Aliphatic chain grafted polypyrrole as a precursor of carbon membrane

Electrically conducting polymers are generally considered as unsuitable precursor for the synthesis of carbon membrane because defects always emerge in the carbon matrixes generated from the pyrolysis of these polymers. However, the conjugated chain structure of this type of polymers permits a high conversion of carbon to graphenes. We found that grafting of dodecylbenzene sulfonic acid (DBSA) chains to the conjugated backbone of polypyrrole (PPy) can effectively halt mudcracks from developing in the carbon matrix. The DBSA side chains impede strong association of the conjugated PPy molecular segments since the root cause of mudcracks is the stacking of PPy segments. A uniform and microcrack-free carbon membrane (3–5 μm thick) was achieved on a porous ceramic substrate by means of solution casting and carbonizing the cast PPy-DBSA layer. It was verified that the solvent used to formulate the PPy-DBSA solution and the final calcination temperature have significant impact on the porous structure of carbon membrane. Besides transmission electron microscopy examination, gas permeation test also unveils the porous features of the carbon membrane. The prevalent transport phenomenon was Knudsen diffusion, signifying that the carbon matrix is characterized by the meso-porous structure.