Isotropic polymeric liquid

To determine if this phenomenon is isolated to amorphous monomers, a liquid crystalline diacrylate (C6M) was polymerized in W7,W82 at temperatures corresponding to the two smectic phases as well as the isotropic phase. The polymerization rate for C6M is plotted as a function of time for representative temperatures in Figure 6. Again, the polymerization shows marked acceleration in the ordered smectic C phase and occurs much faster than the isotropic polymerization. As seen in the HDDA polymerizations, the smectic A rate also lies between the rates of the other two polymerization temperatures. 

A relatively recent field in polymer science and technology is that of the polymeric liquid crystals. Low molecular liquid crystals have been known for a long time already they were discovered almost simultaneously by Reinitzer (1888) and Lehmann (1889). These molecules melt in steps, the so-called mescrphases (phases between the solid crystalline and the isotropic liquid states). All these molecules possess rigid molecular segments, the "mesogenic" groups, which is the reason that these molecules may show spontaneous orientation. Thus the melt shows a pronounced anisotropy and one or more thermodynamic phase transitions of the first order. 

While it was assumed above that only G. is affected by thermal history, in the case of main chain polymeric liquid crystals pronounced time dependent variability in G c has recently also been observed (7,8). It was shown that the lack of equilibrium perfection in the nematic phase can lead to substantial depression of the isotropization temperature T c =T. Thus non-equilibrium mesomorphic states can also, in principle, affect the phase sequence-(enantiotropic, monotropic) in the case of polymeric liquid crystals. 

In this paper, an earlier theory (12-13) for binary mixtures of backbone LCPs (and/or nonpolymeric molecules) in the nematic (N) LC phase and the isotropic (I) liquid phase has been extended to treat binary mixtures in multiple smectic-A (SA) LC phases, the N LC phase, and the I liquid phase. Either component 1 (Cl) and/or component 2 (C2) in the mixture can be a backbone LCP, a nonpolymeric LC molecule, a polymeric non-LC molecule, or a nonpolymeric non-LC molecule. Cl can also be a side-chain LCP or a combined LCP (including a SS LCP). The new theory of this paper is the mixture analogue of an earlier theory for pure (single-component) systems derived and presented in detail in References 3 and 7-10 (see also References 14-23). When only one component is present, the new mixture theory of this paper reduces to this earlier single-component theory. Therefore, only a short summary of the new mixture theory is presented here. 

During the last ten years the interest in polymeric liquid crystals (PLCs) has been growing rapidly. Nevertheless our fundamental understanding of their flow behaviour is still rather limited. This is due to the fact that PLC rheology is much more complicated than that of ordinary isotropic polymeric fluids (1). Systematic and reliable data are lacking so far although this is the kind of information needed for the development and assessment of theoretical models for these unusual fluids. 

Let us consider the three additional examples just mentioned. First, we need to identify the features, in each case, that define the microstructural state. In the case of the emulsion or blend, the most important microscale feature that can be influenced by the flow is the orientation and shape of the disperse-phase bubbles or drops (the mean drop size and drop-size distribution will also generally be important and can be influenced by flow-induced drop breakup and coalescence events, but we will ignore this extra complication for purposes of our current discussion). At equilibrium, the drops will be spherical and the microstructure isotropic. For polymeric liquids, it is the statistical configuration of the polymer molecules... 

Orthoscopic examination with crossed polars is carried out first of all to determine the isotropism or the anisotropism of a sample. The polarization colors, the defects and variation in molecular orientation, and the orientation pattern or texture of liquid crystals are observed in this examination. With a heating stage the temperature of phase transition is also determined. In addition, with use of a compensator, the determination of vibration directions of the ordinary and extraordinary rays, the determination of relative retardation and birefringence are possible. In this section, the optical basics for orthoscopic observations are briefly outlined. The description of textures frequently observed for polymeric liquid crystals is given in Section 4.1.4. 

Freely-suspended Films of Polymeric Liquid Crystals. The stabilization of freely-suspended films by using polymeric liquid crystals is obviously interesting and has been attempted previously. Unfortunately it seems to be extremely difficult to polymerize films of liquid crystalline monomers as these films were reported to always break during polymerization. It seems to be equally difficult to fabricate FS-films of polymeric liquid crystals in their smectic A and smectic C phases, most likely due to their enhanced viscosities. However, if one heats slightly into the isotropic phase it is possible to spread a film across an aperture which thins out to form a truly freely-suspended liquid crystal film after cooling into the smectic phases (57). Films of this type are homeotropic in the smectic A phase and show birefringence when cooled to the ferroelectric smectic C ... 

In conclusion, the molecules of a polymeric liquid in flow, depending on the gradient rate, can be oriented and deformed significantly, compared to the isotropic structure, which prevails in the stationary liquid. If the macromolecules have already been partially oriented into liquid state, the change of the entropy is reduced and the crystals are easily formed. The kinetics of the crystallization process is considerably accelerated and the structure of the crystals that are produced is affected. 

Fluctuation effects are large in polymeric liquid crystals even far from phase transition temperatures. For example, in a novel liquid crystalline elastomer with a SmA-I transition, under an external mechanical stress, it was found in a mean field limit that, well in the isotropic phase, nematic fluctuations dominate with a cross-over temperature closer to the transition where SmA fluctuations become more important [14]. 

Dealy JM, Larson RG (2006) Structure and rheology of molten polymers from polymerization to processability via rheology. Cincinnati Hanser Gardner, Cincinnati Doi M (1981) Molecular dynamics and rheological properties of concentrated solutions of rodlike polymers in isotropic and liquid crystalline phases. J Phys Sci 19 229-243 Doi M, Edwards SF (1978) Dynamics of rod-like macromolecules in concentrated solution. Part 1. J Chem Soc Mol Chem Phys 74 560-570... 

Characterization439 Inherent viscosity before and after solid-sate polymerization is 0.46 and 3.20 dL/g, respectively (0.5 g/dL in pentafluorophenol at 25°C). DSC Tg = 135°C, Tm = 317°C. A copolyester of similar composition440 exhibited a liquid crystalline behavior with crystal-nematic and nematic-isotropic transition temperatures at 307 and 410°C, respectively (measured by DSC and hot-stage polarizing microscopy). The high-resolution solid-state 13C NMR study of a copolyester with a composition corresponding to z2/zi = 1-35 has been reported.441... 

A review of the literature demonstrates some trends concerning the effect of the polymer backbone on the thermotropic behavior of side-chain liquid crystalline polymers. In comparison to low molar mass liquid crystals, the thermal stability of the mesophase increases upon polymerization (3,5,18). However, due to increasing viscosity as the degree of polymerization increases, structural rearrangements are slowed down. Perhaps this is why the isotropization temperature increases up to a critical value as the degree of polymerization increases (18). 

For a nematic polymer in a transition region from LC to isotropic state, maximal viscosity is observed at low shear rates j. For a smectic polymer in the same temperature range only a break in the curve is observed on a lgq — 1/T plot. This difference is apparently determined by the same reasons that control the difference in rheological behaviour of low-molecular nematics and smectics 126). A polymeric character of liquid crystals is revealed in higher values of the activation energy (Ef) of viscous flow in a mesophase, e.g., Ef for a smectic polymer is 103 kJ/mole, for a nematic polymer3 80-140kJ/mole. 

Examples of these formulations are systems based on a difunctional LC epoxy monomer (diglycidyl ether of 4-4 -dihydroxy-Q -methylstilbene), cured with methylene dianiline (Ortiz et al., 1997). The generation of liquid-crystalline microdomains (smectic or nematic) in the final material required their phase-separation before polymerization or at low conversions. This could be controlled through the initial cure temperature. Values of GIc, (kJm-2) were 0.68 (isotropic), 0.75 (nematic), and 1.62 (smectic). The large improvement produced by the smectic microdomains was attributed to an extensive plastic deformation. 

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