Synthesis and mechanical performance characterization of nanocomposite scrolls closely mimicking sponge spicules

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In the second period of this project, the previously established scroll fabrication approach shall be further developed to yield scrolls whose dense interior, comprising intimately connected lamellas and a filled central core, closely mimics the architecture of natural (sponge) spicules. On this basis, the full potential of biomimetics shall be exploited to achieve maximum mechanical performance of the scrolls, effectively combining mechanical flexibility with high strength and toughness. Filling of the free space within scrolls obtained by manual scrolling on a substrate or a self-scrolling process shall be accomplished through low temperature chemical bath deposition of titania nanoparticles. Best mechanical properties shall be achieved via suitable adjustment of the number and thickness ratio of the constituent layers, the inner scroll diameter, the crystallinity and density of the titania particles, as well as the water content adjusted by post-synthesis annealing. Moreover, in order to further approach natural spicules, it is planned to incorporate cellulose nanofiber, whose soft mechanical character is expected to promote mechanical flexibility, and whose tailored surface charge density and length renders them into close-to-ideal nucleation sites for the titania nanoparticles. Combined with a detailed analysis of the micro-/nanoscale structure of the artificial spicules, the major mechanisms of mechanical performance will be identified and contrasted with those operative in their natural counterparts. As another objective to be pursued in parallel, two different types of scroll-based actuators shall be explored in detail. The actuators shall operate based upon changes of humidity of the environment and controlled electrostatic charging, respectively. A major goal is to determine the actuator performance, including their operational life time, as a function of the most relevant parameters, including the number and connectivity of lamellas, the inner diameter and width of the scrolls, as well as the amount of implemented cellulose nanofibers.