Actuation of cylindrical nematic elastomer balloons

Abstract

Nematic elastomers are programmable soft materials that display large, reversible and predictable deformation under an external stimulus such as a change in temperature or light. While much of the work in the field has focused on actuation from flat sheets, recent advances in 3D printing and other methods of directed synthesis have motivated the study of actuation of curved shells. Snap-through buckling has been a topic of particular interest. In this work, we present theoretical calculations to motivate another mode of actuation that combines programmable soft materials as well as instabilities associated with large deformation. Specifically, we analyze the deformation of a cylindrical shell of a patterned nematic elastomer under pressure, show that it can undergo an enormous change of volume with changing temperature and suggest its application as a pump with extremely high ejection fraction.

A mathematical model for the auxetic response of liquid crystal elastomers

“…It is concluded there that, for a theory to be helpful in explaining the elastic responses of a material, it should take into account its properties not only in simple extension and compression, but also in other types of strain . For the nematic elastomer considered in this paper, the mechanical properties under multiaxial deformations [22,53,71,72] deserve to be further investigated.…”

“…To model an incompressible nematic LCE, we first introduce the following isotropic elastic strain-energy function [21,22] (see also [14,17–19,53]), Wfalse(elfalse)false(F,Q,nfalse)=Wfalse(1false)false(Ffalse)+Wfalse(2false)false(boldG−1FboldG0false),where F denotes the deformation gradient from the reference cross-linking state, satisfying trueprefixdetF=1, and n is a unit vector for the (localized) direction of uniaxial nematic alignment in the present configuration, referred to as the director . We denote by boldn0 the reference orientation of the local director corresponding to the cross-linking state.…”

Light-Activated Elongation/Shortening and Twisting of a Nematic Elastomer Balloon

“…To understand the light-activated deformation behaviors of the nematic elastomer balloon, we can derive the governing equations according to the well-known nematic elastomer theory proposed by Bladon et al [ 50 ]. The function of the free energy density can be given as where is the shear modulus and is the deformation gradient tensor in the nematic balloon, which can be written as [ 51 , 52 , 53 ] where , and are extension ratios as follows: …”

Instabilities in liquid crystal elastomers

“…[65][66][67] Theoretical investigations of inflated nematic cylindrical balloons were presented recently as well. 108,109 To compare inflation instabilities in nematic and in purely elastic spheres, we consider the hyperelastic Mooney-Rivlin model 110,111 given by where µ = µ 1 + µ 2 > 0 is the shear modulus at infinitesimal strain. A Mooney-Rivlin-type neoclassical strain-energy function for the nematic material then takes the form Taking a spherical coordinates system with coordinates (R,Θ,Φ) in the reference configuration, we assume that the sphere is deformed by radially symmetric inflation with deformation gradient F = diag (λ −2 , λ, λ), while the natural deformation tensor is G = diag (a −1/3 , a 1/6 , a 1/6 ) and λ > a 1/6 > 1.…”