排序方式: 共有38条查询结果,搜索用时 31 毫秒
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Ioan Paraschiv Paul Delforterie Marcel Giesbers Maarten A. Posthumus 《Liquid crystals》2013,40(8):977-983
The synthesis and phase behaviour of a new series of unsymmetrically substituted hexaalkoxytriphenylene‐based liquid crystals are reported. One of the hexyloxy chains in hexahexyloxytriphenylene (HAT6) is replaced by either a shorter or a longer chain, HAT‐(OC6H13)5(OC n H2n+1). Compounds with chain lengths n of 2–14, 16 and 18 were prepared and investigated. Compounds with n?13 were not liquid crystalline. For all compounds with n?12 Colh textures were observed by polarizing microscopy. X‐ray investigations showed that the intercolumnar distance gradually increased with n from n = 2 to n = 12, while the interdisk distance (3.6 Å) remained constant. A small odd–even effect on the increase of the intercolumn distance with n was observed. This effect was also found in the change of ΔH of isotropization with n. 相似文献
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Ioan Paraschiv Alistair Tomkinson Marcel Giesbers Ernst J. R. Sudh?lter Han Zuilhof Antonius T. M. Marcelis 《Liquid crystals》2013,40(9):1029-1038
The synthesis and thermotropic properties are reported for a series of hexaalkoxytriphenylenes that contain an amide, urea or thiourea group in one of their alkoxy tails. The intermolecular hydrogen bonding abilities of these molecules have a disturbing influence on the formation and stability of the columnar liquid crystalline phases. The stronger the hydrogen bonding the more the liquid crystallinity is suppressed, probably due to disturbance of the π–π stacking of the triphenylene discs. As a direct result, urea‐ and amide‐containing triphenylene derivatives are not liquid crystalline, but several thiourea derivatives show hexagonal columnar mesophases. 相似文献
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Remko Achten Arie Koudijs Marcel Giesbers Antonius T. M. Marcelis Corresponding author Ernst J. R. Sudhölter 《Liquid crystals》2013,40(3):277-285
Two series of non‐symmetric banana‐shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3‐phenylene bis(4‐benzoyloxy)benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X‐ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC8H17 to OC16H33. The other terminal tails are OC11H23, O(CH2)9CH?=?CH2, OC10H21 and O(CH2)8CH?=?CH2. The short‐tailed compounds show monotropic or enantiotropic B1 phases and the long‐tailed compounds the B2 phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B2 phases have layer spacings that suggest a tilt of ~45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric. 相似文献
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Scheres L Rijksen B Giesbers M Zuilhof H 《Langmuir : the ACS journal of surfaces and colloids》2011,27(3):972-980
On H-Si(111) surfaces monolayer formation with 1-alkenes results in alkyl monolayers with a Si-C-C linkage, while 1-alkynes yield alkenyl monolayers with a Si-C═C linkage. Recently, considerable structural differences between both types of monolayers were observed, including an increased thickness, improved packing, and higher surface coverage for the alkenyl monolayers. The precise origin thereof could experimentally not be clarified yet. Therefore, octadecyl and octadecenyl monolayers on Si(111) were studied in detail by molecular modeling via PCFF molecular mechanics calculations on periodically repeated slabs of modified surfaces. After energy minimization the packing energies, structural properties, close contacts, and deformations of the Si surfaces of monolayers structures with various substitution percentages and substitution patterns were analyzed. For the octadecyl monolayers all data pointed to a substitution percentage close to 50-55%, which is due the size of the CH(2) groups near the Si surface. This agrees with literature and the experimentally determined coverage of octadecyl monolayers. For the octadecenyl monolayers the minimum in packing energy per chain is calculated around 60% coverage, i.e., close to the experimentally observed value of 65% [Scheres et al. Langmuir 2010, 26, 4790], and this packing energy is less dependent on the substitution percentage than calculated for alkyl layers. Analysis of the chain conformations, close contacts, and Si surface deformation clarifies this, since even at coverages above 60% a relatively low number of close contacts and a negligible deformation of the Si was observed. In order to evaluate the thermodynamic feasibility of the monolayer structures, we estimated the binding energies of 1-alkenes and 1-alkynes to the hydrogen-terminated Si surface at a range of surface coverages by composite high-quality G3 calculations and determined the total energy of monolayer formation by adding the packing energies and the binding energies. It was shown that due to the significantly larger reaction exothermicity of the 1-alkynes, thermodynamically even a substitution percentage as high as 75% is possible for octadecenyl chains. However, because sterically (based on the van der Waals footprint) a coverage of 69% is the maximum for alkyl and alkenyl monolayers, the optimal substitution percentage of octadecenyl monolayers will be presumably close to this latter value, and the experimentally observed 65% is likely close to what is experimentally maximally obtainable with alkenyl monolayers. 相似文献
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Campos MA Trilling AK Yang M Giesbers M Beekwilder J Paulusse JM Zuilhof H 《Langmuir : the ACS journal of surfaces and colloids》2011,27(13):8126-8133
The preparation and characterization of self-assembled monolayers on copper with n-alkyl and functional thiols was investigated. Well-ordered monolayers were obtained, while the copper remained oxide-free. Direct attachment of N-succinimidyl mercaptoundecanoate (NHS-MUA) onto the copper surface allowed for the successful attachment of biomolecules, such as β-d-glucosamine, the tripeptide glutathione, and biotin. Notably, the copper surfaces remained oxide-free even after two reaction steps. All monolayers were characterized by static water contact angle measurements, X-ray photoelectron spectroscopy, and infrared reflection absorption spectroscopy. In addition, the biotinylated copper surfaces were employed in the immobilization of biomolecules such as streptavidin. 相似文献
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Two series of trimer liquid crystals were investigated that contain a biphenylyl central group and two cholesteryl or dihydrocholesteryl terminal mesogenic groups. Only compounds with even spacers were investigated. The dihydrocholesteryl-containing trimers show a triply intercalated smectic A (SmA) phase when the spacer lengths are greater than 8, whereas the cholesteryl-containing trimers exhibit this triply intercalated SmA phase when the spacer lengths are more than 6. With shorter spacers, a twist grain boundary C* (TGBC*) phase was found. This is revealed by the formation of a typical dotted square grid pattern upon cooling from the chiral nematic (N*) phase in the planar texture. The dots are spaced by a distance of about 1.5-1.8 µm. Upon cooling from the N* phase in the focal conic texture a striped pattern is observed with the same spacing. X-ray diffraction revealed a repeat distance for the TGBC* phase that corresponds with a monolayer ordering. The results show that the weaker interaction between the dihydrocholesteryl groups compared with cholesteryl groups or longer spacers destabilize the monolayer TGBC* phase. 相似文献
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E.V. Kurganova A.J.M. Giesbers R.V. Gorbachev A.K. Geim K.S. Novoselov J.C. Maan U. Zeitler 《Solid State Communications》2010,150(45-46):2209-2211
We have measured the quantum Hall activation gaps in bilayer graphene at filling factors and in high magnetic fields up to 30 T. We find that energy levels can be described by a 4-band relativistic hyperbolic dispersion. The Landau level width is found to contain a field independent background due to an intrinsic level broadening and a component which increases linearly with magnetic field. 相似文献
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Remko Achten Evelien A. W. Smits R. Amaranatha Reddy Marcel Giesbers Antonius T. M. Marcelis Ernst J. R. Sudh lter 《Liquid crystals》2006,33(1):57-65
The synthesis and mesomorphic properties of 30 bent-core compounds with a fluorine substituent in one of the outer rings are reported. The banana-shaped compounds are all derived from resorcinol and contain esters as linking groups between the five aromatic rings. The different mesophases have been characterized by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical investigations. The compounds with the longer terminal chains exhibit an antiferroelectric SmCP phase. Upon introduction of a fluorine substituent the layer spacing increases, as compared with the corresponding unsubstituted compound. The introduction of one terminal vinyl group in the mono-substituted bent-core mesogens has no significant influence on the liquid crystalline properties and the switching remains antiferroelectric. Due to the introduction of the terminal double bond, these banana-shaped compounds are suitable for the preparation of siloxane polymers or attachment to a hydrogen-terminated silicon surface. 相似文献
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Remko Achten Ruud Cuypers Marcel Giesbers Arie Koudijs Antonius T. M. Marcelis Ernst J. R. Sudh lter 《Liquid crystals》2004,31(8):1167-1174
Two series of asymmetric banana-shaped compounds have been synthesized and studied. In the 1,3-phenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the lack of symmetry was derived solely from the difference in length of the two terminal alkoxy chains. In the 3,4'-biphenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the asymmetric nature originates from the 3,4'-substitution of the central biphenyl group and from the difference in length of the two terminal chains. All the melting points of the asymmetrical compounds in the series with the central phenyl unit are lower than those of the symmetrical compounds. The liquid crystalline B1 or B2 phase was retained in all cases. In the series with the central biphenyl unit the compounds with the shortest chain attached to the para-position of the central biphenyl unit have the lowest melting points. A significant lowering of the melting points in comparison with the symmetrically substituted compounds, however, could not be achieved. All the compounds of both series show a layer spacing which is comparable to those of the symmetrically substituted parent compounds. The observed switching behaviour of both the symmetric and asymmetric compounds with a B2 phase was antiferroelectric. 相似文献