Temperature-triggered shape-transformations in layer-by-layer microtubes

One-dimensional layer-by-layer (LbL) nano- and microtubes have been extensively studied for energy and biomedical applications. Here, we report a temperature-triggered transformation in shape for LbL microtubes consisting of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). PAH/PAA microtubes were assembled onto porous sacrificial templates. Released microtubes transform to closed ellipsoids upon heating in water. On the other hand, unreleased microtubes (remaining within the template) exhibit a completely different behavior in which periodic perforations appear, suggestive of Rayleigh instabilities. In both cases, the transformations occurred near and above the glass transition temperature (T_g) of the hydrated PAH/PAA LbL assembly, suggesting that the transformation in shape is tied to the thermal properties of the LbL assembly.