TY - JOUR A1 - Brás, A.R. A1 - Frunza, S. A1 - Guerreiro, L. A1 - Fonseca, I.M. A1 - Corma, A. A1 - Frunza, L. A1 - Dionísio, M. A1 - Schönhals, Andreas T1 - Molecular mobility of nematic E7 confined to molecular sieves with a low filling degree N2 - The nematic liquid crystalline mixture E7 was confined with similar filling degrees to molecular sieves with constant composition but different pore diameters (from 2.8 to 6.8 nm). Fourier transform infrared analysis proved that the E7 molecules interact via the cyanogroup with the pore walls of the molecular sieves. The molecular dynamics of the system was investigated by broadband dielectric spectroscopy (10-2-109 Hz) covering a wide temperature range of ~ 200 K from temperatures well above the isotropic-nematic transition down to the glass transition of bulk E7. A variety of relaxation processes is observed including two modes that are located close to the bulk behavior in its temperature dependence. For all confined samples, two relaxation processes, at frequencies lower than the processes observed for the bulk, were detected. At lower temperatures, their relaxation rates have different temperature dependencies whereas at higher temperatures, they seem to collapse into one chart. The temperature dependence of the slowest process (S-process) obeys the Vogel-Fulcher-Tammann law indicating a glassy dynamics of the E7 molecules anchored to the pore surface. The pore size dependence of both the Vogel temperature and fragility revealed a steplike transition around 4 nm pore size, which indicates a transition from a strong to a fragile behavior. The process with a relaxation rate in between the bulklike and the S-process (I-process) shows no dependence on the pore size. The agreement of the I-process with the behavior of a 5CB surface layer adsorbed on nonporous silica leads to the assignment of E7 molecules anchored at the outer surface of the microcrystals of the molecular sieves. KW - Adsorption KW - Fourier transform spectra KW - Glass transition KW - infrared spectra KW - Molecular sieves KW - Nematic liquid crystals KW - Organic compounds KW - Porous materials PY - 2010 DO - https://doi.org/10.1063/1.3432775 SN - 0021-9606 SN - 1089-7690 VL - 132 SP - 224508-1 - 224508-12 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21510 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -