Contraction/elongation behavior of cation-modified polyacrylonitrile fibers

Abstract

In this paper, the authors present the contraction/elongation behavior of cation-modified Polyacrylonitrile (PAN) fibers, which identifies the fibers to be effectively used as biomimetic actuators and artificial muscles. The research was initiated by realizing that the contraction/elongation behavior of PAN is governed by the diffusional processes of ions/solvents interaction. The PAN fibers were suitably annealed, cross-linked and hydrolyzed to become active. The cation-modification process was performed using KOH, NaOH, and LiOH, respectively, for the boiling and alkaline-soaking mediums. It was found that the PAN fibers, regardless of whether being activated in KOH, NaOH, or LiOH, increased from their initial length after being activated and soaked in distilled water. Lengths then decreased after the fibers were soaked in the bases. Fibers treated with LiOH had the largest increase in length following immersion in distilled water. Fibers soaked in any of the three mediums generally had the same decrease in length following immersion in the alkaline solutions, as also occurred following immersion in HCl. Especially noticeable with the fibers treated with LiOH was that greater displacement in the lengths occurred using the 2 N solutions. It is our general notion that the Osmotic pressure of free ions plays an import role on the properties of PAN. However, the observation that Li + treated PAN fibers exhibit the largest contraction/expansion capability compared to Na + or K + treated PANs, can raise another important issue, i.e. hydration. Realizing that the Osmotic pressure of electrolyte systems is weakly dependent upon the types of ions, it is highly likely that the hydration phenomena of free ions within the PAN network plays a key role on its deformation properties. It should be noted that PAN fibers have the capability of changing their effective longitudinal strain more than 100% and have comparable strength to human muscle.