Mechanics of thick-shell microcapsules made by microfluidics

- Monodisperse polymer microcapsules were fabricated and thoroughly characterized.
- Thin-shell theory is unable to describe capsule mechanical behavior in compression.
- FEM simulations agree well with experimental compression tests for single capsules.
- Simulations allow for prediction of shell fracture behavior under compression.

Double emulsion templates made by microfluidics allow for the production of tailored and monodisperse microcapsules. However, their mechanical properties cannot be predicted by traditional analytical models because of their relatively thick shells. In this work, we produce thick-shelled microcapsules with varying sizes and shell thicknesses and mechanically characterize them in single-capsule compression tests using Weibull statistics. We simulate their compression with finite element modeling and find a good agreement with the experimental results under linear elastic conditions, which enables the prediction of elastic properties based on bulk material parameters. Analysis of the simulated stresses show that capsules with a thickness-to-radius ratio above 20% consistently fail at a constant maximum principal stress in accordance with the brittle nature of their bulk material, enabling the extrapolation of their failure loads as well. Combining this structure-property correlation with processing-structure relationships found in previous studies provides a general predictive framework for the assembly of monodisperse microcapsules with tunable mechanics for protection and/or controlled release of encapsulants.

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