TY - JOUR A1 - Ungureanu, F. A1 - Manea, A.S. A1 - Frunza, L. A1 - Frunza, S. A1 - Ganea, C.P. A1 - Cotorobai, F. A1 - Diamandescu, L. A1 - Schönhals, Andreas T1 - Pentylcyanobiphenyl as test molecule for the acid sites of powdered titanium(IV) oxides: sensitivity of core levels to the local structure N2 - Pentylcyanobiphenyl was used successfully as a test molecule to show the acid sites upon some commercial nanoscaled titanium dioxide materials. The surface interactions were investigated in detail using methods sensitive to the surface or to the bulk material, e.g., X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, and thermal analysis. Different oxidation states of surface Ti ions were revealed. Several species were found: the majority were bonded through the nitrogen lone pair of the cyano group, but bonding to the surface OH groups by benzene π electrons might also appear. The N 1s lines of adsorbed 5CB were able to distinguish between Lewis acid and relatively weak Brønsted acid sites. KW - Infrared spectra KW - Pentylcyanobiphenyl KW - Size dependence KW - Titanium dioxide KW - XPS PY - 2012 DO - https://doi.org/10.1080/15421406.2012.697416 SN - 1542-1406 SN - 0026-8941 VL - 562 IS - 1 SP - 200 EP - 217 PB - Taylor & Francis CY - Philadelphia, PA, USA AN - OPUS4-26397 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 - TY - JOUR A1 - Frunza, L. A1 - Kosslick, H. A1 - Bentrup, U. A1 - Pitsch, I. A1 - Fricke, R. A1 - Frunza, S. A1 - Schönhals, Andreas T1 - Surface layer in composites containing 4-n-octyl-4'-cyanobiphenyl. FTIR spectroscopic characterization N2 - Composites containing 4-n-octyl-4?-cyanobiphenyl (8CB) either confined to nanopores of molecular sieves with very large pores or coating silica nanoparticles of aerosil type at high silica-to-8CB ratios are investigated by IR spectroscopy. Band shape analysis was performed in wavenumber regions in which the peaks due to CN stretching, CH stretching and CH out-of-plane vibrations appear. Some of molecules confined to molecular sieves show spectroscopic features characteristic to a bulk-like 8CB matter located in the centre of the pores or in the inter-grain space. Other features of the IR spectra are due to 8CB molecules located in the surface layer, mostly forming hydrogen bonds between their CN groups and surface OH groups. Another part of the 8CB molecules in the surface layer may also interact by ? electrons of the aromatic rings. Hydrogen bonding is less hindered for the molecules of the surface layers onto aerosil particles than inside pores of the molecular sieves. Comparison is also made with the case of composites based on molecular sieves with small pores. KW - Surface layer KW - Cyanobiphenyls KW - Infrared spectroscopy KW - Band shape analysis PY - 2003 DO - https://doi.org/10.1016/S0022-2860(03)00110-8 SN - 0022-2860 SN - 1872-8014 SN - 0377-046X VL - 651-653 SP - 341 EP - 347 PB - Elsevier CY - Amsterdam AN - OPUS4-2795 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Kosslick, H. A1 - Schönhals, Andreas A1 - Frunza, L. A1 - Enache, I. A1 - Beica, T. T1 - Study of the surface layer of aerosil-8CB composites by TG/DTA/DSC measurements N2 - Thermal analysis measurements were applied to study the behavior of composite systems containing a nematic liquid crystal (LC), 4-n-octyl-4?-cyanobiphenyl (8CB) and aerosil particles. The silica density ?s (g of silica per 1 cm3 of LC) was varied from 0.20 to 12 g/cm3 in order to approach the monomolecular structure of the surface layer. Thus, thermogravimetric (TG) measurements were performed to get information on the LC content of the samples. Moreover, they allowed an unusual application, to characterize the interaction of 8CB molecules with aerosil surface because the corresponding curves show multistep processes the temperatures of which depend on the silica density. Differential thermal analysis (DTA) also indicates several processes. Some of them, mostly due to desorption, are endothermal. Other processes are exothermal, and these are assigned to chemical transformations. The sample with silica density of 12 g/cm3 has no endothermal desorption peak at low temperatures, and has the highest shift for the DTA peaks. It was supposed that its surface layer has a monomolecular structure. For representative samples, TG–DTA studies were supported by FTIR investigations. Thus conventional TG–DTA techniques have provided new tools to characterize the nanocomposites. Differential scanning calorimetry gives the behavior of the phase transitions. Samples with low silica density exhibit a depression of the phase transition temperatures characteristic for the bulk 8CB while those with high silica densities do not show any phase transitions. PY - 2003 DO - https://doi.org/10.1016/S0022-3093(03)00319-3 SN - 0022-3093 VL - 325 IS - 1-3 SP - 103 EP - 112 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-2796 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Frunza, S. A1 - Frunza, L. A1 - Goering, Harald T1 - On the dynamics of the surface layer in octylcynobiphenyl-aerosil nanocomposites T2 - Frühjahrstagung des Arbeitskreises Festkörperphysik bei der DPG CY - Regensburg, Germany DA - 2002-03-11 PY - 2002 SN - 0420-0195 SN - 0372-5448 SN - 0343-9216 IS - CPP 15.11 SP - 438 CY - Bad Honnef AN - OPUS4-2269 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Kosslick, Hans-Jürgen A1 - Frunza, S. A1 - Fricke, R. A1 - Frunza, L. T1 - On the mobility of sodium ions and of confined liquid crystals in molecular sieves of faujasite type N2 - Broadband dielectric spectroscopy (10-2–109 Hz) was employed to study in a rather large temperature interval the molecular dynamics of the composite systems containing a nematic liquid crystal (LC), 4-n-pentyl-4?-cyanobiphenyl, confined to NaY, a zeolite with faujasite structure. Thermal analysis was also performed in order to get information concerning the loading of the zeolite and the possible phase transitions. No phase transitions and no relaxation processes of the LC molecules inside the pores were observed. But remarkably, in the presence of these molecules the dielectric behavior of the faujasite host changes due to modifications appeared in the mobility of Na+ ions. PY - 2002 DO - https://doi.org/10.1016/S0022-3093(02)01472-2 SN - 0022-3093 VL - 307-310 SP - 503 EP - 509 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-1569 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Frunza, L. A1 - Kosslick, H. A1 - Frunza, S. T1 - Unusual relaxation behavior of water inside the sodalite cages of faujasite-type molecular sieves N2 - Broad-band dielectric spectroscopy (10-2 to 109 Hz) is applied to investigate the molecular dynamics of NaY, a zeolite of faujasite structure. A dc conductivity contribution and three relaxation processes were revealed in the dielectric spectra. The relaxation process in the high-frequency range ascribed to orientational fluctuations of water molecules inside the sodalite cages is studied in detail. As a main result it is found that its mean relaxation time has an unusual saddle-like temperature dependence, which obeys neither an Arrhenius nor a Vogel-Fulcher-Tammann law. A quantitative description was given on the basis of a model recently developed by Feldman et al. (J. Phys. Chem. B 2001, 105, 1845) to analyze the dynamics of water confined in nanoporous glasses. Reasonable values for the activation energies of orientational fluctuations and of defect formation as well as for the defect concentration were obtained. PY - 2002 DO - https://doi.org/10.1021/jp021281v SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 106 IS - 36 SP - 9191 EP - 9194 PB - Soc. CY - Washington, DC AN - OPUS4-1571 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Kosslick, H. A1 - Pitsch, I. A1 - Frunza, St. A1 - Schönhals, Andreas T1 - Rotational Fluctuations of Water inside the Nanopores of SBA-Type Molecular Sieves N2 - 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 109 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. PY - 2005 DO - https://doi.org/10.1021/jp044503t SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 109 IS - 18 SP - 9154 EP - 9159 PB - Soc. CY - Washington, DC AN - OPUS4-7611 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Frunza, L. A1 - Tintaru, M. A1 - Enache, I. A1 - Beica, T. A1 - Schönhals, Andreas T1 - Dynamics of the surface layer in cyanobiphenyl-aerosil nanocomposites with a high silica density N2 - Composites were prepared from an aerosil and 4-n-alkyl-4'cyanobiphenyls with five to eight carbon atoms in the alkyl chain. Their high silica density of sim7 g aerosil in 1 cm3 of liquid crystal (LC) allows the observation of the behaviour of a thin cyanobiphenyl layer (having nearly a monolayer structure) on the silica particles. The systems are investigated by dielectric spectroscopy (10-2-109 Hz) in a large temperature range (220-370 K). All the composites show a (main) relaxation process at frequencies much lower than the processes observed for the bulk LC that was assigned to the dynamics of the molecules in the surface layer. The temperature dependence of its characteristic frequencies obeys the Vogel-Fulcher-Tammann law, which is found to be typical for glass-forming liquids. The quasi two-dimensional character of the glass transition in the surface layer is discussed for the first time. At the nematic-to-isotropic transition temperature of the bulk, the composites show a continuous decrease of the characteristic frequencies as a function of the alkyl chain length, while the bulk LCs show the well known odd-even behaviour. The magnitude and temperature dependence of the slow relaxation process in the composites (molecules on an outer surface) agree with those of the same molecules confined to the nanopores of molecular sieves (internal surface). KW - Nanocomposite KW - Surface Layer KW - Liquid Crystals Dielectric Spectroscopy PY - 2004 DO - https://doi.org/10.1080/02678290410001675147 SN - 0267-8292 SN - 1366-5855 VL - 31 IS - 7 SP - 913 EP - 922 PB - Taylor & Francis CY - London AN - OPUS4-4709 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Schönhals, Andreas A1 - Kosslick, H. A1 - Frunza, S. T1 - Relaxation processes of water confined to AIMCM-41 molecular sieves. Influence of the hydroxyl groups of the pore surface N2 - A series of AlMCM-41 molecular sieves was prepared with constant composition (Si/Al = 14.7) and presumably same pore structure but different pore diameters (from 2.3 to 4.6 nm). The pore size distribution is narrow for each sample. The rotational fluctuations of water molecules confined inside the pores were investigated applying broadband dielectric spectroscopy (10-2–107 Hz) over a large temperature interval (213–333 K). A relaxation process, slower than that expected for bulk water, was observed which is assigned to water molecules forming a surface layer on the pore walls. The estimated relaxation time has an unusual non-monotonic temperature dependence, which is rationalized and modeled assuming two competing processes: rotational fluctuations of constrained water molecules and defect formation (Ryabov model). This paper focuses on the defects and notably the influence of the hydroxyl groups of the pore walls. The Ryabov model is fitted to the data and characteristic parameters are obtained. Their dependence on pore diameter is considered for the first time. The found results are compared with those obtained for other types of molecular sieves and related materials. PY - 2008 DO - https://doi.org/10.1140/epje/i2007-10340-y SN - 1292-8941 SN - 1292-895X VL - 26 SP - 379 EP - 386 PB - EDP Sciences CY - Orsay AN - OPUS4-17752 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Schönhals, Andreas A1 - Frunza, S. A1 - Parvulescu, V.I. A1 - Cojocaru, B. A1 - Carriazo, D. A1 - Martín, C. A1 - Rives, V. T1 - Rotational Fluctuations of Water Confined to Layered Oxide Materials - Nonmonotonous Temperature Dependence of Relaxation Times N2 - 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 107 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. The model of Ryabov et al. (J. Phys. Chem. B 2001, 105, 1845) recently applied to describe the dynamics of water molecules in porous glasses is employed also for the layered materials. This model assumes two competing effects: rotational fluctuations of water molecules that take place simultaneously with defect formation, allowing the creation of free volume necessary for reorientation. The activation energy of rotational fluctuations, the energy of defect formation, a pre-exponential factor, and the defect concentration are obtained as main parameters from a fit of this model to the data. The values of these parameters were compared with those found for water confined to nanoporous molecular sieves, porous glasses, or bulk ice. Several correlations were discussed in detail, such as the lower the value of the energy of defect formation, the higher the number of defects. The pre-exponential factor increases with increasing activation energy, as an expression of the compensation law, and indicates the cooperative nature of the motional process. The involvement of the surface OH groups and of the oxygen atoms of the interlayer anions in the formation of hydrogen bonds was further discussed. For the birnessite sample, the relaxation processes are probably overlaid by a dominating conductivity contribution, which is analyzed in its frequency and temperature dependence. It is found that the conductivity of birnessite obeys the characteristics of semiconducting disordered materials. Especially the Barton/Nakajima/Namikawa relationship is fulfilled. Analyzing the temperature dependence of the direct current (dc) conductivity σ0 in detail gives some hint that σ0(T) has also an unusual saddlelike form. PY - 2007 DO - https://doi.org/10.1021/jp0717140 SN - 1089-5639 SN - 1520-5215 VL - 111 IS - 24 SP - 5166 EP - 5175 PB - Soc. CY - Washington, DC AN - OPUS4-15718 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Frunza, S. A1 - Kosslick, H. A1 - Schönhals, Andreas T1 - Phase behavior and molecular mobility of n-octylcyanobiphenyl confined to molecular sieves: Dependence on the pore size PY - 2008 DO - https://doi.org/10.1103/PhysRevE.78.051701 SN - 1539-3755 SN - 1063-651X VL - 78 IS - 5 SP - 051701-1 - 051701-11 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-20881 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 - TY - JOUR A1 - Frunza, S. A1 - Schönhals, Andreas A1 - Frunza, L. A1 - Ganea, P. A1 - Kosslick, H. A1 - Harloff, J. A1 - Schulz, A. T1 - Molecular relaxation processes in a MOF-5 structure revealed by broadband dielectric spectroscopy: signature of phenylene ring fluctuations N2 - 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. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn–O clusters. The processes ('region II') at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. (J. Am. Chem. Soc. 2008, 130, 3246). The carboxylate groups might also be involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region II corresponds nearly to a Debye-like process: This is explained by a well-defined structure of empty pores. PY - 2010 DO - https://doi.org/10.1021/jp1071617 SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 114 IS - 40 SP - 12840 EP - 12846 PB - Soc. CY - Washington, DC AN - OPUS4-22255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Frunza, L. A1 - Ganea, C. P. A1 - Zgura, I. A1 - Bras, A. R. A1 - Schönhals, Andreas T1 - Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species N2 - Surface layers have already been observed by broadband dielectric spectroscopy for Composite systems formed by adsorption of rod-like cyanophenyl derivates as probe molecules on the surface of oxide particles. In this work, features of the surface layer are reported; samples with different amounts of the probe molecules adsorbed onto oxide (nano) particles were prepared in order to study their interactions with the surface. Thermogravimetric analysis (TGA) was applied to analyze the amount of loaded probe molecules. The density of the surface species ns was introduced and its values were estimated from quantitative Fourier transform infrared spectroscopy (FTIR) coupled with TGA. This parameter allows discriminating the composites into several groups assuming a similar interaction of the probe molecules with the hosts of a given group. An influence factor H is further proposed as the ratio of the number of molecules in the surface layer showing a glassy dynamics and the number of molecules adsorbed tightly on the surface of the support: It was found for aerosil composites and used for calculating the maximum filling degree of partially filled silica MCM-41 composites showing only one dielectric process characteristic for glass-forming liquids and a bulk behavior for higher filling degrees. KW - Cyanophenyl molecules KW - Nanoconfinement KW - Surface Species PY - 2016 DO - https://doi.org/10.1140/epjp/i2016-16027-5 SN - 2190-5444 VL - 131:27 IS - 2 SP - 1 EP - 9 PB - Springer AN - OPUS4-35364 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Frunza, L. A1 - Ganea, C. P. A1 - Zgura, I. A1 - Schönhals, Andreas T1 - Density of adsorbed surface species for cyanophemyl benzoates confined to Aerosil 380: Development of the evaluating algorithm for Attachment by two types of bonds N2 - We found previously how to estimate the density of the adsorbed surface species in the case of the molecules interacting to the oxide support surface by one type of bond. Here this algorithm is developed for the case of the molecules which can be bonded to the support surface by two types of bonds. The adsorption assumptions are similar to those considered in the case of only one type of bond. The calculation is exemplified for some composites of cyanophenyl alkylbenzoates (CPnBs) (n is the number of carbon atoms in the alkyl chain) interacting with Aerosil A380. The interaction takes place by hydrogen bonding between the –OH groups or the support and the functional groups of the CPnB molecules. The estimated values of the total surface density of CPnBs agree well with those found for the composites containing related but simpler molecules. KW - Surface species PY - 2019 SN - 1223-7027 VL - 81 IS - 4 SP - 232 EP - 236 PB - University Politehnica of Bucharest CY - Bucharest AN - OPUS4-49615 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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, S. A1 - Schönhals, Andreas A1 - Frunza, L. A1 - Beica, T. A1 - Zgura, I. A1 - Ganea, P. A1 - Stoenescu, D. T1 - Dynamics of cyanophenyl alkylbenzoate molecules in the bulk and in a surface layer adsorbed onto aerosil. Variation of the lengths of the alkyl chain N2 - The molecular mobility of 4-butyl- and 4-pentyl-4'-cyanophenyl benzoate (CP4B, CP5B) and their composites prepared from aerosil A380 was investigated by broadband dielectric spectroscopy in a large temperature range. Thermogravimetric and infrared investigations were additionally performed. High silica density (larger than 7 g aerosil/1 g of liquid crystal) was selected to observe a thin layer adsorbed on the surface of the silica particles. The data were compared with those of the member of the series with six carbon atoms in the alkyl tail. Bulk CP4B and CP5B show the dielectric behaviour expected for liquid crystals. For the composites one relaxation process is observed at frequencies much lower than those for the corresponding bulk, which was assigned to the dynamics of the molecules in a surface layer. The temperature dependence of the relaxation rates (and of the dielectric strength) shows a crossover behaviour with two distinguished regimes. At higher temperatures the data obey the Vogel-Fulcher-Tammann law, whereas an Arrhenius law is observed at lower temperature, in a close similarity to the behaviour of a constrained dynamic glass transition. The estimated Vogel and crossover temperature is independent on the tail length, while the activation energy for the low temperature branch increases weakly with increasing the alkyl tail. KW - Confined liquid crystals KW - Molecules at surfaces KW - Dielectric properties KW - Relaxation processes KW - Glassy dynamics KW - Crossover phenomenon PY - 2010 DO - https://doi.org/10.1016/j.chemphys.2010.04.031 SN - 0301-0104 SN - 1873-4421 VL - 372 IS - 1-3 SP - 51 EP - 60 PB - Elsevier CY - Amsterdam AN - OPUS4-21588 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ryabov, Y. A1 - Gutina, A. A1 - Feldman, Y. A1 - Frunza, S. A1 - Frunza, L. A1 - Schönhals, Andreas T1 - Comment on "investigating hydration dependence of dynamics of confined water: Monolayer, hydration water, and Maxwell-Wagner processes" [J. Chem. Phys. 128, 154503 (2008)] N2 - This comment on the experimental methods and the conclusions of the paper "Investigating hydration dependence of dynamics of confined water: Monolayer, hydration water, and Maxwell–Wagner processes" [ J. Sjöström et al., J. Chem. Phys.128, 154503 (2008) ] exposes serious shortcomings in the understanding and the interpretation of the observed relaxation behavior of confined water presented in the article. There are contradictions between the suggested theory and the experimental observations that mislead the reader. In this comment we prove that the Maxwell–Wagner relaxation cannot explain the nonmonotonous temperature dependence for the process observed in confined water. PY - 2010 DO - https://doi.org/10.1063/1.3451102 SN - 0021-9606 SN - 1089-7690 VL - 133 SP - 037101-1 - 037101-2 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21908 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Frunza, S. A1 - Frunza, L. A1 - Unruh, T. A1 - Frick, B. A1 - Zorn, R. T1 - Vibrational and molecular dynamics of a nanoconfined liquid crystal N2 - The effect of a nanometer confinement on the vibrational and molecular dynamics of a liquid crystals E7 was studied by dielectric spectroscopy (DS) and neutron scattering (NS). E7 undergoes a glass transition phenomenon besides the nematic to isotropic phase transition. As confining host a molecular sieve of the MCM-41 type is used having cylindrical pores with a radius of 1.25 nm. The results obtained by both methods are compared in detail. PY - 2010 DO - https://doi.org/10.1140/epjst/e2010-01329-5 SN - 1951-6355 SN - 1951-6401 VL - 189 IS - 1 SP - 251 EP - 255 PB - Springer CY - Berlin AN - OPUS4-22638 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Frunza, S. A1 - Frunza, L. A1 - Goering, Harald A1 - Sturm, Heinz T1 - On the dynamics of surface layer in octylcyanobiphenyl-aerosil systems N2 - A broadband dielectric study of the dispersions of silica spheres (Aerosil 380) in octylcyanobiphenyl (8CB) with densities between 0.083 and 10 g of silica per 1 cm3 of liquid crystal (LC) is reported. High values of silica densities were achieved for the first time to observe the behaviour of the LC monolayer on the surface of the silica particles. The relaxation characteristic of the bulk LC is noticed especially for the samples with low silica densities. Additionally, a slow relaxation was detected, even at temperatures for which the bulk LC is in the crystalline state. It was assigned to the surface layer of LC molecules. Remarkably, the temperature dependence of the relaxation rates for this slow process shows a behaviour typical for glass-forming liquids. PY - 2001 DO - https://doi.org/10.1209/epl/i2001-00591-8 SN - 0302-072X SN - 0295-5075 SN - 1286-4854 VL - 56 IS - 6 SP - 801 EP - 807 PB - EDP Science CY - Les-Ulis Cedexa, France AN - OPUS4-1572 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Ganea, C. P. A1 - Zgura, I. A1 - Frunza, L. A1 - Schönhals, Andreas T1 - Molecular dynamics in bulk and surface species of cyanophenyl alkyl benzoates with 2, 3 and 7 carbon atoms in the alkyl chain: comparison in the whole homologous series N2 - Molecular mobility of cyanophenyl alkylbenzoates (CPnBs) (n = 2, 3, 7 – number of carbon atoms in the alkyl chain) in the bulk and in composites with aerosil A380 is investigated by broadband dielectric spectroscopy, while thermal analysis and infrared spectroscopy were applied to characterise the molecular species. The work completes preliminary results obtained for the members with n = 4 … 6. An interaction by hydrogen bonding, between aerosil surface – OH groups and – CN or ester groups of the CPnB molecules takes place. It slows down the relaxation process as observed for related composites in comparison to the pure materials. The existence of two types of bonding might be the reason that Vogel temperature for the relaxation process in the surface layer does not show the odd-even effect. Temperature dependence of the relaxation rates for composites shows a crossover behaviour from a high to a low temperature regime. Moreover, the temperature dependence of the dielectric strength is unusual. As the loading degree is similar, comparison of the dielectric, spectroscopic and thermal data obtained here and with the results obtained for the composites with n = 4 … 6 can be directly done. Increasing the number of the members of the homologous series confirms and hardens the preliminary conclusions. KW - Liquid crystals PY - 2019 DO - https://doi.org/10.1080/02678292.2019.1687768 SP - 1 EP - 10 PB - Taylor & Francis AN - OPUS4-49924 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Frunza, L. A1 - Kosslick, H. A1 - Pitsch, I. A1 - Frunza, S. A1 - Schönhals, Andreas T1 - Molecular dynamics of 4n-octylcyanobiphenyl in partially filled nanoporous SBA molecular sieves T2 - 7. European Conference on Liquid Crystals CY - Jaca, Spain DA - 2003-04-06 PY - 2003 AN - OPUS4-4663 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Frunza, L. A1 - Frunza, S. A1 - Kosslick, H. A1 - Schönhals, Andreas A1 - Pitsch, I. A1 - Krause, C. A1 - Kärger, J. T1 - Water relaxation behavior inside the pores and cages of different molecular sieves T2 - 15. Deutsche Zeolith Tagung CY - Kaiserslautern, Germany DA - 2003-03-05 PY - 2003 AN - OPUS4-4658 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Frunza, L. A1 - Frunza, S. A1 - Kosslick, H. A1 - Pitsch, I. A1 - Schönhals, Andreas T1 - Molecular dynamics of surface layer in cyanobiphenyl-aerosil systems with high silica density T2 - 7. European Conference on Liquid Crystals CY - Jaca, Spain DA - 2003-04-06 PY - 2003 AN - OPUS4-4659 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Frunza, L. A1 - Schönhals, Andreas T1 - Relaxation processes of octylcyanobiphenyl in molecular sieves with hexagonal pore structure T2 - Zeolites and Related Materials: Trends, Targets and Challenges CY - Paris, France DA - 2008-06-02 PY - 2008 AN - OPUS4-17994 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Frunza, L. A1 - Schönhals, Andreas A1 - Kosslick, H. A1 - Frunza, S. T1 - Hydroxyl groups on the surface of AIMCM-41 molecular sieves as characterized by rotational fluctuations of confined water T2 - Zeolites and Related Materials: Trends, Targets and Challenges CY - Paris, France DA - 2008-06-02 PY - 2008 AN - OPUS4-17996 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Frunza, L. A1 - Frunza, S.. A1 - Schönhals, Andreas A1 - Frick, B. A1 - Zorn, R. A1 - Unruh, T. T1 - Broadband Dielectric and Neutron Spectroscopy on Nanoconfined Liquid Crystals T2 - 6th International Discussion Meeting Relaxation in Complex Systems CY - Rome, Italy DA - 2009-08-30 PY - 2009 AN - OPUS4-19949 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kosslick, H. A1 - Pitsch, I. A1 - Deutsch, J. A1 - Pohl, M.-M. A1 - Schulz, A. A1 - Vu, A.T. A1 - Nguyen, D.T. A1 - Frunza, L. A1 - Jäger, Christian T1 - Improved large mesoporous ordered molecular sieves - Stabilization and acid/base functionalization N2 - The preparation of nanoporous materials with enhanced stability using an improved synthesis route using reactive inorganic silica and alumina species is reported. This way improved mesoporous molecular sieves were obtained. The synthesized aluminum substituted mesoporous molecular materials (Al-MMS) contain very large pores of 50–200 Å size combined with an improved pore wall thickness. Increased wall thickness and Al substitution lead to an improved chemical stability against alkaline solution. The textural, structural and acid properties are investigated by physico-chemical methods. The catalytic performance acidic materials was tested in the benzoylation reaction; amino functionalized materials were studied in the base catalyzed Michael addition. KW - Nanoporous molecular sieve KW - Al substitution KW - Stability KW - Synthesis KW - Acidity KW - Catalysis PY - 2010 DO - https://doi.org/10.1016/j.cattod.2010.03.005 SN - 0920-5861 VL - 152 IS - 1-4 SP - 54 EP - 60 PB - Elsevier CY - Amsterdam AN - OPUS4-23960 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Zgura, I A1 - Ganea, C. P. A1 - Schönhals, Andreas T1 - Molecular dynamics of alkyl benzoate liquid crystals in the bulk state and in the surface layer of their composites with oxide nanopowders N2 - This paper presents the results concerning monotropic nematic liquid crystals 4-pentylphenyl 40-alkyl benzoate (5PnB) (n = 3 or 5 carbon atoms in the alkyl chain). Their mesophase properties were supported by images of the polarized optical microscopy. Molecular dynamics in the bulk samples or in the composites prepared with aerosil A380 was investigated by broadband dielectric spectroscopy in a large temperature range, appropriately chosen. Thermo gravimetric and infrared investigations were additionally performed. The data were compared with those of structurally related nematics like cyanophenyl pentyl benzoates, which have a cyan group instead of the pentyl chain. The dielectric spectra of the bulk 3P5B and 5P5B demonstrate a dielectric behavior with several relaxation processes as expected for nematic liquid crystals. The temperature dependence of the relaxation rates (and of the dielectric strength) seems to have two distinguished regimes. Thus, in the isotropic state, at higher temperatures the data obey the Vogel–Fulcher–Tammann law, whereas an Arrhenius law is fitted at lower temperature, in a close similarity to the behavior of a constrained dynamic glass transition. Samples with a high density of silica (larger than 7 g aerosil/1 g of 5PnB) were prepared to observe a thin layer adsorbed on the particle surface; it was estimated that almost each guest 5PnB molecule interacts with the aerosil surface. For the composites only one main relaxation process is observed at frequencies much lower than those for the corresponding bulk, which was assigned to the dynamics of the molecules in the surface layer. Infrared spectroscopy shows that these molecules interact with the surface by the ester carbonyl group leading to the monolayer self-assembly at liquid–solid interface. We note once more the importance of the functional unit(s) for the interaction with the hydroxyl groups on the aerosil surface. KW - Liquid crystals PY - 2022 DO - https://doi.org/10.1016/j.molliq.2022.119374 SN - 0167-7322 VL - 359 SP - 1 EP - 11 PB - Elsevier B.V. AN - OPUS4-54867 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -