Influence of filler properties on the mechanical failure of a polymer nanocomposite A. Kutvonen, G. Rossi, T. Ala-Nissilä Multiscale Statistical Physics Group at COMP/Aalto Polymer nanocomposites have a wide range of applications varying from car tyres to advanced coating technologies How do parameters such as loading, filler material and topology influence the nanocomposite mechanical properties? Nanocomposite behaviour during tensile deformation?

Molecular dynamics simulations V(r) -> F(r) -> move ->V(r) Bead-spring model for polymers + Lennard Jones (LJ) – potentials Periodic boundary conditions Fillers with different topologies, masses and sizes MODEL & METHODS

how much system resist strain System equilibrated in NVT ensemble above glass transition temperature Walls are moved with constant velocity METHODS & STRESS – STRAIN CURVES Strain Stress Elastic responseYield point CavitationBig cavity Stress-Strain curve -Indicates how system resists strain

RESULTS 1/3 WHERE DOES THE STRENGTH COME FROM? All neighbours Bead-bead neighbours Filler-filler neighbours Strain Stress 9 Bead-filler neighbours All neighbours Number Fraction Before yield point the density of system is decreasing Number of contacts reduces Fraction bead-filler neighbours is increasing

RESULTS 2/3 Fixed volume loading Size comparison Smaller fillers increase yield stress for cavitation Is it because smaller fillers in total have a larger surface area? No, even with constant surface area the smallest win Smaller ones have better mobility

RESULTS 3/3 & WORK IN PROGRESS Same number of fillers and same mass vs. Triangles might have more rigid behaviour Study of the effects of: Mass of the filler Loading Stick and sheet shaped fillers Branching IN PROGRESS:

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MD SIMULATION PROTOCOL Decompress and find equilibrium volume in microcanonical ensemble Randomize initial positions and compress Equilibration by annealing Pull walls with constant velocity and gather data