Mesophases thermal stability

If we consider the ester groups as being part of the mesogen, then the transition temperatures for the polyesters are shifted with two more carbons to the right side of Figure 7. This will depress the transition temperatures and enlarge the mesophase thermal stability range for the polyethers even more. For the polyester with seven methylene units in the spacer, the data... 

Vastly improved mesophase thermal stabilities were obtained on the introduction... 

Three series of mesomorphic dithiobenzoatogold(III) complexes (2) have been described. They show a SmA mesophase in the range 150-200 °C [8, 9]. The thermal stability of these complexes is low and the clearing transitions occur with... 

Several mixtures of hexanethiol capped gold nanopartides and triphenylene based discotic LCs have been studied. These mixtures display liquid crystal behavior (columnar mesophases) and an enhancement in the DC conductivity, due to the inclusion of gold nanoparticies into the matrix of the organic LC [70]. Other studies of mixtures of gold nanoparticies with mesogens indude a series of cholesteryl phenoxy alkanoates. The inclusion of the nanopartides does not change the inherent liquid crystal properties of the cholesteryl derivative but the mesophases are thermally stabilized [71]. 

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). 

The mesophases formed by liquid crystalline (LC) polymers are well known to impart strength, toughness, and thermal stability to plastics and fibers (1-5). While LC polymers have been widely studied, their potential utility as coatings binders seems to have been overlooked. Among the very few reports that may describe LC polymers in coatings are patents claiming that -hydroxybenzoic acid (PHBA), a monomer commonly used in LC polymers, enhances the properties of polyester powder coatings (6-9). 

Mesophase that is thermodynamically stable over a definite temperature or pressure range. Note The range of thermal stability of an enantiotropic mesophase is limited by the melting point and the clearing point of an LC compound or by any two successive mesophase transitions. 

It is well known that some auxiliary organic components such as mesitylene can expand the mesopores of titania [6] and silica [7]. Here, DDA, TritonX-100, triethanolamine and ethanol were chosen to control the mesophase structure of the Ti-Zr samples. Considering the fast condensation of Ti- or Zr- components, these organic components may help to slow down the condensation and improve the thermal stability. 

Therefore, it is conceivable that the micropore and macropore are interparticle pores, while the mesopore presumably is the intra-particle pore. During the course of calcination, the connection of interparticle was destroyed and this finally resulted in the vanishing of macropore. Because the mesopore was the intraparticle pores, it had relative fine thermal stability though the pore size was enlarged in the calcination. The reasons may be attributed to the steric dispersant effect of non-ionic surfactant PEG [12]. In the synthesis course, PEG gave steric hindrance to the assembling of mesophase and improved the pore structure. 

Polymers with methyl substitution on the central linkage in the stilbene mesogenic group have been prepared, Polymers 4 and 5, and show strictly nematic mesophases . The methyl group seems to act mostly to inhibit the existence of smectic order, but otherwise does not influence the mesophase formation or thermal stability very much. 

There is as yet no clear-cut relationship between the molecular structure of the mesogenic..unit and the type of mesophase it forms, but several generalizations can be made. Gray and Winsor have divided these factors into how the molecular structure (1) is conducive to liquid crystal formation, (2) affects the thermal stability of the mesophase, and (3) favors the occurrence of smectic versus nematic or cholesteric liquid crystals. 

As a result of their low Tg values and lack of crystallinity, many of these polymers showed liquid crystallinity at room temperature. The liquid crystalline mesophases of the monomers were identified as nematic but the polymeric mesophases were not identified, although they possessed a very broad thermal stability between their Tg and their clearing transitions. A mesophase temperature stability of up to 170 °C was observed for the polymers with bicyclohexane central mesogenic units. These polymers showed decreases in Tg and Tj with increased spacer lengths. 

The presence of a methyl substituent in the alkylene segment of polymers I-n decreases the thermal stability of the mesophase by 30-40 K relative to the corresponding unsubstituted samples III-n, whereas the range of persistence remains essentially the same (Figure 1). However, for polymers I-n the isotropization entropies are much lowered and the even-odd alternations are... 

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