Résumé. 2014 Nous examinons les résultats d'expérience de diffusion de neutrons aux petits angles (10-2 q 2 x 10-1 Å-1) par des solutions de sulfonate de polystyrène dans l'eau pour des concentrations supérieures à 0,5 x 10-2 g. cm-3.Avec de l'eau ultra pure, l'absence de diffusion centrale et la présence d'un maximum pour les plus grandes valeurs de q caractérisent la fonction de diffusion S(q). Les deux effets étudiés, variation de la concentration en polyions et addition de sel, conduisent à des résultats différents : la position du maximum varie avec la concentration de polyions alors qu'avec l'addition de sel, on note l'apparition de diffusion centrale et disparition du maximum.Abstract. 2014 Solutions of polyelectrolyte are studied by small angle neutron scattering for c > 0.5 x 10-2 g. cm -3.The function S(q) is characterized by a small value of S'(q ~ 0) and one broad maximum for higher q's

Two new anil molecules exhibiting photochromism in the crystalline state, N-(4-hydroxy)-salicylideneamino-4-(methylbenzoate) (2) and N-(3,5-di-tert-butylsalicylidene)-4-aminopyridine (3), are obtained. Upon irradiation in the UV, the yellow crystals change color to red, owing to enol-keto intramolecular tautomerism. The red color disappears, when crystals are left in the dark or irradiated with visible light. 3 has the most stable keto form among all anil-type photochromic compounds (τ ) 460 days at room temperature). Both exhibit nonlinear optical (NLO) properties and show powder second harmonic generation (SHG) of respectively 10 and 3 times vs urea. X-ray diffraction shows acentric structures where molecules line up "head-to-tail" through hydrogen bonds for 2 (space group Pc), or form a chiral helix 3 (space group P3 2 ). Evidence of reversible structural change is given for 3, and we demonstrate the functionality of this crystal as an NLO switching material, as SHG can be photomodulated by about 30%.