CONCENTRATED SOLUTIONS OF RIGID RODLIKE POLYMERS

As mentioned in Section 9.1, in a solution of rodlike polymers of length L and diameter b, the excluded volume effect becomes important in the concentration regime 

The most spectacular aspect in such a solution is that above a certain concentration, the polymers spontaneously align in a certain direction, and the solution becomes anisotropic without any external fields. Such a solution is called a liquid crystal. 

The term liquid crystal is generally used to represent the state of matter which has the fluidity of a liquid and the molecular ordering of a crystal. Historically, liquid crystals were first found for low molecular weight materials, and a great deal of work has been done for those materials, much of which is summarized in monognq hs.  

On the macroscopic level, nematics have uniaxial symmetry around a certain direction denoted by a unit vector n called the director. There is reflection symmetry with respect to the plane normal to (thus the state designated by n is the same as that designated by —n). 

On the microscopic level, nematics are characterized by the fact that the equilibrium distribution function W( ) for the molecular direction is not isotropic. The anisotropy is conveniently represented by the tensor 

---