Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 49: P14: Polymer Dynamics

CPP 49.4: Poster

Wednesday, March 18, 2015, 10:00–13:00, Poster A

Examination of medium-ranged interactions through optical tweezing of a droplet in a multiphase ternary mixture (PNIPAM/H2O/DMSO) — •Michael Orlishausen and Werner Köhler — Physikalisches Institut, Universität Bayreuth, Universitätsstr. 30, 95447 Bayreuth

Poly-N-isopropylacrylamide (PNIPAM) in acqueous solution can show a cononsolvency effect when mixed with another solvent. A proper concentration of that solvent can result in the shift from a lower (LCST) to an upper critical solution temperature (UCST). In our case, we chose Dimethylsulfoxid (DMSO) and investigated the resulting ternary system at room temperature, and thus below its UCST, using a light microscope and a laser beam (532 nm) focused through the objective, which was utilized both for optical tweezing and local heating. In an unperturbated state the ternary system the sytem consists of myriads of droplets in different phase states with diameters of several microns. Due to the high refractive index of DMSO as a pure component, DMSO-rich droplets can be easily tweezed. When a tweezed droplet is forced through the sample by controlling the position of the beam, a correlated network-like response of the interacting droplets near the perturbation occurs on a length scale of at least 10 microns. The motion of such a droplet also leads to a net growth of its size as a result of a more frequent contact with other droplets of similar composition, even when only moving on a circular path near the initial position. When a water soluble absorbing dye is added, the temperature field induced by the laser moves along with the tweezed droplet.