Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: P4: Computational Physics of Soft Matter

CPP 32.9: Poster

Tuesday, March 17, 2015, 14:00–16:00, Poster B

Comparison of passive and active microrheology for an unentangled polymer melt — •Anja Kuhnhold and Wolfgang Paul — Martin-Luther-Universität Halle-Wittenberg, Halle, Deutschland

We use molecular dynamics simulations to study the microrheology (MR) of an unentangled polymer melt. Microrheology aims at the estimation of the complex shear modulus of a probe from the motion of suspended micro- or nanoscopic particles in the probe.
This motion can either be purely thermal, similar to the Brownian motion, or forced to a specific form, like an oscillation. The former is called passive MR and the latter active MR.
In passive MR the complex modulus is calculated by using a generalized Stokes-Einstein relation. In active MR a corresponding relation depends on the specific form of the motion.
Our system is a melt of short bead-spring polymer chains including one nanoparticle. For the active MR we use an oscillating harmonical potential, similar to the experimental optical tweezer, to force the particle to oscillate with a certain frequency. Passive and active MR give similar results in the linear response regime independent of temperature, and at high temperatures these are equal to the true (reference) bulk modulus. The lower frequency range is better accessible by passive MR while with active MR one can generally reach higher frequencies.