Atomic force microscopy based quantitative mapping of elastic moduli in phase separated polyurethanes and silica reinfor
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Atomic force microscopy based quantitative mapping of elastic moduli in phase separated polyurethanes and silica reinforced rubbers across the length scales Peter Schön1, Kristóf Bagdi2,3, Kinga Molnár2,3, Patrick Markus4, Saurabh Dutta1, Morteza Shirazi5, Jacques Noordermeer5, Béla Pukánszky2,3 and G. Julius Vancso*,1 +
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Materials Science and Technology of Polymers, MESA Institute for Nanotechnology, University of Twente, Enschede, NL-7500, The Netherlands 2 Laboratory of Plastics and Rubber Technology, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, P.O. Box 91, H1521 Budapest, Hungary 3 Institute of Materials and Environmental Chemistry, Chemical Research Center, Hungarian Academy of Sciences, P.O. Box 17, H-1525 Budapest, Hungary 4 Bruker Nederland B.V., Bruynvisweg 16, 1531 AZ Wormer, The Netherlands 5 Elastomer Technology and Engineering, Engineering Technology Department, University of Twente, Enschede, 7500 AE, the Netherlands *Corresponding author: Prof. G. Julius Vancso, Tel: +31-53-4892967 Fax: +31 (0)53 489 3823 E-mail: [email protected] ABSTRACT In the work presented here atomic force microscopy (AFM) based mechanical mapping techniques - HarmoniX imaging and Peak Force Tapping - were applied to determine the surface elastic modulus of phase separated polyurethanes and silica reinforced rubbers across the length scales. Segmented polyether polyurethanes (PUs) were prepared with varying stoichiometric ratio of the isocyanate and hydroxyl groups. The effect of molar mass, as well as the type and number of end-groups on their morphology was investigated. Smooth PU samples for AFM imaging were prepared by ultramicrotonomy. The micro phase separated morphology of the phase separated PUs showed characteristic “fingerprint” AFM phase images. Surface modulus values obtained by AFM were compared to bulk modulus values obtained by tensile testing. The moduli were mapped quantitatively with nanoscale resolution and were in excellent agreement for both AFM modes. Surface mean moduli values do not coincide with bulk values obtained via tensile testing which is attributed to fundamentally different averaging procedures and effects that lead to the respective modulus values obtained via surface and volume averaging. EPDM and SBR rubbers and rubber blends thereof were prepared with varying concentrations of silica nanoparticles and studied in order to investigate the effect of different composition on the resulting morphology (filler distribution) and elastic moduli on a specific rubber or rubber blend sample. Elastic moduli of the rubber and rubber blend samples were first measured by bulk tensile testing. The morphology of the rubber samples was visualized by height and phase imaging. Surface elastic moduli of silica reinforced rubbers and rubber blends were mapped quantitatively and compared with bulk tensile test results. AFM allowed the determination of modulus distributions at the sections imaged. As potential reasons for the observed differences bet
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