2014 L'effet de la température sur les propriétés micellaires de tensioactifs non ioniques a été étudié par déclin de fluorescence (formation d'excimère intramicellaire) du pyrène solubilisé dans les micelles. Pour les surfactants du type C12H25En (E = groupe oxyde d'éthylène; n = 6, 8, 9) le nombre micellaire moyen en nombre N est pratiquement indépendant de la température T quand T TC-35 (TC = température critique du système). Dans le domaine TC-35 T TC, N augmente avec T, jusqu'à TC. Dans le même domaine on note l'existence d'une migration intermicellaire du pyrène. La vitesse de cette migration augmente très rapidement avec T. Ce processus semble se produire par l'intermédiaire de collisions entre micelles accompagnées d'une fusion temporaire et partielle des micelles. Un autre surfactant non ionique étudié, le Triton X-100, se comporte de façon un peu différente : N augmente avec T et le processus de migration existe dans tout le domaine de température étudié. Abstract. 2014 The effect of temperature on the aggregation behaviour of nonionic surfactants in aqueous solution has been investigated by means of transient fluorescence probing (intramicellar excimer formation by pyrene). For surfactants of the C12H25En type (E = ethyleneoxide group, n = 6, 8, 9) the number average aggregation number N of the micelle is nearly independent of the temperature T when T is below TC-35 (TC = critical temperature). In the range TC-35 T TC, N increases with T, up to TC. In the same range, extensive pyrene migration from micelle to micelle is observed. This process is thought to take place through micelle collisions with temporary and partial merging. Triton X-100 was also investigated and found to behave somewhat differently with an increase of N with T and probe migration in the whole T-range.
Mechanical properties of packings of deformable spheres of polyelectrolyte gel are studied experimentally. These particles are plunged into a brine. They have the property to swell and shrink when the concentration of salt of the solution is varied. An oedometric compression is performed imposing cycles of deformation at constant speed and constant salinity Cs. Under many different conditions, we study the laws of deformation relating the macroscopic compression force F , to the macroscopic strain ε. We find empirical non linear relations of the type F ∼ ε m . The values of this exponent m are discussed and compared to the results of measurements on a single sphere compressed on a plane as well as to the results of experiments and simulations on dry model granular assemblies. The swelling and deswelling properties of the spheres are used to perform isotropic compression tests. In this situation we determine the relation between the force at equilibrium and the macroscopic strain ε(Cs). The results are compared with those obtained in the oedometric compression tests.
Nous avons montré que la viscosité de torsion d'un nématique est notablement augmentée par l'addition de chaines polymériques, même à faible concentration. Cet effet est analysé en fonction de la longueur des chaines et du paramètre d'ordre. Les résultats expérimentaux sont en bon accord avec un modèle qui implique une conformation anisotrope du polymère; ils conduisent à une estimation numérique de cette anisotropie, qui semble suffisamment importante pour pouvoir être mesurée directement par une méthode de diffusion aux petits angles.
We present a new experimental device to measure the osmotic pressure in gels. The system has been tested on partially neutralized poly(acrylic acid) gels. The variation of the osmotic pressure with polymer concentration, Φ, and ionization degree, α, is linear, provided that α is not too high (I.e. the counterions do not condense on the chains). These results are in good agreement with theoretical models and with compressibility measurements obtained by light scattering experiments. The very charged gels are also studied, and the results are discussed in the frame of existing theories and experiments.
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