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Notes: Many properties of semi dilute and concentrated polymer solutions can be understood simply in terms of certain scaling laws (1). In the first part of this talk, we present scaling results for various problems connected with colloid science. (1) Near a solid wall (or an interface) when the chains are not adsorbed at the interface, a polymer solution is expected to show a depletion layer of sizeable thickness near the wall (2). (2) The existence of these layers may induce an attraction between colloïdal grains suspended in the solution. This attraction can lead to flocculation when the grain radius b is larger than the correlation length ζ(c) of the solution; in the opposite limit (b 〈 ζ) the attraction is weak (3). (3) We discuss the entropy of polymer chains confined in very narrow tubes of diameter D. For a single chain in a good solvent this problem has been understood sometime ago (4), but for chains in a melt the situation is surprisingly different (5). (4) Freely suspended liquid films occurring for instance in foams should be often stabilised by the addition of long polymer chains (always assuming no adsorption on the limiting surfaces) : the chains lose entropy by confinement, and the result is a stabilisation free energy (per cm2 of film) varying like the inverse film thickness (6).In the second part of the talk, we discuss some aspects of the motions and flows of entangled systems. (1) The cooperative diffusion of the polymer through the solvent (or vice versa) does not involve disentanglements and is amenable to simple scaling laws (7) which have to some extent be confirmed by photon beat experiments (8). It must be emphasized, however, that these laws are valid asymptotically for long chains, in very good solvents, and in a semi dilute regime where the chains do overlap, but where the concentration is still low enough, so that the friction processes are still dominated by the solvent viscosity (as opposed to monomer-monomer friction) : these limitations have not always been appreciated in the literature. (2) The simplest experiment displaying entanglements is based on viscometric flows at low shear rates. However, it has been recently realised that in many practical cases the standard boundary conditions - of zero slip at the walls - do not apply to these flows (9); when the wall is reasonably flat, and does not build strong links with the polymer, the friction forces involved in a finite slip are much weaker than the viscous stresses inside the polymer solution. This must, for instance, lead to strong deviations from the Poiseuille law in a capillary, whenever the tube diameter D is smaller than a characteristic length (of order 0.5 mm in typical cases). (3) A different approach is based on the studies of individual diffusion D* of a labeled chain, for which the reptation model (10) predicts a dependence of the form D* ∼ M-2 on molecular weight. Various systems have been used to measure D* (11) : here the emphasis will be on recent data using the stimulated Rayleigh effect (12) which is particularly well suited for slow diffusion.