Star polymer films for superior impact resistance*

Polymeric films with greater impact and ballistic resistance are highly desired for numerous applications, but molecular configurations that best address this need remain subject to debate. We present a study on the resistance to ballistic impact of thin polymer films using coarse-grained molecular dynamics simulations, investigating melts of star polymers. Increasing the number of arms or their length results in greater specific penetration energy. Greater interpenetration of chains in stars with a higher number of arms allows energy to be dissipated predominantly through rearrangement of the stars internally, rather than chain sliding. During film deformation, stars with a higher number of arms show higher energy absorption rates soon after contact with the projectile, whereas stars with longer arms have a delayed response where dissipation arises primarily from chain sliding, which results in significant back face deformation. Our results suggest that stars may be advantageous for tuning energy dissipation mechanisms of ultra-thin films, setting the stage for a topology-based strategy for the design of impact-resistant polymer films.