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31.
Investigation into syndiotactic polystyrene/naphthalene systems of concentrations ranging from 0 to 78% (w/w) have been carried out by electron microscopy, DSC, and neutron diffraction. It is found that a fibrillar morphology is produced in this solvent, similar to that observed for thermoreversible gels. The temperature-concentration phase diagram suggests the existence of two compounds of differing stoichiometries. Neutron diffraction experiments confirm the existence of compounds in this system. 相似文献
32.
Nina Zagdanskaya Lesya Momot Tatyana Zheltonozhskaya Jean-Michel Guenet Vladimir Syromyatnikov 《Macromolecular Symposia》2003,203(1):193-200
The peculiarities of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), which are characterized by the equal average number (N=9), but various molecular weight (or length) of graft chains, in comparison with individual PAA and PVA, were investigated in aqueous medium. Sharp rise in benzene solubilization in PVA-g-PAA solutions at MPAA higher than 4.3·105 has been established. It was shown that such effect is stipulated by the destruction of intramolecular polymer-polymer complex in the copolymer and increasing the benzene binding to separate PVA-g-PAA groups by means of hydrogen bonds. The changes in the PVA-g-PAA solubilizing ability as the function of temperature were also investigated. The obtained results are discussed from the point of view of conformational transitions of intramolecular polymer-polymer complexes (intraPPC), which exist in copolymers, in dependence on the length of graft chains. 相似文献
33.
Jean-Michel Guenet 《Macromolecular Symposia》2006,241(1):45-50
This paper is intended to review some aspects of fibrillar networks by comparing polymer thermoreversible gels and organogels, the latter being obtained through the self-assembling of small organic molecules. The morphology, the rheological properties and the gelation mechanisms are particularly examined. The possibility of preparing hybrid materials is discussed. 相似文献
34.
Agarose sols have been seen for long as solutions of flexible chains that, on cooling, produce thermoreversible gels through double-helix formation. Investigations of the chain conformation in the sol state by small-angle neutron scattering reveals instead a rigid chain with a very large persistence length (lp > 9 nm). The chain cross-section radius and mass per unit length correspond to characteristics of helices as those described by Foord and Atkins. These results lead one to a reappraisal of the occurrence of double helices in the gelation process, as they rather suggest a transition of the type loose-single helix⇒tight single helix. Studies of gels from agarose/water/cosolvent where the cosolvent is Dimethyl Sulfoxide (DMSO), Dimethyl Formamide (DMF), and Methyl Formamide (MF) have led one to conclude on the formation of agarose/water/ cosolvent ternary complexes. The contrast variation method by neutron scattering gives further support to this assumption. Finally, determination of the gel nanostructure allows one to account for the two regimes observed for the variation of the elastic modulus vs concentration. 相似文献
35.
Dr. Aurélie Guenet Dr. Fabrice Eckes Prof. Dr. Véronique Bulach Dr. Cristian A. Strassert Prof. Dr. Luisa De Cola Prof. Dr. Mir Wais Hosseini 《Chemphyschem》2012,13(13):3163-3171
The α4 atropoisomer of a tetraaryl porphyrin and its PdII complex, both bearing four hydroxyquinolinyl chelating units pre‐organised on the same face of the porphyrin backbone, bind a NdIII centre thus affording either a mononuclear or a heterobinuclear anionic species, respectively. The near‐infrared emission of the lanthanide centred at 1064 nm is observed upon excitation of the Soret band at 425 nm. Sensitisation proceeds mainly from the singlet state of the porphyrin. 相似文献
36.
Antoine Béziau Dr. Stéphane A. Baudron Dr. Aurélie Guenet Prof. Mir Wais Hosseini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(9):3215-3223
A series of novel CdII complexes based on α,β‐unsubstituted dipyrrin ligands (dpm) has been prepared and characterised both in solution and in the solid state. These compounds are of the [Cd(dpm)2] type, with the coordination sphere of the metal centre occupied by two dpm chelates. Interestingly, in contrast to what has been reported for the ZnII analogues, in the presence of a pyridyl‐ or imidazolyl‐appended dpm ligand, the coordination number of the CdII cation can be increased to six, leading to an octahedral coordination sphere. As a consequence, the formation of 1‐, 2‐, and 3D coordination polymers by self‐assembly is observed. Photophysical investigations of the discrete complexes and self‐assembled networks have demonstrated that both types of compounds are luminescent in the solid state. 相似文献
37.
J.M. Guenet 《Macromolecular Symposia》1997,114(1):97-108
The definition of a thermoreversible gel is first discussed through the use of two criteria dealing with topology and with thermodynamics. According to this definition only fibrillar systems, as opposed to spherulitic packings, ought to be considered gels. A simple mechanical test is presented that helps recognize such gels. The gelation mechanisms are briefly reviewed and the importance of the role of the polymer-solvent compound in preventing chain from folding, which favours fibrillar structures, is stressed. Also, the role of such compounds in gel ageing, particularly in the case of PVC, is highlighted. 相似文献
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