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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: Poster: Interfaces and Thin Films (joint session with DECHEMA and VDI)

CPP 9.19: Poster

Montag, 11. März 2013, 17:30–19:30, Poster C

Auxetic behaviour of α-polypropylene with crosshatch structure — •Martin Neumann and Robert Magerle — Chemische Physik, TU Chemnitz, D-09107 Chemnitz

Auxetic materials expand laterally when stretched. We have discovered this unusual behaviour in thin films of elastomeric polypropylene (ePP), a semi crystalline polymer with a low degree of crystallinity. The crystalline lamella are orientated perpendicular to the film plane and branch into daughter lamellae with branching angles of 80^∘ forming a crosshatch structure. With a microtensile testing setup that allows for simultaneous imaging with atomic force microscopy (AFM) we measured series of AFM images during uniaxial elongation of a 1.75 µm thick film. Approximately 10 µm large patches of the crosshatch structure expand perpendicular to the stretching direction. This corresponds to a negative Poisson ratio of -0.2. AFM images taken after stepwise relaxation show, that the auxetic deformation is almost completely reversible. Our results show, that auxetic behaviour is an intrinsic property of α-polypropylene with crosshatch structure. The auxetic behaviour is explained with a model based on elongating lamella branches with fixed branching angles, fixed lamella width, and a conservation of crystalline volume.