Liquid Crystal Templating

Kresge C T, Leonowicz M E, Roth W J, Vartuli J C and Beck J S 1992 Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism Nature 359 710-12... 

Kokufuta, E Jinbo, E, A Hydrogel Capable of Facilitating Polymer Diffusion through the Gel Porosity and Its Application in Enzyme Immobilization, Macromolecules 25, 3549, 1992. Kresge, CT Leonowicz, ME Roth, WJ Vartuli, JC Beck, JS, Ordered Mesoporous Molecular Sieves Synthesized by a Liquid-Crystal Template Mechanism, Nature 359, 710, 1992. 

Olson, D.H., Sheppard, E.W., McCullen, S.B., Higgins, J.B. and Schlenker, J.L. (1992) A new family of mesoporous molecular-sieves prepared with liquid-crystal templates. Journal of the American Chemical Society, 114, 10834-10843. 

Keywords non-isothermal kinetics, open-framework, TG analysis, SBA-3, cetyltrimethylammonium bromide (CTMAB), liquid-crystal templating. 

Figure 30. Representation of the MCM-41-liquid-crystal templating process. [Adapted from (169).]...

In 1992, Mobil researchers reported the discovery of a family of me-soporous molecular sieves prepared with liquid crystal templates [18]. One member of this family, designated MCM-41, has hexagonally packed pores, which are highly monodisperse. Moreover, the size of these pores can be... 

Membrane templating is capable of producing a range of structures in various sizes. However, the degree of control is not at the molecular scale. An alternative templating method that has molecular-level control over the pore size and the ability to produce ordered arrays of pores is lyotropic liquid crystal templates [53]. Lyotropic liquid crystals are surfactant phases produced at high percentages of surfactant to solvent. 

Figure 1.15 TEM image of Pt nanoparticles that have been produced by lyotropic liquid crystal templating. Porous structures can be seen and are spaced in an hexagonal array. (Reprinted with permission from Ref [54], 1997 Wiley-VCH Verlag GmbH, Co. KCaA.)...

Zeolitic structures with pore sizes of 2000 to 10000 pm are known as mesoporous solids, and can be formed by a method known as liquid crystal templating (LCT). The combination of a suitable cationic surfactant together with silicate anions form arrays of rod-like surfactant micelles (Figure 3.7) surrounded by a polymeric siliceous framework. On calcination the mesoporous structure is formed. 

FIGURE 3.7 The formation of mesoporous MCM-41 by liquid crystal templating. 

FIGURE 7.21 (a) Possible preparative route for the formation of MCM-41 by liquid crystal templating (b) computer graphic of ethane and methane molecules inside one of the hexagonal pores of MCM-41. See colour insert following page 356. (Courtesy of Vladimir Gusev, Romania.)... 

Fig. 77. Schematic drawing of the liquid-crystal templating mechanism. Hexagonal arrays of cylindrical micelles form (possibly mediated by the presence of silicate ions), with the polar groups of the surfactants (light grey) to the outside. Silicate species (dark grey) then occupy the spaces between the cylinders. The final calcination step burns off the original organic material, leaving hollow cylinders of inorganic material [473]...

In-depth investigations into the formation process of these composite materials— which can be rightly called complex—have found that two different mechanisms can be involved On one hand, in true liquid-crystal templating (TLCT), the concentration of the surfactant is so high that under the prevailing conditions (temperature, pH) a... 

Figure 3.4 Formation of mesoporous materials by structure-directing agents (a) true liquid-crystal template mechanism, (b) cooperative liquid-crystal template mechanism.

Stucky et al.10 and Monnier and coworkers.11 A more recent study by Gov and coworkers showed that, on addition of the silica source, the interactions between surfactant molecules are changed to reduce their curvature leading to structural changes in the mesophase.12 However, when the syntheses are performed at high surfactant concentrations, they are considered to proceed through a preexisting liquid crystal template (route c in Fig. 16.2).13... 

Kresge, C. T., Leonowicz, M. E., Roth, W. J., Vartuli, J. C. and Beck, J. S. Ordered mesoporous molecular-sieves synthesized hy a liquid-crystal template mechanism, Nature, 1992, 359, 710-712. 

Fig. 3. Schematic representation of the formation of MCM-41 by the liquid-crystal templat-ing mechanism, (a) Hexagonal array of cylindrical micelles (b) the same, with silicate species between the cylinders and (c) hollow cylinders of MCM-41 after thermal elimination of organic material. (Rouquerol, Rouquerol and Sing, 1999).

Different mechanisms for the interactions between the silicate precursors and the organic template as well as the liquid crystal templating mechanisms have been discussed (Ying, Mehnert, and Wong, 1999 Tanev and Pinnavaia,... 

For mesoporous silica (pore 0>2O A), successful results were obtained by the synthesis of the MCM family of silicates and aluminosilicates (of Section II.B). Their preparation is achieved by liquid crystal templating and micellar phases (hexagonal MCM-41, cubic MCM-48, laminar MCM-50)36,37 and further developments are currently reviewed38. 

In addition to the opportunities for new materials synthesis and characterization along these lines, transport properties, rheology, and processing techniques for liquid crystal polymers are essentially unexplored. Experiences with synthesis of polymer structure based on these liquid crystal templates may open up other creative avenues for template synthesis, for example, inside other crystalline structures, chlathrates, or zeolites, or on surfaces [4], Composites, alloys, or mixtures of liquid crystalline and flexible polymers may produce new materials. 

As mentioned previously, mesoporous inorganic materials can be formed by one of two reaction pathways, liquid-crystal templating and cooperative self-... 

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