3D Printing of Liquid Crystal Elastomer Foams for Enhanced Energy Dissipation Under Mechanical Insult

Abstract

Polymer foams are an essential class of lightweight materials used to protect assets against mechanical insults, such as shock and vibration. Two features are important to enhance their energy absorption characteristics: the foam structure and the matrix phase mechanical behavior. This study investigates novel approaches to control both of these features to enhance the energy absorption capability of flexible lattice foams. First, we consider 3D printing via digital light processing (DLP) as a method to control the foam mesostructure across a suite of periodic unit cells. Second, we introduce an additional energy dissipation mechanism in the solid matrix phase material by 3D printing the lattice foams with polydomain liquid crystal elastomer (LCE), which undergo a mechanically induced phase transition under large strains. This phase transition is associated with LC mesogen rotation and alignment and provides a second mechanism for mechanical energy dissipation in addition to the viscoelastic relaxation of the polymer network. We contrast the 3D printed LCE lattices with conventional, thermomechanically near-equivalent elastomer lattice foams to quantify the energy-absorbing enhancement the LCE matrix phase provides. Under cyclic quasi-static uniaxial compression conditions, the LCE lattices show dramatically enhanced energy dissipation in uniaxial compression compared to the non-LCE equivalent foams printed with a commercially available photocurable elastomer resin. The lattice geometry also plays a prominent role in determining the energy dissipation ratio between the LCE and non-LCE foams. We show that when increasing the lattice connectivity, the foam deformation transitions from bending-dominated to stretching-dominated deformations, which generates higher axial strains in the struts and higher energy dissipation in the lattice foam, as stretching allows greater mesogen rotation than bending. The LCE foams demonstrate superior energy absorption during the repeated dynamic loading during drop testing compared with the non-LCE equivalent foams, demonstrating the potential of LCEs to enhance physical protection systems against mechanical impact.

Soft elasticity optimises dissipation in 3D-printed liquid crystal elastomers

“…One of the most exciting but often overlooked applications for liquid crystal elastomers (LCEs) is for use in strain-rate-dependent impact absorbing devices. [1][2][3][4][5] In 2001, Clarke et al reported that LCEs -which incorporate the anisotropic ordering of liquid crystals into elastic polymer networks -demonstrate elevated loss tangents (𝑡𝑎𝑛(δ) = G''/G) as high as 1.5 when held at temperatures between their glass transition and nematic-to-isotropic transition temperatures (Tg and TNI respectively). 6 These values of 𝑡𝑎𝑛(δ) correspond to highly viscous and dissipative materials and are far greater than values (~0.1) found in traditional isotropic elastomers.…”

A Liquid Crystal Elastomer‐Based Unprecedented Two‐Way Shape‐Memory Aerogel

“…However, to the best of our knowledge, 2W‐SMPAs have not been reported to date. [ 13 , 14 ] So, the design, preparation and characterization of 2W‐SMPAs with reversible shape‐morphing capability and porous structures are all new challenges. Herein, we present the first 2W‐SMPA sample, for which reversible shape deformation from a permanent shape (permanent shape 1) to the other permanent shape (permanent shape 2) under stimuli has been realized (Figure 1b ).…”

Unlocking Entropic Elasticity of Nematic Elastomers Through Light and Dynamic Adhesion

“…[3][4][5][6] Moreover, nematic LCEs [1,7] exhibit unique mechanical properties, such as a higher viscoelasticity and a soft elasticity, by which the materials can deform under little increase in stress. The ability to reversibly switch them to a classic rubber elasticity, which is attained in an isotropic state by increasing the temperature (T), or light irradiation, [8][9][10][11] can further provide an LCE with a dynamic nature in terms of mechanical damping, [12][13][14] adhesion, [15,16] and friction. [17] Although their applicability as dynamic functional units has been well demonstrated in these systems, the changes to the underpinning mechanical properties, for example, stress-strain and viscoelastic responses associated with the phase transition, remain largely unexplored.…”