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1.
Haitao Yu 《Tetrahedron》2005,61(37):8932-8938
A new family of coumarin derivatives containing amide group with different alkyl chain lengths was synthesized and their properties as organogelators were evaluated. It was found that the organogelation abilities were not obviously affected by the alkyl spacer length of amide group. Helical morphologies formed either in nonpolar or high polar solvents by most of the gelators. Occurrence of reversible and stereoselective photodimerization of the gel formed by 4-(7′-coumarinoxy)-N-octadecylbutanamide (3a) in cyclohexane was confirmed by 1H NMR, UV absorption, and fluorescence spectra. The photoreaction of the gel proceeded without any dissolution, but the drastic microscopic changes of gel morphologies accompanied with the irradiation were identified using SEM and AFM investigations. 相似文献
2.
Molecular mechanism of physical gelation of hydrocarbons by fatty acid amides of natural amino acids
Asish Pal 《Tetrahedron》2007,63(31):7334-7348
A variety of fatty acid amides of different naturally occurring l-amino acids have been synthesized and they are found to form gels with various hydrocarbons. The gelation properties of these compounds were studied by a number of physical methods including FTIR spectroscopy, X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, rheology, and it was found that gelation depended critically on the fatty acid chain length and the nature of the amino acid. Among them l-alanine based gelators were found to be the most efficient and versatile gelators as they self-assemble into a layered structure to form the gel network. Mechanisms for the assembly and formation of gels from these molecules are discussed. 相似文献
3.
Carlos Rodríguez-Abreu Massimo Lazzari Dharmesh Varade Masaya Kaneko Kenji Aramaki Manuel Arturo López Quintela 《Colloid and polymer science》2007,285(6):673-680
The structure and rheological properties of a poly(dimethylsiloxane)-graft-poly(oxyethylene) copolymer at high concentrations
in block-selective solvents were studied by small-angle X-ray scattering (SAXS) and rheometry. Analysis of SAXS data indicates
that quasispherical, reverse micellar aggregates (with no ordered packing) are present in concentrated solutions of the copolymer
in nonpolar solvents, and that upon addition of water, the size of such aggregates increases due to the solubilization inside
the micellar cores. The viscosity of concentrated polymer solutions increases exponentially as water is added, and finally,
viscoelastic, gel-like behavior is found in the vicinity of the phase separation limit. It was found that small silver nanoparticles
with an average diameter of ≈3 nm can be synthesized inside the copolymer aggregates without the need of a reducing agent;
namely, particles embedded in a viscoelastic matrix are obtained. The synthesis seems to follow first-order kinetics.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
4.
Helena Grigoriew Andrzej Temeriusz Dagmara Chmielewska Jerzy Gronkowski Monika Mirkowska 《Journal of Sol-Gel Science and Technology》2007,44(3):249-254
Organogels, formed of polar and apolar glucose-based gelators with organic solvents, were studied using USAXS. The polarity
was introduced by attaching the NO2 group to the gelator molecule. The USAXS data were processed using fractal analysis, pair distribution function and Guinier
approximation. It was found that the number of molecules, i.e. also the size of the primary aggregates in these gels structure,
were strongly dependent on the gelator polarity, while several other structural parameters, e.g. the shape of the aggregates
and the mechanism of their aggregation to the secondary structure, remained unsusceptible to it. 相似文献
5.
Butylamide-terminated poly(amidoamine) dendrons with either a Boc group (C-n (n = 1, 2, 3)) or a carboxyl group (E-n (n = 1, 2)) at the focal point, as a new kind of dendritic gelators, were synthesized and their gelation properties were studied by TEM, WAXD, SAXS, NMR,and FTIR spectroscopy. It was found that the structure of focal groups impacted greatly on their gelation ability and the dendrons with higher generations facilitated the gel phase assembly. Hydrogen-bonding and hydrophobic interactions were proved to be the main driving forces responsible for the fibrous assembly with the diameter in the range of 30-100 nm. The molecular packing pattern of the xerogels of C-2, C-3, E-1, and E-2 all showed a lamellar structure, which was revealed by WAXD and SAXS. 相似文献
6.
Li-Yan You 《Tetrahedron》2009,65(45):9494-12
This paper describes an investigation of the structural and side-chain factors for the formation of vesicles and gels by hydrogen bonding-mediated aromatic hydrazide foldamers. Six foldamers and one straight analog that bear discrete side chains have been synthesized. SEM and AFM studies reveal that the molecules with the appended 2-(2-(dialkyl-amino)-2-oxoethylamino)-2-oxoethoxyl chains form vesicles, hydrogels or organogels, depending on the solvents. Both the inner amide units and the terminal N,N-dialkylamide units in the chains are revealed to play essential roles in controlling the self-assembly. The former facilitates it by forming the intermolecular hydrogen bonding, while the latter modulates it by providing solubility and balancing the hydrophobicity of the whole molecules in solvents of varying polarity. 相似文献
7.
This paper compares and contrasts the behavior of two different gelators using rheological and neutron scattering methods. The flow properties of a steroid-made paramagnetic organogel in cyclohexane are presented. The original gelator STNO is important in the class of organogels as being one of the most documented and as such is a good candidate for comparisons with another reference system, the 12-hydroxy stearic acid (HSA) gel. The linear viscoelastic regime of deformations of STNO gels is identified and analyzed in the context of self-assembled fibrillar networks. The linear elasticity scales with the concentration as G′ α C2 similarly with HSA organogels, and both systems can be considered as cellular materials. Rheological and neutron scattering experiments show that the kinetics of gel formation exhibits long equilibration times corresponding to the elaboration of entangled fibrillar aggregates. Comparison of the linear elasticities between STNO and HSA gels demonstrates that HSA gels are much more stiffer (G′HSA/G′STNO∼2700). Contributions from the cross-sectional sizes, the mesh size of the networks, the solubility concentrations, and the Young's modulus of the materials are discussed. Non-linear flow properties are also compared using thixotropic loops. They indicate that the transduction of the chirality from the molecular to the supramolecular stages is more efficient with STNO gels having strong chiral junction zones. Simplified scattering and optical protocols are proposed to facilitate comparisons between different organogels. 相似文献
8.
Physical gelation can be induced in various organic and silicone-based liquids, as well as in polymeric melts, upon addition
of 1,3:2,4-dibenzylidene sorbitol (DBS). Such gels are stabilized by the formation of a percolated DBS network composed of
highly interconnected nanofibrils. In this study, we explore several factors affecting the rheological properties of poly(propylene
glycol) (PPG) gelled by DBS. To ascertain the effect of PPG molecular weight (MPPG) on gel formation and rheology, we have investigated three series of DBS-induced PPG gels in which MPPG varies from 425 g/mol to 4000 g/mol. Dynamic stress measurements reveal that the DBS concentration identifying the onset
of PPG gelation decreases with increasing MPPG. Since the solubility parameter (δs) of PPG decreases sharply as MPPG increases over this MPPG range, this observation suggests that DBS gelation is sensitive to δs of the matrix liquid, in agreement with previously reported data collected from DBS-gelled solvents. Moreover, the elastic
modulus and yield stress are found to increase with increasing (i) DBS concentration for the three series of PPG/DBS gels
examined here and (ii) recovery time after cessation of an introductory shear.
Received: 22 February 2000 Accepted: 9 August 2000 相似文献
9.
10.
Poly (styrene-co-furfuryl methacrylate) networks were prepared by the Diels-Alder (D-A) reaction in solution at 25 °C between the linear copolymer and bismaleimide (BM). The resultant crosslinked polymers were swollen to equilibrium in toluene at 25 °C and swelling properties were studied by gravimetric and dimensional measurements. The swelling behaviour of these organogels depended on the composition of the copolymer and the concentration of BM used. Shear and Young’s moduli and the effective crosslinking densities (νe) were determined by compression (stress)-strain measurements. The theoretical crosslinking density was higher than the νe for all the crosslinked copolymers. An endothermic peak without Tg was observed on the DSC curve on heating the dry crosslinked polymer. On reheating a Tg at ≈98 °C was found, which is attributed to presence of linear copolymer produced by the retro D-A reaction in the first heating. The thermal stability of a crosslinked copolymer under nitrogen and air showed differences with the stability of the linear copolymer. The increase in viscosity of the solution during the D-A reaction was followed with time, for initial linear copolymers of different molecular weights. It was found that onset of gelation increased to longer reaction times the lower the molecular weight of copolymer. 相似文献