Controlling the degradation and erosion of polymer networks finds various applications ranging from the design of functional soft materials to recycling of thermosets. In addition, nanogel particles adsorb and spread over liquid-liquid interfaces and the controlled degradation of these adsorbed nanogels can provide a way to control interface topography at the nanoscale. In this work we study the controlled photodegradation of hydrogel films and nanogel particles. We use the Dissipative Particle Dynamics (DPD) simulation approach with an adapted form of the modified Segmental Repulsive Potential (mSRP) to analyze controlled degradation and erosion in these systems. The process of degradation of the polymers, or the process of breaking covalent bonds is modeled using a stochastic approach that reproduces first order degradation reaction kinetics. We use tetra-arm polyethylene glycol (tetra-PEG) based networks as a model system and identify the reverse gel point for these networks as a critical fraction of degradable bonds that need to be broken. The measured reverse gel point corresponds to the value expected for bond percolation on a diamond lattice and scales with initial number of tetra-arm precursors. Erosion or mass loss from the degrading gels is affected strongly by factors such as the thickness of polymer films and the polymer-solvent interaction. To analyze degradation of nanogels, we first simulate degradation of particles suspended in a solvent and measure the evolution of the size and shape of these particles as the degradation reaction proceeds. Further, we simulate the adsorption and spreading of nanogels onto the interface between two liquids and compare the size and shape evolution of nanogels degrading at the interface with those degrading in the bulk. We measure an extent of spreading during degradation at the interface and our results indicate that controlled degradation enhances the extent of spreading and interfacial coverage of nanogel particles.

Mesoscale modeling of controlled degradation and erosion phenomena in polymer networks

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