Rheology liquid-crystalline polymers

Liquid crystalline polymers (LCPs), 49 melt rheology of, 52 Liquid crystalline (LC) state, 48-49 Liquid crystalline thermotropic polyesters, 20... 

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

Liquid-crystalline polymers with stiff backbones have many static and dynamic solution properties markedly distinct from usual flexible polymers. For example, their solutions are transformed from isotropic to liquid crystal state with increasing concentration. While very high in the concentrated isotropic state, their viscosity decreases drastically as the concentration crosses the phase boundary toward the liquid crystal state. The unique rheological properties they exhibit in the liquid crystal state are also remarkable. 

RHEOLOGICAL PROPERTIES OF THERMOTROPIC LIQUID CRYSTALLINE POLYMERS... 

The big difference between normal isotropic liquids and nematic liquids is the effect of anisotropy on the viscous and elastic properties of the material. Liquid crystals of low molecular weight can be Newtonian anisotropic fluids, whereas liquid crystalline polymers can be rate and strain dependent anisotropic non-Newtonian fluids. The anisotropy gives rise to 5 viscosities and 3 elastic constants. In addition, the effective flow properties are determined by the flow dependent and history dependent texture. This all makes the rheology of LCPs extremely complicated. 

Beekmans F, "Rheology and Changes in Structure of Thermotropic Liquid Crystalline Polymers", PhD Thesis, Delft, 1997. 

Liquid crystalline polymers (LCPs) have gained attraction as materials with interesting optical, mechanical and rheological properties [3-7]. This review summarizes research on thermotropic liquid crystalhne polymers synthesized by metathesis routes, as this chemistry has proven to be a versatile way to build up well-defined polymer architectures [8]. Recent results promise to ejq)and the possible uses of these methods. 

The rheological and flow properties of ordered block copolymers are extraordinarily complex these materials are well-deserving of the apellation complex fluids. Like the liquid-crystalline polymers described in Chapter 11, block copolymers combine the complexities of small-molecule liquid crystals with those of polymeric liquids. Hence, at low frequencies or shear rates, the rheology and flow-alignment characteristics of block copolymers are in some respects similar to those of small-molecule liquid crystals, while at high shear rates or frequencies, polymeric modes of behavior are more important. 

This chapter provides an overview of current researches on liquid crystalline polymers (LCPs). Topics include syntheses of main-chain and side-chain LCFs, structured characterization of LCFs and LCP networks and rheology and processing. Applications of LCP/polymer blends as self-reinforced polymers and electro-optical meterials are also discussed. 

Burghardt, W.R. Molecular orientation and rheology in sheared lyotropic liquid crystalline polymers. Macromol. Chem. Phys. 1998, 199 (4), 471-488. 

S.D. Rheological differences among liquid-crystalline polymers. II. Disappearance of negative N1 in densely packed lyotropes and thermotropes. 

Harrison, P. Navard, P. Cidade, M.T. Investigation of the band texture occurring in acetoxy-propyl cellulose thermotropic liquid crystalline polymer using rheo-optical, rheological, and light scattering techniques. Rheol. Acta 1999, 38 (6), 594-605. 

S. Saengsuwan, S. Bualek-Limcharoen, G. R. Mitchell, and R. H. Olley. Thermotropic liquid crystalline polymer (Rodrun LC5000)/polypropylene in situ composite films Rheology, morphology, molecular orientation and tensile properties. Polymer, 44 3407-3415, 2003. 

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