Molecular relaxation processes in a MOF-5 structure revealed by broadband dielectric spectroscopy: signature of phenylene ring fluctuations.

The molecular mobility of a MOF-5 metal-organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed. The temperature dependence of their relaxation rates follows an Arrhenius law.

Involvement of cyan and ester groups in surface interactions of aerosil-cyanophenyl alkyl benzoate systems with high silica density: Infrared investigations.

Composites prepared from aerosil A380 and liquid crystals (LCs) of 4-n-alkyl-4'-cyanophenyl benzoate type, with four to six carbon atoms in the alkyl chain were investigated by infrared spectroscopy. Their high silica content (of 2-7 g aerosil/1 g of LC) was given by thermogravimetric investigations and allows the observation of a rather thin LC layer on the silica particles. Several surface species onto the external surface of the grains were demonstrated.

Phase behavior and molecular mobility of n-octylcyanobiphenyl confined to molecular sieves: dependence on the pore size.

The molecular dynamics of 4-n-octyl-4'-cyanobiphenyl (8CB) confined inside the pores of a series of AlMCM-41 samples with the same structure, constant composition (SiAl=14.7) but different pore sizes (diameter between 2.3 and 4.

Composites containing confined n-octyl-cyanobiphenyl: monomer and dimer species in the surface layer by in situ FTIR spectroscopy.

Confinement of 4-n-octyl-4'-cyanobiphenyl (8CB) to nanoporous molecular sieves with hexagonal structure of cylindrical pores (4.6nm diameter) is studied. Thermogravimetric investigations have indicated that the pores are completely filled.

Rotational fluctuations of water confined to layered oxide materials: nonmonotonous temperature dependence of relaxation times.

The rotational molecular dynamics of water confined to layered oxide materials with brucite structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(7) Hz and in a broad temperature interval. The layered double hydroxide samples show one relaxation process, which was assigned to fluctuations of water molecules forming a layer, strongly adsorbed to the oxide surface. The temperature dependence of the relaxation rates has an unusual saddlelike shape characterized by a maximum.

Rotational fluctuations of water inside the nanopores of SBA-type molecular sieves.

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.