Rolling Dynamics of Nanoscale Elastic Shells Driven by Active Particles

Abstract

Self-propelled elastic shells capable of transducing energy to rolling motion could have potential applications as drug delivery vehicles. To understand the dynamics of the nanoscale size elastic shells, we performed molecular dynamics simulations of shells filled with a mixture of active and passive beads placed in contact with an elastic substrate. The shell skin is made of cross-linked polymer chains. The energy transduction from active beads to elastic shell results in stationary, steady rolling, and accelerating states depending on the strength of the shell–substrate adhesion and the magnitude of a force applied to the active beads. In the stationary state, the torque produced by a friction (rolling resistance) force in the contact area balances that due to the external force generated by the active beads, and the shell sticks to the substrate. In the steady rolling state, a rolling friction force balances the driving force, and the shell maintains a constant rolling velocity. The scaling relationship between the magnitude of the driving force and the shell velocity reflects a viscoelastic nature of the shell skin deformation dynamics. In the accelerating state, the energy supplied to a system by active beads exceeds the energy dissipation due to viscoelastic shell deformation in the contact area. Furthermore, the contact area of the shell with a substrate decreases with increasing shell instantaneous velocity.

Leveraging the Polymer Glass Transition to Access Thermally Switchable Shear Jamming Suspensions

“…As the thermomechanical properties of these networks represent a critical aspect of this work, they were evaluated by preparing monolithic P-9 , P-29 , and P-50 films, which were characterized by dynamic mechanical analysis (DMA) in both the dry (see Figures S6 and S7) and carrier-fluid-swollen states (Figure ) for a better representation of the suspension environment. As expected, the polymer networks synthesized using this chemistry exhibit a relatively narrow glass transition window, consistent with literature examples. , The ratio of loss to the storage modulus (tan δ) provides a measure of the mechanical losses due to dissipation at the molecular scale. , In general, the peak in tan δ is seen around T g because polymer chains just start to become mobile at that temperature but still experience high molecular friction, leading to higher dissipation than in the glassy or rubbery states. The thermomechanical T g of the materials, designated by the peak in the dissipation factor tan δ, is comparable to that from the DSC measurements for the dry and immersed film (see Figures S6 and S7).…”

“…52,53 The ratio of loss to the storage modulus (tan δ) provides a measure of the mechanical losses due to dissipation at the molecular scale. 44,55 In general, the peak in tan δ is seen around T g because polymer chains just start to become mobile at that temperature but still experience high molecular friction, leading to higher dissipation than in the glassy or rubbery states. The thermomechanical T g of the materials, designated by the peak in the dissipation factor tan δ, is comparable to that from the DSC measurements for the dry and immersed film (see Figures S6 and S7).…”