Long range three dimensional order

In the first case, there is only partial instead of complete long-range three-dimensional order. Fiber spectrum features are diffuse haloes (besides sharp reflections) on the layer lines. 

Examples of mesomorphic forms characterized by disorder in the conformation of the chains have already been described in Section 2.6. For instance, a mesomorphic form is present in the high-temperature form I of polytetrafluoro-ethylene.106,107 In this phase the chains are in disordered conformation due to the presence of helix reversals along the chains.108-110 Moreover, intermolec-ular disorder is also present due to the random rotations of the chains around the chain axes.109 A long-range three-dimensional order is present only in the pseudohexagonal placement of the chain axes.107,109... 

Solid polymers can occur in the amorphous or crystalline state. Polymers in the amorphous state are characterized by a disordered arrangement of the macromolecular chains, which adopt conformations corresponding to statistical coils. The crystalline state is characterized by a long-range three-dimensional order (order extending to distances of hundreds or thousands... 

Between the crystalline state (characterized by a long-range three-dimensional order), and the amorphous isotropic state, there is an intermediate state of matter referred to as liquid crystal. It is specific to certain molecules, which simultaneously exhibit order like crystals and flow like fluids. Reinitzer, who observed that cholesteric esters form opaque liquids that become transparent upon raising the temperature, is considered as the precursor of this field. In addition to the term liquid crystal, mesomorphic or mesophase can also be used (from Greek mesos meaning median ) to name this intermediate state between an isotropic liquid state and the three-dimensional crystalline order as first proposed by Friedel. Molecules that adopt a preferential orientation and result in an anisotropy are called mesogens. 

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