TY - JOUR A1 - Frunza, S. A1 - Schönhals, Andreas A1 - Goering, Harald A1 - Manaila-Maximean, D. A1 - Beica, T. A1 - Frunza, L. A1 - Moldovan, R. T1 - Dynamics of Cyanophenyl Alkybenzoate molecules in a surface layer adsorbed onto Aerosil. I. Cyanophenyl Hexylbenzoate N2 - A composite prepared from aerosil A380 and the liquid crystal (LC) 4-hexyl-4'-cyanophenyl benzoate (CP6B) was investigated by broadband dielectric spectroscopy in a large temperature range. The selected high silica density (ca. 7 g aerosil/1 g of CP6B) allows the observation of a thin layer (two-monolayer structure) adsorbed on the surface of the silica particles. For the composite one relaxation process is observed at frequencies much lower than that of the processes found for bulk CP6B. It is assigned to the dynamics of the molecules in the surface layer. The temperature dependence of its relaxation rates obeys the Vogel-Fulcher-Tammann law, which is characteristic for glass-forming liquids. The quasi 2D character of the observed glassy dynamics in the surface layer is discussed. The temperature dependence of the CP6B relaxation in the composite is compared with that of related hexylcyanobiphenyl molecules in the surface layer of aerosil composite with a similar concentration. KW - Cyanophenyl-alkylbenzoates KW - Dielectric spectroscopy KW - Infrared spectroscopy KW - Liquid crystals KW - Thermal analysis KW - Aerosil composites PY - 2008 DO - https://doi.org/10.1080/15421400802430448 SN - 0026-8941 SN - 1543-5318 VL - 495 SP - 60/[412] EP - 79/[431] PB - Gordon & Breach CY - London AN - OPUS4-19063 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Frunza, S. A1 - Zgura, I. A1 - Beica, T. A1 - Gheorghe, N. A1 - Ganea, P. A1 - Stoenescu, D. A1 - Dinescu, A. A1 - Schönhals, Andreas T1 - Involvement of cyan and ester groups in surface interactions of aerosil-cyanophenyl alkyl benzoate systems wih high silica density: infrared investigations N2 - 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. Arguments are given that monomer and dimer species are present in the bulk cyanophenyl benzoate materials while bulk-like species along with hydrogen-bonded ones coexist in the so-called surface layer of the composites. The main interaction of LC molecules with the aerosil surface is by hydrogen bonding taking place with the involvement of the cyan group. There is a contribution of ester carbonyl group to these surface interactions but this cannot be well quantified. KW - Cyanophenyl alkyl benzoate KW - Aerosil composites KW - Infrared spectra KW - Band shape analysis PY - 2010 DO - https://doi.org/10.1016/j.saa.2009.12.029 SN - 1386-1425 SN - 0370-8322 SN - 1873-3557 SN - 0584-8539 VL - 75 IS - 4 SP - 1228 EP - 1235 PB - Elsevier CY - Amsterdam AN - OPUS4-20997 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -