A crystalline artificial muscle allows the paper doll to do sit-ups

The scary movies on moving dolls, like Anabelle and Chucky, are popular in theaters this summer. Meanwhile, a much less threatening animated doll makes the chemists talk. The researchers gave an aluminum "paper doll" the ability to move and sit-ups with a new material called organic covalent polymer (polyCOF). They report their results in ACS Central Science.

Scientists produce conventional COFs by linking simple organic building blocks, such as carbon-containing molecules with boric acid or aldehyde groups, with covalent bonds. Orderly porous structures have great potential for various applications, including catalysis, gas storage and drug delivery. However, FCOs generally exist in the form of crystalline powders of nanometric or microscopic size which are fragile and can not be transformed into larger sheets or membranes that would be useful for many practical applications. Chen Yao, Ma Shengqian, Zhang Zhenjie and his colleagues wondered if they could improve the mechanical properties of FOCs by using linear polymers as building blocks.

The researchers based their polyCOF on an existing COF structure, but during the synthesis of the compound, they added polyethylene glycol (PEG) to the reactants. The PEG chains filled the pores of the COF, creating a more compact, consistent and stable structure. In contrast to the original COF, polyCOF could be incorporated into flexible membranes that are folded, twisted or stretched repeatedly without damage. To demonstrate how polyCOF could be used as an artificial muscle, the team made a doll containing the membrane as a size and an aluminum foil as other parts. When exposed to ethanol fumes, the doll sits; when the vapors were removed, he went to bed. The researchers repeated these actions several times, causing the doll to do "sit-ups". The expansion of the polyCOF pores during gas binding probably explains the callisthenia of the doll, according to the researchers.