Modeling the nanoscratching of self-healing materials

Abstract

We use computational modeling to determine the mechanical response of crosslinked nanogels to an atomic force microscope (AFM) tip that is moved through the sample. We focus on two-dimensional systems where the nanogels are interconnected by both strong and labile bonds. To simulate this system, we modify the lattice spring model (LSM) to extend the applicability of this method to a broader range of elastic materials. Via this modified LSM, we model each nanogel as a deformable particle. We utilize the Bell model to describe the bonds between these nanogel particles, and subsequently, simulate the rupturing of bonds due to the force exerted by the moving indenter. The ruptured labile bonds can readily reform and thus can effectively mend the cavities formed by the moving AFM tip. We determine how the fraction of labile bonds, the nanogel stiffness, and the size and velocity of the moving tip affect the self-healing behavior of the material. We find that samples containing just 10% of labile bonds can heal to approximately 90% of their original, undeformed morphology. Our results provide guidelines for creating reconfigurable materials that can undergo self-repair and thereby withstand greater mechanical stress under everyday use.

Modeling Self-Healing Mechanisms in Coatings: Approaches and Perspectives

“…Bond remodeling as a response of mechanical stimulus in cross-linked nanogel particles, and its potential role in the design and evaluation of different self-healing routes and materials [8], has been addressed in a number of works by Balazs and co-workers [26][27][28][29][30][31]. The central idea in these works rests on an accurate representation of the interactions between a basic element, an hexagonal nanogel particle ( Figure 1a) [26][27][28] or a solid spherical core ( Figure 1b) [29][30][31], and its surrounding analogues. Each pair of analogue elements share a number of strong (permanent) and/or weak (labile) bonds that break and (re-)form to accommodate the demands of the macroscopic material.…”

“…In the most general context, F total shall account for viscous forces, elastic forces F elas due to material deformation, forces due to node-to-node bonds (F bond ) and externally applied forces. Duki et al [27] include the effects of finite elasticity by introducing a neo-Hookean elastic potential, from which obtaining F elas . However, the networks constructed from bonding of spherical nanoparticles does not require such derivations [29][30][31].…”

Designing Silk-silk Protein Alloy Materials for Biomedical Applications

“…A simulation program is written in C programming language that can be used on a single or multiprocessor computer system. A lattice-spring-mass (LSM) model was used to simulate the alloy-proteins [36][37][38][39] . The LSM model gives a simple description of the net force on a mass when attached to a spring and one can solve the force equation to understand the motion for each mass.…”

“…Represent a single protein as a coarse-grained particle that has a mass of m. 2. Use a Hookean or a neo-Hookean spring to represent a bond 38,39 . By interlinking a finite number of particles with springs, one can make a sub-alloy domain that represents a stable building block of the alloy-proteins.…”

“…However, the stronger bonds will be ruptured irreversibly. The existence of the weak bonds allows the alloy-protein to keep its structural integrity under external stress [36][37][38][39][40][41] . This numerical simulation uses a mathematical model developed through a bottom-up approach that is based on finite element methods through lattice-spring model [36][37][38][39][40][41] .…”