We propose a model giving the conformation of a star shaped polymer by taking into account the radial variation of the monomer concentration ϕ( r). For an isolated star when increasing r (at the centre of the star r = 0), the variation of ϕ (r) is first given by a constant value (r < f 1/2 l) then has a (r/l)-1 variation (for f1/2 / < r < f1/2 ν-1 /) and finally a (r/l)-4/3 variation (for r > f1/2 ν-1 l); wh ere f is the number of branches, N the number of monomers in a branch and ν and l are the excluded volume and the length associated to a monomer. For all these cases, it is shown that the size of a branch is always larger than that of a linear polymer made of N monomers. Beyond the overlapping concentration the star conformation is obtained from two characteristic lengths essentially : χ(c ) a radius inside which the branches of the other stars do not penetrate, this radius defines a domain where the conformation of a star is similar to that of an isolated one. Beyond χ(c) the interpenetration of branches is characterized by a screening length ξ(c) very similar to that found for semi-dilute solutions of linear polymers. For all these regimes the variation of the size of a star is predicted as a function of N, f, v and c

Résumé. 2014 Abstract. 2014 We analyse the theoretical behaviour of macromolecular chains dissolved in a good solvent, and confined into tubes (or slits) of diameter D comparable to the coil radius. The repulsive interactions between monomers are taken into account by a scaling method which goes beyond the usual Flory Huggins approach.For the slit problem, we find five different regimes (depending on the concentration C and on the diameter D) with smooth cross-overs at all boundaries. For the tube problem, one of these regimes disappears and two cross-over lines merge, giving rise to a line of stronger discontinuity. This is related to the fact that, when D decreases down to the monomer size, different coils cannot overlap each other at all.For all regimes that thermodynamic properties, the local correlations and the overall chain size are estimated. The scaling arguments, however, predict only the power laws (in C and D) for all these quantities, and do not give precise numerical coefficients.

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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

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