Influence of filler properties on the mechanical failure of a polymer nanocomposite

A. Kutvonen , G. Rossi , T. Ala-NissiläMultiscale 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

ε bf=4εnb ε ff=ε nb5

εnbkBT

=0.7

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

Str

ess

Elastic response Yield point Cavitation Big cavity

Stress-Strain curve-Indicates how system resists strain

RESULTS 1/3WHERE DOES THE

STRENGTH COME FROM?

All neighbours

Bead-bead neighbours

Filler-filler neighbours

Strain

Str

ess

9

Bead-filler neighbours

All neighbours

Num

ber

Fra

ctio

nF

ract

ion

Fra

ctio

n 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:

Thank you for your attention!

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