ETD

• glass transition
• mechanical response
• modeling & simulations
• Molecular Dynamics
• phase separation
• porous system

Porous materials have become a highly attractive topic in multiple research fields, thanks to the many and various applications which include energy storage and conversion, drugs delivery, tissue engineering. Polymers, in particular, provide several advantages as a constitutive material, since they are lightweight, do not contain heavy metals, and are highly functionalizable. Due to this growing interest and even to extend the applicability range, it is interesting to investigate the mechanical properties of these materials.
The aim of this thesis is to characterise via Molecular Dynamics (MD) simulations the mechanical response of a model porous glassy system, obtained by phase separation of a Coarse-Grained polymer melt.
After equilibration, the system is instantaneously quenched in temperature at constant volume. Negative pressure is created in the system, which leads to viscoelastic phase separation. For target temperatures below the glass transition, the process can be arrested, leading to a bicontinuous sponge-like structure
The mechanical response of the system is studied through the athermal quasi-static deformation protocol, which consists in applying elementary strain steps, followed by energy minimisation.
Young’s and shear modulus are found to be quite low, as one would expect for a porous system.
For large deformations, stress-strain curves show a highly intermittent behaviour, showing avalanches of plastic events.