arXiv subjects

Marco Aurelio Galvani Cunha

Publications and source records attributed to Marco Aurelio Galvani Cunha.

3 recordsLinked to original sources

arXiv2024

Building rigid networks with prestress and selective pruning

Biopolymer networks from the intracellular to tissue scale display high rigidity and tensile stress while having coordinations well below the normal threshold for mechanical rigidity. The elastic filaments in these networks are often severed by enzymes in a tension-inhibited manner. The effects of such pruning on the mechanics of prestressed networks have not been studied. We show that networks pruned by a tension-inhibited method remain rigid at much lower coordinations than randomly pruned ones. These findings suggest a possible reason for the repeated evolution of tension-inhibited filament-severing proteins.

cond-mat.soft↗

arXiv2022

Probing the nonequilibrium dynamics of stress, orientation and entanglements in polymer melts with orthogonal interrupted shear simulations

Both entangled and unentangled polymer melts exhibit stress overshoots when subject to shearing flow. The size of the overshoot depends on the applied shear rate and is related to relaxation mechanisms such as reptation, chain stretch and convective constraint release. Previous experimental work shows that melts subjected to interrupted shear flows exhibit a smaller overshoot when sheared after partial relaxation. This has been shown to be consistent with predictions by constitutive models. Here, we report molecular dynamics simulations of interrupted shear of polymer melts where the shear flow after the relaxation stage is orthogonal to the original applied flow. We observe that, for a given relaxation time, the size of the stress overshoot under orthogonal interrupted shear is larger than observed during parallel interrupted shear, which is not captured by constitutive models. Differences in maxima are also observed for overshoots in the first normal stress and chain end-to-end distance. We also show that measurements of the average number of entanglements per chain and average orientation at different scales along the chain are affected by the change in shear direction, leading to non-monotonic relaxation of the off-diagonal components of orientation and an appearance of a 'double peak' in the average number of entanglements during the transient. We propose that such complex behavior of entanglements is responsible for the increase in the overshoots of stress components, and that models of the dynamics of entanglements might be improved upon by considering a tensorial measurement of entanglements that can be coupled to orientation.

cond-mat.soft↗

arXiv2020

Effect of flow-induced molecular alignment on welding and strength of polymer interfaces

Structures formed by fused filament fabrication are often substantially weaker than those made with conventional techniques, and fail at the welds between successive layers. One factor that may influence strength is flow-induced alignment of deposited material. Recent work suggests that alignment reduces the entanglement density and thus should accelerate welding by diffusion. Here, coarse-grained molecular simulations are used to test the effect of molecular alignment on diffusion and weld strength. While standard measures show a decrease of the entanglement density with alignment, there is no change in the rate of diffusion normal to the interface or the rate of formation of entanglements across the interface. The time for chain reorientation also remains equal to the equilibrium disentanglement time $τ_d$. Despite this, simulations of mechanical tests show that welds formed from aligned states are weaker until several $τ_d$. This is not because the weld itself is weaker, but because aligned material near the weld is weaker than unaligned material. The maximum shear strength and tensile fracture energy of welded systems are the same as bulk systems with the same alignment.

cond-mat.soft↗