Horror movies about dolls that can move around, like Chucky and Anabelle, have been popular. For now, a much less frightening animated doll has chemists interested. Scientists have managed to make a foil “paper doll” to move and do sit-ups using a new material called polymer covalent organic frameworks (polyCOFs). They have published their results in ACS Central Science.
Researchers create conventional COFs by connecting basic organic building blocks, for example, carbon-containing molecules with aldehyde groups or boric acid, with covalent bonds. The ordered, porous structures display great potential for numerous applications, including gas storage, catalysis, and drug delivery.
However, COFs usually exist as nano- or micro-sized crystalline powders that are fragile and cannot be made into membranes or larger sheets that would be beneficial for various practical applications. Yao Chen, Shengqian Ma, Zhenjie Zhang, and colleagues speculated if they could enhance COFs’ mechanical properties by employing linear polymers as a building block.
The scientists based their polyCOF on a current COF structure, but during the compound’s synthesis; they incorporated polyethylene glycol (PEG) to the reactants. The PEG chains connected the pore space of the COF, making a more cohesive, compact, and steady structure. Contrary to the original COF, the polyCOF could be added into flexible membranes that were twisted, bent, or stretched over and over again without damage.
To show how polyCOFs could be applied as an artificial muscle, the team created a doll whose waist was made up of the membrane and its other parts were made using aluminum foil. When exposed to ethanol vapors, the doll sat up; when the vapors were removed, it laid down.
The scientists did these actions several times, making the doll perform “sit-ups”. The opening out of polyCOF pores upon binding the gas likely elucidates the doll’s calisthenics, the scientists say.
The authors received funding from the National Natural Science Foundation of China, Tianjin Natural Science Foundation of China and the National Science Foundation.