Expansion and rupture of charged microcapsules
  We study the deformations of pH-responsive spherical microcapsules -- micrometer-scale liquid drops surrounded by thin, solid shells -- under the influence of electrostatic forces. When exposed to a large concentration of NaOH, the microcapsules become highly charged, and expand isotropically. We find that the extent of this expansion can be understood by coupling electrostatics with shell theory; moreover, the expansion dynamics is well described by Darcy's law for fluid flow through the microcapsule shell. Unexpectedly, however, below a threshold NaOH concentration, the microcapsules begin to disintegrate, and eventually rupture; they then expand non-uniformly, ultimately forming large, jellyfish-like structures. Our results highlight the fascinating range of behaviors exhibited by pH-responsive microcapsules, driven by the interplay between electrostatic and mechanical forces. 
Sujit S. Datta, Alireza Abbaspourrad, David A. Weitz
cond-mat.soft cond-mat.mes-hall cond-mat.mtrl-sci physics.flu-dyn