(226aa) Temperature-Triggered Shape Transformations in Layer-By-Layer Microtubes

Nano- and microstructured layer-by-layer (LbL) assemblies have been extensively studied for various applications. In particular, one-dimensional LbL microtubes have gained interest for their ability to shrink or swell in response to changes in pH. For LbL microtubes, surface interactions dominate over bulk behavior, leading to a variety of interesting responses to temperature. Here, it is shown that temperature can also be utilized as a trigger for shape transformations, and the results are markedly different from the case where pH is used. We report a temperature-triggered transformation of LbL microtubes of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). PAH/PAA nanotubes were prepared using the polycarbonate (PC) membranes as sacrificial porous templates. Transformation of both freely released nanotubes and unreleased nanotubes (remain within the template) was investigated in aqueous media as a function of temperature and time using confocal laser scanning microscopy and scanning electron microscopy. When released microtube suspensions were incubated at high temperatures, the microtubes became shorter, fatter, and ellipsoid in shape. In contrast, unreleased microtubes showed periodic perforations on the surface following thermal treatment, which was suggestive of Rayleigh instabilities. In both cases, pronounced transformation occurred above the hydrated glass transition temperature of the PAH/PAA multilayer.