Liquid crystal polymers lyotropic

Goltner, C. G Henke, S. Weissenberger, M. C. Antonietti, M. 1998. Mesoporous silica from lyotropic liquid crystal polymer templates. Angew. Chem. Int. Ed. 37 613-616. 

Both thermotropie and lyotropic liquid crystal polymers exhibit eharacteristic micro-strueture features [9,10]. Anisometrieal monomers such as rods or disks are conneeted to ehains in an appropriate manner. These anisometrieal monomers are considered the mesogens and may be part of main ehain LCP, side chain LCP, or of both types together (Fig. 6). Flexible spacers of nonmesogenic character are located between the mesogens. A sufficient flexibility is a prerequisite for the liquid crystal formation with an increase in temperature or solvent concentration. 

Ding, J. H., and Gin, D. L., Catalytic Pd nanoparticles synthesized using a lyotropic liquid crystal polymer template, Chem. Mater. 12,22 (2000). 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

C.G. Goltner, S. Henke, M.C. Weissenberger, and M. Antonietti, Mesoporous Sibca from Lyotropic Liquid Crystal Polymer Templates. Angew. Chem., Int. Ed., 1998, 37, 613 16. 

Walker, L. Wagner, N. Rheology of region I flow in a lyotropic liquid-crystal polymer the effects of defect texture. J. Rheol. 1994, 38 (5), 1525-1547. 

One of the most intriguing orientation phenomena seen in rigid-chain liquid crystal polymers is that of banding. The texture appears in samples which have been sheared and oriented in extensional flow, as contrasting bands normal to the direction of extensional flow. The phenomenon was observed in Kevlar fibres by Dobb et al It has since been reported in other lyotropic liquid crystal polymers " and in thermotropic random copolymers. In the latter studies a... 

If a polymer is to be a lyotropic liquid crystal polymer, it must firstly be fairly rigid and secondly it must dissolve in a solvent. These two requirements are often mutually exclusive in that rigid stractures are usually not soluble. Accordingly, drastic solvents such as sulfuric acid are often required. 

An important class of lyotropic liquid crystal polymers are the aramid polymers such as polyparabenzamide... 

Special attention has been given to lyotropic liquid crystal polymer solutions that are characterized by a wide range of unusual rheological phenomena (Peuvrel and Navard 1990,1991 Marrucci and Greco 1993). The viscosity of such solutions presents a particular variation with concentration. Isotropic solutions exhibit a monotonic increase in shear viscosity with their increasing concentration. The viscosity reaches a maximum value, which indicates the transition from isotropic to anisotropic state. Upon formation of the anisotropic phase, the viscosity starts to decrease. From then on, the viscosity begins to increase exponentially as the concentration continues to increase (Figure 5.3). 

E. M. Andresen and G. R. Mitchell, Orientational behaviour of thermotropic and lyotropic liquid crystal polymer systems under shear flow. Europhys. Lett. 43, 296-301 (1998). 

Zhu H.G., Jones D.J., Zajac J., Roziere J., Dutartre R. Periodic large mesoporous organosilicas from lyotropic liquid crystal polymer templates. Chem. Cornmun. 2001 2568-2569... 

Schematic illustration of some different phase structures (direct or reverse) observed in liquid crystalline domains of lyotropic liquid crystal polymers.

Although the phase structures presented by thermotropic and lyotropic liquid crystal polymers are usually different this is not always true. For example, cubic phases are more abundant in lyotropic liquid crystals, but some thermotropic phthalocyanine derivatives [39,40] also exhibited this kind of phase... 

Zhou M, Kidd TJ, Noble RD, Gin DL. Supported lyotropic liquid-crystal polymer membranes promising materials for molecular-size-selective aqueous nanofiltration. Adv Mater 2005 17 1850-3. 

---