ABSTRACT
Recently, the chain dynamics of molten polymers in confined geometries has been investigated, using NMR. Some of these experiments have been performed on poydimethylsiloxane (PDMS) confined in planar nanolayers involving non-adsorbant solid surfaces. Here the data obtained on various PDMS systems are compared. The common property to these systems is that the local dynamics is anisotropic and the chain segments are undergoing uniaxial fluctuations around the normal n to the layers. Our data clearly show that the sign of the degree of orientational order S ( i.e. the direction of the fluctuations around n) and the broadening of the order distribution P( S) both result from the relative influence of the impenetrable interfaces and anchoring junctions on the segment behaviour.
ABSTRACT
The PDMS lamellar sublayers of a poly(styrene)-poly(dimethylsiloxane) diblock (PS-PDMS) and PS-PDMS-PS triblocks are investigated by NMR and dielectric spectroscopy. Some segments of the confined PDMS chains display anisotropic orientational fluctuations along the interfaces with the PS glassy blocks, whereas the others display fluctuations rather parallel to the lamellae normal. This coexistence results from a competitive ordering effect induced by the glassy interfaces and the chain-end anchoring junctions. The distribution of PDMS relaxation times within the sublayers is also examined: in particular, a slowing down of the segmental motions, together with a broadening of this distribution, are detected.
ABSTRACT
The segmental ordering within a lamellar polystyrene-polydimethylsiloxane diblock (PS-PDMS) was examined by NMR. A non-uniform stretching of the PDMS chains was evidenced. Although chain segments displaying isotropic reorientational motions are present along the chains, relaxation measurements on the free PDMS extremities demonstrate that these latter are oriented and submitted to a non-zero constraint. This specific result allows to precise some features of the order distribution within the lamellae.
ABSTRACT
The dynamics of polydimethylsiloxane chains confined between air and a solid, wettable, and nonadsorbing surface is investigated using deuterium NMR. Chain segments in such molten films undergo uniaxial reorientations around the normal to the surfaces. The influence of the film thickness proves this dynamic uniaxiality involves rapid segment diffusion between both surfaces which impose a high degree of planar orientation. This segmental ordering is observed over a thickness range which depends on the degree of chain entanglements.
