Influence of the nematic order on the rheology and conformation of stretched comb-like liquid crystalline polymers

2000 ◽  
Vol 1 (4) ◽  
pp. 301 ◽  
Author(s):  
V. Fourmaux-Demange ◽  
A. Brûlet ◽  
F. Boué ◽  
P. Davidson ◽  
P. Keller ◽  
...  
Keyword(s):  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Crystalline Polymers ◽  
Nematic Order

Liquid crystalline polymers: self-organization and assembly

1993 ◽  
Vol 344 (1672) ◽  
pp. 403-417 ◽  
Keyword(s):  
Liquid Crystals ◽  
Self Assembly ◽  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Side Chain ◽  
Simple Liquid ◽  
Crystalline Polymers ◽  
Nematic Order ◽  
Nematic State ◽  
Chain Conformations

Liquid crystal forming monomers, typically rods, can be polymerized to form long mesogenic molecules. In contrast to simple rods, these polymers often have internal degrees of freedom so that they display the subtle behaviour of both high polymers and simple liquid crystals. They can have the rod elements either concatenated as a back-bone to give main chain (MC), or pendant to a back-bone to give side chain (SC) liquid crystals, or both. The physics unique to liquid crystalline polymers (LCPS) comes from their shape being dependent on the state of nematic order. Simple systems remain molecular rods (or disks) on ordering whereas a chain extends or flattens (depending on whether or not the nematic order is prolate or oblate). New phenomena as a result of this occur in situations as disparate as networks and, it is predicted, in dielectric response. We examine both SC and MC LCPS and the mechanisms by which they order lyotropically (in solution) and therm otropically (in the melt). Various types of models will be discussed in general and then restricted to the therm otropic case, lyotropic systems being discussed in Lekkerkerker & Vroege (this volume). The transition to the ordered state is first order as in simple nematics. The main characteristics of this state are modified chain conformations and, additionally for side chain polymers, transitions between various novel competing nematic states. A form of self-assembly that is a delicate function of the nematic order is observed in transesterifying LCPS. The number of chain ends is conserved but material exchanged between chains according to whether they are in the isotropic or nematic state. We review a model of this type of self-assembly.

Nematic Order Drives Phase Separation in Polydisperse Liquid Crystalline Polymers

2000 ◽  
Vol 33 (6) ◽  
pp. 2060-2068 ◽  
Author(s):  
F. Elias ◽  
S. M. Clarke ◽  
R. Peck ◽  
E. M. Terentjev
Keyword(s):  
Phase Separation ◽  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Crystalline Polymers ◽  
Nematic Order

Structure-property relations of liquid crystalline polymers

1987 ◽  
Vol 45 ◽  
pp. 460-463
Author(s):  
Linda C. Sawyer
Keyword(s):  
Solid State ◽  
Liquid Crystalline ◽  
Structural Model ◽  
Crystalline Polymer ◽  
Liquid Crystalline Polymers ◽  
Mechanical Anisotropy ◽  
Structure Property ◽  
Preparation Methods ◽  
Crystalline Polymers ◽  
Extended Chain

Recent liquid crystalline polymer (LCP) research has sought to define structure-property relationships of these complex new materials. The two major types of LCPs, thermotropic and lyotropic LCPs, both exhibit effects of process history on the microstructure frozen into the solid state. The high mechanical anisotropy of the molecules favors formation of complex structures. Microscopy has been used to develop an understanding of these microstructures and to describe them in a fundamental structural model. Preparation methods used include microtomy, etching, fracture and sonication for study by optical and electron microscopy techniques, which have been described for polymers. The model accounts for the macrostructures and microstructures observed in highly oriented fibers and films.Rod-like liquid crystalline polymers produce oriented materials because they have extended chain structures in the solid state. These polymers have found application as high modulus fibers and films with unique properties due to the formation of ordered solutions (lyotropic) or melts (thermotropic) which transform easily into highly oriented, extended chain structures in the solid state.

Factors affecting microstructural scale in liquid crystalline polymers

1990 ◽  
Vol 48 (4) ◽  
pp. 220-221
Author(s):  
Christine M. Dannels ◽  
Christopher Viney
Keyword(s):  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Factors Affecting ◽  
Crystalline Polymers ◽  
Thermal Expansion Coefficients ◽  
Low Thermal Expansion ◽  
Lower Viscosity ◽  
Fine Microstructure ◽  
Planar Orientation ◽  
Strength And Stiffness

Processing polymers from the liquid crystalline state offers several advantages compared to processing from conventional fluids. These include: better axial strength and stiffness in fibers, better planar orientation in films, lower viscosity during processing, low solidification shrinkage of injection moldings (thermotropic processing), and low thermal expansion coefficients. However, the compressive strength of the solid is disappointing. Previous efforts to improve this property have focussed on synthesizing stiffer molecules. The effect of microstructural scale has been overlooked, even though its relevance to the mechanical and physical properties of more traditional materials is well established. By analogy with the behavior of metals and ceramics, one would expect a fine microstructure (i..e. a high density of orientational defects) to be desirable.Also, because much microstructural detail in liquid crystalline polymers occurs on a scale close to the wavelength of light, light is scattered on passing through these materials.

Gas sorption in thermotropic liquid-crystalline polymers

1990 ◽  
Vol 9 (11) ◽  
pp. 1280-1283 ◽  
Author(s):  
C. Carfagna ◽  
E. Amendola ◽  
G. Mensitieri ◽  
L. Nicolais
Keyword(s):  
Liquid Crystalline ◽  
Liquid Crystalline Polymers ◽  
Gas Sorption ◽  
Crystalline Polymers ◽  
Thermotropic Liquid Crystalline Polymers
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