Inflation-induced torsion and bulging of a nematic elastomer balloon

Abstract

The liquid crystal mesogens in a nematic elastomer film under simple uniaxial tension may reorientate and in turn lead to shear of the film. This shear effect under simple loading has potential applications in artificial muscles, micro nano devices, biomedical instruments and other fields. When a nematic elastomer film is fabricated into a cylindrical balloon as a pneumatic artificial muscle, it has presented abnormal inflation behaviors including inflation-induced axial contraction. During the inflation process, the nematic elastomer balloon may also have shear/torsion effect due to the reorientation of the helically distributed liquid crystal mesogens. Based on the nematic elastomer theory proposed by Bladon et al., the torsion and bulging of a cylindrical nematic elastomer balloon under the combined action of axial tension and inflating pressure are theoretically investigated in this paper. In the cases of different axial tensions, the inflation process of the balloon shows a variety of torsion and bulging performances. The initial mesogen director also has a great influence on its torsion and bulging behaviors. The results of this paper further deepen the understanding of the inflation behaviors of a nematic elastomer balloon, and provide guidance for its applications in artificial muscles, soft robots and other fields.