the concentration needed to form the anisotropic, birefringent polymer solution. Strong organic acids, eg, trifluoroacetic acid are most effective and can produce an anisotropic phase with concentrations as low as 28% (58). Trifluoroacetic acid has been studied with cellulose triacetate alone or in combination with other solvents (59—64) concentrations of 30—42% (wt vol) triacetate were common. 

These phenomena are most rapid and easiest to observe in fairly concentrated aqueous detergent solutions, that is, minimally 2—5% detergent solutions. In a practical quaHtative way, this is a familiar effect, and there are many examples of the extraordinary solvency and cleaning power of concentrated detergent solutions, for example, in the case of fabric pretreatment with neat heavy-duty Hquid detergents. Penetration can also be demonstrated at low detergent concentrations. As observed microscopically, the penetration occurs in a characteristic manner with the formation of a sheathlike stmcture, termed myelin they are filled with isotropic Hquid but have a Hquid crystalline birefringent skin. 

B. Zimm. Dynamics of polymer molecules in dilute solutions viscoelasticity, low birefringence and dielectric loss. J Chem Phys 24 269-278, 1956. 

Tsvetkov, V. and Andreeva, L. Flow and Electric Birefringence in Rigid-Chain Polymer Solutions. Vol. 39, pp. 95-207. 

Many papers deal with the crystallization of polymer melts and solutions under the conditions of molecular orientation achieved by the methods described above. Various physical methods have been used in these investigations electron microscopy, X-ray diffraction, birefringence, differential scanning calorimetry, etc. As a result, the properties of these systems have been described in detail and definite conclusions concerning their structure have been drawn (e.g.4 13 19,39,52)). 

Fig. 70. Optical micrograph of the birefringence zone in a PEO solution (100 ppm, 4.106 MW). The dotted line delineated the contour of the nozzle...

Isihara, A. and Guth, E. Theory of Dilute Macromolecular Solutions. Vol. 5, pp. 233-260. Janeschitz-Kriegl, H. Flow Birefringence of Elastico-Viscous Polymer Systems. Vol. 6, pp. 170-318. 

Zimm, BH, Dynamics of Polymer Molecules in Dilute Solution Viscoelasticity, Flow Birefringence and Dielectric Loss, Journal of Chemical Physics 24, 269, 1956. 

The physical properties (7-10) of our E-V copolymers are sensitive to their microstructures. Both solution (Kerr effect or electrical birefringence) and solid-state (crystallinity, glass-transitions, blend compatibility, etc.) properties depend on the detailed microstructures of E-V copolymers, such as comonomer and stereosequence distribution. I3C NMR analysis (2) of E-V copolymers yields microstructural information up to and including the comonomer triad level. However, properties such as crystallinity depend on E-V microstructure on a scale larger than comonomer triads. 

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