Liquid crystal polymers classification

Over the past two decades, liquid crystal polymers (LCP s) have received a considerable amount of attention in both academic and industrial laboratories. Often termed mesomorphic (meaning having "middle form"), liquid crystalline phases have a degree of order between that of the zero ordered liquid and that of the three dimensional crystal lattice. Recent reviews of liquid crystal polymers have provided a fundamental understanding of the synthesis, classification, morphology, and rheology of this unique class of materials (52-541. 

Soft materials such as liquid crystals, polymers, biomaterials, and colloidal systems touch every aspect of our lives. Not surprisingly, the rapid growth of these fields over the past few decades has resulted in an explosion of soft matter research groups worldwide. Fundamentals of Soft Matter Science introduces and explores the scientific study of soft matter and molecular self-assembly, covering the major classifications of materials, their structure and characteristics, and everyday applications. 

L2 General Classification of Liquid-Crystal Polymers and Networks... 

Polymer liquid crystals or liquid crystal polymers , is a question that baffled the editor. Several reasons for using the one or the other were put forward by several authors. Professor Brostow, who has given a classification of different architectures, prefers to go in a natural progression from monomer liquid crystals to polymer liquid crystals. On the other hand, to call the book Polymer Liquid Crystals may imply that the subject is about liquid crystals when it is really about polymers. A majority of the contributing authors preferred the term liquid crystal polymer , and as such the editor has taken refuge in the majority view. 

In many cases, these polymer chains take on a rod-like (calamitic LCPs) or even disc-like (discotic LCPs) conformation, but this does not affect the overall structural classification scheme. There are many organic compounds, though not polymeric in nature, that exhibit liquid crystallinity and play important roles in biological processes. For example, arteriosclerosis is possibly caused by the formation of a cholesterol containing liquid crystal in the arteries of the heart. Similarly, cell wall membranes are generally considered to have liquid crystalline properties. As interesting as these examples of liquid crystallinity in small, organic compounds are, we must limit the current discussion to polymers only. 

Thus, polymers with mesogenic groups in side chains form structural mesophases of the same types as low-molecular liquid crystals. This makes it possible to apply traditional mesophase classification for the description of the structure of LC polymers. At the same time, the structure of some of comb-like polymers (see Table 5) considered as crystalline, may probably be treated as one of highly-ordered smectic mesophases (SH or Sj), whose study is only started74). 

Unfortunately, at present, the relevant literature not only lacks classification of experimental data on polymeric liquid crystals, but also criteria determining the existence of the liquid crystalline state in polymers are nowhere to be found. More often than not, certain authors refer to polymer systems under study or specific states of these systems as liquid-crystal ones without sufficient grounds. 

Electrohydrodynamic instabilities in nematics could be classified according to the dependence of the threshold voltage (or field) on the physical parameters of the liquid crystal, cell geometry, field firequency, etc. Arising domain patterns also differ by the period of the structure and its orientation with respect to the initial director. We hope that this classification proves to be useful, both for finding similar instability phenomena in other liquid crystals (cholesteric, smectic, polymer liquid crystals, etc.) and for practical purposes in avoiding parasitic scattering and hysteresis effects which are undesirable in many applications. 

The polarizing light microscopy is the simplest method available to identify LC phases. This optical method has been used since the discovery of liquid crystals and has led to nematic, cholesteric and smectic classifications. The appearance of a specific texture of the melt is usually a function of the types of LC phase, and it is often possible to directly identify the type of LC phase present in a polymer melt by this optical method. The textures of various LC phases are caused by the existence of different types of defect present in the LC phases. It should be noted that microscopic observations are sometimes misleading because the development of specific textures in an LC phase can occur with great difficulty. This problem arises owing to their multiphase nature (the coexistence of polycrystalline and amorphous phases), polydispersity and/or higher viscosities of LCPs melts compared with those of LMLCs. In most cases, LCPs must be annealed for hours or days at suitable temperatures to develop specific textures. 

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