Dresden 2014 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 54: Poster Session 3

CPP 54.54: Poster

Donnerstag, 3. April 2014, 15:00–19:00, P2

Laser Heated Nanoparticles in a Thermoresponsive PNIPAM Polymer — •Michael Orlishausen and Werner Köhler — Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth

Thermoresponsive polymers have gained wide attention in large areas of polymer physics and physical chemistry. We have investigated laser-heated gold nanoparticles (GNPs) in aqueous solutions of Poly-N-Isopropylacrylamide (PNIPAM) by means of optical microscopy. Gold colloids with radii of 125nm show high absorption around 532nm due to their plasmon resonance. Hence they can be used as effectively point-like heat sources, well below the diffraction limit. We have found that for small laser powers a circular two-phase region grows around the GNP, whose radius grows linearly with increasing power. Due to high surface temperatures well above 500K, a solvent-bubble, which is stabilized by Marangoni-convection, forms around the GNP. In our experiments, we have found that the estimated temperature on the surface of that bubble fits the calculated boiling point of water when taking the Laplace-pressure inside the bubble into account. At constant heating power the two-phase-region also shows a time evolution that can potentially be described on the basis of a demixing delay that depends on the local temperature difference to the critical temperature.