Both of the time intervals are negatively correlated, while a statistical evaluation of only one swelling cycle for an ensemble of microparticles with different stabilities did not reveal any significant correlation between the two parameters. We observed that the duration of the first swelling step increased during the sequence, while the second step became shorter.
Both the swelling steps and the subsequent de-swelling process proceed reversibly and at an unchanged rate over a sequence of at least three pH exchange cycles. We performed pH jump experiments between pH 11 and pH 1 on a single micro-particle and analyzed the swelling-induced size changes with system dynamics modeling.
So far, nothing is known about the reversibility of the swelling/de-swelling steps. Solvent uptake occurs in two phases and results in disintegration if de-swelling is not triggered by acidification. Microparticles prepared from the milk protein casein have a porous and flexible inner structure with water-filled channels and cavities. Solvent flows in the fL/s range across the total surface of a casein microparticle cause its expansion and shrinkage.
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