Confinement of nematic liquid crystals in SBA mesoporous materials

Frunză, Ligia; Frunzǎ, S.; Schönhals, Andreas; Bentrup, Ursula; Fricke, R.; Pitsch, I.; Kosslick, H.

doi:10.1016/s0167-2991(02)80296-8

Cited by 11 publications

(6 citation statements)

References 22 publications

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“…5 Detailed knowledge of the diffusion and more general of the molecular mobility of adsorbates in such porous materials is therefore essential. However, there are only a few papers dealing with the dynamical behavior of polar, low-molecular-weight adsorbates confined to MCM-41-type molecular sieves, [6][7][8][9][10][11] and very few results referring to SBA materials have been published so far. 8,12 In this paper first results concerning the molecular mobility of water molecules confined to SBA-type nanoporous materials with a hexagonal or a cellular structure studied by dielectric spectroscopy in a broad frequency and temperature interval are presented.…”

Section: Introductionmentioning

confidence: 99%

Rotational Fluctuations of Water inside the Nanopores of SBA-Type Molecular Sieves

et al. 2005

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The rotational molecular dynamics of water confined to nanoporous molecular sieves of a regular hexagonal (SBA-15) and of a foamlike pore structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(9) Hz and in a broad temperature interval. Two relaxation processes were observed: the process at lower frequencies is related to water molecules forming a layer, which is strongly adsorbed at the pore surface, whereas the relaxation process at higher frequencies is assigned to fluctuations of water molecules situated close to the center of the pore. The relaxation times of the low-frequency process for both materials and of the high-frequency process for the SBA-15 material have an unusual saddlelike temperature dependence, reported here for the first time. To describe this temperature dependence, a model developed for water confined to nanoporous glasses by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] was applied, which considers two competing effects. The characteristic features of these two competing processes were compared with those reported for other porous systems.

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Section: Introductionmentioning

confidence: 99%

Rotational Fluctuations of Water inside the Nanopores of SBA-Type Molecular Sieves

et al. 2005

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“…On the basis of IR spectra, a strong interaction between the complex and the silanol groups of the host was suggested. Siliceous nanoporous materials had a weaker interaction than Al-containing forms . Catalysts were tested in the epoxidation of 1,2-dihydronaphthalene with sodium hypochlorite (Scheme ).…”

Section: Adsorption Methodsmentioning

confidence: 99%

Noncovalent Immobilization of Enantioselective Catalysts

2008

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“…DSC measurements were used to study the phase transition temperatures for the liquid crystal embedded in the pores of the nanoporous molecular sieves. It was found that the temperature of the N-I transition is clearly shifted downward 24 . The freezing temperature under these confined conditions is also depressed when comparing with the bulk, but changes of the other phase transitions are less evident due to the peak rounding.…”

Section: Lc-surface Interactionsmentioning

confidence: 99%

Dynamic behavior of hybrid organic-inorganic composites: liquid crystals confined in SBA-15 mesoporous materials

Frunză

Kosslick²,

Schönhals

et al. 2002

SPIE Proceedings

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Molecular dynamics of a nematic liquid crystal, 4n-octylcyanobiphenyl, confined to two types of SBA-type nanoporous molecular sieves were studied by broadband dielectric spectroscopy in order to obtain information about the liquid crystal-surface interactions. The temperature interval of the dielectric measurements was large, covering all the states of the bulk liquid crystal. It is found that there are several relaxation processes covering the large frequency range. A bulklike relaxation comes from the liquid crystal molecules located in the center of the pores, which rather do not feel the effect of the pore walls. Another relaxation comes from the molecules located in the surface layer. The latter process is much slower than the bulk-like relaxation. The differences observed between the dynamic behavior of the liquid crystal confined to the two types of nanoporous materials are related to pore size, pore shape and liquid crystal-surface interactions.

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Confinement of nematic liquid crystals in SBA mesoporous materials

Cited by 11 publications

References 22 publications

Rotational Fluctuations of Water inside the Nanopores of SBA-Type Molecular Sieves

Rotational Fluctuations of Water inside the Nanopores of SBA-Type Molecular Sieves

Noncovalent Immobilization of Enantioselective Catalysts

Dynamic behavior of hybrid organic-inorganic composites: liquid crystals confined in SBA-15 mesoporous materials

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