Although discotic liquid crystals are attractive functional materials, their use in electronic devices is often restricted by high melting and clearing points. Among the promising candidates for applications are [15]crown‐5 ether‐based liquid crystals with peripheral n‐alkoxy side chains, which, however, still have melting points above room temperature. To overcome this problem, a series of o‐terphenyl and triphenylene [15]crown‐5 ether derivatives was prepared in which δ‐methyl‐branched alkoxy side chains of varying lengths substitute the peripheral linear alkoxy chains. The mesomorphic properties of the novel crown ethers were studied by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction. δ‐Methyl branching indeed lowers melting points resulting in room‐temperature hexagonal columnar mesophases. The mesophase widths, which ranged from 87 to 30 K for o‐terphenyls, significantly increased to 106–147 K for the triphenylenes depending on the chain lengths, revealing the beneficial effect of a flat mesogen, due to improved π–π interactions. 相似文献
Porous polymer foams (poly-Pickering-HIPEs) have been synthesised from stable high internal phase emulsion templates solely stabilised by low concentrations of functionalised titania nanoparticles. 相似文献
The aeration of emulsions with tailored properties and structure is of widespread importance in processing of foods and cosmetics. This report addresses the micro-cellular foam formation of carbon dioxide-saturated oil-in-water emulsions triggered by the application of a controlled pressure drop. The experimental setup combines a stirred pressure vessel with a pressure cell-equipped rheometer and pneumatic expansion valves. This allows to systematically study the process of gas dissolution, bubble nucleation, and growth under defined pressure, temperature, and flow conditions. Investigations on the impact of relevant process parameters show that dissolved gas fraction, emulsion viscosity, and shear rate have a major influence on foam formation. Dissolution of carbon dioxide leads to a viscosity reduction of the emulsion which and is described by a viscosity reduction factor. The point of bubble nucleation is derived from rheological patterns during depressurization. Experiments show that lower emulsion viscosity and higher shear rate favor bubble nucleation upon pressure release. Rheological results are supported by video analysis as the setup allows capturing nucleation, growth, and destabilization of bubbles as a function of pressure, supersaturation, and time. The results of this work yield the understanding of the high-pressure foaming mechanism from a rheological perspective and foster the design of such processes. 相似文献
The synthesis and structural characterization of three heterometallic rings templated about imidazolium cations is reported. The compounds are [2,4‐DiMe‐ImidH][Cr7NiIIF8(O2CtBu)16] 1 (2,4‐DiMe‐ImidH=the cation of 2,4‐dimethylimidazole), [ImidH]2[Cr6NiII2F8(O2CCtBu)16] 2 (ImidH=the cation of imidazole), and [1‐Bz‐ImidH]2 [Cr7NiII2F9(O2CtBu)18] 3 (1‐Bz‐ImidH=the cation of 1‐benzylimidazole). The structures show the formation of octagonal arrays of metals for 1 and 2 and a nonagon of metal centers for 3 . In all cases the edges of the polygon are bridged by a single fluoride and two pivalate ligands, and the position of the divalent metal centers cannot be distinguished by X‐ray diffraction. Magnetic studies combined with EPR spectroscopy allow the characterization of the magnetic states of the compounds. In each case the exchange is antiferromagnetic with a magnetic exchange parameter J≈?5.8 cm?1, and it is not possible to differentiate the exchange between two CrIII centers (JCrCr) from the exchange between a CrIII and a NiII center (JCrNi). For 2 there is evidence for the presence of at least two, possibly four, linkage isomers of the heterometallic ring, caused by the presence of two divalent metal centers in the ring. The EPR spectroscopy of 3 suggests an S=1/2 ground state of the ring and that it is likely that only one linkage isomer is present. 相似文献
The [1,1′‐biisoquinoline]‐4,4′‐diol ( 4a ), which was obtained as hydrochloride 4a ?2 HCl in two steps starting from the methoxymethyl (MOM)‐protected 1‐chloroisoquinoline 8 (Scheme 3), opens access to further O‐functionalized biisoquinoline derivatives. Compound 4a ?2 HCl was esterified with 4‐(hexadecyloxy)benzoyl chloride ( 5b ) to give the corresponding diester 3b (Scheme 4), which could not be obtained by Ni‐mediated homocoupling of 6b (Scheme 2). The ether derivative 2b was accessible in good yield by reaction of 4a ?2 HCl with the respective alkyl bromide 9 under the conditions of Williamson etherification (Scheme 4). Slightly modified conditions were applied to the esterification of 4a ?2 HCl with galloyl chlorides 10a – h as well as etherification of 4a ?2 HCl with 6‐bromohexyl tris(alkyloxy)benzoates 11b , d – h and [(6‐bromohexyl)oxy]‐substituted pentakis(alkyloxy)triphenylenes 14a – c (Scheme 5). Despite the bulky substituents, the respective target 1,1′‐biisoquinolines 12, 13 , and 15 were isolated in 14–86% yield (Table). 相似文献
New uses for ALD : By applying standard metal oxide atomic layer deposition (ALD) to two types of porphyrins, site‐specific chemical infiltration of substrate molecules is achieved: Diethylzinc can diffuse into the interior of porphyrin supramolecular structures and induce metalation of the porphyrin molecules from the vapor phase. A=Ph, p‐HO3SC6H4.
The fabrication of nanoporous templates from poly(styrene)-b-poly(methyl methacrylate) diblock copolymer thin films (PS-b-PMMA, volume ratio 70:30) on silicon requires precise control of interfacial energies to achieve a perpendicular orientation of the PMMA cylindrical microdomains relative to the substrate. To provide a simple, rapid, yet tunable approach for surface neutralization, we investigated the self-assembled ordering of PS-b-PMMA diblock copolymer thin films on silicon substrates modified with a partial monolayer of octadecyldimethyl chlorosilane (ODMS), i.e., a layer of ODMS with a grafting density less than the maximum possible monolayer surface coverage. We demonstrate herein the fabrication of nanoporous PS templates from annealed PS-b-PMMA diblock copolymer thin films on these partial ODMS SAMs. 相似文献
The present study describes a novel approach based on electrochemical impedance measurements to follow the adsorption of giant liposomes on protein-coated solid surfaces with a time resolution in the order of seconds. The technical key features are circular gold-film electrodes as small as a few hundred micrometers in diameter and measurements of the electrode capacitance using AC signals in the kilohertz regime. Using Monte Carlo simulations, we were able to support the experiments and extract the rate constant of liposome adsorption. Besides monitoring the adsorption of liposomes on protein-coated surfaces, we also applied this technique to study shape fluctuations of the adsorbed vesicles and compared the corresponding power spectra with those recorded for hard particles and living animal cells. 相似文献