Motion control in free-standing shape-memory actuators

Abstract

In this work, free-standing shape-memory thermally triggered actuators are developed by laminating "thiol-epoxy"-based glassy thermoset (GT) and stretched liquid-crystalline network (LCN) films. A sequential curing process was used to obtain GTs with tailored thermomechanical properties and network relaxation dynamics, and also to assemble the final actuator. The actuation extent, rate and time were studied by varying the GT and the heating rate in thermoactuation with an experimental approach. The results demonstrate that it is possible to tailor the actuation rate and time by designing GT materials with a glass transition temperature close to that of the liquid-crystalline-to-isotropic phase transition of the LCN, thus making it possible to couple the two processes. Such coupling is also possible in rapid heating processes even when the glass transition temperature of the GT is clearly lower than the isotropization temperature of the LCN, depending on the network relaxation dynamics of the GT and the presence of thermal gradients within the actuators. Interestingly, varying the GT network relaxation dynamics does not affect the actuation extent. As predicted by the analytical model developed in our previous work, the modulus of the GT layer is mainly responsible for the actuation extent. Finally, to demonstrate the enhanced control of the actuation, specifically designed actuators were assembled in a three-dimensional actuating device able to make complex motions (including "S-type" bending). This approach makes it possible to engineer advanced functional materials for application in self-adaptable structures and soft robotics.

Functional liquid crystalline epoxy networks and composites: from materials design to applications

“…While the preparation of lightly crosslinked LCENs has been reported by Giamberini et al as early as 1995 [126], these materials have not received much attention until the inspiring work by Pei et al in 2014 [35]. Since then considerable progress has been made in the area and resulted in several smart materials with fascinating functionalities [127][128][129][130][131][132][133][134].…”

Shape-Memory Polymeric Artificial Muscles: Mechanisms, Applications and Challenges

“…Later on, many attempts were carried out to achieve the stress-free two-way shape-memory effect to overcome the limitation of constant force by utilizing a variety of methods, such as bilayer polymeric laminate [ 50 ], core-shell composites [ 51 , 52 ], and crystalline polymeric multi-networks [ 53 , 54 , 55 ]. Along with these other methods, free-standing [ 56 ], autonomous [ 57 ], and controlled shape-memory actuation [ 58 ] methods were introduced by using a glassy thermoset-stretched liquid crystalline network, epoxy-based shape-memory lightly cross-linked network, and carbon nanotube/epoxy shape-memory LCE, respectively. The general design principle for all of the above free-standing two-way SMEs was the preparation of anisotropic networks (or built-in stress) that can provide an actuating force for reversible two-way SME without an external load.…”

Thermal/Near‐Infrared Light Dual‐Responsive Reversible Two‐Way Shape Memory cEVA/2D‐MoO2 Composite for Multifunctional Applications

“…Based on whether the persistent external stress is needed in the two‐way shape memory cycles, the 2W‐SMPs can be split into quasi two‐way and reversible two‐way shape memory polymers (quasi 2W‐SMPs and reversible 2W‐SMPs), which respectively exhibit two‐way shape memory property under constant external stress and stress‐free condition. [ 18,19,25 ] In view of the practical application prospects, the 2W‐SMPs without the need of persistent external stress is more suitable for the design of actuators, [ 26 ] biomedical, [ 27 ] smart gripper, [ 21 ] and soft robotics, [ 23 ] and has become a research hotspot in recent years.…”