Modeling and application of polymeric microgels

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Nikolov, Svetoslav Valeriev
Alexeev, Alexander
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This work develops a mesoscale hydrogel model that is based on dissipative particle dynamics (DPD). The model is used to study the mechanics and kinetics of different microgel systems. Firstly, we examine how the swelling curves and microgel kinetics vary for microgel particles with different network properties. In our simulations we find that during deswelling the network is highly inhomogeneous as the polymer chains bundle and cluster with nearby neighbors. Depending on the microgel network parameters this can either speed-up or arrest the deswelling. To determine how the microgel mechanics vary throughout the volume phase transition we evaluate the bulk and Young’s moduli at different solvents. The mechanical results show good agreement with Flory-Rehner theory signifying that our model can capture both the microgel kinetics and mechanics. We leverage single microgel particle results to probe the behavior of microgel suspensions at different packing fractions and solvencies. Our findings demonstrate that mechanical responses are guided by the single particle modulus. We show that loss and storage moduli data can be scaled onto two master curves, when normalizing by the crossover frequency and storage modulus. Using our mesoscale model, we construct various hydrogel-based microdevices, including self-folding microsheets, a self-propelling bi-layered microswimmer, and an active microcapsule. The self-folding microsheets are shown to produce different 3D structures like helical coils and microtubules depending on the initial 2D geometry. The novel active-passive bilayer microswimmer generates time irreversible motion and achieves self-propulsion due to the timescale mismatch between de/swelling and bending. The active microcapsule can selectively capture nanoparticles from the external solvent at predefined rates, controlled by the actuation period.
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