Polyphilic compounds

Fig. 13. X-ray intensity profile with diffi action vector along qx (in the plane of layers) in the smectic X phase for the mixture of polyphilic compounds M70. The solid line through the data points is the smn of three Lorentzian peaks which are shown hy broken curves (Blinov et al. [44])...

Fig. 14. Temperature dependences of the layer spacing in the smectic Ad and Cd phases for terminally polar polyphilic compounds F4H11OCB (squares), FsHnOCB (circles), FgHioOCB (triangles) and FioHnOCB (diamonds). The arrows indicate the smectic Ad - smectic Cd phase transition points (Ostrovskii et al. [45])...

Fig. 16a-c. Structure of the smectic Aj and Ca layers for the polyphilic compound FsHnOCB a smectic Aj layers b steric mismatch in the limit case of hilayer A2 layering c smectic Ca layers... 

Recently, polyphilic compounds have been reported, where an Rp-chain and a carbosilane chain were attached at opposite sides of a terphenyl or oligo (p-phenylene ethinylene) core [42], Compound 188 with the longest oligo (p-phenylene ethinylene) core shows two hexagonal columnar phases separated by a thermoreversible continuous (second order) phase transition with critical behavior upon approaching the transition temperature. Based on XRD data it was... 

Most of the amphiphiles discussed hitherto have only two distinct parts in their molecules which are different in their polarity. Polyphilic compounds possess more than two of them (see Fig. 33) depicting the cal-amitic biphenyl derivative 50 with three different parts a polyfluorinated one, an alkoxy chain, and the aromatic (biphenyl) section. The mesomorphic properties of this triphilic examples are compiled in Table 15. 

The polyphilic quality leads to a further ordering of the molecules in their meso-phase Fig. 34 gives a simple schematic drawing of a directed lamellar phase. The molecules have a polar orientation within the layers and long range correlations between them. This special mesophase structure causes macroscopically polar properties. With regard to this kind of molecular arrangement some polyphilic compounds have been successfully studied in respect of ferroelectric properties [161-165]. 

Actually, such bowl phases are still to be found. However, polar achiral phases have been observed in the so-called polyphilic compounds [8]. The rod-like molecules of these compounds consist of distinctly different chemical parts, a hydrophilic rigid core (a biphenyl moiety) and hydrophobic perlluoroalkyl- and alkyl-chains at opposite edges. Such molecules form polar blocks that, in turn, form a polar phase manifesting pyroelectric and piezoelectric properties with a field-induced hysteresis characteristic of ferroelectric phases. 

Compounds like 88 (Fig. 25a), in which the Rp-segments are decoupled from the rod-like core by longer aliphatic spacers, can be regarded as polyphilic ABC molecules which are expected to lead to triply segregated smectic phases as shown in Fig. 19c. However, in compound 88, for example, the SmA-phase is composed of only two sets of distinct sublayers, though there are three mutually incompatible... 

Fig. 46 Examples of polyphilic rod-like compounds and possible modes of self-assembly of compound 174 (a) segregated non-centrosymmetric layer which would lead to longitudinal ferroelectricity if adjacent layers would organize with the same direction and (b) non-segregated centrosymmetric layer [297]...

Attaching only one lateral chain to the rod-like core (T-shaped amphiphiles 181-183) gave rise to LC honeycomb phases where the cross-section of the honeycomb walls contains two rods arranged side-by-side, i.e., the honeycombs have double walls (Fig. 61a) [8]. However, attaching two lateral chains to opposite sides of the aromatic core (X-shaped polyphiles like compound 187) generates polygonal honeycombs with walls that are only one molecule thick (Fig. 61b) [319]. As a consequence of the thinner walls, effectively more space is left available for the lateral chains inside the cells. Hence, honeycombs with smaller cells could be achieved by using two short lateral chains instead of only one chain with the same total volume [330]. 

Based on the concept of competitive polyphilicity, it was possible to increase the complexity of LC phases considerably [3, 4, 9, 137-140]. This concept was successfully applied to two types of T-shaped ternary amphiphiles, namely bolaamphiphiles [141, 142] and facile amphiphiles [143-147]. Both kinds of compounds are composed of rodlike aromatic cores, two end-groups, and one (T-shaped), two (X-shaped) or more chains attached laterally to the core. Numerous honeycomb-like... 

In conclusion, electric field effects in liquid crystals is a well-developed branch of condensed matter physics. The field behavior of nematic liquid crystals in the bulk is well understood. To a certain extent the same is true for the cholesteric mesophase, although the discovery of bistability phenomena and field effects in blue phases opened up new fundamental problems to be solved. Ferroelectric and antiferroelectric mesophases in chiral compounds are a subject of current study. The other ferroelectric substances, such as discotic and lyotropic chiral systems and some achiral (like polyphilic) meso-genes, should attract more attention in the near future. The same is true for a variety of polymer ferroelectric substances, including elastomers. 

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