The Impact of a Solid Surface on the Structure and Dynamics of Polymer Melts

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We propose a combined experimental and theoretical investigation of the effect of a solid (metal) surface on the structure, conformation and dynamics of polymer melts in contact to this substrate. Poly(isoprene) (PI), poly(butadiene) (PB), and poly(ethylene) (PE) will be studied in contact with various metal surfaces (gold, silver and platinum) used as solid supports. These substrates will allow us to investigate the effect of the different surfaces on the polymer structural properties. We will additionally modify metal surfaces (e.g. thiol SAMs) to systematically change the polymer/substrate interaction from essentially attractive via neutral to repulsive in order to investigate bulk properties in contact to surfaces. The basic experimental approach for probing the inter-phase between the polymer and the solid is based on surface plasmon optics (PSP) with an emphasis on long-range (LRSP) and short-range surface plasmon modes (SRSP). The evanescent character of these surface-electromagnetic waves provides exquisite interfacial sensitivity and selectivity, with no interference from bulk contributions to the detected signal. By varying the wavelength of the employed laser light source or by using Au layers of different thicknesses, we can continuously tune the depth of the evanescent (i.e., exponentially decaying) optical field extending from the substrate surface into the polymer sample from about 10nm (1/e decay length) to beyond 1micron. Thus, we can probe the full range of the solid/polymer system with 2 different regimes, i.e., a polymer/solid interface and a “semi-infinite” polymeric interphase extending normal to the interface into the bulk polymer. For the theoretical studies multi-scale methods that combine atomistic and coarse-grained (CG) simulations will be used. The combined hierarchical use of atomistic and CG simulations in the polymer/solid systems will allow us to calculate the correct time scales in the CG simulations and to quantitatively study the effect of the surface on the structure and the dynamics of long entangled polymer melts.