The interaction of Polycaprolactone (PCL) with droplets of a microemulsion is studied with Quasi-Elastic Light Scattering and Small Angel X-Ray Scattering. At constant droplet size we vary the PCL concentration and there is clear evidence for an increasing attractive interaction of the droplets from structural investigations with small-angle X ray scattering (SAXS). The collective diffusion coefficient (Dc) of the droplets are monitored with Quasi-Elastic Light Scattering (QELS). We mainly focus on the variation of the dynamic behavior as a function of the PCL concentration and length scale (M.W.=5000 and 10000) in microemulsion. With increasing PCL concentration and length scale the dynamics of the system slows down and one relaxation processes distinguished for each samples. A hard sphere model with depletion potential can fit well the SAXS experiment of microemulsion mixed with PCL. The results shows with increase of PCL on microemulsion the size of droplets is constant at 83Å but the size ratio of polymer to droplets is changing.

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