Liquid crystallinity polymers

A novel second-order nonlinear optical medium which should offer considerable fabrication flexibility has been described. The physics of alignment of the highly nonlinearly polarizable moiety was discussed. However, observation of complex dynamical and thermal behavior indicates that an important role is played by the polymer liquid crystalline host. Additional properties of modified members of this family of lc polymers were consequently investigated. The explanations of guest alignment stabilization and thermal dependence of the alignability remain unresolved issues. 

An earlier study of the molecularly doped polymer liquid crystalline system shown in Figure 6.9 revealed more complex behavior (27, 32). In this study, the amount of induced nonlinearity was path dependent, with the largest observed value occurring when poling was done near Tg ( 25 C). The host polymer exhibits a nematic-to-isotropic transition at = 100 C and a nematic texture between Tg and. Poling at 50 C produces a decrease in approximately 1 order of magnitude. The l/T dependence... 

Investigations into the Structure of Liquid-Crystalline Polymer—Liquid-Crystalline... 

Some polymers manifest liquid crystalline ordering, which does not have the full long-range three-dimensional periodicity of crystallinity but is far more ordered than amorphicity. Since many excellent books and articles have been published on such polymers and the author does not have much that is new to add to this background information, very little will be said about polymer liquid crystallinity in this book. Van Krevelen [3] has reviewed liquid crystallinity in polymers in a readable manner and discussed its effects on properties for which quantitative structure-property relationships are available. Adams et al [41] have published a valuable compendium of articles covering the theory, synthesis, physical chemistry, processing and properties of liquid crystalline polymers. Woodward [42] has discussed and illustrated liquid crystallinity in polymers with many beautiful micrographs. 

The purpose of this chapter is to explain theoretically the formation of liquid crystal phases in polymer systems and to provide the basic concepts for designing and synthesizing liquid crystalline polymers. Liquid crystalline polymers combine features of both polymers and liquid crystals, thus we discuss the materials from two sides liquid crystallinity and polymer properties. Theoretical descriptions have encountered many difficulties in the past. One is that the present theoretical understanding of neither polymers or liquid crystals is complete. 

Like other crystalline polymers, liquid crystalline polymers can also exhibit multiple melting peaks when studied with DSC. Multi-melting is common to crystalline polymers including single crystals of polyethylene. For example, Bair et al. (1967) found the single crystals of PE grown... 

Specific blends, which could offer an interesting combination of properties with proper com-patibilization, include PPS/PSE, PEl/PPS, PA/PSE, PA/PEI, and PC/PPS. Patent activity has been noted for most of these blend combinations as well as other selected blends involving engineering polymers as noted in Table 17.3. A number of recent patent and published papers have discussed blends of engineering polymers with various specialty polymers including high temperature polymers, liquid crystalline polymers (LCP s), conductive polymers, and as matrix materials for molecular composites. These will be discussed in the following sections. 

The symmetry requirements necessary for ferroelectricity in low-molecular mass compounds, which were discussed in Section 1.1.3, are valid for polymer mesophases too. If a tilted chiral smectic phase is stable after a polymerization process it must be ferroelectric. Following this idea, the first polymer liquid crystalline ferroelectric has been synthesized by Shibayev et al. [160]. Its spontaneous polarization did not differ very much from the precursor monomer [161]. After polyvinylidene fiuoride (PVF2)... 

Optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are major techniques for the assessment of morphology of semicrystalline polymers, liquid-crystalline polymers and polymer blends. The list of applications in other areas of polymer science and technology is extensive. 

These materials are compatible with semiconductor technology. Low-oost thin films or waveguiding structures of polymers can be fabricated easily by fomiliar spincoating processes which meet the requirements of integrated nonlinear optics. Polymers and. in particular, side-chain polymers, liquid crystalline or amorphous ones, offer a high potential for molecular engioeering. 

Krishnan, S., Kwark, Y.-J., and Ober, C.K. (2004) Fluorinated polymers Liquid crystalline properties and applications in lithography. Chemical Record, 4,315-330. 

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