Fig. 5
From: Onion-like multilayered polymer capsules synthesized by a bioinspired inside-out technique
Multilayer capsules with specific layers responsive to external stimuli. In a, a two-layer capsule is shown with an inner layer of nonionic polymer (DMAA) and an outer layer of anionic polymer, obtained by copolymerization of DMAA with sodium acrylate (SA) (designated as DMAA–SA). At pH 3, the two layers have the same thickness. At pH 7, the carboxylate groups in the DMAA–SA layer become deprotonated, causing the anionic gel to swell, and thus the thickness of the DMAA–SA layer increases substantially. In b, a three-layer capsule is shown, where layers 1 and 3 are DMAA (non-responsive), while layer 2 is NIPA (thermoresponsive). At ambient temperature (25 °C), all layers are transparent gels. Upon heating to 40 °C, which is above the lower critical solution temperature (LCST) of NIPA, the NIPA layer becomes turbid. Scale bars are 500 µm in a and 1 mm in b
