Lyotropics elastic properties

Flexibihty of the moieties is another important parameter because it was recently shown that flexible objects require larger volume fractions to undergo nematic ordering. Flexibihty also reduces the nematic order parameter at the transition. Intuitively, very flexible mineral polymers should not show any orientational order at rest, but may display a strong flow birefringence. Thus, any soluble system where the structural unit in the solid state is anisotropic may not necessarily be a lyotropic Hquid crystal. For example, in solution a polymer is much less constrained than in the soHd state, and hence one must consider the elastic properties of the polymer chain and whether the anisotropic units still exist in solution. As shown recently for the case of the complex fluid with a min-... 

The discussion of mechanical properties comprises the various contributions of elastic, viscoelastic and plastic deformation processes. Often two characteristic stress levels can be defined in the tensile curve of polymer fibers the yield stress, at which a significant drop in slope of the stress-strain curve occurs, and the stress at fracture, usually called the tensile strength or tenacity. In this section the relation is discussed between the morphology of fibers and films, made from lyotropic polymers, and their mechanical properties, such as modulus, tensile strength, creep, and stress relaxation. 

We conclude the discussion on TCP rheology by drawing attention to the phenomenon of band formation - a serpentine distortion of the director field caused by shearing [107], Although the mechanism is not fully understood (two orthogonal deformations of the director field appear [108] to be necessary simple shear and perhaps Frank elasticity orthogonal to the shear direction), it would appear to be very important in processing LCPs. A periodic orientational distortion reminiscent of the banded texture is observed in monofilaments that are spun from lyotropic LCPs, and its influence on the ultimate mechanical properties of the fiber has been discussed (see below). 

As mentioned, a lot of theoretical and experimental studies have been performed to understand physics and rheological properties of lyotropic LCPs. The molecular Doi approach with many improvements and experimental tests is well presented in the literature (e.g., see Ref. [5]). But the thermotropic LCPs were poorly understood till recently, in spite of many attempts to develop either nematodynamic or molecular description of their flow properties. The beauty of continuum approach is that it can be applied to molecular nematics ofboth different types, as well as to the nonyielding suspensions with shaped particles. Yet, general nematodynamic theories are multi-parametric. For example, the general LEP continuum LC theory contains five constitutive parameters [2]. Similarly, de Gennes potential proposed for the monodomain description of general weakly elastic behavior of LCE has also five parameters [37]. Because viscoelasticity is a combination of elastic and viscous effects, it is expected that even in easy theoretical schemes, the continuum approach to viscoelastic polymer nematodynamics should involve at least 10 constitutive parameters. 

A lyotropic L.C. consists of two or more components that exhibit L.C. properties in certain concentration ranges. In the lyotropic phases, solvent molecules fill the space around the compounds to provide fluidity to the system. In contrast to thermotropic L.C.s, these lyotropics have another degree of freedom, i.e., the concentration, which enables them to induce a variety of different phases. Since lyotropic L.C.s rely on a subtle balance of intermolecular interactions, it is often more difficult to analyse their structures and properties than those of thermotropic L.C.s. Lyotropic L.C. nanostructures are abundant in living systems. Accordingly, lyotropic L.C.s attract particular attention in the field of biomimetic chemistry. In particular, biological membranes and cell membranes are a form of L.C. Their constituent rod-like molecules e.g., phospholipids) are organized perpendicularly to the membrane surface, yet the membrane is fluid and elastic. The constituent molecules can flow in-plane quite easily, but tend not to leave the membrane, and can flip from one side of the membrane to the other with some difficulty. These... 

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