Solid mesophases

Liquid crystalline mesophases can also be prepared in non-aqueous solution. Using ethanolic solutions of non-ionic block copolymers as a medium, Zhao et for example, have developed a route by which mesoporous metal phosphates and borates can readily be prepared. A mixture of the metal alkoxide and the acidic chloride is used to give a complex in ethanolic solution. This acid-base pair reacts in one component of the liquid crystalline assembly to give a mesophase solid of uniform composition. Evaporation of the ethanol leaves the mesostructure. This appears to be one of the most promising routes to the formation of non-silica mesoporous solids. Many reports of these solids have appeared, particularly of metal oxides such as titanium dioxide, but loss of ordering on the mesoscale frequently occurs upon template removal. The route of Sanchez, which involves the use of titanate precursor species in the sol-gel, is a promising approach to stable mesostructured titania that retains its porosity. 

Figure 1.11 Transition temperatures for n-ASOB from DSC measurements [111]. Open symbols are for transitions approached from higher temperatures and solid symbols are for transitions approached from lower temperatures. Circles isotropic-mesophase squares mesophase-solid triangles solid-solid.

P. Kekicheff, H. K. Christenson. Forces measured in a swollen smectic lyotropic lamellar mesophase confined between solid surfaces. Phys Rev Lett (55 2823-2826, 1989. 

Solid-state C NMR techniques have been applied to the characterization of the different phases of several polybibenzoates [25,30], including P7MB, PDTMB and PTEB. The last two polymers offer the advantage of the stability of the mesophase at room temperature. The spectra corresponding to the pure mesophase of these samples only exhibited a broad component, while the spectra of the annealed samples were separated into two components crystal and noncrystal. The shapes of the mesophase and the noncrystal components are very similar, and only modest variations in the relaxation times were observed between these two components. The degree of crystallinity of these samples was determined... 

The boundary layers, or interphases as they are also called, form the mesophase with properties different from those of the bulk matrix and result from the long-range effects of the solid phase on the ambient matrix regions. Even for low-molecular liquids the effects of this kind spread to liquid layers as thick as tens or hundreds or Angstrom [57, 58], As a result the liquid layers at interphases acquire properties different from properties in the bulk, e.g., higher shear strength, modified thermophysical characteristics, etc. [58, 59], The transition from the properties prevalent in the boundary layers to those in the bulk may be sharp enough and very similar in a way to the first-order phase transition [59]. 

The existence of the mesophase layer has been proved by infra-red spectroscopy, ESP, NMR, electron microscopy and other experimental methods. Moreover, it has been also proved that the thickness of this layer depends on the polymer cohesion energy, free surface energy of the solid, and on the flexibility of the polymer chains. 

The experimental data show that the magnitude of the heat capacity (or similarly of the specific heat) under adiabatic conditions decreases regularly with the increase of filler content. This phenomenon was explained by the fact that the macromolecules, appertaining to the mesophase layers, are totally or partly excluded to participate in the cooperative process, taking place in the glass-transition zone, due to their interactions with the surfaces of the solid inclusions. 

FIG. 35 The phase behavior of dodecane sulfonic acid with water. O, Doubly refracting material appears as the isotropic solution is cooled. <3, Isotropic solution appears as the liquid crystal is heated. CD, Crystalline solid disappears on heating. Pairs of solid points connected with the vertical dashed lines mark the appearance and disappearance of pseudoisotropy as samples are heated. The area ABC, within which the intermediate mesophase exists alone, is not precisely determined. 

One type of material that has transformed electronic displays is neither a solid nor a liquid, but something intermediate between the two. Liquid crystals are substances that flow like viscous liquids, but their molecules lie in a moderately orderly array, like those in a crystal. They are examples of a mesophase, an intermediate state of matter with the fluidity of a liquid and some of the molecular order of a solid. Liquid crystalline materials are finding many applications in the electronics industry because they are responsive to changes in temperature and electric fields. 

Liquid crystals have a degree of order characteristic of solid crystals, but they can flow like viscous liquids. They are mesophases, intermediate between solids and liquids their properties can be modified by electric fields and changes in temperature. 

The liquid crystalline phase is called a mesophase and is intermediate between solid and liquid. In this mesophase the molecules show liquid-like long-range behaviour, Le. are essentially disordered, but also some crystal-like... 

Liquid crystals form a state of matter intermediate between the ordered solid and the disordered liquid. These intermediate phases are called mesophases. In the crystalline state the constituent molecules or ions are ordered in position and orientation, whereas in the liquid state the molecules possess no positional and orientational ordering. Liquid crystals combine to some extent the properties of both the crystalline state (optical and electrical anisotropy) and the liquid state (fluidity). 

Many of the investigated mesogenic compounds show solid state polymorphism. In order to obtain useful information about the arrangement of the molecules in the mesophase from the X-ray data of the single crystals, it is important to investigate the crystal structure of those solid phase which transforms into the liquid crystalline phase. For instance, only the crystal structures of the low temperature solid phases of the compounds MBBA [138, 139], MHPOBC [159], and T15 [81] could be determined, but the... 

The conventional liquid state is described as the isotropic phase. The temperature at which the compound passes from the solid phase into a mesophase is described as the melting point and the transition temperature between a mesophase and an isotropic liquid is described as the clearing point. 

Characterization of the samples by TGA and CHN analysis shows that the template was effectively removed (C < 0.2 wt%). Small-angle X-ray scattering data of the calcined solid shows a reduction in the unit cell due to thermal shrinkage, while the values for the Fenton samples coincide with the starting precursor. Our approach therefore completely preserves the unit cell corresponding to the diameter of the micelles contained in the mesophase. 

Most solid materials produce isotropic liquids directly upon melting. However, in some cases one or more intermediate phases are formed (called mesophases), where the material retains some ordered structure but already shows the mobility characteristic of a liquid. These materials are liquid crystal (LCs)(or mesogens) of the thermotropic type, and can display several transitions between phases at different temperatures crystal-crystal transition (between solid phases), melting point (solid to first mesophase transition), mesophase-mesophase transition (when several mesophases exist), and clearing point (last mesophase to isotropic liquid transition) [1]. Often the transitions are observed both upon heating and on cooling (enantiotropic transitions), but sometimes they appear only upon cooling (monotropic transitions). 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

The simple gold 3-alkylpyrazol complex (31) has been reported showing a monotropic SmA mesophase in the range of 65-52 °C and luminescence in the solid state [60]. 

Bayon, R., Coco, S. and Espinet, P. (2005) Gold Liquid Crystals Displaying Luminescence in the Mesophase and Short F... F Interactions in the Solid State. Chemistry - A European Journal, 11, 1079-1085. 

Arias, J., Bardaji, M. and Espinet, P. (2008) Luminescence and Mesogenic Properties in Crown-Ether-Isocyanide or Carbene Gold(I) Complexes Luminescence in Solution, in the Solid, in the Mesophase, and in the Isotropic Liquid State. Inorganic Chemistry, 47, 3559-3567. 

The family of primary silver thiolate compounds AgSC H2n+1 ( = 4, 6, 8, 10, 12, 16, or 18), which in the solid state consists of 2x,[AgSR] layers, behaves as thermotropic liquid crystals. On heating, they display successively lamellar (smectic A), cubic, and micellar mesophases.969... 

Type 1 gels are mesophases that are so highly ordered that they resist disruption of their structure and are thus extraordinarily viscous, to the point of appearing solid-like, even though no high molecular weight species need be present in the system. Surfactants, both synthetic (e.g., sodium dodecylsulfate) and natural (e.g., phospholipids), and clays are typical representatives of this class. 

High porosity carbons ranging from typically microporous solids of narrow pore size distribution to materials with over 30% of mesopore contribution were produced by the treatment of various polymeric-type (coal) and carbonaceous (mesophase, semi-cokes, commercial active carbon) precursors with an excess of KOH. The effects related to parent material nature, KOH/precursor ratio and reaction temperature and time on the porosity characteristics and surface chemistry is described. The results are discussed in terms of suitability of produced carbons as an electrode material in electric double-layer capacitors. 

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