In this paper we report on investigations into the short-range molecular structure of pregels (aggregates formed in dilute solutions) and gels as a function of ageing time, temperature and solvent type. In some solvents (diethyl oxalate and bromobenzene) it is found that the structure of the pregels is cylinder-like or ellipsoidlike. The structure is seen to be the same for the gels and the pregels in the investigated range of transfer momentum which leads us to conclude that the gels are probably fiber-like, a statement in agreement with the morphology observed by Yang and Geil. The fiber section is also about the same order of magnitude as that reported by these authors. Also, further evidence is given for the existence of a second type of physical knot, different from those formed by the more syndiotactic sequences. The validity of the molecular structures deduced from these experiments is discussed in the light of macroscopic properties such as compression modulus and swelling.

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Résumé. 2014 La spectroscopie EXAFS au seuil K du cuivre a été utilisée pour décrire l'environnement local des atomes de cuivre dans les phases cristalline et mésomorphe colomnaire du stéarate de cuivre. Dans les colonnes de la phase mésomorphe, les groupes polaires s'empilent de manière très régulière ; les molécules de savon y interviennent à l'état dimérisé, formant des complexes binucléaires de géométrie « plan-carré » comme à l'état cristallin. Les atomes de cuivre sont beaucoup plus proches entre eux à l'intérieur d'un même dimère (2,7 Å) qu'entre deux dimères successifs (3,2 Å) le long de l'axe des colonnes de la phase mésomorphe. Abstract. 2014 Copper-K edge EXAFS spectroscopy has been used to probe the local environment of copper atoms in the crystalline and columnar mesomorphic phases of copper stearate. In the columns of the mesophase, polar groups are stacked one over the other very regularly ; the soap molecules are dimerized, and form binuclear complexes like in the crystalline state. The copper atoms are closer within a single dimer (2.7 Å) than between two successive dimers (3.2 Å) along the axis of the column in the mesophase.J. Phys. France 49 (1988) [345][346][347][348][349][350][351][352]