Mesophases morphology

Whereas the mesophase morphologies of compounds 35-37 depend on the size ratio of polar and apolar segments, the mesophase stabilities are mainly influenced... 

Besides the simple effects of mesophase stabilization by increased polar-apolar incompatibility and modification of mesophase morphology due to size effects, there are additional specific effects based on the lipophobicity (R[ -RH incompatibility) and rigidity of perfluorinated segments. In this respect it is important to... 

Fig. 47 (a) Examples of polyphilic molecules with star shaped molecular topologies and (b) their mesophase morphologies [295]. (c) Janus-type porphyrin 177 [277] and (d) modes of self assembly of the completely RF-substituted porphyrin 156 left, for structure see Fig. 42, Colortho G -29 °C Colortho199 °C Iso) and the partly fluorinated porphyrin 177 right, ColTeJp2mg, Cr -22 °C Co n,Jp2mg 163 °C Iso) Colortho = orthorhombic columnar 3D phases (b) Reproduced with permission [295], copyright 2008, The Royal Society of Chemistry (RSC) (d) reproduced with permission [277], copyright 2011, American Chemical Society (ACS)...

Polymers with poly(ethylene oxide) spacers were shown to have transition temperatures similar to those for polymers with polymethylene spacers of the same length, but the mesophases formed could be quite different, which again emphasizes the importance of the spacer in determining mesophase morphology. Furthermore, polymers with polysiloxane spacers and mesogenic units, identical to those present in polymers with polymethylene spacers having a comparable number of bonds, showed different mesophase structures in addition to much lower transition temperatures. 

Mesophase Morphologies of Silicone Block Copolymers in a Selective Solvent Studied by SAXS... 

C. Tschierske, Micro-segregation, molecular shape and molecular topology partners for the design of liquid crystalline materials with complex mesophase morphologies, J. Mater. Chem. 11(11), 2647-2671, (2001). 

The questions concerning the nature of nematic PLC morphology and of the molecular organization on the local scale still remain open. If the N phase does indeed tolerate nematic—isotropic fluctuations (the liquid fringed micelle model) is not clear why such fluctuations appear in the chemically ordered P5 and not in Pi polymers. It is clear, however, that mesophase morphology and the macroscopic properties that are affected by it are influenced by thermal history, as is illustrated below. 

Mesophase morphology becomes progressively homogenized upon isothermal aging in the nematic temperature range. The peak maximum moves to higher temperatures and the peak itself becomes... 

Numerous studies have been reported on the investigation of the PUs and other elastomeric materials hysteresis behaviour [284-293]. As shown, the hysteresis and the associated mechanical loss processes can be partly attributed to the breakdown and reformation of the mesophase morphology during mechanical cycling [284],... 

The synthesis of a great number of materials that exhibit the nematic phase has achieved many different goals. Firstly, much knowledge has been acquired of the effect of stmctural features and various combinations of stmctiual features on melting points, mesophase morphology, and stability. Secondly, many physical properties have been evaluated for a great niunber of nematic liquid crystals and the resrrlts have been linked to the stmcture. Thirdly, mixtures of nematic materials have been formulated that have been... 

Note that this phase sequence, can be universally observed in the thermotropic phase sequence of block copolymers and low-molecular-mass amphiphiles as well as in lyotropic detergent solvent systems. In addition to the phase sequence described above, several additional intermediate phases can occur at the transitions between different mesophase morphologies. The bicontinuous cubic phases Cub are often also included in these intermediate phases. 

There can surely be no better way of beginning a review of the physical properties of nematic liquid crystals than by discussing the effects of changing molecular structure on the melting point, transition temperatures and mesophase morphology. Such parameters are the most fundamental physical properties of liquid crystalline materials, and yet they are frequently undervalued or simply taken for granted. 

Many other structural possibilities for the terminal chains can have a great influence on melting point, transition temperatures and mesophase morphology. For example, branched chains are common, usually for the purpose of generating a chiral centre for chiral nematic or chiral smectic C liquid ciystals. The effect of the branch is to broaden the molecules and hence the transition temperatures are usually depressed significantly, often with the largest reduction in the smectic phase stability, but melting points are often not so much affected (compare compounds 29 and 30) [32]. 

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